Precision Analysis of Polymer Rheology by Simultaneous Measurement of Viscoelasticity and Birefringence

Recent progress of molecular rheology for various polymeric systems by a rheo-optical method using simultaneous measurements of stress and birefringence is briefly reviewed. The advantage of the method is that the stress can be disassembled into its components following the birefringence response. The scope of this review is to elucidate the significance of the viscoelastic segment and also to extend the stress-optical rule to inhomogeneous systems. Firstly, effects of highly branched structures on the viscoelastic segment size is examined with bottle-brush type poly(macromonomer) and highly crosslinked thermoset resins. These studies indicate the importance of internal motions of the viscoelastic segments such as bending and tension modes in addition to the reorientation mode of the segments. These modes can be separately estimated with the aid of the rheo-optical measurements. The estimation of the bending mode is particularly important for the relaxation dynamics of tightly entangled systems of semiflexible polymers. Secondly, the extension of the stress-optical rule for inhomogeneous systems is discussed. In these systems, the concept of phase stresses and strains is quite important to understand their molecular rheology, and the stresses can be estimated from the rheo-optical measurements.