The invention provides apparatus and methods for mapping conduction pathways and creating lesions in the heart wall for the treatment of atrial fibrillation. The apparatus may include at least one epicardial ablation probe having a plurality of electrodes for creating a lesion. The apparatus and method facilitate the formation of a lesion which electrically isolates the pulmonary veins from the surrounding myocardium.

This invention relates generally to the diagnosis and treatment of electrophysiological diseases of the heart, and more specifically to devices and methods for epicardial mapping and ablation for the treatment of atrial fibrillation.
Atrial fibrillation results from disorganized electrical activity in the heart muscle, or myocardium. The surgical maze procedure has been developed for treating atrial fibrillation and involves the creation of a series of surgical incisions through the atrial myocardium in a preselected pattern so as to create conductive corridors of viable tissue bounded by scar tissue. While very effective in treating atrial fibrillation, the maze procedure is highly invasive, high in moribidity and mortality, and difficult to perform by even the most skilled surgeons. The procedure not only requires a median sternotomy or other form of gross thoracotomy for access to the heart, but requires stopping the heart and establishing cardiopulmonary bypass, to which a significant part of the trauma, morbidity and mortality of the maze procedure may be attributed.
As a less invasive alternative to the surgical incisions used in the maze procedure, transmural ablation of the heart wall has been proposed. Such ablation may be performed either from within the chambers of the heart (endocardial ablation) using endovascular devices (e.g. catheters) introduced through arteries or veins, or from outside the heart (epicardial ablation) using devices introduced into the chest through surgical incisions. Various ablation technologies have been proposed, including cryogenic, radiofrequency (RF), laser and microwave. The ablation devices are used to create elongated transmural lesionsxe2x80x94that is, lesions extending through a sufficient thickness of the myocardium to block electrical conductionxe2x80x94which form the boundaries of the conductive corridors in the atrial myocardium. Perhaps most advantageous about the use of transmural ablation rather than surgical incisions is the ability to perform the procedure on the beating heart without the use of cardiopulmonary bypass.
In performing the maze procedure and its variants, whether using ablation or surgical incisions, it is generally considered most efficacious to include a transmural incision or lesion that isolates the pulmonary veins from the surrounding myocardium. The pulmonary veins connect the lungs to the left atrium of the heart, and join the left atrial wall on the posterior side of the heart. This location creates significant difficulties for endocardial ablation devices for several reasons. First, while many of the other lesions created in the maze procedure can be created from within the right atrium, the pulmonary venous lesions must be created in the left atrium, requiring either a separate arterial access point or a transeptal puncture from the right atrium. Second, the elongated and flexible endovascular ablation devices are difficult to manipulate into the complex geometries required for forming the pulmonary venous lesions and to maintain in such positions against the wall of the beating heart. This is very time-consuming and can result in lesions which do not completely encircle the pulmonary veins or which contain gaps and discontinuities. Third, visualization of endocardial anatomy and endovascular devices is often inadequate and knowing the precise position of such devices in the heart can be difficult, resulting in misplaced lesions. Fourth, ablation within the blood inside the heart can create thrombus which, in the right chambers, is generally filtered out by the lungs rather than entering the bloodstream. However, on the left side of the heart where the pulmonary venous lesions are formed, thrombus can be carried by the bloodstream into the coronary arteries or the vessels of the head and neck, potentially resulting in myocardial infarction, stroke or other neurologic sequelae. Finally, the heat generated by endocardial devices which flows outward through the myocardium cannot be precisely controlled and can damage extracardiac tissues such as the pericardium, the phrenic nerve and other structures.
If, on the other hand, epicardial ablation devices are utilized to form the pulmonary venous lesions, other challenges are presented. First, the posterior location of the pulmonary veins is extremely difficult to access through thoracic incisions without gross manipulations of the heart. Such manipulations are not generally possible if minimally-invasive techniques are being utilized via small thoracic access ports, or if the procedure is being performed on a beating heart without cardiopulmonary bypass. Further complicating epicardial access are the pericardial reflections, where the pericardium attaches to the heart wall near the pulmonary veins. The pericardial reflections are located so as to prohibit positioning a device completely around the pulmonary veins without cutting away or puncturing through the reflections. Such cutting or puncturing of the pericardial reflections is risky and difficult, particularly if working through small incisions in the chest without a clear view and open access to the posterior side of the heart. Furthermore, surgical repair of any damaged tissue is almost impossible without highly invasive open heart surgery.
What are needed, therefore, are devices and methods for forming transmural lesions that isolate the pulmonary veins from the surrounding myocardium which overcome these problems. The devices and methods will preferably be utilized epicardially to avoid the need for access into the left chambers of the heart and to minimize the risk of producing thrombus. The devices and methods should be useful through small access ports in the chest using minimally invasive techniques. The devices and methods will preferably avoid the need for cutting or puncturing the pericardial reflections, however, the pericardial reflections may be cut without departing from the scope of the invention. The devices and methods should further be useful on the beating heart without requiring the use of cardiopulmonary bypass and should not require significant manipulation or retraction of the heart.
The present invention meets these and other objectives by providing epicardial ablation devices and methods useful for creating transmural lesions that electrically isolate the pulmonary veins for the treatment of atrial fibrillation. The devices and methods may be utilized through a small access port in the chest, preferably through a subxiphoid penetration, and positioned within the pericardium and around the pulmonary veins. Advantageously, the devices and methods do not require the large thoracic incision used in the conventional maze procedure, and may be used on the beating heart without cardiopulmonary bypass. By eliminating the need for ablation within the left atrium, the risk of thrombus formation is minimized. The devices and methods of the invention are more easily visualized, faster to use, and more accurately positionable than known cardiac ablation catheters and devices, enable the formation of continuous, uninterrupted lesions around the pulmonary veins, and protect extracardiac tissues from injury.
In a first embodiment, a method of forming a transmural lesion in a wall of the heart adjacent to the pulmonary veins comprises the steps of placing at least one ablation device through a thoracic incision and through a pericardial penetration so that the at least one ablation device is disposed in contact with an epicardial surface of the heart wall; positioning the at least one ablation device adjacent to the pulmonary veins on a posterior aspect of the heart while leaving the pericardial reflections intact; and transmurally ablating the heart wall with the at least one ablating device to create at least one transmural lesion adjacent to the pulmonary veins. The ablation device is preferably placed through a small puncture, incision, or access port in the chest, either between the ribs or in a subxiphoid position, for minimal trauma, with visualization provided by fluoroscopy, endoscopy, transesophageal echocardiography, or other conventional form of minimally-invasive imaging. While the method may be performed with the heart stopped and circulation supported with cardiopulmonary bypass, the method is preferably performed with the heart beating so as to minimize morbidity, mortality, complexity and cost.
In another aspect of the invention, an apparatus for forming a transmural lesion in the heart wall adjacent to the pulmonary veins comprises, in a preferred embodiment, an elongated flexible shaft having a working end and a control end; an ablation device attached to the working end for creating a transmural lesion in the heart wall; a control mechanism at the control end for manipulating the working end; and a locating device near the working end configured to engage one or more of the pulmonary veins, or a nearby anatomical structure such as a pericardial reflection, for positioning the working end adjacent to the pulmonary veins. The locating device may comprise a catch, branch, notch or other structure at the working end configured to engage one or more of the pulmonary veins or other anatomical structure such as the inferior vena cava, superior vena cava, aorta, pulmonary artery, left atrial appendage, right atrial appendage, or one of the pericardial reflections. The ablation device may be a radiofrequency electrode, microwave transmitter, cryogenic element, laser, ultrasonic transducer or any of the other known types of ablation devices suitable for forming transmural lesions. Preferably, the apparatus includes a plurality of such ablation devices arranged along the working end in a linear pattern suitable for forming a continuous, uninterrupted lesion around or on the pulmonary veins.
The working end may additionally include one or more movable elements that are manipulated from the control end and which may be moved into a desired position after the working end has been located near the pulmonary veins. Slidable, rotatable, articulated, pivotable, bendable, pre-shaped or steerable elements may be used. Additional ablation devices may be mounted to these movable elements to facilitate formation of transmural lesions. The movable elements may be deployed to positions around the pulmonary veins to create a continuous transmural lesion which electrically isolates the pulmonary veins from the surrounding myocardium.
In addition, a mechanism may be provided for urging all or part of the working end against the epicardium to ensure adequate contact with the ablation devices. This mechanism may be, for example, one or more suction holes in the working end through which suction may be applied to draw the working end against the epicardium, or an inflatable balloon mounted to the outer side of the working end such that, upon inflation, the balloon engages the inner wall of the pericardium and forces the working end against the epicardium. This also functions to protect extracardiac tissues such as the pericardium from injury by retracting such tissues away from the epicardial region which is being ablated, and, in the case of the balloon, providing an insulated barrier between the electrodes of the ablation probe and the extracardiac tissues.
The apparatus may be either a single integrated device or two or more devices which work in tandem. In either case, the apparatus may have two or more tips at the working end which are positioned on opposing sides of a tissue layer such as a pericardial reflection. A device may be provided for approximating the two free ends on opposing sides of the tissue layer, such as an electromagnet mounted to one or both of the free ends. In this way, a continuous lesion may be created in the myocardium from one side of the pericardial reflection to the other without puncturing or cutting away the pericardial reflection.
The apparatus may further include a working channel through which supplemental devices may be placed to facilitate visualization, tissue manipulation, supplementary ablation, suction, irrigation and the like.
The apparatus and methods of the invention are further useful for mapping conduction pathways in the heart (local electrograms) for the diagnosis of electrophysiological diseases. Any of the electrodes on the apparatus may be individually selected and the voltage may be monitored to determine the location of conduction pathways. Alternatively, the apparatus of the invention may be used for pacing the heart by delivering current through one or more selected electrodes at levels sufficient to stimulate heart contractions.
Additionally, although the ablation apparatus and methods of the invention are preferably configured for epicardial use, the principles of the invention are equally applicable to endocardial ablation catheters and devices. For example, an endocardial ablation apparatus according to the invention would include a locating device configured to engage an anatomical structure accessible from within the chambers of the heart such as the coronary sinus (from the right atrium), pulmonary artery (from the right ventricle), or the pulmonary veins (from the left atrium), and the ablation device would be positionable in a predetermined location relative to the locating device. The endocardial apparatus could further include suction holes, expandable balloons, or other mechanisms for maintaining contact between the ablation device and the interior surface of the heart wall.
In another aspect of the present invention, an anchor is used to hold a part of the device while displacing another part of the device. The anchor is preferably a balloon but may also be tines, a suction port or a mechanically actuated device. After actuating the anchor, a proximal portion of the device may be moved by simply manipulating the device or by advancement or withdrawal of a stylet.
The present invention is also related to a method of creating a continuous ablation lesion in tissue underlying a pericardial reflection without penetrating the pericardial reflection. First and second ablating devices are introduced into the space between the pericardium and the epicardium. The first ablating device is positioned on one side of the pericardial reflection and the second ablating device is positioned on the other side of the pericardial reflection. Tissue beneath the pericardial reflection is then ablated with one or both of the devices to create a continuous lesion beneath the pericardial reflection. The devices may be aligned across the pericardial reflection by any suitable method such as with magnetic force, use of an emitter and sensor, or by marking the pericardial reflection on one side and locating the mark from the other side of the pericardial reflection. The emitter and sensor may work with electromagnetic radiation such as light, ultrasound, magnetic field, and radiation.
In yet another aspect of the invention, the ablating device may have a guide portion which aligns the device between the pericardium and epicardium. The guide portion may be a continuous strap or a number of discrete guide portions. The guide portions may be fins, wings or one or more laterally extending elements such as balloons. The guide portions may be individually actuated to align the device and ablate discrete locations of the tissue along the ablating device.
The ablating device may also be advanced into position over a guide. The guide is preferably a guidewire but may be any other suitable structure. The guide may also lock into position with a coaxial cable or locking arm. The guide is advanced ahead of the ablation device and positioned along the desired ablation path. The ablating device is then advanced or retracted along the guide. The ablating device preferably includes a device for locating previously formed lesions so that subsequent lesions will merge with previously formed lesion to create a continuous, transmural lesion. The device for locating previously created lesions may be pacing and sensing electrodes or electrodes which simply measure electrical impedance.
Although cutting through the pericardial reflections has certain risks, the methods and devices of the present invention may, of course, be practiced while cutting through the pericardial reflections. After penetrating through the pericardial reflection, the ablating device may interlock with another part of the same device or with a separate device.
Other aspects and advantages of the invention are disclosed in the following detailed description and in the accompanying drawings.

Apparatus and method for diagnosis and therapy of electrophysiological disease


A method is provided for controlling the appearance of a video game game character, as the character traverses a path displayed on a display screen; wherein the method is used in a video game system which includes a graphics controller, digital memory and a display screen, the method comprises the steps of: displaying a banked path segment in which the game character is displayed upright at at least one location on the banked path and is displayed upside down at at least one other location on this banked path; storing multiple sprite patterns representative of the appearance of the character at different locations on the banked path as the character traverses the banked path; tracking the character location on the banked path as the character traverses the banked path; retrieving the stored sprite patterns that portray the character at different locations on the banked path; and displaying a character using the retrieved patterns such that the character has different appearances at different locations on the banked path.

1. Field of the Invention
The invention relates generally to video games, and more specifically, to video games that employ a playfield that scrolls relative to a game character in order to show character motion through the playfield.
2. Description of the Related Art
Video games are well known in which a game character, or sprite, follows a prescribed path through a scrolled playfield in response to the commands of a user who is playing the game. The user operates an input device which includes a control console which may include a "joy stick" used to control character movement. A user command issued through the input device for the character to move right results in the playfield scrolling to the left which creates the impression that the character is moving to the right relative to the playfield. Conversely, a user command for the character to move left results in the playfield scrolling to the right which creates the impression that the character is moving to the left. During such scrolling the character image ordinarily remains fixed near the center of the screen display despite the appearance of movement relative to the playfield.
In typical video games, the input device permits the user to command the character to perform numerous activities such as to jump or to crouch down or to speed-up or to slow-down. Often, a game character takes on different appearances as it engages in different activities. For example, when the character moves at slower speeds, its legs, arms and torso may be fully visible as the playfield scrolls slowly. However, when the character speeds up, most of the character image may be portrayed as a blur with only the character head being fully recognizable while the playfield scrolls rapidly. Moreover, the character may have one portrayal when it crouches and another portrayal when it jumps. Additionally, there may be special character antics that involve a series of images, such as tumbling, throwing a kick or "flying" through the air.
A challenge associated with implementing such video games is to produce a playfield which has a variety of images and obstacles. For example, there may be mountains to climb, canyons to jump over or enemies to defeat. In the midst of all of this activity, changes in the appearance and movements of the character and the playfield must occur smoothly and quickly so as not to distract the user or detract from the excitement of a high speed action packed video game.
Consequently, certain uniform techniques often are employed to control the movement and appearance of game characters and the playfield. These techniques include defining a path to be followed by the character through the playfield. The character moves along the path in response to user commands. For example, if the path ascends to the right, and the user commands the character to move to the right, then the character is depicted climbing the path to the right as the playfield scrolls to the left. If the user subsequently commands the character to move back towards the left, then the character will be shown descending the path to the left as the playfield scrolls to the right.
The image of the character moving along the path is produced under the control of a computer program. Character movement is constrained by the program such that as the character moves left or right, it always tries to maintain contact with the path. If the character jumps, for example, it soon returns (falls) to the path. If the path includes a discontinuity such as an on-screen image of a cliff, for example, then a character running off the edge of the cliff might fall to another path at the base of the cliff; or it might jump across the chasm at the edge of the cliff and land on a path opposite the cliff. The user controls character movement, but the program ensures that the character generally follows the path.
While paths through the playfield generally have been an acceptable way to constrain character movement, there have been shortcomings with there use. For example, a typical earlier method for making sure that a character follows the path is to use collision blocks. As the character moves in response to user commands, a computer program references stored collision blocks to determine the exact path to be followed in response to such commands. Specifically, the playfield is divided into graphics blocks. As the character traverses individual graphics path blocks, a path control program references individual collision blocks that correspond to such graphics path blocks. A collision block is used to determine, for example, whether the path within a graphics path blocks is level, inclined or drops off a cliff.
A problem associated with such prior methods is that it may be desirable for the character to proceed along a path that corkscrews or turns upside down or banks (or is inclined) sideways. Since a typical earlier path program operates by keeping a character firmly planted on a path as if due to the force of gravity, the character ordinarily would fall off such a banked or upside down path.
Thus, there has been a need for improved graphics techniques which display banked, upside down or sideways path segments. The present invention meets this need.


The introduction of nanotubes in a liquid provides a means for changing the physical and/or chemical properties of the liquid. Improvements in heat transfer, electrical properties, viscosity, and lubricity can be realized upon dispersion of nanotubes in liquids; however, nanotubes behave like hydrophobic particles and tend to clump together in liquids. Methods of preparing stable dispersions of nanotubes are described and surfactants/dispersants are identified which can disperse carbon nanotubes in aqueous and petroleum liquid medium. The appropriate dispersant is chosen for the carbon nanotube and the water or oil based medium and the dispersant is dissolved into the liquid medium to form a solution. The carbon nanotube is added to the dispersant containing the solution with agitation, ultrasonication, and/or combinations thereof.

1. Technical Field
Methods are described and surfactants are identified which can disperse carbon nanotubes in aqueous and petroleum liquid medium utilizing selected dispersants and mixing methods to form stable carbon nanotube dispersions.
2. Description of the Prior Art
Carbon nanotubes are a new form of the material formed by elemental carbon, which possess different properties than the other forms of the carbon materials. They have unique atomic structure, very high aspect ratio, and extraordinary mechanical properties (strength and flexibility), making them ideal reinforcing fibers in composites and other structural materials.
Carbon nanotubes are characterized as generally to rigid porous carbon three dimensional structures comprising carbon nanofibers and having high surface area and porosity, low bulk density, low amount of micropores and increased crush strength. The instant process is applicable to nanotubes with or without amorphous carbon.
The term xe2x80x9cnanotubexe2x80x9d refers to elongated structures having a cross section (e.g., angular fibers having edges) or diameter (e.g., rounded) less than 1 micron. The structure may be either hollow or solid. Accordingly, the term includes xe2x80x9cnanofibrilsxe2x80x9d and xe2x80x9cbucky tubesxe2x80x9d. Such structures provide significant surface area when incorporated into a structure because of their size and shape. Moreover, such fibers can be made with high purity and uniformity.
Preferably, the nanotube used in the present invention has a diameter less than 1 micron, preferably less than about 0.5 micron, and even more preferably less than 0.1 micron and most preferably less than 0.05 micron.
The term xe2x80x9cinternal structurexe2x80x9d refers to the internal structure of an assemblage including the relative orientation of the fibers, the diversity of and overall average of fiber orientations, the proximity of the fibers to one another, the void space or pores created by the interstices and spaces between the fibers and size, shape, number and orientation of the flow channels or paths formed by the connection of the void spaces and/or pores. The structure may also include characteristics relating to the size, spacing and orientation of aggregate particles that form the assemblage. The term xe2x80x9crelative orientationxe2x80x9d refers to the orientation of an individual fiber or aggregate with respect to the others (i.e., aligned versus non-aligned). The xe2x80x9cdiversity ofxe2x80x9d and xe2x80x9coverall averagexe2x80x9d of fiber or aggregate orientations refers to the range of fiber orientations within the structure (alignment and orientation with respect to the external surface of the structure).
Carbon nanotubes can be used to form a rigid assemblage or be made having diameters in the range of 3.5 to 70 nanometers. The nanotubes, fibrils, bucky tubes and whiskers that are referred to in this application are distinguishable from continuous carbon fibers commercially available as reinforcement materials. In contrast to nanotubes, which have desirably large, but unavoidably finite aspect ratios, continuous carbon fibers have aspect ratios (L/D) of at least 104 and often 106 or more. The diameter of continuous fibers is also far larger than that of nanotubes, being always  greater than 1.0 micron and typically 5 to 7 microns. Continuous carbon fibers are made by the pyrolysis of organic precursor fibers, usually rayon, polyacrylonitrile (PAN) and pitch. Thus, they may include heteroatoms within their structure. The graphitic nature of xe2x80x9cas madexe2x80x9d continuous carbon fibers varies, but they may be subjected to a subsequent graphitization step. Differences in degree of graphitization, orientation and crystallinity of graphite planes, if they are present, the potential presence of heteroatoms and even the absolute difference in substrate diameter make experience with continuous fibers poor predictors of nanofiber chemistry.
Carbon nanotubes are typically hollow graphite tubules having a diameter of generally several to several tens nanometers. Carbon nanotubes exist in many forms. The nanofibers can be in the form of discrete fibers or aggregate particles of nanofibers. The former results in a structure having fairly uniform properties. The latter results in a structure having two-tiered architecture comprising an overall macrostructure comprising aggregate particles of nanofibers bonded together to form the porous mass and a microstructure of intertwined nanofibers within the individual aggregate particles. For instance, one form of carbon fibrils are characterized by a substantially constant diameter, length greater than about 5 times the diameter, an ordered outer region of catalytically grown, multiple, substantially continuous layers of ordered carbon atoms having an outside diameter between about 3.5 and 70 nanometers, and a distinct inner core region. Each of the layers and the core are disposed substantially concentrically about the cylindrical axis of the fibril. The fibrils are substantially free of pyrolytically deposited thermal carbon with the diameter of the fibrils being equal to the outside diameter of the ordered outer region.
Moreover, a carbon nanotube suitable for use with the instant process defines a cylindrical carbon fibril characterized by a substantially constant diameter between 3.5 and about 70 nanometers, a length greater than about 5 times the diameter and less than about 5000 times the diameter, an outer region of multiple layers of ordered carbon atoms and a distinct inner core region, each of the layers and the core being disposed concentrically about the cylindrical axis of the fibril. Preferably the entire carbon nanotube is substantially free of thermal carbon overcoat. The term xe2x80x9ccylindricalxe2x80x9d is used herein in the broad geometrical sense, i.e., the surface traced by a straight line moving parallel to a fixed straight line and intersecting a curve. A circle or an ellipse are but two of the many possible curves of the cylinder. The inner core region of the nanotube may be hollow, or may comprise carbon atoms which are less ordered than the atoms of the outer region. xe2x80x9cOrdered carbon atoms,xe2x80x9d as the phrase is used herein means graphitic domains having their c-axes substantially perpendicular to the cylindrical axis of the nanotube. In one embodiment, the length of the nanotube is greater than about 20 times the diameter of the nanotube. In another embodiment, the nanotube diameter is between about 7 and about 25 nanometers. In another embodiment the inner core region has a diameter greater than about 2 nanometers.
Dispersing the nanotubes into organic and aqueous medium has been a serious challenge. The nanotubes tend to aggregate, form agglomerates, and separate from the dispersion.
Some industrial applications require a method of preparing a stable dispersion of a selected carbon nanotube in a liquid medium.
For instance, U.S. Pat. No. 5,523,006 by Strumban teaches the user of a surfactant and an oil medium; however, the particles are Cuxe2x80x94Nixe2x80x94Snxe2x80x94Zn alloy particles with the size from 0.01 micron and the suspension is stable for a limited period of time of approximately 30 days. Moreover, the surfactants don""t include the dispersants typically utilized in the lubricant industry.
U.S. Pat. No. 5,560,898 by Uchida et al. teaches that a liquid medium is an aqueous medium containing a surfactant; however, the stability of the suspension is of little consequence in that the liquid is centrifuged upon suspension.
U.S. Pat. No. 5,853,877 by Shibuta teaches dispersing disentangled nanotubes in a polar solvent and forming a coating composition with additives such as dispersing agents; however, a method of obtaining a stable dispersion is not taught.
U.S. Pat. No. 6,099,965 by Tennent et al. utilizes a kneader teaching mixing a dispersant with other reactants in a liquid medium using a high-torque dispersing tool, yet sustaining the stability of the dispersion does not appear to be taught nor suggested.
None of the conventional methods taught provide a process for dispersing and maintaining nanotubes in suspension as described and claimed in the instant invention as follows.
In this invention physical and chemical treatments are combined to derive a method of obtaining a stable nanotube dispersion.
The present invention provides a method of preparing a stable dispersion of a selected carbon nanotube in a liquid medium, such as water or any water based solution, or oil, with the combined use of surfactants and agitation (e.g. ultrasonication) or other means of agitation. The carbon nanotube can be either single-walled, or multi-walled, with typical aspect ratio of 500-5000; however, it is contemplated that nanotubes of other configurations can also be utilized with the instant invention. It is contemplated that a mixture containing carbon nanotubes having a length of 1 micron or more and a diameter of 50 nm or less. The raw material may contain carbon nanotubes having a size outside of the above ranges. The carbon nanotube is not required to be surface treated providing a hydrophilic surface for dispersion into the aqueous medium, but optionally may be treated. The selected surfactant is soluble or dispersible in the liquid medium.
The term xe2x80x9csurfactantxe2x80x9d in the instant invention refers to any chemical compound that reduces surface tension of a liquid when dissolved into it, or reduces interfacial tension between two liquids, or between a liquid and a solid. It is usually, but not exclusively, a long chain molecule comprised of two moieties: a hydrophilic moiety and a lipophilic moiety. The xe2x80x9chydrophilicxe2x80x9d and xe2x80x9clipophilicxe2x80x9d moieties refer to the segment in the molecule with affinity for water, and that with affinity for oil, respectively. It is a broad term that covers all materials that have surface activity, including wetting agents, dispersants, emulsifiers, detergents and foaming agents, etc. The term xe2x80x9cdispersantxe2x80x9d in the instant invention refers to a surfactant added to a medium to promote uniform suspension of extremely fine solid particles, often of colloidal size. In the lubricant industry the term xe2x80x9cdispersantxe2x80x9d is general accepted to describe the long chain oil soluble or dispersible compounds which function to disperse the xe2x80x9ccold sludgexe2x80x9d formed in engines. These two terms are mostly interchangeable in the instant invention; however, in some cases the term xe2x80x9cdispersantxe2x80x9d is used with the tendency to emphasize, but not restrict to, the ones commonly used in the lubricant industry.
The method of making a stable particle-containing dispersions includes physical agitation in combination with chemical treatments. The physical mixing includes high shear mixing, such as with a high speed mixer, homogenizers, microfluidizers, a Kady mill, a colloid mill, etc., high impact mixing, such as attritor, ball and pebble mill, etc., and ultrasonication methods. The mixing methods are further aided by electrostatic stabilization by electrolytes, and steric stabilization by polymeric surfactants (dispersants).
The chemical treatment and the use of the claimed surfactants/dispersants are critical to long term stability of the nanotube fluid mixtures. The treatment involves dissolving a selected dispersant into a selected liquid medium. The chemical method includes a two-step approach: dissolving the dispersant into the liquid medium, and then adding the selected carbon nanotube into the dispersant liquid medium mixture with mechanical agitation and/or ultrasonication. These steps can be reversed but may not produce as satisfactory a result. The liquid medium can be water or any water solution, a petroleum distillate, a petroleum oil, synthetic oil, or vegetable oil. The dispersant for the oily liquid medium is a surfactant with low hydrophile-lipophile balance (HLB) value (HLB less than 8) or a polymeric dispersant of the type used in the lubricant industry. It is preferably nonionic, or a mixture of nonionics and ionics. A preferred dispersant for the aqueous liquid medium is of high HLB value (HLB greater than 10), preferably a nonylphenoxypoly(ethyleneoxy)ethanol-type surfactant. The uniform dispersion of nanotubes is obtained with a designed viscosity in the liquid medium. The dispersion of nanotubes may be obtained in the form of a paste, gel or grease, in either a petroleum liquid medium or an aqueous medium.
This dispersion may also contain a large amount of one or more other chemical compounds, preferably polymers, not for the purpose of dispersing, but to achieve thickening or other desired fluid characteristics.
It is an object of the present invention to provide a method of preparing a stable dispersion of the carbon nanotube in a liquid medium with the combined use of dispersants and physical agitation.
It is another object of the present invention to utilize a carbon nanotube that is either single-walled, or multi-walled, with typical aspect ratio of 500-5000.
It is another object of the present invention to utilize carbon nanotubes which may optionally be surface treated to be hydrophilic at surface for ease of dispersing into the aqueous medium.
It is another object of the present invention to utilize a dispersant that is soluble for a selected liquid medium.
It is another object of the present invention to utilize a method of preparation dissolving the dispersant into the liquid medium first, and then adding the carbon nanotube into the mixture while being strongly agitated or ultrasonicated.
It is another object of the present invention to add the carbon nanotube into the liquid while being agitated or ultrasonicated, and then adding the surfactant.
It is another object of the present invention to utilize a petroleum distillate or a synthetic petroleum oil as the liquid medium.
It is another object of the present invention to utilize a liquid medium of the type used in the lubricant industry, or a surfactant, or a mixture of surfactants with a low HLB ( less than 8), preferably nonionic or mixture of nonionic and ionic surfactant. More typically, the dispersant can be the ashless polymeric dispersant used in the lubricant industry.
It is another object of the present invention to utilize a dispersant-detergent (DI) additive package typical sold in the lubricant industry as the surfactant/dispersant.
It is another object of the present invention to utilize a liquid medium consisting of water or any water based solution.
It is another object of the present invention to utilize a dispersant having a high HLB ( greater than 10), preferably nonylphenoxypoly-(ethyleneoxy)ethanol-type surfactants.
It is another object of the present invention to utilize a uniform dispersion with a designed viscosity having a nanotube in petroleum liquid medium.
It is another object of the present invention to obtain a uniform dispersion in a form as a gel or paste containing nanotubes in petroleum liquid medium or aqueous medium.
It is another object of the present invention to obtain a uniform dispersion of nanotubes in a form as a grease obtained from dispersing carbon nanotube in petroleum liquid medium or aqueous medium.
It is another object of the present invention to form a uniform and stable dispersion of carbon nanotubes containing dissolved non-dispersing, xe2x80x9cotherxe2x80x9d compounds in the liquid oil based medium.
It is yet another object of the present invention to form a uniform and stable dispersion in a form containing carbon nanotubes with dissolved non-dispersing, xe2x80x9cotherxe2x80x9d compounds in the liquid water medium.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
The present invention provides a method a dispersing carbon nanotubes into a liquid medium. As set forth above, the nanotubes can be either single-walled, or multi-walled, having a typical nanoscale diameter of 1-500 nanometers. More typically the diameter is around 10-30 nanometers. The length of the tube can be in submicron and micron scale, usually from 500 nanometers to 500 microns.
More typical length is 1 micron to 100 microns. The aspect ratio of the tube can be from hundreds to thousands, more typical 500 to 5000. The surface of the nanotube can be treated chemically to achieve certain level of hydrophilicity by activated carbon treatment, vapor disposition of chemicals, and/or treatment with a strong acid or base, or the carbon nanotubes, fibers, particles or combination thereof can be utilized as is from the production.
A preferred embodiment utilized a carbon nanotube product obtained from Carbolex at the University of Kentucky which contains amorphous carbon particles. The Carbolex carbon nanotubes comprise single walled nanotubes, multi-wall nanotubes, and combinations thereof. Moreover, the combination can include small fractions of the carboneous materials made up of partially disordered spherical particles and/or short carbon nanotubes.
The petroleum liquid medium can be any petroleum distillates or synthetic petroleum oils, greases, gels, or oil-soluble polymer composition. More typically, it is the mineral basestocks or synthetic basestocks used in the lube industry, e.g., Group I (solvent refined mineral oils), Group II (hydrocracked mineral oils), Group III (severely hydrocracked oils, sometimes described as synthetic or semi-synthetic oils), Group IV (polyalphaolefins), and Group VI (esters, naphthenes, and others). One preferred group includes the polyalphaolefins, synthetic esters, and polyalkylglycols.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-octenes), poly(1-decenes), etc., and mixtures thereof; alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di-(2-ethylhexyl)benzenes, etc.); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.), alkylated diphenyl, ethers and alkylated diphenyl sulfides and the derivatives, analogs and homologs thereof and the like.
Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc. constitute another class of known synthetic oils.
Another suitable class of synthetic oils comprises the esters of dicarboxylic acids (e.g., phtalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene glycol monoether, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azealate, dioctyl phthalate, didecyl phthalate, dicicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid, and the like.
Esters useful as synthetic oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. Other synthetic oils include liquid esters of phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid, etc.), polymeric tetrahydrofurans and the like.
Preferred polyalphaolefins (PAO), include those sold by Mobil Chemical company as SHF fluids, and those sold by Ethyl Corporation under the name ETHYLFLO, or ALBERMARLE. PAO""s include the Ethyl-flow series by Ethyl Corporation, xe2x80x9cAlbermarle Corporation,xe2x80x9d including Ethyl-flow 162, 164, 166, 168, and 174, having varying viscosity from about 2 to about 460 centistokes.
Mobil SHF-42 from Mobil Chemical Company, Emery 3004 and 3006, and Quantum Chemical Company provide additional polyalphaolefins basestocks. For instance, Emery 3004 polyalphaolefin has a viscosity of 3.86 centistokes (cSt) at 212xc2x0 F. (100xc2x0 C.) and 16.75 cSt at 104xc2x0 F. (40xc2x0 C.). It has a viscosity index of 125 and a pour point of xe2x88x9298xc2x0 F. and it also has a flash point of 432xc2x0 F. and a fire point of 478xc2x0 F. Moreover, Emery 3006 polyalphaolefin has a viscosity of 5.88 cSt at +212xc2x0 F. and 31.22 cSt at +104xc2x0 F. It has a viscosity index of 135 and a pour point of xe2x88x9287xc2x0 F. It also has a flash point of +464xc2x0 F. and a fire point of +514xc2x0 F.
Additional satisfactory polyalphaolefins are those sold by Uniroyal Inc. under the brand Synton PAO-40, which is a 40 centistoke polyalphaolefin. Also useful are the Oronite brand polyalphaolefins manufactured by Chevron Chemical Company.
It is contemplated that Gulf Synfluid 4 cSt PAO, commercially available from Gulf Oil Chemicals Company, a subsidiary of Chevron Corporation, which is similar in many respects to Emery 3004 may also be utilized herein. Mobil SHF-41 PAO, commercially available from Mobil Chemical Corporation, is also similar in many respects to Emery 3004.
Preferably the polyalphaolefins will have a viscosity in the range of about 2-40 centistoke at 100xc2x0 C., with viscosity of 4 and 10 centistoke being particularly preferred.
The most preferred synthetic based oil ester additives are polyolesters and diesters such as di-aliphatic diesters of alkyl carboxylic acids such as di-2-ethylhexylazelate, di-isodecyladipate, and di-tridecyladipate, commercially available under the brand name Emery 2960 by Emery Chemicals, described in U.S. Pat. No. 4,859,352 to Waynick. Other suitable polyolesters are manufactured by Mobil Oil. Mobil polyolester P-43, M-045 containing two alcohols, and Hatco Corp. 2939 are particularly preferred.
Diesters and other synthetic oils have been used as replacements of mineral oil in fluid lubricants. Diesters have outstanding extreme low temperature flow properties and good residence to oxidative breakdown.
The diester oil may include an aliphatic diester of a dicarboxylic acid, or the diester oil can comprise a dialkyl aliphatic diester of an alkyl dicarboxylic acid, such as di-2-ethyl hexyl azelate, di-isodecyl azelate, di-tridecyl azelate, di-isodecyl adipate, di-tridecyl adipate. For instance, Di-2-ethylhexyl azelate is commercially available under the brand name of Emery 2958 by Emery Chemicals.
Also useful are polyol esters such as Emery 2935, 2936, and 2939 from Emery Group of Henkel Corporation and Hatco 2352, 2962, 2925, 2938, 2939, 2970, 3178, and 4322 polyol esters from Hatco Corporation, described in U.S. Pat. No. 5,344,579 to Ohtani et al. and Mobil ester P 24 from Mobil Chemical Company. Mobil esters such as made by reacting dicarboxylic acids, glycols, and either monobasic acids or monohydric alcohols like Emery 2936 synthetic-lubricant basestocks from Quantum Chemical Corporation and Mobil P 24 from Mobil Chemical Company can be used. Polyol esters have good oxidation and hydrolytic stability. The polyol ester for use herein preferably has a pour point of about xe2x88x92100xc2x0 C. or lower to xe2x88x9240xc2x0 C. and a viscosity of about 2-460 centistoke at 100xc2x0 C.
Group III oils are often referred to as hydrogenated oil to be used as the sole base oil component of the instant invention providing superior performance to conventional motor oils with no other synthetic oil base or mineral oil base.
A hydrogenated oil is a mineral oil subjected to hydrogenation or hydrocracking under special conditions to remove undesirable chemical compositions and impurities resulting in a mineral oil based oil having synthetic oil components and properties. Typically the hydrogenated oil is defined as a Group III petroleum based stock with a sulfur level less than 0.03, severely hydrotreatd and isodewaxed with saturates greater than or equal to 90 and a viscosity index of greater than or equal to 120 may optionally be utilized in amounts up to 90 percent by volume, more preferably from 5.0 to 50 percent by volume and more preferably from 20 to 40 percent by volume when used in combination with a synthetic or mineral oil.
The hydrogenated oil my be used as the sole base oil component of the instant invention providing superior performance to conventional motor oils with no other synthetic oil base or mineral oil base. When used in combination with another conventional synthetic oil such as those containing polyalphaolefins or esters, or when used in combination with a mineral oil, the hydrogenated oil may be present in an amount of up to 95 percent by volume, more preferably from about 10 to 80 percent by volume, more preferably from 20 to 60 percent by volume and most preferably from 10 to 30 percent by volume of the base oil composition.
A Group I or II mineral oil basestock may be incorporated in the present invention as a portion of the concentrate or a basestock to which the concentrate may be added. Preferred as mineral oil basestocks are the ASHLAND 325 Neutral defined as a solvent refined neutral having a SABOLT UNIVERSAL viscosity of 325 SUS @ 100xc2x0 F. and ASHLAND 100 Neutral defined as a solvent refined neutral having a SABOLT UNIVERSAL viscosity of 100 SUS @ 100xc2x0 F., manufactured by the Marathon Ashland Petroleum.
Other acceptable petroleum-base fluid compositions include white mineral, paraffinic and MVI naphthenic oils having the viscosity range of about 20-400 centistokes. Preferred white mineral oils include those available from Witco Corporation, Arco Chemical Company, PSI and Penreco. Preferred paraffinic oils include solvent neutral oils available from Exxon Chemical Company, HVI neutral oils available from Shell Chemical Company, and solvent treated neutral oils available from Arco Chemical Company. Preferred MVI naphthenic oils include solvent extracted coastal pale oils available from Exxon Chemical Company, MVI extracted/acid treated oils available from Shell Chemical Company, and naphthenic oils sold under the names HydroCal and Calsol by Calumet, and described in U.S. Pat. No. 5,348,668 to Oldiges.
Finally, vegetable oils may also be utilizes as the liquid medium in the instant invention.
The selected aqueous medium is water, or it can be any water-based solution including alcohol and its derivatives, such as glycols or any water-soluble inorganic salt or organic compound.
Dispersant Used in Lubricant Industry
Dispersants used in the lubricant industry are typically used to disperse the xe2x80x9ccold sludgexe2x80x9d formed in gasoline and diesel engines, which can be either xe2x80x9cashless dispersantsxe2x80x9d , or containing metal atoms. They can be used in the instant invention since they have been found to be an excellent dispersing agent for soot, an amorphous form of carbon particles generated in the engine crankcase and incorporated with dirt and grease.
The ashless dispersants commonly used in the automotive industry contain an lipophilic hydrocarbon group and a polar functional hydrophilic group. The polar functional group can be of the class of carboxylate, ester, amine, amide, imine, imide, hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhydride, or nitrile. The lipophilic group can be oligomeric or polymeric in nature, usually from 70 to 200 cabon atoms to ensure oil solubility. Hydrocarbon polymers treated with various reagents to introduce polar functions include products prepared by treating polyolefins such as polyisobutene first with maleic anhydride, or phosphorus sulfide or chloride, or by thermal treatment, and then with reagents such as polyamine, amine, ethylene oxide, etc.
Of these ashless dispersants the ones typically used in the petroleum industry include N-substitued polyisobutenyl succinimides and succinates, allkyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate copolymers, alkylmethacrylate-polyethylene glycol methacrylate copolymers, and polystearamides. Preferred oil-based dispersants that are most important in the instant application include dispersants from the chemical classes of alkylsuccinimide, succinate esters, high molecular weight amines, Mannich base and phosphoric acid derivatives. Some specific examples are polyisobutenyl succinimide-polyethylenepolyamine, polyisobutenyl succinic ester, polyisobutenyl hydroxybenzyl-polyethylenepolyamine, bis-hydroxypropyl phosphorate. The dispersant may be combined with other additives used in the lubricant industry to form a xe2x80x9cdispersant-detergent (DI)xe2x80x9d additive package, e.g., Lubrizol(trademark) 9802A, and the whole DI package can be used as dispersing agent for the nanotube suspension.
For instance, LUBRIZOL 9802A is described in the technical brochure (MATERIAL SAFETY DATA SHEET No. 1922959-1232446-3384064) by The Lubrizol Corporation in Wickliffe, Ohio and is hereby incorporated by reference. LUBRIZOL 9802A is described as a motor oil additive is believed to contain as an active ingredient a zinc dithiophosphate and/or zinc alkyldithiophosphate.
LUBRIZOL 4999 is described in its Technical Brochure (MATERIAL SAFETY DATA SHEET No. 1272553-1192556-3310026) by the Lubrizol Corporation in Wickliffe, Ohio and is hereby incorporated by reference. LUBRIZOL 9802A is described as a engine oil additive and contains as an active ingredient from 5 to 9.9 percent of a zinc alkyldithiophosphate.
OLOA 9061 is described in Technical Brochure xe2x80x9cMATERIAL SAFETY DATA SHEET No. 006703xe2x80x9d by Chevron Chemical Company LLC and is hereby incorporated by reference. OLOA 9061 is described as zinc alkyl dithiophosphate compound.
IGEPAL CO-630 is described in Technical Brochure xe2x80x9cMATERIAL SAFETY DATA SHEETxe2x80x9d from Rhodia Inc. and is hereby incorporated by reference. IGEPAL CO-630 is described as a nonylphenoxy poly(ethyleneoxy) ethanol, branched compound.
Alternatively a surfactant or a mixture of surfactants with low HLB value (typically less than or equal to 8), preferably nonionic, or a mixture of nonionics and ionics, may be used in the instant invention.
The dispersant for the water based carbon nanotube dispersion should be of high HLB value (typically less than or equal to 10), preferable nonylphenoxypoly (ethyleneoxy) ethanol-type surfactants are utilized.
In both the water and oil based cases, the dispersants selected should be soluble or dispersible in the liquid medium.
The dispersant can be in a range of up from 0.001 to 30 percent, more preferably in a range of from between 0.5 percent to 20 percent, more preferably in a range of from between 1.0 to 8.0 percent, and most preferably in a range of from between 2 to 6 percent. The carbon nanotube can be of any desired weight percentage in a range of from 0.0001 up to 50 percent. For practical application it is usually in a range of from between 0.01 percent to 2 percent, and most preferably in a range of from between 0.05 percent to 0.5 percent. The remainder of the formula is the selected oil or water medium.
It is believed that in the instant invention the dispersant functions by adsorbing onto the surface of the carbon nanotube. The dispersant contains a hydrophilic segment and a hydrophobic segment which surrounds the carbon particles thereby providing a means for isolating and dispersing the carbon particles. The selection of a dispersant having a particular HLB value is important to determine the dispersant characteristics such as rate and the degree of stabilization over time.
This dispersion may also contain a large amount of one or more other chemical compounds, preferably polymers, not for the purpose of dispersing, but to achieve thickening or other desired fluid characteristics.
The viscosity improvers used in the lubricant industry can be used in the instant invention for the oil medium, which include olefin copolymers (OCP), polymethacrylates (PMA) hydrogenated styrene-diene (STD), and styrene-polyester (STPE) polymers. Olefin copolymers are rubber-like materials prepared from ethylene and propylene mixtures through vanadium-based Ziegler-Natta catalysis. Styrene-diene polymers are produced by anionic polymerization of styrene and butadiene or isoprene. Polymethacrylates are produced by free radical polymerization of alkyl methacrylates. Styrene-polyester polymers are prepared by first co-polymerizing styrene and maleic anhydride and then esterifying the intermediate using a mixture of alcohols.
Other compounds which can be used in the instant invention in either the aqueous medium or the oil medium include: acrylic polymers such as polyacrylic acid and sodium polyacrylate, high-molecular-weight polymers of ethylene oxide such as Polyox(copyright) WSR from Union Carbide, cellulose compounds such as carboxymethylcellulose, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), xanthan gums and guar gums, polysaccharides, alkanolamides, amine salts of polyamide such as Disparlon AQ series from King Industries, hydrophobically modified ethylene oxide urethane (e.g., Acrysol series from Rohmax), silicates, and fillers such as mica, silicas, cellulose, wood flour, clays (including organoclays) and nanoclays, and resin polymers such as polyvinyl butyral resins, polyurethane resins, acrylic resins and epoxy resins.
Chemical compounds such as plasticizers can also be used in the instant invention and may be selected from the group including phthalate, adipates, sebacate esters, and more particularly: glyceryl tri(acetoxystearate), epoxidized soybean oil, epoxidized linseed oil, N,n-butyl benzene sulfonamide, aliphatic polyurethane, epoxidized soy oil, polyester glutarate, polyester glutarate, triethylene glycol caprate/caprylate, long chain alkyl ether, dialkyl diester glutarate, monomeric, polymer, and epoxy plasticizers, polyester based on adipic acid, hydrogenated dimer acid, distilled dimer acid, polymerized fatty acid trimer, ethyl ester of hydrolyzed collagen, isostearic acid and sorbian oleate and cocoyl hydrolyzed keratin, PPG-12/PEG-65 lanolin oil, dialkyl adipate, alkylaryl phosphate, alkyl diaryl phosphate, modified triaryl phosphate, triaryl phosphate, butyl benzyl phthalate, octyl benzyl phthalate, alkyl benzyl phthalate, dibutoxy ethoxy ethyl adipate, 2-ethylhexyldiphenyl phosphate, dibutoxy ethoxy ethyl formyl, diisopropyl adipate, diisopropyl sebacate, isodecyl oleate, neopentyl glycol dicaprate, neopenty glycol diotanoate, isohexyl neopentanoate, ethoxylated lanolins, polyoxyethylene cholesterol, propoxylated (2 moles) lanolin alcohols, propoxylated lanoline alcohols, acetylated polyoxyethylene derivatives of lanoline, and dimethylpolysiloxane. Other plasticizers which may be substituted for and/or used with the above plasticizers including glycerine, polyethylene glycol, dibutyl phthalate, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and diisononyl phthalate all of which are soluble in a solvent carrier.
The physical mixing includes high shear mixing, such as with a high speed mixer, homogenizers, microfluidizers, a Kady mill, a colloid mill, etc., high impact mixing, such as attritor, ball and pebble mill, etc., and ultrasonication methods.
Ultrasonication is the most preferred physical method in the instant invention since it is less destructive to the carbon nanotube structure than the other methods described. Ultrasonication can be done either in the bath-type ultrasonicator, or by the tip-type ultrasonicator. More typically, tip-type ultrasonication is applied for higher energy output. Sonication at the medium-high instrumental intensity for up to 30 minutes, and usually in a range of from 10 to 20 minutes is desired to achieve better homogeneity.
One dismembrator useful for preparing the instant invention is a Model 550 Sonic dismembrator manufactured by Fisher Scientific Company, located in Pittsburgh Pennsylvania. The instruction manual Publication No. FS-IM-2 published in November of 1996 describing the use of the Fisher Scientific Model 550 Sonic Dismembrator is hereby incorporated by reference. The generator power supply converst conventional 50/60 Hz AC line power to 20 kHZ electrical energy which is fed to the converter where it is transformed to mechanical vibration. The heart of the convertor is a lead zirconate titanate (Piezoelectric) crystal which, when subjected to an alternating voltage, expands and contracts. The convertor vibrates in the longitudinal direction and transmits this motion to the horn tip immersed in the liquid solution. Cavitation results, in which microscopic vapor bubbles are formed momentarily and implode, causing powerful shock waves to radiate throughout the sample from the tip face. Horns and probes amplify the longitudinal vibration of the convertor; higher amplification (or gain) results in more intense cavitational action and greater disruption. The larger the tip of the probe, the larger the volume that can be processed but at lesser intensity. The convertor is tuned to vibrate at a fixed frequency of 20 kHZ. All horns and probes are resonant bodies, and are also tuned to vibrate at 20 kHZ. Of course it is contemplated that other models and competing ultrasonic mixing devices could be utilized in accordance with the present invention.
The raw material mixture may be pulverized by any suitable known dry or wet grinding method. One grinding method includes pulverizing the raw material mixture in the fluid mixture of the instant invention to obtain the concentrate, and the pulverized product may then be dispersed further in a liquid medium with the aid of the dispersants described above. However, pulverization or milling reduces the carbon nanotube average aspect ratio.
The instant method of forming a stable suspension of nanotubes in a solution consist of two primary steps. First select the appropriate dispersant for the carbon nanotube and the medium, and dissolve the dispersant into the liquid medium to form a solution, and second add the carbon nanotube into the dispersant containing solution while strongly agitating, ball milling, or ultrasonication of the solution.
The present invention is further described and illustrated in the following examples:

Preparation of stable nanotube dispersions in liquids


A method and system for high speed data access of a banked cache memory. In accordance with the method and system of the present invention, during a first cycle, in response to receipt of a request address at an access controller, the request address is speculatively transmitted to a banked cache memory, where the speculative transmission has at least one cycle of latency. Concurrently, the request address is snooped in a directory associated with the banked cache memory. Thereafter, during a second cycle the speculatively transmitted request address is distributed to each of multiple banks of memory within the banked cache memory. In addition, the banked cache memory is provided with a bank indication indicating which bank of memory among the multiple banks of memory contains the request address, in response to a bank hit from snooping the directory. Thereafter, data associated with the request address is output from the banked cache memory, in response to the bank indication, such that access time to a high latency remote banked cache memory is minimized.

1. Technical Field
The present invention relates in general to an improved method and system for accessing cache memory within a data processing system, and in particular, to an improved method and system for high speed access to a banked cache memory. Still more particularly, the present invention relates to an improved method and system for high speed access to a high latency remote banked cache memory wherein the access time to the cache memory is minimized.
2. Description of the Related Art
A digital computer system utilizes a central processing unit and a computer main memory to perform a wide range of functions. Such circuitry permits repetitive functions to be carried out at rates much higher than if the corresponding functions could be performed manually. Memory locations provide storage from which data can be read or to which data can be written.
As technology develops, multiple processors and multiple levels of memory and cache have been added to digital computer systems. In addition, the utilization of on-chip and off-chip cache continues to increase processing capabilities. In general, requests come from a system bus to a processor system that includes a processor core and multiple levels of on-chip and off-chip cache. The processor system then performs a snoop to detect whether the requested data is available in the on-chip cache. In addition, the processor system typically snoops an off-chip cache associated therewith. From the snoop return, the request may be directed to a particular cache in order to access the requested data.
Several types of memory have been developed which may be utilized as on-chip cache, off-chip cache and/or main memory. These random access memories (RAM) are preferably semi-conductor based memory that can be read from and written to by the central processing unit and other hardware devices. The storage locations within RAM can be accessed in any order. For example, one type of RAM which is well known in the art is a dynamic RAM (DRAM). Dynamic RAM is typically utilized for storing large increments of data. In particular, DRAMs store information in integrated circuits containing capacitors. Because capacitors lose their charge over time, DRAM circuits typically include logic to refresh the DRAM chips continuously. While a DRAM chip is being refreshed, the chip cannot be read by the processor, which leads to wait states while the DRAM chips is being refreshed. Another type of RAM which is well known in the art is static RAM (SRAM). SRAMs store information in logic circuits known as flip-flops, which retain information as long as there is enough power to run the device. SRAMs do not have the delay states inherent in DRAMs, however SRAM circuitry is more complex than DRAM circuitry and is typically utilized in smaller increments.
In general, memory devices such as SRAM and DRAM are formed in memory locations which form memory arrays. The memory locations of the memory arrays are identified by memory addresses. When memory locations of a memory array are to be accessed, the addresses of the memory locations are provided to decoder circuitry of the memory device, as is well known in the art. The decoder circuitry decodes the address signals applied thereto to permit access to the memory locations identified by the address signals. Typically, multiple banks of SRAM or DRAM may be placed together whereby a controller controls access to each bank of memory and routes addresses to the proper bank of memory within the banked cache memory.
In a recent configuration of processor/memory devices, a processor accesses an on-chip level-one (L1) cache which comprises small, fast SRAM, an on-chip level-two (L2) cache which comprises banked SRAM and an off-chip level-three (L3) cache which comprises banked DRAM cache. In addition, the processor may access a main memory which is shared among multiple devices. There is a greater latency inherent in accessing data from off-chip memories than from on-chip memories. However, off-chip memories are typically larger than on-chip memories and thus can provide large amounts of data for a single access. Among the off-chip memories, a processor can access an L3 cache much more quickly than a main memory, particularly when the main memory is shared by multiple processors.
Several methods have been developed to reduce the latency inherent in accessing a remote L3 cache and in accessing banked DRAM cache to determine which bank of memory to access next. According to one method known as bank parking, for each request from a system bus, a speculative access to the bank of memory that was previously accessed is made. By this method, speculative access is only beneficial if the bank of memory that was previously accessed is requested again. According to another method known as redundant access, each bank of memory is a clone of all other banks of memory. Therefore, for each request, the same address is passed to each bank of memory whereby any available banks of memory can respond to the request. In order for redundant access to be beneficial, a small number of banks of memory and small amount of cache in each bank of memory are utilized. However, it is preferable to utilize a large number of banks and a large amount of cache in each bank for an L3 cache.
In view of the foregoing, it is therefore desirable to provide a method of accessing a high latency banked cache memory and in particular accessing off-chip banked DRAM cache from a processor, whereby fast access to the cache is provided.
In view of the foregoing, it is therefore an object of the present invention to provide an improved method and system for accessing cache memory within a data processing system.
It is another object of the present invention to provide an improved method and system for high speed access to a banked cache memory.
It is yet another object of the present invention to provide an improved method and system for high speed access to a high latency remote banked cache memory wherein the access time to the cache is minimized.
In accordance with the method and system of the present invention, during a first cycle, in response to receipt of a request address at an access controller, the request address is speculatively transmitted to a banked cache memory, where the speculative transmission has at least one cycle of latency. Concurrently, the request address is snooped in a directory associated with the banked cache memory. Thereafter, during a second cycle the speculatively transmitted request address is distributed to each of multiple banks of memory within the banked cache memory. In addition, the banked cache memory is provided with a bank indication indicating which bank of memory among the multiple banks of memory contains the request address, in response to a bank hit from snooping the directory. Thereafter, data associated with the request address is output from the banked cache memory, in response to the bank indication, such that access time to a high latency remote banked cache memory is minimized.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.

Method and system for high speed access to a banked cache memory

International Business Machines Corporation


An ink jet ink composition comprising from about 0.5% to about 30% by weight of a pigment, a carrier and a dispersant, the dispersant comprising an anionic derivative of an ethoxylated alkylphenol-formaldehyde resin, the ratio of dispersant:pigment being from about 0.1:1 to about 5:1.

This invention relates to a dispersant for a pigment-based ink jet ink.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate (paper, transparent film, fabric, etc.) in response to digital signals. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging. The inks used in ink jet printers are generally classified as either dye-based or pigment-based.
A dye is a colorant which is molecularly dispersed or solvated by a carrier. The carrier can be a liquid or a solid at room temperature. A commonly used carrier is water or a mixture of water and organic co-solvents. Molecules of the carrier surround each individual dye molecule. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor lightfastness. When water is used as the carrier, such inks also generally suffer from poor water fastness.
In pigment-based inks, the colorant exists as discrete particles. These pigment particles are usually treated with addenda known as dispersants or stabilizers which serve to keep the pigment particles from agglomerating and settling out of the carrier. Water-based pigment-based inks are prepared by incorporating the pigment in the continuous water phase by a milling and dispersing process. Pigment-based inks require a water-soluble dispersant in the pigment slurry during the milling process. Such a dispersant is necessary to produce a stable colloidal mixture and an ink that can be xe2x80x9cjettedxe2x80x9d reliably without clogging the print head nozzles.
Dispersing agents in an ink jet ink have the dual function of helping to break down pigments to sub-micron size during the milling process and of keeping the colloidal dispersion stable and free from flocculation for a long period of time. In general, dispersions suffer from poor colloidal stability due to particle agglomeration and/or sedimentation, thus limiting the usefulness of the dispersions in inks.
Many dispersing agents are very selective in their ability to disperse these pigments to sub-micron size. This is probably one of the many reasons for the wide variety of known dispersing agents. In many instances, each class of pigments may require a specific dispersing agent. Another problem encountered with some dispersing agents is that the resulting inks suffer from unacceptable image quality properties. This can include unacceptable coalescence, banding, bleeding, densities, or other defects seen on the final printed image. Yet another problem with many commercially available dispersants is that they yield dispersions with very low surface tensions. Thus, there is a continuing need for improved dispersing agents for pigment-based inks.
German patent application DE 19850152 discloses the use of ethoxylated alkyl-phenol surfactants for use in the preparation of pigment-based inks for ink-jet printing. However, there is a problem with these dispersants in that pigment dispersions using them have an unacceptably large particle size and are unstable at high temperatures, as will be shown hereinafter.
German patent application DE 19801759 discloses the use of sulfonated aromatic derivatives as dispersants for a wide range of pigment preparations including those in ink-jet printing. However, these dispersants differ significantly in structure to the materials employed in the invention.
It is an object of this invention to provide a dispersant for a pigment-based ink jet ink which will enable the particle size of the dispersed pigment to be lower than that obtained using prior art dispersants disclosed for such use. It is another object of this invention to maintain such particle size for the pigment when the dispersion is held at high temperatures. It is another object of this invention to provide a dispersant for pigment-based ink-jet inks which will produce images which have a high D-max and which are free of defects.
These and other objects are achieved in accordance with this invention which relates to an ink jet ink composition comprising from about 0.5% to about 30% by weight of a pigment, a carrier and a dispersant, the dispersant comprising an anionic derivative of an ethoxylated alkylphenol-formaldehyde resin, the ratio of dispersant:pigment being from about 0.1:1 to about 5:1.
Use of the dispersants in the invention will produce pigment dispersions on the order of 0.1 xcexcm or less in size during the milling process. These dispersions are also characterized by excellent colloidal stability and lack of flocculation and/or sedimentation on keeping at high temperatures. In addition, these dispersing agents are useful with a wide variety of pigments.
Any anionic derivative of an ethoxylated alkylphenol-formaldehyde resin dispersant may be used in the invention provided it produces the desired results. In a preferred embodiment of the invention, the dispersant has the formula:
wherein: each R independently represents a linear or branched alkyl, alkenyl, or arylalkyl group having from about 4 to about 30 carbon atoms;
x is an integer from 0 to 20;
y is an integer from 1 to 20; with the proviso that x+y is from 2 to 20;
z is an integer from 4 to 20;
A is an anionic group, such as sulfate, sulfonate, phosphate, phosphonate or carboxylate; and
M is a cationic group, such as an alkali metal, alkaline earth metal, ammonium or substituted ammonium.
In a preferred embodiment of the invention, each R independently represents a linear or branched alkyl, alkenyl, or arylalkyl group having from about 6 to 15 carbon atoms, preferably from about 8 to about 12 carbon atoms. In another preferred embodiment, x+y is from 4 to 12, preferably 6 to 8. In still another preferred embodiment, z is an integer from 6 to 14, preferably from 8 to 12.
The ethoxylated alkylphenol-formaldehyde resin dispersant of the invention is a comb-like material which possesses multiple hydrophobic blocks and multiple hydrophilic blocks.
In the present invention, any of the known pigments can be used. Pigments can be selected from those disclosed, for example, in U.S. Pat. Nos. 5,026,427; 5,085,698; 5,141,556; 5,160,370 and 5,169,436, the disclosures of which are hereby incorporated by reference. The exact choice of pigment will depend upon the specific color reproduction and image stability requirements of the printer and application. For four-color printers, a combination of cyan, magenta, yellow, and black (CMYK) pigments should be used. An exemplary four color set is copper phthalocyanine (pigment blue 15), quinacridone magenta (pigment red 122), pigment yellow 74 or pigment yellow 155 and carbon black (pigment black 7). Another exemplary four color set is bis(phthalocyanyl-alumino)tetra-phenyldisiloxane cyan pigment, quinacridone magenta (pigment red 122), pigment yellow 74 or pigment yellow 155 and carbon black (pigment black 7). In a preferred embodiment of the invention, the pigment has a particle size of from about 10 nanometers to about 1000 nanometers.
As noted above, the ink jet ink composition of the invention comprises from about 0.5% to about 30% by weight of a pigment. In a preferred embodiment of the invention, the ink composition comprises from about 1% to about 5% by weight of the pigment.
The carrier employed in the invention can be, for example, water or a mixture of water and at least one water soluble co-solvent. Selection of a suitable mixture depends on requirements of the specific application, such as desired surface tension and viscosity, the selected pigment, drying time of the pigmented ink jet ink, and the type of paper onto which the ink will be printed. Representative examples of water-soluble co-solvents that may be selected include (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; (3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such as ethyl acetate, ethyl lactate, ethylene carbonate and propylene carbonate; (5) polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol 1,2,6-hexanetriol and thioglycol; (6) lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl (or -ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, triethylene glycol mono-methyl (or -ethyl) ether and diethylene glycol di-methyl (or -ethyl) ether; (7) nitrogen-containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and (8) sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone.
A humectant may also be employed in the ink jet composition of the invention to help prevent the ink from drying out or crusting in the orifices of the printhead. Examples of humectants which can be used include polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol 1,2,6-hexanetriol and thioglycol; lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl or mono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether, triethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol di-methyl or di-ethyl ether, and diethylene glycol monobutylether; nitrogen-containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone. A preferred humectant for the composition of the invention is diethylene glycol, glycerol, or diethylene glycol monobutylether. The humectant may be present in any amount effective for the intended purpose. In general, good results have been obtained when the humectant is present in an amount of up to about 70% by weight of the ink jet ink composition, preferably from about 5 to about 50%.
Ink Preparation
A preferred method for making the inks of the invention is disclosed in U.S. Pat. No. 5,679,138, the disclosure of which is hereby incorporated by reference. In general it is desirable to make the pigmented ink jet ink in the form of a concentrated mill grind, which is subsequently diluted to the appropriate concentration for use in the ink jet printing system. This technique permits preparation of a greater quantity of pigmented ink from the equipment. If the mill grind was made in a solvent, it is diluted with water and optionally other solvents to the appropriate concentration. If it was made in water, it is diluted with either additional water or water miscible solvents to make a mill grind of the desired concentration. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density, and print area coverage for the particular application.
In the case of organic pigments, the ink may contain up to approximately 30% pigment by weight, preferably approximately 1.0 to 5%, by weight of the total ink composition for most thermal ink jet printing applications. The amount of aqueous carrier medium is in the range of approximately 70 to 99.8 weight %, preferably approximately 90 to 99.8 weight %, based on the total weight of the ink. A mixture of water and a polyhydric alcohol, such as diethylene glycol, is preferred as the aqueous carrier medium. In the case of a mixture of water and diethylene glycol, the aqueous carrier medium usually contains from about 30% water/70% diethylene glycol to about 95% water/ 5% diethylene glycol. The preferred ratios are approximately 60% water/40% diethylene glycol to about 95% water/ 5% diethylene glycol. Percentages are based on the total weight of the aqueous carrier medium.
Jet velocity, separation length of the droplets, drop size and stream stability are greatly affected by the surface tension and the viscosity of the ink. Pigmented ink jet inks suitable for use with ink jet printing systems should have a pH in the range of 5 to 9. Anionic and cationic surfactants may be used in the invention as disclosed in U.S. Pat. Nos. 5,324,349; 4,156,616 and 5,279,654 as well as many other surfactants known in the ink jet ink art. Commercial surfactants include the Surfynols(copyright) from Air Products; the Zonyls(copyright) from DuPont Corp. and the Fluorads(copyright) from the 3M Co.
Acceptable viscosity""s are no greater than 20 centipoise, and preferably in the range of about 1.0 to about 10.0, preferably 1.0 to 5.0 centipoise at room temperature.
The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltages and pulse widths for thermal ink jet printing devices, driving frequencies of the piezo element for either a drop-on-demand device or a continuous device, and the shape and size of the nozzle.
Other ingredients are also commonly added to ink jet inks. A penetrant (0-10 wt. %) may be added to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. A preferred penetrant for the inks of the present invention is n-propanol at a final concentration of 1-6 wt. %. A biocide (0.01-1.0 wt. %) may be added to prevent unwanted microbial growth which may occur in the ink over time. A preferred biocide for the inks of the present invention is Proxel(copyright) GXL (Zeneca Colours Co.) at a final concentration of 0.05-0.5 wt. %. Additional additives which may optionally be present in ink jet inks include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, and defoamers.
The ink jet inks provided by this invention are employed in ink jet printing wherein liquid ink drops are applied in a controlled fashion to an ink receptive layer substrate, by ejecting ink droplets from the plurality of nozzles, or orifices, in a print head of ink jet printers
Ink-receptive substrates useful in ink jet printing are well known to those skilled in the art. Representative examples of such substrates are disclosed in U.S. Pat. Nos. 5,605,750; 5,723,211; and 5,789,070 and EP 813 978 A1, the disclosures of which are hereby incorporated by reference.
Commercially available ink jet printers use several different methods to control the deposition of the ink droplets. Such methods are generally of two types: continuous stream and drop-on-demand.
In drop-on-demand systems, a droplet of ink is ejected from an orifice directly to a position on the ink receptive layer by pressure created by, for example, a piezoelectric device, an acoustic device, or a thermal process controlled in accordance digital data signals. An ink droplet is not generated and ejected through the orifices of the print head unless it is needed. Ink jet printing methods, and related printers, are commercially available and need not be described in detail.
The following examples illustrate the utility of the present invention.