model (7) proved to be very useful in this respect to deduce Rheo-optical techniques are used here to probe the development droplet sizes from the linear viscoelastic spectrum (8). of the morphology in transparent polymeric emulsions. The evolu-Rheo-optical techniques constitute a useful alternative to tion of the droplet geometry is monitored in situ by means of follow the evolution of the structure during flow in real time. linear conservative dichroism and flow small-angle light scattering Their application in studying the morphology of complex (SALS). An interrupted step-up in shear rate is used to generate fluids has been reviewed recently by Fuller (9). SΓΈndergaard distorted droplets. Once the flow rate is stopped the droplets can and Lyngaae-JΓΈrgensen used light scattering as well as light relax either by retraction or by breakup. These relaxation mechanisms can be distinguished by the techniques used here, and structransmittance to track particle size during coalescence and tural relaxation times can be derived from either dichroism or to determine the aspect ratio of the dispersed phase during light scattering experiments. During filament breakup the SALS shear flow (10). Yang et al. (11) extended the range of pattern exhibits two secondary streaks that can be associated with rheo-optical techniques by monitoring the evolution of the capillary instabilities. From the kinetics of the corresponding remicrostructure during flow with linear conservative dichrolaxation, the breakup time of the fibrils can be estimated. The ism in addition to transmitted light intensity and small angle combination of size information derived from light scattering exlight scattering (SALS). Linear conservative dichroism periments with breakup times deduced from dichroism measuremeasurements have been applied successfully in the past to ments or SALS experiments also provides a new rheo-optical detect structural changes during flow in other materials such method for estimating the interfacial tension in transparent immiscible blends. α§ 1998 Academic Press
as particulate (e.g., ( 12)) and phase-separating (e.g., (13)) Key Words: immiscible blends; interfacial tension; relaxation; systems. In the case of immiscible polymer blends, the size, rheo-optics.
shape, and orientation of the inclusions all alter the global anisotropy and consequently could affect the dichroism. Using the combination of linear conservative dichroism and