Although the recent theory of Larson-Doi's constitutive equations is thought to be the first one applicable to the phenomenological flow behaviors for the textured lyotropic liquid crystalline polymer (LCP) systems, there remain for the theory some shortcomings or discrepancies which are not enough to predict the defect density evolution of the system.
To overcome the shortcomings, the concept of initial domain state is introduced to the Larson-Doi's defect density evolution equation stopping the indefinite coarsening of domain at the shear cessation. The revised version with the initial domain state, thus, can make the theory apply to the low shear rate region (Onogi-Asada's first shear thinning region) as well as the region of intermediate shear rate (Onogi-Asada's Newtonian plateau). Moreover, the "Region 0" recently observed by Sigillo-Grizzuti may be also predicted with a sense of the initially, randomly distributed domain state responsible for the constant viscosity at very low shear rate.
Shear thinning behaviors at low shear rate region were observed through the consideration of complex viscosities at low frequency levels, which were obtained from the small-amplitude oscillatory experiment for the aqueous liquid crystalline hydroxypropylcellulose solutions. Moreover, it is also confirmed that the modified defect density evolution equation makes the balance between the Frank elastic energy and viscous flow energy better by the comparison of the storage and loss moduli obtained from the dynamic tests.
As transient flow experiment, an intermittent forward flow was applied for the LCP samples with varying the rest time which might be considered as a factor controlling the initial domain state before the flow imposition. The transient stress responses resulted for each rest time could provide the fact that the time scale of equilibrium domain state was strongly related with the amplitude ratio between first maximum and steady state of the oscillatory stress response.
