Origins of Microstructural Transformations in Charged
Vesicle Suspensions: The Crowding Hypothesis
- Publication date
- Publisher
Abstract
It is observed that
charged unilamellar vesicles in a suspension
can spontaneously deflate and subsequently transition to form bilamellar
vesicles, even in the absence of externally applied triggers such
as salt or temperature gradients. We provide strong evidence that
the driving force for this deflation-induced transition is the repulsive
electrostatic pressure between charged vesicles in concentrated suspensions,
above a critical effective volume fraction. We use volume fraction
measurements and cryogenic transmission electron microscopy imaging
to quantitatively follow both the macroscopic and microstructural
time-evolution of cationic diC18:1 DEEDMAC vesicle suspensions at
different surfactant and salt concentrations. A simple model is developed
to estimate the extent of deflation of unilamellar vesicles caused
by electrostatic interactions with neighboring vesicles. It is determined
that when the effective volume fraction of the suspension exceeds
a critical value, charged vesicles in a suspension can experience
“crowding” due to overlap of their electrical double
layers, which can result in deflation and subsequent microstructural
transformations to reduce the effective volume fraction of the suspension.
Ordinarily in polydisperse colloidal suspensions, particles interacting
via a repulsive potential transform into a glassy state above a critical
volume fraction. The behavior of charged vesicle suspensions reported
in this paper thus represents a new mechanism for the relaxation of
repulsive interactions in crowded situations