Polydisperse spheres allow for important model results for a broad range of biological and nanotechnological systems. In particular, the interior of biological cells is filled by a mixture of diverse proteins at high volume fractions. The related crowding effect induces dramatically varied dynamics, in particular when approaching conditions of dynamical arrest at high volume fractions.
Using the model protein alpha crystallin from the bovine eye lens, we have obtained high-quality experimental data using dynamic light scattering, which indicate an unusal complex relaxation phenomena of the gradient diffusion with three well-separated decays. From theoretical considerations, one decay might be linked to the polydispersity, whereas the other two might correspond to the well-known alpha and beta relaxation in concentrated colloidal solutions.
We are planning to use mode-coupling theory to understand the physical origin of the three decays, and computer simulations are in this context essential to pin down the relevant signatures. Given the large length scales relevant to this relaxation phenomena, we will run Brownian dynamics in large boxes, which combined with high volume fraction amounts to large particle numbers up to 1 million particles. We will investigate the resulting dynamical signatures as a function of volume fraction, and use different forms of polydispersity as well as a monodisperse system for comparison.
This project is part of a larger effort involving experimental, computational, and theoretical components to understand the interactions and dynamics of crystallin proteins in crowded solutions. In this context, the proposed project will contribute a detailed understanding how precursors of dynamical arrest in polydisperse systems manifest themselves, with potential relevance to eye conditions such as presbyopia.