Chemical vapor deposition (CVD) is a widely practiced methodology for preparing conformal polymeric coatings, such as poly(p-xylylene) (PPX). CVD-based PPX coatings can be applied to a broad range of materials, including low-vapor pressure liquid droplets, in which the polymer forms into a thin layer encapsulating the liquid droplets. Previously, we explored the CVD of PPX onto surfaces coated with a thin layer of liquid crystal (LC). Instead of forming a conformal PPX coating encapsulating the LC layer, PPX assembled into an array of high-aspect ratio nanofibers inside the LC layer. The LC layer was demonstrated to act as a template where the anisotropic internal ordering of the LC facilitated the formation of nanofibers. In this study, we demonstrated that CVD of chiral-substituted poly(p-xylylene) onto LC template permits the assembly of twisted polymer nanofibers. The twist direction is governed by the handedness of the chiral substituents, and the degree of twisting depends on the enantiomeric excess of the chiral substituents. Analysis of the twisted nanofibers using circular dichroism spectroscopy suggests that the polymer grows along the fiber axis. The twisting of the nanofibers originates from the skewed π-π stacking between the chiral-substituted poly(p-xylylene) chains that occurs due to the presence of the asymmetric chiral substituent on the polymer chains. When assembled in cholesteric LC templates, the polymer can form into nanofibers with hierarchical helicity. The twisted nanofibers can be attractive as supports for fabricating chiral metamaterials and chiral catalysts, as well as for sensing and separation applications.

Directed assembly of twisted polymeric nanofibers via chemical vapor deposition in liquid crystals

254th National Meeting (2017)

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