(604h) Instantaneous Formation and Aging Behavior of Charged Vesicle Gels

Colloidal dispersions of cationic bilayer vesicles serve as base materials for commercial household products. During the manufacturing process, these dispersions are subject to a number of expansion/contraction flows. The long-term stability of such dispersions can depend, amongst other factors, on their processing history. Here, we study dispersions of charged multilamellar vesicles (MLVs) made from the cationic surfactant diethylesterdimethyl ammonium chloride (DEEDMAC), whose bilayers are in the crystalline (solid) state at room temperature. Typically under the application of shear, MLV dispersions display strong shear-thinning behavior. However when subject to a contraction flow through an extruder, above the main phase transition temperature of the bilayers, we find that such vesicle dispersions instantaneously transform into a ‘jammed’, glassy-state at the extruder outlet. The glassy dispersions behave as stiff gels, having visco-elastic moduli that are several orders of magnitude higher than their un-extruded counterparts. We use tools such as rheology and cryo TEM imaging to probe mechanisms that lead to the formation of such vesicle gels. Further, we closely examine the subsequent aging or breakdown of their microstructure; a process which occurs over time scales that depend on the dispersion composition as well as the thermotropic phase behavior of the surfactant.