Anticipating colloidal instabilities in cationic vesicle dispersions by measuring collective motions with dynamic light scattering.

Vesicle dispersions are useful for many applications from medicinal to consumer products. However, using these dispersions requires some knowledge of and control over their colloidal properties. Measuring interparticle interactions between vesicles should allow framing the problem in terms of Smoluchowski kinetic models and consequently anticipating time-dependent aggregation and coalescence for the dispersions. However, this can be a difficult task for many complex mixtures. A primary goal of this paper is to show that it is possible to measure interparticle potential between small vesicles by measuring the concentration-dependent collective motion using dynamic light scattering. These measurements allow determination of the second virial coefficient for the dispersion, providing a convenient platform for summing all contributions to the interaction potential over all vesicle conformations, thus making the analysis of complex mixtures more tractable. As a verification of the approach, a comparison is made to dispersions in which the stability is governed solely by electrostatics, using existing techniques to anticipate instabilities. A second goal of this paper is to build a simple potential model in which the Smoluchowski model can be used to quantitatively anticipate the aggregation behavior of the small vesicle dispersion. Together, these observations constitute a convenient approach to anticipating the behavior of vesicle (and other) dispersions in complex mixtures.