Sculpting the shapes of giant unilamellar vesicles using isotropic-nematic-isotropic phase cycles.

Understanding how soft matter deforms in response to mechanical interactions is central to the design of functional synthetic materials as well as elucidation of the behaviors of biological assemblies. Here we explore how cycles of thermally induced transitions between nematic (N) and isotropic (I) phases can be used to exert cyclical elastic stresses on dispersions of giant unilamellar vesicles (GUVs) and thereby evolve GUV shape and properties. The measurements were enabled by the finding that I-N-I phase transitions of the lyotropic chromonic liquid crystal disodium cromoglycate, when conducted via an intermediate columnar (M) phase, minimized transport of GUVs on phase fronts to confining surfaces. Whereas I to N phase transitions strained spherical GUVs into spindle-like shapes, with an efflux of GUV internal volume, subsequent N to I transitions generated a range of complex GUV shapes, including stomatocyte, pear- and dumbbell-like shapes that depended on the extent of strain in the N phase. The highest strained GUVs were observed to form buds (daughter vesicles) that we show, via a cycle of I-N-I-N phase transitions, are connected via a neck to the parent vesicle. Additional experiments established that changes in elasticity of the phase surrounding the GUVs and not thermal expansion of membranes were responsible for the shape transitions, and that I-N-I transformations that generate stomatocytes can be understood from the Bilayer-Coupling model of GUV shapes. Overall, these observations advance our understanding of how LC elastic stresses can be regulated to evolve the shapes of soft biological assemblies as well as provide new approaches for engineering synthetic soft matter.

Redox-Responsive Polymer Template as an Advanced Multifunctional Catalyst Support for Silver Nanoparticles.

Hybridization of metal nanoparticles (NPs) with redox-switchable polymer supports not only mitigates their aggregation, but also introduces interfacial electron pathways desirable for catalysis and numerous other applications. The large surface area and surface accessible atoms for noble metal nanoparticles (e.g., Ag, Au, Pt) offer promising opportunities to address challenges in catalysis and environmental remediation. Herein, AgNPs were supported onto redox-switchable polyaniline that acts as an advanced multifunctional conducting template for enhanced catalytic activity. At the initial stage of reduction of Ag+, leucoemeraldine is oxidized in situ to pernigraniline (PG), which acts as interfacial pathway between NPs for electron transport. With the contribution of BH4-, PG acts as an electron-acceptor site, which creates interfacial electron-hole pairs, serving as additional active catalytic reduction sites. The use of a redox-responsive composite system as a template enhances catalyst performance through adjustable charge injection across interfacial sites, along with catalyst reusability for the reduction of 4-nitrophenol (4-NPh). Strikingly, from X-ray photoelectron spectroscopy results it was observed that in situ reduction of Ag+ onto the conductive polymer alters the electronic character of the catalyst. The unique multielectronic effects of such Ag-supported NPs enrich the scope of such catalytic systems via a tunable interface, diversified catalytic activity, fast kinetics, minimization of AgNPs aggregation, and maintenance of high stability under multiple reaction cycles.