Effect of Chiral Polymers on Lyotropic Liquid Crystals

Abstract

Formation of the cholesteric phase in aqueous lyotropic liquid crystals doped with cellulose derivatives has been studied utilizing hot stage polarized microscopy. Three ionic surfactantssodium decyl sulfate, cesium pentadecafluorooctanoate, and myristyltrimethylammonium bromidewere employed to obtain anionic or cationic lyonematics. After addition of chiral polymers (at polymer concentration ∼0.05−0.750 wt %) the samples were sealed in flat glass capillaries, and a magnetic field was applied to enhance the homogeneous orientation and formation of the fingerprint texture. Out of seven various cellulosic derivatives (five nonionic, one cationic, and one anionic), nonionic hydroxypropyl cellulose was the only compound that induced the cholesteric phase. The effective helical twisting power (HTP) of hydroxypropyl cellulose is 3−4 times higher in anionic lyonematics than in cationics. In both cationic and anionic media, the HTP decreases with an increase in the molecular weight of the chiral polymer. This behavior can be attributed to two factors: (i) inhomogeneous distribution of chiral centers (formation of polymer bound chiral micelle clusters) and (ii) the finite character of intermicellar chiral distortion forces. The pitch of the polymer-doped cationic chiral lyonematic decreases as the temperature rises, indicating a closer packing along the helical axis with an increase in the thermal motion of the system.