Title of Invention: Systems and methods for particulate removal using polymeric microstructures Abstract: Systems and methods for removing particles from a surface of a substrate without damage to the substrate are provided. The disclosed systems/methods use polymeric microstructures, e.g., microfibrils, to remove micrometric and sub-micrometric particles from a substrate surface by establishing interfacial interactions with the particles that effectively debond the particles from the surface of the substrate. The disclosed systems/methods have wide ranging applications, including particle removal in art conservation processes, microelectronic applications, optical applications and any other field that stands to benefit from precise removal of particles/dust from a surface without damage to the surface. Detailed Description: Part general_description_paragraphs: Part CROSS-REFERENCE TO RELATED APPLICATION: The present application claims priority benefit to a provisional patent application filed in the U.S. Patent Office entitled “Systems and Methods for Particulate Removal Using Polymeric Microfibrils,” which was filed on Oct. 30, 2015, and assigned Ser. No. 62/248,834. The entire content of the foregoing provisional patent application is incorporated herein by reference. Part BACKGROUND: Part 1. Technical Field: The present disclosure relates to systems and methods for removing particles from a surface of a substrate without damage to the substrate and, more particularly, to systems/methods that use polymeric microstructures to remove micrometric and sub-micrometric particles from a substrate surface by establishing interfacial interactions with the particles that effectively debond the particles from the surface of the substrate. The disclosed systems and methods have wide ranging applications, including particle removal in art conservation processes, microelectronic applications, optical applications and any other field that stands to benefit from precise removal of particles/dust from a surface without damage to the surface. Part 2. Background Art: Removal of micrometric and sub-micrometric contaminant particles—loosely referred to as dust—from solid surfaces is a critical and exacting challenge in various areas of science and technology, including microelectronics, aerospace, optics, xerography, and adhesive bonding.[1-5] While removal of relatively large (>10 μm) particles from a surface is generally achievable, e.g., by blowing the particles from the surface with a gas jet,[3] removal of smaller (e.g., micrometric and sub-micrometric) particles is usually carried out with wet cleaning techniques, including conventional solvent cleaning methods and more advanced acoustic cleaning approaches.[3, 6] Although traditional wet cleaning techniques are commonly employed, they present substantial disadvantages and/or limitations, including limited efficiency in removal of sub-micrometric (<0.3 μm) particles, incompatibility with chemical-sensitive materials, re-deposition from contaminated chemicals, environmental damage, and also possible liquid residue on the surface that may cause adhesion of remaining particles.[2, 3] For these reasons, removal of dust particles using dry cleaning techniques (e.g., cleaning with laser beam, microabrasive particles, argon/nitrogen aerosols, and carbon dioxide snow jet) have gained increasing attention in recent decades.[3, 4, 7, 8] Although dry cleaning approaches do not have many of the drawbacks of the wet cleaning methods, they have one major disadvantage. In particular, previously developed dry cleaning approaches can damage the surface of the substrate upon removal of the surface contaminants.[7, 9] In particular, effective dry cleaning approaches generally rely on energy transfer from an impacting source (e.g., a laser beam or accelerated microparticles) to the contaminant particles, in order to provide a sufficient amount of energy to overcome the dust particles' adhesion to the surface of the substrate.[3, 4] However, the mechanical and thermal stresses associated with detachment of the dust particles from the surface in the noted dry cleaning approaches may also adversely cause damage and even material loss at the surface of the substrate itself.[7, 9] Thus, despite efforts to date, a need remains for effective techniques for removal of particles, particularly micrometric and sub-micrometric particles, from a surface that does not damage and/or alter the surface. The systems and methods of the present disclosure address the foregoing needs, and overcome the disadvantages/limitations of prior art particle removal techniques. Part SUMMARY: The present disclosure provides advantageous systems and methods for removing particulate contamination, e.g., micrometric and sub-micrometric particles, from a solid substrate surface using polymeric microstructures, e.g., microfibrils or micropillars, also known as μ-dusters. The disclosed microstructures, i.e., μ-dusters, are effective in establishing interfacial interactions with the particles to be removed from the surface, thereby debonding the particles from the substrate surface. According to exemplary embodiments of the present disclosure, polymeric microstructures of controlled interfacial and geometrical properties are effective in removing micrometric and sub-micrometric contaminant particles from a solid surface without damaging the underlying substrate. Once these cleaning materials are brought into contact with a contaminated surface, due to their soft and flexible structure, they develop intimate contact with both the surface contaminants and the substrate. While these intrinsically non-sticky cleaning materials have minimal interfacial interactions with the substrate, they produce strong interfacial interactions with the contaminant particles, achieving detachment of the particles from the surface upon retraction of the cleaning material. Unlike flat substrates of the same material, using microstructures of controlled interfacial and geometrical properties also allows elimination of the adsorbed particles from the contact interface. By moving the adsorbed particles from the tip to the side of the microstructures, e.g., fibrils, and consequently removing them from the contact interface, the disclosed polymeric microstructures are highly effective in cleaning contaminant particles from a surface. Thus, the disclosed systems and methods advantageously facilitate a thorough yet nondestructive cleaning of dust particles from solid surfaces, and demonstrate the benefits offered by micro-structured surfaces in development of interfacially-active materials and devices. The terms “microstructure” and “μ-duster” are used interchangeably herein. In each case, the terms refer to thread-like or fiber-like structures, generally arranged in an array defining spaces therebetween. The terms “microfibril” and “micropillar” and the terms “fibril” and “pillar” are also used interchangeably herein. These terms refer to specific implementations of microstructures/μ-dusters, as described herein below. The disclosed systems/methods are both effective and nondestructive in removing micrometric and sub-micrometric particulate contamination from solid surfaces. The microstructures, e.g., micro-scale fibrillar structures, are generally formed from elastic and low-surface-energy polymeric materials. Once the polymeric microstructures, e.g., microfibrils/micropillars, are brought into contact with a contaminated surface, the soft and flexible characteristics associated with the disclosed microstructures establish intimate contact with both the surface contaminants and the substrate. While these intrinsically non-sticky microstructures, e.g., microfibrils/micropillars, have minimal interfacial interactions with the substrate, development of strong interfacial forces between the disclosed microstructures and the contaminant particles advantageously facilitate detachment of the particles from the surface of the substrate upon retraction/removal of the microstructures therefrom. Of note, the interaction of the disclosed microstructures with the surface of the substrate is so minimal as to impart essentially no physical effect to the surface, thereby preventing damage to the surface in connection with the particle removal process. Indeed, the systems and methods of the present disclosure generally employ microstructures, e.g., microfibril/micropillar, structures of controlled geometrical and interfacial properties which allow elimination/removal of adsorbed micrometric and sub-micrometric particles from the contact interface (e.g., by moving the particles from the tip to the side of the fibrils), thereby effectuating nondestructive cleaning/particle removal. The disclosed polymeric microstructures offer a new paradigm for thorough cleaning of micrometric and sub-micrometric dust particles from solid surfaces, while leaving the underlying substrate completely intact. The disclosed systems and methods have wide ranging applications, including particle removal in art conservation processes, microelectronic applications, optical applications and any other field that stands to benefit from precise removal of particles/dust from a surface without damage to the surface. Additional features, functions and benefits of the disclosed systems and methods will be apparent from the description which follows. Part DESCRIPTION OF EXEMPLARY EMBODIMENTS: As noted above, the present disclosure provides systems and methods for removing particles (e.g., micrometric and sub-micrometric particles) from a surface of a substrate without damage to the substrate. The systems/methods employ polymeric microstructures, e.g., microfibrils/micropillars, that establish interfacial interactions with the particles that permit removal/disassociation of the particles from the substrate without damage to the surface. The disclosed systems and methods have wide ranging applications, including particle removal in art conservation processes, microelectronic applications, optical applications and any other field that stands to benefit from precise removal of particles/dust from a surface without damage to the surface. Experimental studies have demonstrated the efficacy of polymeric microfibrils for removal of micrometric and sub-micrometric particles without surface damage. In an experimental study, silica particles were used as the contaminants and a poly(methyl methacrylate) (PMMA) thin film was used as the substrate. Fibrillar structures of various geometrical properties (2-50 μm in diameter with aspect-ratios of ˜2) were used to remove spherical, mono-disperse silica particles (with nominal diameters of 0.26-7.75 μm) from the surface of PMMA thin films (260±5 nm (n=6) in thickness). The microfibrils were fabricated from an elastic and low-surface-energy polymer, namely, polydimethylsiloxane (PDMS). PDMS was chosen for this purpose because it has low surface energy and high elasticity, properties that minimize the interfacial interactions and mechanical stresses between the cleaning material and the substrate. On the other hand, as an elastic and electrically nonconductive polymer which can develop intimate contact with other surfaces, PDMS can generate strong interfacial interactions with the contaminant particles, stronger than those between the particles and the substrate (PMMA). Having stronger interfacial interactions at the PDMS/silica interface grants the detachment of the contaminant particles from the PMMA surface upon retraction of the cleaning material from the substrate. Although advantageous implementations and results achievable with the disclosed systems and methods are described herein with reference to exemplary microstructures, e.g., microfibrils fabricated from PDMS that are used for removal of silica particles from a PMMA substrate, it is to be understood that alternative polymeric materials may be used to fabricate microstructures, e.g., microfibrils/micropillars, according to the present disclosure. The disclosed microstructures may be used to remove a range of contaminants from various substrate surfaces, e.g., PMMA substrates/materials, Teflon AF thin films, glass, etc., as will be readily apparent to persons skilled in the art from the description provided herein. In order to quantify the interfacial interactions of silica particles with the PMMA substrate and the PDMS microfibrils, the adhesion forces between 7.75 μm silica particles and both PMMA and PDMS were measured using an atomic force microscope. As shown in FIG. 1.A1 and FIG. 1.A2, under a typical preload of 100 nN, the adhesion force (Fpull-off) between a 7.75 μm silica particle (FIG. 1.A3) and PDMS was 270.6±10.3 nN (n=10), which is about five (5) times larger than the adhesion force between the silica particle and PMMA (Fpull-off=56.0±4.2 nN (n=10)). The systems and methods of the present disclosure take advantage of the stronger adhesion forces generated between PDMS/silica particles as compared to adhesion forces between PDMS/PMMA. In particular, it is noted that interfacial interactions at both PDMS/silica and PMMA/silica interfaces are only van der Waals (“vdW”), capillary, and/or electrostatic forces. Van der Waals interactions naturally exist between two materials in contact,[10] while capillary interactions generally become effectual in humid conditions.[10, 11] Electrostatic interactions, on the other hand, can be formed upon contact of any two surfaces, even if the contacted surfaces were electrically neutral in the first place.[12, 13] The magnitude of the vdW interaction force between two substrates can be determined by using the Hamaker method.10 Using this method, the vdW-driven adhesion force (FvdW) interacting between phase 1 (silica microparticles) and phase 2 (PDMS or PMMA) across medium 3 (air) at the separation distance D can be calculated by FvdW=−A132R/6D2, where R is the radius of the silica microparticles and A132 is the Hamaker constant between phase 1 and phase 2, interacting across medium 3.10 The corresponding Hamaker constant for each contact interface (i.e., PDMS/silica and PMMA/silica interface) can be determined according to the Lifshitz model (Equation 1). Based on this model A 132 ≈ 3 4 ⁢ kT ⁡ ( ɛ 1 - ɛ 3 ɛ 1 + ɛ 3 ) ⁢ ( ɛ 2 - ɛ 3 ɛ 2 + ɛ 3 ) + 3 ⁢ ⁢ h ⁢ ⁢ υ e 8 ⁢ 2 ⁢ ( n 1 2 - n 3 2 ) ⁢ ( n 2 2 - n 3 2 ) ( n 1 2 + n 3 2 ) 1 2 ⁢ ( n 2 2 + n 3 2 ) 1 2 ⁢ { ( n 1 2 + n 3 2 ) 1 2 + ( n 2 2 + n 3 2 ) 1 2 } Equation ⁢ ⁢ 1 where k is Boltzmann's constant, T is the temperature, h is Planck's constant, and υe is the electron absorption frequency (typically around 3×1015 l/s).10 ε1, ε2, and ε3 are the corresponding dielectric constants of phase 1, phase 2, and medium 3, respectively, while n1, n2, and n3 are the refractive indices of phase 1, phase 2, and medium 3, respectively.10 Using the Lifshitz model and considering the dielectric constants of PDMS, PMMA, and silica as 2.7,14 4.0,15 and 3.8,10 respectively, and their refractive indices as 1.41,14 1.49,15 and 1.45,10 the Hamaker constant for the PMMA/silica contact in dry conditions would be equal to 6.4×10−20 J, while that for the PDMS/silica contact would be 5.5×10−20 J. Knowing the Hamaker constants of the PDMS/silica and PMMA/silica interfaces and assuming that PDMS and PMMA surfaces (with the roughness average (Ra) values of 1.5±0.1 nm (n=5) and 0.8±0.1 nm (n=5), respectively) come into intimate molecular contact with silica particles (i.e., D≈0.3 nm),10 then according to the Hamaker method, it is expected that PDMS and PMMA develop very close vdW forces (FvdW,PDMS=−394 nN while FvdW,PMMA=−460 nN). Other than the Hamaker model, the well-known Johnson-Kendall-Roberts (JKR) model can also be employed to determine the magnitude of the vdW interaction force between two substrates in intimate contact.16 According to this model, the absolute value of the vdW adhesive force between a 7.75 μm silica particle and PMMA is about −1.1 μN, similar to that between the particle and PDMS (FvdW,PDMS=−1.0 μN). It is clear that theoretically, PDMS and PMMA are expected to develop relatively similar vdW forces upon intimate contact with a 7.75 μm silica particle. Even so, the measured adhesion forces (Fpull-off) of PDMS were about five times larger than those of PMMA (see FIG. 1.A1 and A2). More importantly, the actual measured adhesion forces (Fpull-off) of these polymers (270.6±10.3 nN for PDMS and 56.0±4.2 nN for PMMA (n=10)) were significantly smaller than the theoretical FvdW values, which were expected to be developed if vdW interactions were fully functional at the surface of these polymers. One of the reasons for the adhesion difference between PDMS and PMMA and also for the deviation of the experimental results from the theoretical estimates is the inability of the chosen polymers to develop an intimate molecular contact with silica particles.17, 18 More specifically, both PDMS and PMMA are required to reach an intimate molecular contact of ˜0.3 nm with silica particles in order to achieve the estimated vdW adhesion forces. However, due to natural roughness at the surface of these polymers (Ra,PDMS=1.5±0.1 nm (n=5); Ra,PMMA=0.8±0.1 nm (n=5)), achieving this close proximity throughout the entire contact zone, and thus effective vdW interactions at the contact interface, is challenging. In order to elucidate the importance of the effect of the nanoasperities of the surface of these polymers on declining the magnitude of their vdW interfacial forces, the modified Rumpf model (Equation 2) has been employed.18 According to this model, the vdW interaction force between a smooth spherical particle of radius R (phase 1) and a flat polymeric substrate (phase 2, with root mean square roughness parameter RRMS) can be calculated using F vdW = A 132 ⁢ R 6 ⁢ ⁢ H 0 2 [ 1 1 + R 1.48 ⁢ ⁢ R RMS + 1 ( 1 + 1.48 ⁢ ⁢ R RMS H 0 ) 2 ] Equation ⁢ ⁢ 2 where H0 is the distance of closest approach between the two surfaces (˜0.3 nm).18 Using Equation 2 and considering that RRMS,PDMS=1.9±0.2 nm (n=5) and RRMS,PMMA=1.0±0.1 nm (n=5), while assuming that the nanoasperities at the surface of these polymers are not deformable, it is expected that PDMS develops vdW forces of about 4 nN upon contact with a 7.75 μm silica particle, while PMMA should generate vdW forces of about 13 nN at the same contact. From the estimation of vdW interfacial forces by the modified Rumpf model, it is clear that the presence of nanoasperities at the surface of PDMS and PMMA can result in significant decrease in vdW interfacial forces of these polymers. It should be also noted that in the above analysis, for the sake of simplicity, it has been assumed that the surface of the employed silica particles were atomically smooth. Even so, it is expected that the roughness at the surface of silica particles also partly contribute in decreasing the achievable vdW adhesive forces by increasing the actual separation distance between the particles and the polymer surfaces. While roughness—even at nanometric and sub-nanometric scales—can significantly decrease the ultimate vdW interaction force between two substrates, it is expected that most nanoasperities at the surface of soft materials (like PDMS and PMMA) are squeezed out upon contact with a comparatively more rigid material like silica (with Young's modulus of ˜71.7 GPa).19 Therefore, to shed light on the effect of the mechanical properties of these polymers and, accordingly, the deformation of their surface nanofeatures upon contact with silica particles, the penetration depth (δ) of silica particles into these polymers were calculated using the JKR model. In general, it is expected that all surface asperities with a height equal or smaller than 6 values are squeezed out during contact with silica particles.20 According to the JKR model, the penetration depth of a 7.75 μm silica particle in PMMA and PDMS (under the applied load of 100 nN) is ˜3 and 207 nm, respectively. Therefore, by considering that the maximum peak height (RP) for PDMS (30.4±7.9 nm (n=5)) is just one seventh of the particle penetration depth in this polymer, while the penetration depth of the silica particle in PMMA (˜3 nm) is smaller than the RP value for this polymer (5.9±0.5 nm (n=5)), it is clear that, in comparison to PMMA, PDMS should have generated much better intimate contact with silica particles. On the whole, it can be inferred that vdW-driven adhesion forces of PDMS—upon contact with a 7.75 μm silica particle—changes in the range of 4 to 394 nN, while those of PMMA are between 13 and 460 nN. Analysis of vdW interactions also clearly shows that while PDMS and PMMA theoretically have similar ability in formation of vdW interactions upon contact with silica particles, it is expected that PDMS generates larger vdW forces than PMMA, seeing that it develops better intimate contact in comparison to PMMA. In contrast to vdW forces, the contribution of capillary forces in the overall interfacial interaction forces (Fpull-off) of both PDMS and PMMA can be simply neglected. The formation of capillary forces in the current system is very doubtful since experiments were carried out at a relative humidity (RH) of 10±1% (T=20±1° C.), where adsorption of sufficient amounts of water at the contact interface to form capillary bridges is unlikely.[11, 21] Even so, it should be considered that water monolayers still can be adsorbed on the surface of the employed materials (even at this level of humidity), especially the hydrophilic ones.11, 21 Water monolayers do not produce capillary forces, but they can affect—and particularly decrease—the short-range vdW forces between two contacted surfaces.21 From this perspective and in order to ascertain whether water monolayer adsorption is the cause of the significantly smaller adhesion of PMMA in comparison to PDMS, an extreme case where the hydrophobic PDMS/silica interface is presumed to be completely dry (i.e., vdW forces were considered to be in full effect) while a water monolayer is assumed to be present at the hydrophilic PMMA/silica interface (i.e., vdW forces were declined by a monolayer of water), may be evaluated. Considering that a monolayer of water is present at the contact interface between PMMA and silica, the vdW interaction forces still can be calculated by FvdW=−A132R/6D2, but by replacing A132 with Aeff, the effective Hamaker constant of the system. Aeff for PMMA/silica can be determined from Aeff=fAdry+ρf′Awet,21 where f is the areal fraction of the silica surface which is in direct contact with the PMMA substrate, while f′ is the areal fraction of the silica surface which is in contact with PMMA through a monolayer of water. Awet and Adry are the Hamaker constants in wet and dry conditions, respectively. ρ is the relative water coverage of the surface, which can be calculated by the Langmuir adsorption isotherm as ρ = H H + exp ⁡ ( - E kT ) ≈ H · exp ⁡ ( E kT ) ≈ 1.22 ⁢ ⁢ H Equation ⁢ ⁢ 3 where H is the humidity and E is the adsorption energy, which is typically much smaller than the thermal energy (kT) at room temperature.21 In Equation 3, it may be assumed that for a hydrophilic substrate like PMMA or silica, E=(AwAs)1/2/16π≈0.2 kT,21 where Aw=3.7×10−20 J for water,10 whereas, according to the Lifshitz model (Equation 1), As is equal to 6.0×10−20 J for silica and 6.9×10−20 J for PMMA. Doing so, the relative water coverage of the surface (ρ) for PMMA and silica would be ˜0.12. In other words, according to the Langmuir adsorption isotherm, about 12% of the surface of a hydrophilic material (such as PMMA (θPMMA=82±1° (n=8)) or silica (θsilica=70±20 (n=8))) can get covered with a monolayer of water at RH of 10±1%. Using f′=1.2f for an intimate contact,21 and knowing that Adry=6.4×10−20 J and Awet=0.8×10−20 J for PMMA/silica—according to the Lifshitz model (Equation 1)—the effective Hamaker constant in presence of a monolayer of water for PMMA/silica would be equal to 2.9×10−20 J, approximately half of the Hamaker constant of PDMS/silica in dry conditions (5.5×10−20 J). Even in this extreme scenario, the Hamaker constant of the dry PDMS/silica interface is only about twice larger than the Hamaker constant of the wet PMMA/silica interface, a significantly lower ratio than the actual five-fold adhesion difference between PDMS and PMMA (see FIGS. 1.A1 and A2). Therefore, it can be concluded that water monolayer adsorption is not the main reason behind the significantly smaller adhesion of silica particles to PMMA in comparison to PDMS, although it may be a minor contributor. Another cause for the large adhesion difference between PDMS and PMMA upon contact with silica particles can be the difference in electrostatic interactions of these polymers formed via surface charging. In general, when any two—similar or dissimilar—materials touch each other, electric charges transfer from one surface to the other,12, 22 resulting in the development of a net negative charge on one substrate and a net positive charge on the other.23 Formation of an electrical double layer at the contact interface via this contact electrification (CE) phenomenon, which is usually more pronounced in the case of insulating materials,24-26 gives rise to electrostatic interactions between the triboelectrically-charged objects.12, 13 In order to determine the occurrence of CE and the extent of the electrostatic interactions arising therefrom, the magnitude of electric charges that build up upon contact of silica with both PDMS and PMMA were measured. Because the direct measurement of CE-generated charge densities during adhesion tests with silica microparticles is technically very difficult, due to very small area of contact, contact charge measurements were carried out upon contact with a 25.4 mm diameter polished silica disc (Ra,silica=1.0±0.1 nm (n=5)). Using image charge analysis (details can be found in the Experimental section),12, 13, 27 the absolute value of the surface charge densities formed upon contact of PDMS with silica were found to be 1.5±0.1 mC/m2 (n=10), three times larger than those of PMMA with silica (0.5±0.1 mC/m2 (n=10)). To obtain an approximation of the electrostatic force (Felc) that these surface charge densities can produce, the well-known simple capacitor model (Equation 4), which describes the electrostatic interaction force between two charged flat parallel sheets, was employed.25 According to this model, the magnitude of the electrostatic force (Felc) between a flat silica plate and a polymer thin film can be simply determined from27 F elc = - a ⁢ ⁢ σ s 2 2 ⁢ ⁢ ɛ 0 ⁢ ɛ r Equation ⁢ ⁢ 4 where a is the area of contact, σs is the contact surface charge density, ε0 is the permittivity of free space, and εr is the effective dielectric constant of the contact interface, which can be obtained from27 D + d p + d si ɛ r = D ɛ D + d p ɛ p + d si ɛ si Equation ⁢ ⁢ 5 where D is the actual separation distance between the polymer and silica, while dp and dsi are the charge penetration depths in the polymer and silica, respectively. In Equation 5, εp, εsi, and εD are the dielectric constants of the polymer, silica, and separating medium, respectively. Using the simple capacitor model and further assuming the ideal conditions where no charge backflow happens upon retraction of the contacted materials from each other,12, 13 it was determined that the electrostatic adhesion strength (i.e., adhesion force per unit surface area) of PDMS upon contact with silica is 4.4±0.8 N/cm2, which is about nine times larger than that of PMMA (0.5±0.1 N/cm2). With the knowledge of adhesion strength values for PDMS and PMMA and in order to estimate the magnitude of CE-generated electrostatic adhesion forces for contact of these polymers with 7.75 μm silica particles, it is assumed that electric charges are separated only at the contact zone between the particles and the polymers. Doing so, the radius of the charged area for PDMS and PMMA is considered equal to the radius of contact area for these polymers (˜1.5 μm for PDMS and ˜0.2 μm for PMMA), which have been obtained using the JKR model (details can be found below). By knowing the areas of contact and by approximating the contact interfaces of silica microparticles and the polymers as those between two flat parallel plates, the CE-generated electrostatic forces of PDMS and PMMA upon contact with 7.75 μm silica particles should be approximately 311.0 and 0.6 nN, respectively. Analysis of CE-generated electrostatic interactions of PDMS and PMMA by the simple capacitor model clearly demonstrates that PDMS generates significantly larger electrostatic adhesion forces in comparison to PMMA. The relatively larger charge densities, and so the CE-driven electrostatic interaction forces of PDMS—which are still typical for an intimate contact—are most likely due to better conformability of this polymer and its propensity in formation of intimate contact with silica particles.12, 13, 27 While the presence of surface nanofeatures and the ability to develop intimate contact indirectly influence the electrostatic adhesion forces by affecting the surface charge densities, it should be noted that at the current length scales, CE-driven electrostatic forces are independent of the separation distance and, accordingly, the presence of nanoasperities at the surface (see Equation 4). As a result, the effect of interfacial deformations (i.e., deformation of surface nanoasperities of PMMA and PDMS) in the estimated electrostatic adhesion strengths of these polymers has been neglected. While the simple capacitor model has given an estimate about the CE-generated electrostatic interactions of PDMS and PMMA (˜311.0 and 0.6 nN, respectively), finding the exact share of electrostatic forces (Felc) in the overall interfacial forces (Fpull-off) of these polymers upon contact with silica microparticles is technically very challenging, if not impossible. This difficulty is mainly because of uncertainties in finding the area over which charge separation has happened. Unlike vdW forces, CE-driven electrostatic interactions are dependent on the apparent area of contact, specifically, on the area over which charge separation has happened (see Equation 4). While the apparent area of contact can be simply estimated using various contact mechanics models (such as the JKR model employed herein), the area of charging during contact cannot be accurately predicted for many contacts, particularly for those where the area of contact is very small.28, 29 The reason is that upon contact between two substrates, electric charges can develop outside and around the periphery of the contact zone, as well as inside the contact zone. Although charging outside the contact zone can be practically negligible for macrocontacts, for micro/nanocontacts, this charging can be very important given that the size of the contact area and the charged area for these contacts are significantly different.28, 29 Despite the fact that determination of the actual area of charging during contact is not practical, a simplifying assumption can nevertheless be made in order to obtain an approximation of the magnitude of the maximum CE-driven electrostatic forces which can be generated in our system. In particular, for contact between a 7.75 μm silica particle and PDMS or PMMA, the radius of the charged area can be considered equal to the radius of the charged particle (˜3.9 μm). This simplifying assumption is not unrealistic, considering that for microcontacts, charging usually takes place in length scales similar to the size of the contacted objects.28, 29 For instance, upon contact between a ˜10 μm spherical probe and a flat PMMA sample, charging over an area of ˜10 μm has been reported.29 Therefore, by approximating the radius of the charged area of our polymers equal to the radius of the charged particles (˜3.9 μm), while knowing that electrostatic adhesion strengths of PDMS and PMMA are equal to ˜4.4 and 0.5 N/cm2, respectively, it can be indicated that the maximum CE-driven electrostatic forces for PDMS and PMMA upon contact with 7.75 μm silica particles should be approximately 2.1 μN and 238.9 μN, respectively. Overall, analysis of CE-driven electrostatic interactions of PDMS and PMMA indicates that the electrostatic forces of these polymers upon contact with 7.75 μm silica particles should be in the ranges of 311.0 nN-2.1 μN and 0.6-238.9 nN, respectively. Although finding the exact input of CE-generated electrostatic interactions in the overall interfacial interactions of these polymers is very difficult to achieve, similar to vdW forces, analysis of these forces for PDMS and PMMA clearly shows that PDMS is expected to generate significantly larger surface charge densities and accordingly electrostatic adhesion forces in comparison to PMMA. Despite the fact vdW forces of PDMS are also more effective than those of PMMA, it is highly likely that CE-driven electrostatic forces are the main interfacial forces that have allowed PDMS to develop significantly larger adhesion forces in comparison to PMMA. In fact, CE-driven electrostatic interactions are most likely the regulating interfacial interactions in the current system, given that in regular environments where dust cleaning is usually carried out, the electrostatic interactions of micrometric and sub-micrometric particles generally exceed the other physical interfacial forces.3 Given that in comparison to PMMA, PDMS generates stronger interfacial interaction forces with silica particles, regardless of the origin of these interfacial forces, it is expected that even an unstructured, flat PDMS sheet should be able to remove silica particles from the surface of a contaminated PMMA substrate. To test this hypothesis, silica microparticles of different sizes were cleaned from the surface of PMMA thin films by gently tapping unstructured PDMS sheets (used as the control samples) on various spots on the contaminated thin films. FIGS. 2.A1-A3, show the typical scanning electron microscope (SEM) images of a monolayer of 0.26, 1.70, and 7.75 μm silica particles deposited on PMMA thin films, while FIGS. 2.B1-B3 show the same contaminated surfaces after they were cleaned using unstructured PDMS sheets. The strong interfacial interactions of PDMS with silica particles allow unstructured, flat PDMS sheets to remove most of the sub-micrometric and almost all the micrometric contaminant particles from the PMMA substrates. Even so, the accumulation of the particles in localized regions at the surface of the PDMS sheets (see FIGS. 2.C1-C3) result in damaging the surface of the mechanically-delicate PMMA thin films, mostly in the form of small dents. It is worthwhile mentioning that the extent and density of damages formed over PMMA thin films during cleaning by flat PDMS sheets were variant between samples. These variations were expected, given that the extent and density of damages inherently depend on various factors, such as the magnitude of the applied compressive force, duration of its application, variations in the thickness of the PMMA thin films, possible solvent residue in the thin films, mechanical and material properties of the dust particles, and also the hardness of the material beneath the PMMA films. Unlike unstructured PDMS sheets, as can be seen in FIGS. 3.A1-A3, PDMS μ-dusters of controlled feature sizes (FIGS. 3.B1-B3) do not cause any visible damage to the surface of the substrate during the cleaning process, while they effectively clean both micrometric and sub-micrometric contaminant particles from the surface. The nondestructive yet effective cleaning performance of PDMS μ-dusters is partly due to the flexible structure of these cleaning materials. The flexibility of the fibrillar cleaning materials make possible the development of intimate contact and therefore, effective interfacial interactions of PDMS μ-dusters with the contaminant particles.30, 31 Additionally, at macroscale, fibrillar structures exhibiting exemplary geometrical properties as disclosed herein (i.e., flat tips with rounded edges) have been shown to generate smaller adhesion forces in comparison to flat substrates of the same material.31, 32 In other words, because of the particular geometrical properties of exemplary PDMS μ-dusters disclosed herein, adhesion of these cleaning materials to the substrate is smaller than that of a flat PDMS sheet to the substrate. Consequently, the adhesion-driven mechanical stresses that these μ-dusters may apply to the substrate upon their removal from the surface are also minimized, helping to mitigate the possibility of damage to the surface of the substrate during cleaning. In addition to flexibility and minimal adhesion to the substrate, another significant characteristic which allows the nondestructive cleaning by PDMS μ-dusters is an ability of the disclosed cleaning materials to eliminate the adsorbed particles from the tips of their pillars, and thus from the contact interface. As depicted in FIG. 4.AF, when PDMS μ-dusters come into contact with silica particles (FIG. 4.B), the particles in contact with the tip of the pillars adhere to the cleaning material, due to strong interfacial interactions of PDMS with silica particles. As shown by the arrow in FIG. 4.B, the PDMS μ-dusters are brought into contact with the surface of the substrate supporting the silica particles in a direction that is normal to the surface. Once the pillars are pulled away from the surface, the adhered particles become detached from the substrate (FIG. 4.C). As shown by the arrow in FIG. 4.C, the PDMS μ-dusters are pulled away from the surface of the substrate supporting the silica particles in a direction that is normal to the surface. However, when new particles are brought into contact with the pillars during subsequent cleaning steps (FIG. 4.D), the previously-adsorbed particles move away from the vicinity of the tip of the pillars and roll up the walls of the pillars toward the vacant area between the pillars (FIG. 4.E). This action advantageously prevents accumulation of particles at the contact interface over the course of multiple cleaning steps and, accordingly, decreases the possibility of damaging the substrate during the cleaning process. As shown by the arrows in FIGS. 4.E and 4.F, the PDMS μ-dusters are again brought into contact with and pulled away from the surface of the substrate supporting the silica particles in a direction that is normal to the surface. Of note, the transfer of particles from the tip of the pillars to the empty space between them also makes possible the employment of small samples of a fibrillar cleaning material to clean large areas of a contaminated substrate. For instance, if the adsorbed particles are effectively moved to the vacant area between the pillars and get closely packed in that space, geometrical analysis indicates that a 1 cm2 sample of 50 μm PDMS μ-dusters should be able to clean over 9 cm2 area of a substrate contaminated with a monolayer of 7.75 μm silica particles. However, the present disclosure is not limited by or to such sizing and/or contaminant-capture capacity. Rather, the noted geometrical analysis is merely illustrative of the effectiveness of the systems and methods of the present disclosure in capturing significant amounts of contaminants in an efficient and effective manner. According to exemplary embodiments of the present disclosure, the disclosed microstructures may be characterized by certain geometrical properties. In particular, the diameter of the cleaning pillars (dPi) should generally not be excessively larger than the diameter of the contaminant particles (dPa). For instance, as can be seen in FIG. 5.A1, a PMMA substrate contaminated with 0.26 μm particles cannot be entirely cleaned with 50 μm PDMS μ-dusters. Since the size of the employed pillars is much larger than that of the particles (dPi/dPa≈192), the adsorbed particles are not expelled from the tip of the pillars upon multiple contacts (see FIG. 5.A2). In this case, the tip of each pillar is acting as a flat substrate; limited space at the tip leads to the saturation of the tip with the relatively small particles (FIG. 5.A2), preventing contact between the remaining particles on the contaminated substrate and the cleaning material. Notably, the cleaning efficiency of these large micropillars in removing sub-micrometric particles is even lower than that of a flat substrate (compare FIGS. 2.B1 with 5.A1), because the effective contact area of the hexagonally-patterned PDMS micropillars—with a wall-to-wall distance equal to the diameter of each pillar—is ˜39% of that of a flat PDMS sheet. According to experimental studies in systems with dPi/dPa values of approximately 3, 6, 8, 12, 20, and 192, it can be concluded that when the pillar diameter is less than approximately eight times larger than the particle diameter (i.e., dPi/dPa≤˜8), the adsorbed particles are effectively removed from the tip of the cleaning pillars, allowing effective and nondestructive cleaning of the contaminant particles from the substrate. This is evident in FIG. 5.B1, which shows the successful removal of 7.75 μm particles from the PMMA substrate by 50 PDMS μ-dusters, which were demonstrated to be ineffective in fully cleaning sub-micrometric particulate contaminations of 0.26 μm from the same substrate (see FIG. 5.A1). As can be seen in FIG. 5.B2, at dPi/dPa of ˜6, the relatively large, 7.75 μm particles leave the vicinity of the tip of the pillars upon multiple contacts and as a result, the contaminant particles can be successfully transferred from the surface of the substrate to the surface of the cleaning material, while there is no visible damage at the surface of the cleaned substrate. According to the present disclosure, migration of particles from the microstructure tip to the wall not only depends on the geometrical properties of the microstructures, e.g., microfibrils/micropillars, but also on their interfacial properties. The disclosed microstructures must develop strong interfacial interactions with the contaminant particles in order to be able to remove them from the substrate in the disclosed systems/methods. However, if the adsorbed particles stick very strongly to the tip of the pillars, their movement away from the tip upon multiple contacts will be limited and, as a result, complete cleaning of the substrate with these pillars may not be achieved. In an experimental study, the interfacial interactions at the surface of PDMS μ-dusters were enhanced by improving their tendency in generating CE-driven electrostatic forces. To do so, 50 PDMS μ-dusters were coated with a self-assembled monolayer (SAM) of a fluorine-based silane coupling agent (perfluorooctyltrichlorosilane, FOTS). As can be seen in FIG. 5.C1, the PMMA surface contaminated with 7.75 μm silica particles can only be partially cleaned by using these comparatively stickier SAM-coated PDMS μ-dusters. In this case, because of the strong interfacial interactions of FOTS-coated μ-dusters with the adsorbed microparticles, the particles are not expelled from the tips of the pillars of these cleaning materials (FIG. 5.C2). Therefore, due to the limited effective contact area of the employed fibrillar structure (˜39% of a flat surface), only partial cleaning was achieved by using these relatively stickier micropillars. Unlike uncoated PDMS pillars, FOTS-coated PDMS pillars cannot remove the adsorbed particles from their tips because of the stronger interfacial interactions of FOTS-coated μ-dusters in comparison to uncoated PDMS μ-dusters. More specifically, by coating the PDMS surface with a FOTS SAM, the overall adhesion force (Fpull-off) required to detach a 7.75 μm silica particle from the cleaning material was increased to 310.9±14.5 nN (n=10) for FOTS-coated PDMS (FIG. 6.A), from 270.6±10.3 nN (n=10) for PDMS (FIG. 1.A2). The stronger adhesion of FOTS-coated PDMS μ-dusters in comparison to uncoated PDMS μ-dusters is not because of the changes in the vdW interaction forces caused by SAM coating, given that FOTS coating decreases the magnitude of the van der Waals interaction forces at the surface of PDMS. For instance, by coating the surface of PDMS with a FOTS layer, the van der Waals-driven jump-to-contact adhesion force (Fjtc)[37]—upon contact with a 7.75 μm silica particle—dramatically drops from 50.9±4.3 nN (n=10) for PDMS to 5.3±2.8 nN (n=10) for FOTS-coated PDMS (see FIGS. 1.A2 and 6.A). In general, between two smooth materials of similar mechanical properties, the material with stronger vdW interactions usually generates larger jump-to-contact adhesion forces. With FOTS-coated PDMS generating smaller jump-to-contact adhesion forces in comparison to PDMS, while being even softer than PDMS (Young's modulus of PDMS=2.7±0.3 MPa (n=10); Young's modulus of FOTS-coated PDMS=0.3±0.1 MPa (n=10)), it is clear that coating the PDMS surface by FOTS has decreased the magnitude of the vdW interaction forces at the surface of PDMS. In addition to reducing van der Waals interaction forces, FOTS coating also slightly decreases the propensity of the PDMS surface for forming capillary interactions, given that FOTS-coated PDMS is slightly more hydrophobic than PDMS itself (θFOTS-PDMS=111±1°>θPDMS=108±1°; (n=8))[10, 11, 21] While FOTS SAM reduces the affinity to generate both van der Waals and capillary interactions, like other SAMs, it can improve the surface charging, and as a result, surface electrostatic interactions.[13, 38, 39] In particular, by coating the surface of PDMS with FOTS, the CE-generated surface charge densities increased from 1.5±0.1 mC/m2 (n=10) for PDMS to 1.8±0.1 mC/m2 (n=10) for FOTS-coated PDMS. According to the simple capacitor model (Equation 4) and as depicted in FIG. 6.B, even this slight increase in surface charging can result in significant enhancement of CE-electrostatic adhesion strengths from 4.4±0.8 N/cm2 for PDMS to 6.0±0.8 N/cm2 for FOTS-coated PDMS, which reasonably matches the experimental adhesion measurement results. In summary, the disclosed systems and methods are effective in removing particulate contamination from solid surfaces using conformal, polymeric fibrillar microstructures. The CE-driven interfacial interactions of the fabricated micropillars with the contaminant particles allow complete or substantially complete and effective removal of micrometric and sub-micrometric particles from the surface of the substrate. Unlike unstructured, flat sheets of the same material, polymeric μ-dusters do not cause any visible damage to the surface of the substrate. The cleaning performance of the fibrillar cleaning materials relies on the geometrical and interfacial properties of the fabricated micropillars, allowing the removal of the adsorbed particles away from the tip of the pillars and, accordingly, the contact interface, helping to achieve nondestructive, but effective cleaning. The effective cleaning performance of the disclosed polymeric microstructures is demonstrated by the AFM images from contaminated PMMA thin films taken before and after cleaning set forth in FIG. 7, as well as additional SEM images from the contaminated substrates and the cleaning materials taken after cleaning set forth in FIG. 8. More particularly, the images in FIG. 7 demonstrate nondestructive cleaning performance of PDMS μ-dusters taken by characteristic atomic force microscopy (AFM) at different magnifications from fixed spots on the surface of a contaminated PMMA thin film (A1 and A2) before soiling the surface with 7.75 μm silica particles and (B1 and B2) after cleaning the surface using 50 μm PDMS μ-dusters (scale bars: 1.0 μm for A1 and B1 and 4.0 μm for A2 and B2). 7.75 μm silica particles were chosen for AFM analysis since they could damage the PMMA thin films in larger areas, so damages caused by these particles were easier to track using AFM. AFM analysis was performed at four fixed spots over each sample, while the AFM tests at each magnification were individually replicated three times. Test spots for each sample (i.e., a 22×22 mm2 PMMA thin film) were located at corners of a square (which was marked under the glass coverslip before preparing the thin film) with a side length of ˜7 mm at the center of the sample. Even though—after cleaning—locating the exact place where AFM images were previously taken was not efficient, similarity of the average of the Ra values of the samples (measured at multiple fixed spots both before cleaning (Ra,before=0.6±0.1 nm (n=12) for 5×5 μm2 tests and Ra,before=0.7±0.2 nm (n=12) for 20×20 μm2 tests) and after cleaning (Ra,after=0.5±0.1 nm (n=12) for 5×5 μm2 tests and Ra,after=0.6±0.1 nm (n=12) for 20×20 μm2 tests) confirms the nondestructive performance of PDMS μ-dusters in removing silica particles from the surface of PMMA thin films. With reference to FIG. 8, scanning electron microscope (SEM) images are provided from the surface of contaminated PMMA thin films taken after cleaning (A1) 0.26 and (A2) 1.70 μm silica particles from their surfaces, using PDMS μ-dusters of (B1) 5 and (B2) 20 μm in diameter, respectively. The SEM images from the μ-dusters were taken from a 45° angle and clearly demonstrate the effectiveness of the systems/methods of the present disclosure. Part EXPERIMENTAL RESULTS: Part 1. Experimental Procedure—First Experimental Regimen: Polydimethylsiloxane (PDMS), as two-part Sylgard 184 Silicone Elastomer Kit, was acquired from Dow Corning. Poly(methyl methacrylate) (PMMA, average molecular weight (Mw)≈350,000), anisole (ReagentPlus, ≥99%), chloroform (ReagentPlus, ≥99.8%), pentane (anhydrous, ≥99%), trichloro(octadecyl)silane (OTS, ≥90%), and trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FOTS, ≥97%) was purchased from Sigma. Spherical monodisperse silica microspheres, with nominal diameters of 0.26, 1.70, and 7.75 μm (coefficient of variation <10%), were obtained from Cospheric LLC. Ultra-smooth, mirror-finished copper sheets (99%, 28 gauge), which had a plastic protective layer, were obtained from Fire Mountain Gems and Beads. After cutting the copper sheets into 5×5 cm2 sheets and in preparation for spin-coating the polymer thin films, first the protective plastic layers were removed. Then, each sheet was cleaned individually using a commercial metal cleaner (Autosol Metal Polish from Autosol LLC.). After further cleaning by ultrasonication in pure ethanol for 40 min, the cleaned copper sheets were rinsed with ethanol and, to prevent their oxidation in air, they were kept in ethanol prior to coating them with the polymers. For fabrication of PDMS micropillars (2, 5, 20 and 50 μm in diameter with aspect ratios of ˜2), the PDMS prepolymer (with base-to-catalyst weight ratio of 10:1) was poured over the photolithographic silicon master-molds, containing holes of specific geometrical properties. The thickness of the polymer backing layer was adjusted to ˜1.5 mm by using a polytetrafluoroethylene (PTFE, Teflon) spacer. The cast polymer was degassed and then cured at 90° C. for 120 min Only the 2 μm PDMS pillars were cured at 135° C., in order to enhance their mechanical strength and lower the chance of their collapse and buckling during the cleaning process. The polymer and the mold were cooled down to room temperature for several hours, and then the cured polymer was gently peeled off from the mold. To easily release the cured polymer from the mold, the mold was coated in advance with a self-assembled monolayer (SAM) of OTS. The mold for the fabrication of the 2 μm PDMS pillars was coated with a SAM of FOTS instead of OTS, considering that OTS coating was not very effective for removal of these small pillars from their mold. Flat PDMS reference samples were prepared with the same procedure as that used for the preparation of micropillars, but against a flat, OTS-coated silicon wafer. In preparation for SAM-coating of the silicon molds and also flat silicon wafers with OTS, each silicon substrate was first cleaned by ultrasonication in pure chloroform at 40 kHz for 5 min, using Branson B5510 Ultrasonic Cleaner (Emerson Industrial Automation). Then, the substrate was immersed in a 0.8 mM solution of OTS in a mixture of pentane and chloroform (with 4:1 volumetric ratio). After 10 min, the sample was removed from the solution and subsequently ultrasonicated in pure chloroform for another 10 min, in order to remove the physically-adsorbed molecules from the surface. At the end, the sample was nitrogen dried and annealed under vacuum at 90° C. for 60 min. SAM-coating of the silicon mold for fabrication of the 2 μm pillars as well as that of the PDMS samples with FOTS was carried out in the gas phase—under vacuum—at 110° C. for 60 min, in presence of 200 μL of FOTS and several milliliters of water. Prior to SAM-coating of the PDMS samples, they were plasma treated (using a PDC-32G plasma cleaner from Harrick Plasma) for 2 min, in order to activate the surface of the PDMS samples. The PMMA thin films were spin-coated onto glass cover slips (2.2×2.2×0.1 cm3, from VWR International LLC.), which were plasma treated beforehand for 1 min. PMMA solution (5 wt % PMMA in anisole) was spin-coated onto the cover slips at 1500 rpm for 30 s, using a WS-400-6NPP Spin Coater (Laurell Technologies Corporation). PMMA thin films for charge measurements—with a thickness of 4.2±0.1 μm (n=6)—were produced from a 15 wt % solution of PMMA in anisole, which was spin-coated onto 5×5 cm2 copper sheets
{'bibliographic_information': "{'country': 'US', 'doc-number': '15772274', 'kind': 'B2', 'date': '20161028', 'invention_title': 'Systems and methods for particulate removal using polymeric microstructures'}", 'source_file': './grant/2021/ipg210511.xml', 'source_data': 'USPTO-Grant'}