Optical flow birefringence

The classical viscoelastic properties are the dynamic shear moduli, written in the frequency domain as the storage modulus G ( y) and the loss modulus G a>), the shear stress relaxation function G t), and the shear-dependent viscosity j (k). Optical flow birefringence and analogous methods determine related solution properties. Nonlinear viscoelastic phenomena are treated briefly in Chapter 14. 

Figure 13.40 Optical flow birefringence studies of400 kDa polystyrene in Aroclor 1248 at concentrations (a) 9.09, and (b) 105 g/1, based on measurements of Lodge and Schrag(50). Results in the original paper were replotted from magnitude-phase angle representation to the in-phase, out-of-phase representation permitting direct comparison of the results above with the mechanical dynamic moduli. In (b) the vertical axis is a log scale covering 17 orders of magnitude.

Oberhauser, et al. also present orientation angle and birefringence from optical flow birefringence measurements. Tapadia and Wang(14) and Boukany, et a/. (15) interpret the overshoot and undershoot processes in terms of fluids that have become habituated to a particular rate of shear, so when the shear rate is changed they are initially in the state pertaining to the former shear rate, and only gradually achieve the state characteristic of the new steady-state shear rate. 

Lodge, T. P. Rheo-Optics Flow Birefringence, Chap. 9 of Macosko, C. W. Rheology Principles, Measurements and Applications. (1994) VCH Publishers, NY, Weinheim... 

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