Effect of molecular weight on the birefringence of lyotropic liquid crystalline ethyl cellulose and hydroxypropyl cellulose

Abstract

An Abbe refractometer (Shimazu Seisakusho Ltd., Bausch & Lomb 3L type) with a rotatable polarizer mounted on the eyepiece was used for determining two principal refractive indices: extraordinary refractive index n, and ordinary refractive index no. The birefringence An was defined as the difference between n, and no. The sample solutions relatively low MW could be spread out over the measuring prism with ease; however, the sample solutions of relatively high MW (especially, in the case of the HPC-D system) could not be done with ease and were allowed to equilibrate for about 2 h because of those high viscosities. As the equilibrium refractive indices, the measured values were independent of the direction of wiping the prism surfaces and of the shear effect.2*6 The sample solution was renewed at each temperature to minimize the effect of thermal history on the refractive indices. A more detailed description of the refractometry is given elsewhere?,'

Formation of Gels in Ethylcellulose Solutions. An Interpretation from Dynamic Viscoelastic Results

“…Notwithstanding research devoted to lyotropic solutions of ethylcellulose (EC), which has deserved several publications, − as far as we know no scientific information on thermoreversible gels based on this cellulose derivative has been available until now. In this paper we analyze the viscoelastic response of EC gels in three diester solvents, in an attempt to understand the mechanism of gelation and to contribute to reach a more general perspective on thermoreversible gels with data of a different system.…”