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Topography-guided buckling of swollen polymer bilayer films into three-dimensional structures
Jeong, J.,Cho, Y.,Lee, S.,Gong, X.,Kamien, R.,Yang, S.,Yodh, A. G. Royal Society of Chemistry 2017 Soft matter Vol.13 No.5
<P>Thin films that exhibit spatially heterogeneous swelling often buckle into the third dimension to minimize stress. These effects, in turn, offer a promising strategy to fabricate complex three-dimensional structures from two-dimensional sheets. Here we employ surface topography as a new means to guide buckling of swollen polymer bilayer films and thereby control the morphology of resulting three-dimensional objects. Topographic patterns are created on poly(dimethylsiloxane) (PDMS) films selectively coated with a thin layer of non-swelling parylene on different sides of the patterned films. After swelling in an organic solvent, various structures are formed, including half-pipes, helical tubules, and ribbons. We demonstrate these effects and introduce a simple geometric model that qualitatively captures the relationship between surface topography and the resulting swollen film morphologies. The model's limitations are also examined.</P>
Synergistic assembly of nanoparticles in smectic liquid crystals
Honglawan, Apiradee,Kim, Dae Seok,Beller, Daniel A.,Yoon, Dong Ki,Gharbi, Mohamed A.,Stebe, Kathleen J.,Kamien, Randall D.,Yang, Shu The Royal Society of Chemistry 2015 SOFT MATTER Vol.11 No.37
<P>We report synergistic co-assembly between smectic A liquid crystal (SmA LC) and planar anchoring fluorosilane functionalized silica (F-SiO<SUB>2</SUB>) nanoparticles (NPs). Both scanning electron microscope (SEM) images and grazing incidence X-ray diffraction (GIXD) patterns show that when cooled from the isotropic phase to SmA phase, F-SiO<SUB>2</SUB> NPs (100–500 nm in diameter) migrate from the bottom to the top of the LC film through the central cusp defects of toric focal conic domains (TFCDs). When the NPs form a monolayer on top, replacing the LC/air interface, vertically aligned SmA layers are formed between the top and bottom planar surfaces. When F-SiO<SUB>2</SUB> NP diameter is small (<500 nm), we observe a weak-anchoring regime, where NPs do not cause appreciable layer curvature and NP migration is driven by surface energy. When F-SiO<SUB>2</SUB> particle diameter > 500 nm, strong distortions occur in the smectic layers, and the particle is found suspended at the TFCD defect core. The knowledge of the intermediate states of the NP/LC hybrid structures will provide valuable insights to assemble functional nanomaterials such as quantum dots and metallic NPs in an anisotropic medium, and take advantage of their collective assembly behaviors to create more complex and dynamic structures.</P> <P>Graphic Abstract</P><P>When cooled from the isotropic phase to smectic A phase of liquid crystals (LCs), planar anchoring SiO<SUB>2</SUB> nanoparticles migrate as a group through the central cusp defects of toric focal conic domains, leading to the formation of vertically aligned LC layers between the top and bottom planar surfaces. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5sm01458a'> </P>