Characterization of polymer dispersions by Fourier transform rheology

Fourier transform rheology is a very sensitive technique to characterize no n-linear rheological fluid properties. It has been applied here for the fir st time to polymer dispersions in water and the results are compared to tho se from conventional rheology. namely steady and small amplitude oscillator y shear experiments. The investigated systems are mainly based on styrene a nd n-butylacrylate. A first attempt was made to evaluate how far colloidal parameters like part icle volume fraction and ionic strength as well as chemical composition and surface characteristics of the dispersed particles are reflected in FT-rhe ology spectra. Significantly different non-linearities are observed for hig hly concentrated dispersions of particles with different T-g. These differe nces are not detected in linear oscillatory shear and show up in steady she ar only at significantly higher shear rates. Particle surface characteristics influence the non-linear response in oscil latory shear significantly and the intensity of the overtones is found to b e higher for a dispersion of particles with a "hairy" swollen surface layer as compared to a system of smooth particles, although the solids content w as adjusted to match the steady shear viscosity. The intensity of the overtones in FT-rheology strongly decrease upon diluti on. At a solid content below 35% no differences are observed in the FT-expe riments for the systems investigated here. whereas the differences in stead y shear are very pronounced in this concentration range. A significant influence of added salt onto the non-linear response is detec ted for some systems, which might be correlated to the stability of these s ystems. The observed phenomena certainly cannot be explained in terms of constituti ve equations or microstructural statistical mechanical models at present. T hus, FT-rheology yields information complementary to classical steady or li near oscillatory shear experiments.