Abstract
Vitrification in a dilute colloidal system needs an asymmetric particle composition (a mixture of nano and micro colloids) to materialize. The volume fraction of the large particles increases (up to ≈0.58) driven by depletion forces produced by the smaller colloids. Such entropic forces are short-ranged and attractive. We found a different type of dynamical arrest in an extremely dilute asymmetric mixture of nanovesicles and polystyrene microparticles, where energy, instead of entropy, is the main protagonist to drive the arrest. Furthermore, when the vesicles go through the gel-fluid phase transition, the mean square displacements of the microparticles suffer a sudden splitting indicating a viscous jump. If the vesicles are doped with negatively charged lipids, particles and vesicles repel each other and the rheology of the mixture becomes athermal and Newtonian. Our findings are important to understand caging phenomena in biological systems, where diverse electrostatic distributions are present.
Highlights
Research to understand the physical subtleties behind the formation of vitri ed states, is still very active in the so matter scienti c community.[1,2,3,4,5] it is hard to describe it in a few words, a succinct description of a vitri cation process should include the fact that when a colloidal system vitri es, either by adding mass, reducing volume or temperature, or by shear, there appears a prominent dynamical arrest of the colloids
We found a different type of dynamical arrest in an extremely dilute asymmetric mixture of nanovesicles and polystyrene microparticles, where energy, instead of entropy, is the main protagonist to drive the arrest
We have measured the mean square displacements (MSD) of tracer particles in a suspension of small unilamellar vesicles (SUV) made of different lipid compositions at various temperatures
Summary
Research to understand the physical subtleties behind the formation of vitri ed states, is still very active in the so matter scienti c community.[1,2,3,4,5] it is hard to describe it in a few words, a succinct description of a vitri cation process should include the fact that when a colloidal system vitri es, either by adding mass, reducing volume or temperature, or by shear, there appears a prominent dynamical arrest of the colloids This phenomenon is observed in hard-sphere mixtures,[1,2,5,6] but in so ones.[3,7]. In so systems, a good model for the smaller colloids is provided by star polymers.[3,9]
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