Side Chain Effect of Hydroxypropyl Cellulose Derivatives on Reflection Properties

Abstract

Some cellulose derivatives are known to exhibit thermotropic and lyotropic cholesteric liquid crystal (CLC) phases with a visible reflection feature by changing the side chains and mixing with specific solvents, respectively. Although many studies have been reported so far, most of the derivatives have the side chains of linear alkyl groups, but not the bulky phenyl groups. In this report, we synthesized a series of hydroxypropyl cellulose (HPC) derivatives that possessed both linear propionyl esters and bulky (trifluoromethyl)phenyl carbamates in the side chains. The reflection peaks of HPC derivatives shifted to longer wavelengths upon heating due to an increase in the CLC helical pitch. Such thermally induced shifting behavior of the reflection peak was crucially dependent on not only the propionyl esterification degree, but also the substituents in the side chains of HPC derivatives. When the side chains of HPC were chemically modified with both propionyl esters and bulky substituents such as 3,5-bis(trifluoromethyl)phenyl carbamates, the reflection peaks emerged at longer wavelengths at the same temperature. This probably happened because of the steric hindrance of bulky side chains, as supported by the empirical molecular modeling calculation. Although the occupied volumes of (trifluoromethyl)phenyl groups were independent of the CLC phase temperature with visible Bragg reflection, the substituent position, i.e., substituent orientation of trifluoromethyl groups affected the CLC phase temperature. Moreover, we found that the hydrogen bonds between carbamate moieties in the HPC side chains play an important role in the thermally induced shift of reflection peaks.

Liquid crystal behavior of cellulose nanoparticles‐ethyl cellulose composites: Preparation, characterization, and rheology

“…25 Some proteins, heterocyclic compounds, detergents, and cellulose derivatives can form LC mesophases. [26][27][28] With regard to cellulose derivatives, the ethyl cellulose (EC), hydroxypropyl cellulose and cellulose acetate are able to form both lytropic and thermotropic LC phases. These derivatives can form chiral nematic phase due to chairality (optical properties) of cellulose backbone and its rigid helical conformation.…”

Playing the blues, the greens and the reds with cellulose-based structural colours

“…Actually, the structural colours present in cellulosics are due to cholesteric phases that are obtained from lyotropic and/or thermotropic systems that were much studied in the eighties [12][13][14][15][16][17][18] . After the preliminary studies many other works were performed in order to obtain different coloured thermotropic cellulose derivatives, at room temperature, and to better understand the formation of right-and left-handedness in cellulose-based helicoidal liquid crystalline phases [19][20][21][22][23][24][25][26] . The photonic characteristics of the thermotropic, as well as lyotropic cellulosic systems, were found to depend on temperature, pressure, concentration, type of solvent and cellulose derivative.…”

Cellulose Ether-Based Liquid Crystal Materials: Review Article

“…These materials show characteristic optical textures similar to un-crosslinked cellulose-based liquid crystal polymers although welldefined patterns typical of cholesteric structures were not observed [66,67]. The esterification of HPC by a series of aliphatic acid esters exhibited characteristic features of cholesteric LC phases between their glass transition and isotropization temperatures [68,69]. This literature confirmed that an increase in the number of methylene units in the side chains of this series of aliphatic acid esters of (2-hydroxypropyl) cellulose, led to an increase in the layer spacing values for the cholesteric LC phases measured by WAXD.…”