Non-adsorbing polymers are added to colloidal dispersions to tailor their rheological properties. However, this leads to a number of undesirable phenomena including phase separation and gel collapse. Because they affect the stability of many food and personal care products, understanding and controlling these issues remains a crucial aim. In this study, we present the time-dependent collapse and microstructure of depletion-induced vesicle gels. The vesicle dispersion is prepared from a commercial-grade dichain cationic surfactant through a standard milling process (d_mean=256nm and Φ=0.46). As a depletant, we add the cationic poly(diallyldimethylammoniumchloride) (MW=14.5kDa and R_g=11.2nm). To investigate the phase behavior, vesicles (Φ=0.05~0.3) are systematically mixed with polymer (Cp=0.01~2.0wt%). As density gradients build up, an interface is developed between a vesicle-rich phase and a polymer-rich phase upto Cp=0.2wt%. Increasing the polymer concentration further forms a gel, which subsequently collapses. Height profiles are characterized by a slow initial rising for a finite delay time, a rapid collapse, and a slow final compaction to an equilibrium height. The time-scale associated with the collapse rate is predicted by the poroelastic model [1]. However, we observe a remarkably different polymer concentration dependence on the collapse rate. Unlike other colloidal gels [2], we find the delay time decreases with increasing polymer concentration. We show this surprising behavior can be explained by considering the permeability for solvent backflow [3], which is directly related to the characteristic pore area of the gel obtained using confocal microscopy.

[1] Manley et al. (2005), [2] Kilfoil et al. (2003), [3] Buscall and White (1987)