Butterfly wings, peacock feathers, opals and pearls are some of nature’s jewels that use nanostructures to dazzle us with color. It’s accomplished through the way light reaches our eyes after passing through the submicroscopic mazes within these materials.
The seemingly effortless way that nature creates this effect is now rivaled by a rapid and simple method developed through a collaboration of researchers from North Carolina State University (NCSU), Arizona State University (ASU) and the Universidad Complutense de Madrid (UCM).
Professor Orlin Velev and graduate student researcher Vinayak Rastogi in the Department of Chemical Engineering at NCSU have shown how colloid chemistry methods originally used to form particle aggregates from nanoparticles can be used to quickly make particles with dazzling colors simply by letting a suspension of nanoparticles dry on a superhydrophobic surface.
Superhydrophobicity is a property of a material that repels water like ducks’ feathers or lotus leaves. It has been used commercially in textiles, coatings and building materials.
The basic idea behind the process is akin to stacking round fruits or vegetables in a supermarket produce bin in high, neat rows to keep the produce from falling to the floor as customers pick them out. Doing this with nanoscale particles of different sizes leads to opalescence, since some colors of light are reflected differently depending on the size of the holes between the nanoparticles and the angle from which they are viewed.
Normally, carefully arranging the nanoparticles in neat rows requires a complex series of steps with oily solvents and water mixtures requiring extensive washing afterwards to remove the solvents.
Now, with the help of researchers at ASU, this process has been made as simple as placing a drop on a superhydrophobic surface and letting it dry for one to two hours.
The researchers call these one- to two-millimeter particles “nanojewels.”
Velev and Rastogi of NCSU developed the method with help of several colleagues, including: Manuel Marquez, an adjunct professor in the Harrington Department of Bioengineering in ASU’s Ira A. School of Engineering, and Antonio Garcia, a professor in the bioengineering department and director of the Laboratory for Personalized Molecule Measurement; and professors Sonia Melle and Oscar Calderon in the School of Optics at UCM.
Rastogi’s presentation at the 82nd ACS Colloid & Surface Science Symposium on June 18, 2008 titled “Synthesis of Light-Diffracting Colloidal Crystal Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface” and a paper just published in the journal Advanced Materials (published Online: July 28, 2008), authored by these researchers, describes how for the first time superhydrophobic surfaces are shown to play an important role in making new materials.
In the paper, they describe how different nanoparticles of various sizes can produce “nanojewels” of various colors that display different optical properties.
“These nanojewels can potentially find application in photonics, drug delivery, special coatings, sensors and microfluidics,” Velev explains.
Indeed, many researchers around the world are working on ways to make similar two-dimensional and three-dimensional photonic crystals to fabricate light-emitting diodes, optical fibers for communications, submicroscopic lasers, ultrawhite pigments, antennas and reflectors, and optical integrated circuits.
The biggest stumbling blocks in making these materials is finding ways of making photonic crystals with uniform properties in very large quantities and in minimizing imperfections in structure that reduce the quality of the final product.
This new process is certainly easy to replicate to make large quantities, and superhydrophobic surfaces lead to structures that naturally form ordered structures.
Superhydrophobic surfaces allow nanojewels to be created from a single drop of water containing nanoparticles, because of several effects.
First, the drop stays in the shape of a ball because water does not spread on it while the nanoparticles are held in the drop due to the surface tension of water.
Compared to drying the drop in air, which is a fast evaporation process that causes the water in the drop to distort and flow, the drop gently dries on the superhydrophobic surface.
This lets the nanoparticles get as close to each other as possible, swirling in a slow circular motion until all of the water evaporates.
When nanoparticles of two different sizes are used in the same drop, the smaller ones move to the surface of the drop while the bigger ones stay in the middle. This is because the smaller ones have more Brownian motion and are elevated to the surface with the water molecules that are subsequently evaporating at the surface, leaving all of the nanoparticles behind to form the nanojewels.
“Besides the dazzling look of these nanojewels, the most exciting thing about this work is that it opens up many interesting possibilities in quickly and inexpensively making new materials with nanoparticles”, Marquez says.
“By understanding how different particle sizes determine the colors produced, these nanojewels can be designed for applications in optical communication systems,” Melle adds.
As more nanoparticles and nanostructures come into the marketplace, technologies that can quickly assemble the structures so that their unique size and properties can be employed in new devices will be important to the growth of nanotechnology and related industries.
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Mabawa ya vipepeo, manyoya ya pawn, opals na lulu ni baadhi ya vito vya asili ambavyo hutumia miundo ya nanostructures kutupendeza kwa rangi. Ni kutimizwa kupitia njia mwanga kufikia macho yetu baada ya kupita kupitia labyrinths submicroscopic ndani ya vifaa hivi. Njia ya asili ya kuunda athari hii sasa inashindana na njia ya haraka na rahisi iliyoundwa kupitia ushirikiano wa watafiti kutoka Chuo Kikuu cha Jimbo la North Carolina (NCSU), Chuo Kikuu cha Jimbo la Arizona (ASU) na Chuo Kikuu cha Complutense cha Madrid (UCM). Profesa Orlin Velev na mwanafunzi wa kuhitimu, mtafiti Vinayak Rastogi katika Idara ya Uhandisi wa Kemikali katika NCSU wameonyesha jinsi mbinu za kemia ya colloid ambazo zilitumiwa awali kuunda chembechembe kutoka kwa nanoparticles zinaweza kutumiwa kwa haraka kutengeneza chembechembe zenye rangi ya kuvutia kwa kuruhusu kusimamishwa kwa nanoparticles kukauka kwenye uso wa superhydrophobic. Superhydrophobicity ni mali ya nyenzo ambayo inakataa maji kama ducks <unk> manyoya au majani ya lotus. Imekuwa kutumika kibiashara katika nguo, coatings na vifaa vya ujenzi. Wazo la msingi la mchakato huu ni kama kuweka matunda au mboga za mviringo katika sanduku la bidhaa za maduka makubwa katika safu za juu, za kawaida ili kuzuia bidhaa hizo zisianguke sakafuni wakati wateja wanazitwaa. Kwa kufanya hivyo na chembe za nanoscale za ukubwa tofauti, huongoza kwa opalescence, kwani rangi zingine za mwanga huonyeshwa tofauti kulingana na ukubwa wa mashimo kati ya nanoparticles na pembe ambayo zinaonekana. Kwa kawaida, kuweka nanoparticles katika safu za utaratibu inahitaji mfululizo tata wa hatua na solvents mafuta na mchanganyiko wa maji ambayo inahitaji kuosha sana baada ya kuondoa solvents. Sasa, kwa msaada wa watafiti wa ASU, mchakato huu umefanywa rahisi kama kuweka tone kwenye uso wa superhydrophobic na kuiacha kukauka kwa saa moja hadi mbili. "Wanasayansi hao wanawaita chembechembe hizo zenye urefu wa milimita moja hadi mbili ""nanojewel"" na Velev na Rastogi wa Chuo Kikuu cha Chuo Kikuu cha Marekani cha NCSU waliendeleza mbinu hiyo kwa msaada wa wenzake kadhaa, ikiwa ni pamoja na Manuel Marquez, profesa msaidizi katika Idara ya Bioengineering ya Harrington katika Chuo Kikuu cha Marekani cha Arizona." Antonio Garcia, profesa katika idara ya bioengineering na mkurugenzi wa Maabara ya Upimaji wa Molekuli ya Kibinafsi, na profesa Sonia Melle na Oscar Calderon katika Shule ya Optics katika UCM. "Rastogi, katika makala yake ya kwanza katika ACS Colloid & Surface Science Symposium, Juni 18, 2008 yenye kichwa ""Synthesis of Light-Diffracting Colloidal Crystal Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface"" na makala iliyochapishwa katika jarida la Advanced Materials (ichapishwa mtandaoni Julai 28, 2008), alielezea jinsi kwa mara ya kwanza nyuso za superhydrophobic zinaonyeshwa kuwa na jukumu muhimu katika kutengeneza vifaa vipya." Katika karatasi, wao kuelezea jinsi tofauti nanoparticles ya ukubwa mbalimbali inaweza kuzalisha "nanojewels" ya rangi mbalimbali ambayo kuonyesha mali tofauti optical. "Nanojewels hizi zinaweza kupata matumizi katika photonics, utoaji wa dawa, mipako maalum, sensorer na microfluidics", Velev anaelezea. Watafiti wengi duniani kote wanafanya kazi kwa njia za kutengeneza fuwele za photonic za vipimo viwili na vitatu ili kutengeneza diodes za kutoa mwanga, nyuzi za macho kwa ajili ya mawasiliano, lasers za submicroscopic, rangi za ultraviolet, antena na reflectors, na mzunguko wa macho. Vizuizi vikubwa katika kutengeneza vifaa hivi ni kutafuta njia za kutengeneza fuwele za photonic zenye sifa sawa kwa wingi sana na kupunguza kasoro katika muundo ambazo hupunguza ubora wa bidhaa ya mwisho. Utaratibu huu mpya ni rahisi kuiga na kuunda vipimo vingi, na nyuso superhydrophobic kuongoza kwa miundo ambayo kwa kawaida fomu utaratibu miundo. Superhydrophobic nyuso kuruhusu nanojewels kuundwa kutoka tone moja ya maji yenye nanoparticles, kwa sababu ya athari kadhaa. Kwa mfano, kwa sababu ya umbo la mpira, maji hayataenea kwenye mtiririko huo, na nanoparticles huhifadhiwa ndani ya mtiririko huo kwa sababu ya mvutano wa uso wa maji. Kwa kulinganisha na kukausha matone katika hewa, ambayo ni mchakato wa evaporation haraka ambayo husababisha maji katika matone kupotosha na mtiririko, matone kavu upole juu ya uso superhydrophobic. Hii inaruhusu nanoparticles kupata karibu na kila mmoja kama iwezekanavyo, swirling katika mwendo polepole mviringo mpaka maji yote evaporates. Wakati nanoparticles mbili tofauti ukubwa ni kutumika katika tone moja, ndogo kuhamia juu ya uso wa tone, wakati kubwa kubaki katikati. Kwa sababu ndogo zaidi zina mwendo wa Brownian zaidi na huinuliwa kwenye uso na molekuli za maji ambazo baadaye huyeyuka kwenye uso, na kuacha nanoparticles zote nyuma kuunda nanoreals. "Zaidi ya sura ya kuvutia ya nanojewels hizi, jambo la kusisimua zaidi kuhusu kazi hii ni kwamba inafungua uwezekano mwingi wa kuvutia katika haraka na bei nafuu ya kufanya vifaa vipya na nanoparticles, "Marquez anasema. "Kwa kuelewa jinsi ukubwa tofauti wa chembe huamua rangi zinazozalishwa, vito hivi vya nano vinaweza kubuniwa kwa matumizi katika mifumo ya mawasiliano ya macho", Melle anaongeza. Kwa kuwa nanoparticles na nanostructures zaidi kuja katika soko, teknolojia ambayo inaweza haraka kukusanya miundo ili ukubwa wao wa kipekee na mali inaweza kutumika katika vifaa vipya itakuwa muhimu kwa ukuaji wa nanotechnology na viwanda vinavyohusiana. Namba hii ya ukurasa: