The rheology of polymeric liquid crystals

Abstract

The molecular theory of Doi has been used as a framework to characterize the rheological behavior of polymeric liquid crystals at the low deformation rates for which it was derived, and an appropriate extension for high deformation rates is presented. The essential physics behind the Doi formulation has, however, been retained in its entirety. The resulting four-parameter equation enables prediction of the shearing behavior at low and high deformation rates, of the stress in extensional flows, of the isotropic-anisotropic phase transition and of the molecular orientation. Extensional data over nearly three decades of elongation rate (10 . 2 -101 ) and shearing data over six decades of shear rate (10 -2-104 ) have been correlated using this analysis. Experimental data are presented for both homogeneous and inhomogeneous shearing stress fields. For the latter, a 20-fold range of capillary tube diameters has been employed and no effects of system geometry or the inhomogeneity of the flow-field are observed. Such an independence of the rheological properties from these effects does not occur for low molecular weight liquid crystals and this is, perhaps, the first time this has been reported for polymeric lyotropic liquid crystals; the physical basis for this major difference is discussed briefly.

Rheology of polysaccharide systems

“…It was shown that the negative normal stress region roughly corresponds to the transition from tumbling to nonperiod conditions, encompassing the small y range of the oscillating regime [589], and that a kink appears in the viscosity curve in the same region. with extensional data over nearly three decades of elongation rate and shearing data over six decades of shear rate has been obtained for a hydroxypropylcelluloselglacial aClltic acid lyotropic system [592].…”

Fiber motion and rheology of suspensions with uniform fiber orientation

“…Bercraft and Metzner 16 performed a "molecular approach" based on a modification of the molecular theory of Doi for liquid crystalline polymers 17,18 to take into account the macroscopic dimensions of the fibers. They obtained good predictions for steady rheological measurements.…”

Numerical simulation of three-dimensional flows of liquid crystalline polymers in rectangular abrupt contraction and expansion channels

“…The modified Doi model [2] was employed as a constitutive equation. The orientation of the molecules was described by an orientational order parameter tensor…”

“…In the numerical simulation of the flows in complex geometries, Doi model [1] with the quadratic closure was used to clarify the general appearance of molecular orientation induced by complex flow fields, despite lack of tumbling. Numerical simulations for complex flows of LCPs using the modified Doi model [2] were carried out [3−6] . Most numerical computations, however, treated two-dimensional flows and the three-dimensional orientational behavior in complex flow fields has not been understood sufficiently.…”