Charley Schaefer

University of York

Charley Schaefer is a soft-matter theorist who develops new models and simulation techniques to study the collective dynamics of complex (bio)molecular systems. He  gained his MSc in Chemical Engineering at the Eindhoven University of Technology in the Netherlands, where he studied the self-assembly of supramolecular polymers for biomedical applications (MRI contrast agent). He then gained his PhD at the Applied Physics department at the same University, where he theoretically studied liquid-liquid phase separation (LLPS) of polymer-based blends in an evaporating solvent for organic solar cells. During his postdoctoral work at the University of Durham and (currently) the University of York, he gained interest in 'intrinsically disordered proteins' owing to both their simularities and differences from common polymers. In particular, he has studied how this class of proteins undergo LLPS and lead to the formation of 'membraneless organelles' in living bacteria to survive anti-biotics, and of 'pyrenoid' structures in algae - which are responsible for 20-30% of global CO2 fixation.  His main interest in IDPs revolves around the flow-induced self-assembly of silk fibres. His interest is to study what properties of silk nature has optimised (processing efficiency and fibre functionality), and how these properties are encoded in the amino-acid sequence. He intends to exploit these new insights to reduce the environmental footprint of the industral spinning process, and to design a novel class of artificial silks.


Wednesday April 19th

Flow-Induced Self-Assembly of Silk Fibres

Silk fibres have an out-of-equilibrium semi-crystalline structure that emerges in response to shear and extensional flow. This process of natural silk spinning requires orders of magnitude less energy input than for the industrial spinning of synthetic polymer fibres.
By applying the sticky-reptation model to linear viscoelastic data of the silk solution, we discovered that the dynamical response of the disordered protein is akin to that of an associating entangled polymer. To understand how this class of polymers responds to strong flow, we developed a coarse-grained polymer model that describes the intermolecular reversible crosslinks in an effective environment. Through simulations, and supported by analytical approximations, we found that the stochastic opening and closing of reversible crosslinks leads to the emergence of highly disperse dynamical chain conformations. We found that the fraction of highly stretched chain segments, which are needed to nucleate crystals, is finely controlled and optimised by both the molecular design of the polymer and by the flow rate.