Department Seminar: Microscale and nanoscale experimental colloidal model systems: Switchable gelation and macromolecular crowding

Presented by

Dr. Anand Yethiraj, Memorial University

Abstract

I will describe an experimental colloid science approach to studying two problems, on two different lengthscales, in condensed matter and biophysics. 
 
Gels are amorphous materials -- ubiquitous in food, cosmetics, printing, cement -- that are characterized by the pr esence of an open percolating network. Colloids and polymers (and biopolymers and other macromolecules) in solution will form gels at relatively low volume fraction, provided the interactions are sufficiently attractive. Gels age and collapse irreversibly in ways that are poorly understood. Using a switchable external field, we probe reversibility and irreversibility in gel-forming systems using confocal microscopy.
 
On the other hand, the innards of living cells are very crowded environments with large/small, charged/uncharged, hydrophobic/hydrophilic macromolecules, and knowing how individual proteins behave in the presence of this crowding is challenging. We use a bottom-up colloidal model approach with polymer as protein and colloid as crowder. Using a nanoscale polysucrose colloid, Ficoll, as a model crowder, we examine size and diffusion of a model polymer in crowded solution using NMR, in tandem with small-angle neutron scattering and rheology. We compare these results with those in more realistic crowding solutions.