Exploring self-assembly behavior of elastin-like polypeptides

Aqueous solutions of commercial poly(oxyethylene) – poly(oxypropylene) – poly(oxyethylene), triblock co-polymers (PEOx – PPOy – PEOx, Pluronics©) undergo both micellization and structural arrangement as a function of increasing temperature. In the case of Pluronic F127 (PEO100 – PPO65 – PEO100), this structural arrangement is observed macroscopically as a liquid to gel transition for polymer concentrations > 15 w/v%. This self – assembly and ordering can be controlled through both composition and temperature. In addition to this thermoresponsive behavior, dispersions containing low concentrations of both F127 and inorganic Laponite nanoparticles have been shown to undergo a liquid to gel transition upon UV exposure when a photoacid generator (PAG) is added as a third component. This transition is attributed to interactions between the Laponite particles within the system. We recently reported on the factors affecting macromolecular gel formation and kinetics using photorheology. However, the UV – induced structural changes causing gelation are not well – understood. Here, we use in – situ small angle x-ray scattering (SAXS) studies to probe the solution organization of these systems. Simultaneous UV – SAXS experiments were conducted to investigate the UV – induced structural changes. The experimental results were correlated to the macroscopic gelation kinetics investigated separately via photorheology to better understand the physical interactions and changes leading to gelation. Presentation Preference: no preference whether contributed talk or poster Milos Knezevic and Mark Warner Theory of photoresponsive ferroelectric liquid crystals Photoferroelectrics are materials in which ferroelectricity can be affected by exposure light. Liquid crystals can acquire photoferroelectric properties by dissolving small quantity of a photochemical isomer in a ferroelectric host phase. In the case of ferroelectric smectic C* liquid crystals, the rod-like trans isomer of the azobenzene fits well into the structure of a smectic C* phase. On the other hand, the smectic C* order can be locally disturbed by the presence of photochemically-induced, bend-shaped cis isomers. In particular, the spontaneous polarization can be changed by interaction with light. We use a model of nonlinear optical absorption to describe trans – cis state transitions along with their spatial dependence, and the process of thermal relaxation back to the trans state. Our predictions for polarization both in static and dynamic regime are in good qualitative agreement with experimental results. Computational models of stiff fiber networks: linear and nonlinear elasticity A. J. Licup and F. C. MacKintosh Department of Physics and Astronomy, VU University Amsterdam, The Netherlands (Dated: May 1, 2012) The response of living cells to mechanical stress is governed by the viscoelasticity of complex networks of stiff filamentous proteins that make up the cytoskeleton. At a larger scale, cells interact mechanically with extracellular matrices that also consist of stiff fiber networks. Recent theoretical research on such systmes has aimed to explain the microscopic origins of viscoelasticity. These models have highlighted the importance of effects such as the semiflexible nature of the constituent filaments, network geometry, and connectivity. We develop lattice-based simulation methods to study the mechanics of random fiber networks, in which we are able to independently control these various aspects. We report results for both linear and nonlinear elastic properties of fiber networks. We also examine the validity of continuum elasticity for these networks. Polymer networks with mobile force-applying crosslinks Student: Jacob Mohau Mateyisi Supervisor: Kristian Müller-Nedebock Co-supervisor: Leandro Boonzaaier