Optimized Soft Lithography Method for Polymer Cholesteric Liquid Crystal Flakes Fabrication

Abstract

Polymer cholesteric liquid crystal (PCLC) flakes are gaining increasing interest for a wide variety of applications because of their unique optical properties and capabilities. Soft lithography is the most effective way to fabricate regularly shaped PCLC flakes. However, it is not easy to peel the flakes from the mold without breaking them. In order to peel the PCLC flakes from the patterned polydimethylsiloxane (PDMS) mold in a convenient way, in this paper, a method of coating a layer of polyvinyl alcohol (PVA) on a PDMS mold was proposed. The influence of the thickness of the PVA layer on the shape of the PCLC flakes and the release time from the PDMS mold were investigated. The results show that the presence of the PVA layer can speed up the release of the PCLC flakes and help maintain the shape effectively. Notably, the utilization of a PVA layer makes the PDMS mold recyclable. The influence of PCLC flake shape was also studied. This work will promote the development of switchable PCLC flake-based technologies.

Responsive Photonic Liquid Crystalline Flakes Produced by Ultrasonication

“…In all previously reported cases where ChLC flakes are used as optically active components for flexible reflective displays, [ 17,19,21,26,37 ] windows, [ 29 ] circular polarization‐dependent security labels, [ 11 ] or as effect pigments for decorative coatings, [ 14 ] the cholesteric material is based on a densely crosslinked polymer network with a static photonic structure.…”

“…[ 22,23 ] A variety of manufacturing methods have been described, including cryogenic [ 22 ] and mechanical [ 24,25 ] fracturing, and soft lithography. [ 17,21,26 ] Ultrasonication, a technique used in cellular biology and chemistry to release cell contents by rupturing cell membranes [ 27 ] and as method to deaggregate nanoparticles, [ 28 ] has been presented once, but not for responsive photonic LC networks. [ 29 ] Herein, we present ultrasonication as a viable method of reducing the ChLCN film dimensions while preserving the stimulus‐responsive color change capabilities of the particles and show thorough characterization of the material along all steps of fabrication and incorporation in a binder material.…”

A Cr Anti-Sticking Layer for Improving Mold Release Quality in Electrochemical Replication of PVC Optical Molds

“…The microlens array or microprisms array on the thin optical films is formed by imprinting the cavities of the nickel mold, which is obtained by electrodeposition of nickel on an original mold [10]. Therefore, the shape accuracy, dimensional accuracy, and surface finishing of the nickel mold are the source of optical thin film quality assurance [11,12,13,14].…”