Evidence of shear rate dependence on restructuring and breakup of latex aggregates

Small-angle static light scattering has been used to probe the evolution of aggregate size and structure in the shear-induced aggregation of latex par ticles. The size of aggregates obtained from the particle-sizing instrument (Coulter LS230) was compared with the size of those obtained with another approach utilizing the Guinier equation on the scattering data. Comparison of the two methods for studying the effects of mixing on the evolution of t he aggregate size with time revealed similar trends. The aggregate structur es were quantified in terms of their fractal dimensions on the grounds of t he validity of Rayleigh-Gans-Debye scattering theory for the fractal aggreg ates. Analysis of the scattering patterns of aggregates verified that restr ucturing of the aggregates occurred as the aggregates were exposed to certa in shear environments, resulting in a scale-dependent structure that could not be quantified by a fractal dimension. The effect of restructuring on ag gregate size was particularly noticeable when the aggregates were exposed t o average shear rates of 40 to 80 s(-1), whereas no significant restructuri ng occurred at lower shear rates. At 100 s(-1), the fragmentation of aggreg ates appeared to be more significant than aggregate compaction. (C) 2001 Ac ademic Press.