CREEP BEHAVIOR IN VACUO FOR HYDROXYPROPYL CELLULOSE CAST FILMS

Abstract

Solutions of hydroxypropyl cellulose (HPC) in N. N-dimethylacetamide (DMAc) form cholesteric liquid crystal above a certain critical concentration. Two kinds of HPC films were cast from the isotropic concentrated solution at different temperatures (-18 and room temperature); HPC film cast at -18°C (HPC-A) appears to remain the cholesteric order in the liquid crystalline solution relatively well than HPC-B (cast at room temperature). The creep behavior of those solid HPC films was determined in vacuo as a function of stress or temperature and was analyzed on the basis of Eyring's activated process. The effect of the casting condition on the creep behavior and Eyring's activation parameters (activation volume V and activation energy ΔU) was discussed. HPC-A exhibited less creep strain than HPC-B. Eyring's activated process could be applied to the creep behavior of HPC films. V of HPC-A was smaller than that of HPC-B. V increased with temperature. V appeared to be smaller than the apparent volume of liquid crystalline domain. ΔU for HPC-A was smaller than that for HPC-B. Further study requires to fully clarify those creep behavior of cellulosic liquid crystalline films.