Abstract

A fast-switching, tunable color filter was found in a copolymer network liquid crystal (LC), which was in situ generated in a conventional LC test cell with parallel aligned glass plates and investigated with polarized light. Polarization filters were used to convert the tunable optical phase retardance of the test cells to birefringence colors as is always possible in a LC test cell with carefully adjusted cell gap and effective birefringence. The cell gap of the samples could be adjusted to a value of 9 μm, which is not easily possible in a polymer LC composite without creating defects. In these samples, the typical pastel colors seen frequently in birefringent samples could be avoided. The transmittance spectra were recorded and converted to CIE 1931 color coordinates, which showed that the colors seen had a reasonable distance to the white point. The electro-optic switching times of the samples were investigated: Fast responses of $t_{\mathrm{on}}+t_{\mathrm{off}}<5\mathrm{ms}$ were found, which is an impressive speed for tunable birefringence colors in LCs and LC composites. Upon increasing addressing voltages, a blueshift of the peak seen in the transmittance spectra was observed. The samples consisted of copolymer network LC, generated from a reactive mixture with mesogenic monomer and nonmesogenic comonomer. The tunable color was seen selectively in samples with dodecyl acrylate as comonomer. The experiments show how even a straightforward electro-optic experiment still can result in unexpended findings, which may expand the use of LC composites in nondisplay applications. The polymer morphology in samples with a larger cell gap was investigated with scanning electron microscopy, and interdefect distances of $\approx 40\mathrm{\mu m}$ were found. The appearance of defects in test cells with a cell gap of 9 μm could be avoided because the cell gap was much smaller than the measured interdefect distances in test cells with a larger cell gap.

© 2019 Optical Society of America

Electrically tunable birefringence of a polymer composite with long-range orientational ordering of liquid crystals

Byeongdae Choi, Seongkyu Song, Soon Moon Jeong, Seok-Hwan Chung, and Anatoliy Glushchenko
Opt. Express 22(15) 18027-18035 (2014)

Switchable gratings by spatially periodic alignment of liquid crystals via patterned photopolymerization

Jian Zhou, David M. Collard, and Mohan Srinivasarao
Opt. Lett. 31(5) 652-654 (2006)

Fast-response infrared phase modulator based on polymer network liquid crystal

Fenglin Peng, Haiwei Chen, Suvagata Tripathi, Robert J. Twieg, and Shin-Tson Wu
Opt. Mater. Express 5(2) 265-273 (2015)

Using birefringence colors to evaluate a tunable liquid-crystal q-plate

David Marco, María del Mar Sánchez-López, Pascuala García-Martínez, and Ignacio Moreno
J. Opt. Soc. Am. B 36(5) D34-D41 (2019)

Polarized photoluminescence of the polymer networks obtained by in situ photopolymerization of fluorescent monomer in a nematic liquid crystal

Vijay Kumar Baliyan, Vineet Kumar, Jinsoo Kim, and Shin-Woong Kang
Opt. Mater. Express 6(9) 2956-2965 (2016)