Abstract:

Presented a comprehensive review of rheol. theory, modeling, and simulation of surfactant nematic liq. cryst. phases, including calamitic and discotic micellar solns. and wormlike micelles. A review of verifiable rheol. liq. crystal models for lyotropic nematics highlighting the mechanisms that control orientation behavior under shear, anisotropic viscoelasticity, and non-Newtonian behavior. Since defects and textures are essential characteristics of these materials that affect the flow properties, an in-depth review of phys. and rheophys. defects is presented, including defect nucleation and coarsening processes. The theory for micellar nematics is applied to textures, flow birefringence, phase transition under shear, orientation fluctuations, and flow alignment, and the predictions are compared with exptl. data. The theory is finally applied to transient shear flows of wormlike micellar nematic solns., and the predicted banded textures and transient stress responses are compared to rheol. expts. The predictions provide a new way to ext. addnl. information from exptl. rheol. data and allow to distinguish the role of liq. cryst. properties such as viscoelastic anisotropy, flow alignment, coupling between orientation kinematics, and flow kinematics. The rheol. predictions show a strong similarity with other nematic materials, including low-molar-mass thermotropes and lyotropic nematic polymers. [on SciFinder(R)]