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Liquid crystal-templated synthesis of polymeric microparticles with complex nanostructures

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2019
Akdeniz, Burak
Liquid crystals (LC), when combined with photolithography, enable synthesis of microparticles with two- and three-dimensional shapes and internal complexities. We prepared films of nematic LCs using mixtures of reactive (RM257) and non-reactive mesogens (E7) with controlled alignment of LCs at the confining surfaces, photopolymerized the RM257 using a photomask, and then extracted the unreacted mesogens to yield polymeric microparticles. The extraction resulted in a controlled anisotropic shrinkage with an amount dependent on the RM257 content and the direction dependent the on LC alignment. Moreover, control over the aspect ratio, size and thickness of the microparticles were obtained with a coefficient of variance less than 2%. In addition, non-parallel LC anchoring at the two surfaces resulted in a controllable right- or left-handed twisting of microparticles (Chapter 4). Besides these results, we used circular, triangular, rectangular, square, star and heart shaped lithography masks to provide initial shapes to the microparticles (Chapter 5). The configuration of the reactive and non-reactive mesogen mixtures maintained initially played a critical role in determining the chiral twisting and bending of the microparticles. We found that the pitch size of the bulk chiral twisting of the polymeric microparticles to depend linearly on the angle of chiral twist of the LCs, whereas it is independent of the length and thickness of the objects ranging from 1.5 µm to 160 µm in thickness and 100 µm to 2.45 cm in length. The shapes of the polymeric microparticles synthesized from LC films with bent in the ordering of LC molecular templates, however, were critically dependent on the thickness of the microparticles. We found that this was due to the interplay between the elastic energy and surface anchoring of the LCs. The critical role of LC elasticity was observed for thicknesses below 20 µm, whereas surface ordering played critical role on the thickness of the films above 20 µm (Chapter 5). Overall, the proposed method was shown to provide a precise control over the three-dimensional architectures of the objects ranging sizes covering the microscopic and macroscopic scales. The library of the microparticles demonstrated in this study may find substantial use in applications including drug delivery, emulsions, separations and sensors, besides their potential in revealing new fundamental concepts in self-assembly and colloidal interactions.