TRANSIENT SHEAR RESPONSE OF LIQUID CRYSTAL-FORMING HYDROXYPROPYL CELLULOSE SOLUTION IN DIMETHYLACETAMIDE .1. STRESS GROWTH AND RELAXATION BEHAVIOR

The stress growth and relaxation behavior of liquid crystalline hydrox ypropyl cellulose solutions in dimethylacetamide was characterized by using exponential functions. The parameters evaluated for the stress g rowth and relaxation processes were compared and the shear history eff ect on the parameters was determined. The exponential functions propos ed were valid for our system. The isotropic solutions had one retardat ion time and one relaxation time, whereas the liquid crystalline solut ions had plural retardation and relaxation times. The concentration de pendence of the parameters for the stress growth process was similar t o that for the stress relaxation process and to that for the steady-st ate shear viscosity. The stress growth and relaxation behavior for the liquid crystalline solutions was originated from the change (deformat ion or decrease) in liquid crystalline domains. The deformation of liq uid crystalline domains with shear seemed to be slower than the recove ring of the domains to original shape. The stress growth process was a progressive event, whereas the relaxation process was a sudden event. Stress relaxation behavior for the liquid crystalline solutions was s ensitive to the shear history. (C) 1994 John Wiley & Sons, Inc.