Quiescent and flow-induced transitional behavior of hydroxypropylcellulose solutions

The flow-induced transition of liquid crystalline polymers (LCPs) is studied by rheological techniques. Aqueous solutions of hydroxypropylcellulose (HPC) in water are adopted as a model LCP system. Nonisothermal oscillatory tests are first used to quantitatively determine the “rheological” phase diagram of the HPC/water system under quiescent conditions. The phase diagram compares well with those obtained by other, more conventional techniques. Superposition of oscillatory and steady shear flow is then used to describe the nonisothermal flow-induced transition. In this case, it is shown that a critical shear stress must be reached to effectively induce the isotropic/mesophase transition. Stress-loop experiments are also used to identify the isothermal flow-induced transition, and to provide information on the transition kinetics.