AGING EFFECTS ON THE RHEOLOGY OF LC SOLUTIONS OF HYDROXYPROPYLCELLULOSE

We apply the recently developed continuum theory of liquid crystalline polymers(1) to interpret the behavior of the shear viscosity eta(gamm a overdot) and the first normal-stress difference N-1(gamma overdot) m easured for liquid crystalline solutions (c=37%, c>c) of HPC (Aldrich , M(w)=100,000) in acetic acid (AA) with different ages: 1 day, 1 mont h and 2 years. eta/(gamma overdot) and N-1(gamma overdot) were measure d over four decades in gamma overdot. N-1(gamma overdot) is observed t o change from positive to negative and again to positive, as the shear rate gamma overdot increases. eta(gamma overdot) shows a small newton ian plateau at low shear rates and a strong shear-thinning at higher v alues of gamma overdot. The rate of decrease of eta(gamma overdot) in this region is not monotonous, as usual, but shows an ''hesitation'' s imilar to one previously observed in a different system(2). The aging effect promotes a ''depolymerization''(3) of HPC. This, in turn, shoul d have a strong influence on the behavior of N-1(gamma overdot) and et a(gamma overdot) which is indeed observed(4). All these observations c an be rationalized within the framework of the theory(1).