TABLE OF CONTENTS There are many examples of complex, multicomponent liquids that undergo real and apparent changes in phase when subjected to external fields. There are numerous observations of such phenomena for the case of flow fields, all showing a marked turbidity of the samples when a sufficiently strong flow field is applied. As discussed in section 10.1.6, the first studies of this phenomena analyzed this effect as the manifestation of a true, flow induced phase transition, and correlated the onset of turbidity with die measured normal stresses in the fluids [89]. Such a correlation was suggested by models of the thermodynamics of the mixtures wherein the effects of the flow were included by adding a term to the free energy that was proportional to the deformation of the end-to-end distance of the polymer chains. This approach was later criticized by researchers using an alternative description that envisioned the appearance of turbidity as a consequence of a coupling of concentration fluctuations in the material to the stresses generated by the flow [92,93,94]. This latter approach has the advantage of leading to a prediction of die structure factor, which can be directly observed using small-angle light scattering. This procedure was outlined in section 10.1.6 and led to the SALS pattern shown in Figure 10.2 for the specific case of a two-dimensional, extensional flow field. This simple example modeled the rheology of a polymer liquid a second-order fluid.
In this case study, the use of...
