Colloquium: Dr. Alan R. DentonDepartment of Physics North Dakota State University Fargo, ND
Multiscale Modeling of Screening and Crowding in Soft Materials
Soft materials composed of mixtures of macromolecules (e.g., polymers or colloids) have attracted much recent attention for their rich morphologies and phase behavior and their promise for engineering novel materials. For example, colloidal crystals can serve as templates for fabricating "inverse opals" -- highly porous materials, whose micron-sized cavities affect light propagation -- with potential applications to quantum computers. The ability to independently vary size and charge ratios of different species greatly expands the possibilities for tuning interparticle interactions and stabilizing unusual phases. In modeling soft materials, coarse-grained approaches often prove essential to surmount computational challenges posed by multiple length and time scales. In this talk, I will outline a practical approach to modeling effective interactions in ultra-polydisperse mixtures for input to statistical mechanical theories and computer simulations. Using a sequential coarse-graining procedure, I will show that a mixture of charged colloids and nanoparticles can be mapped onto a one-component model of pseudo-colloids interacting via a screened-Coulomb (Yukawa) effective pair potential, with relevance for stability of pharmaceuticals and other suspensions. For mixtures of polymers and nanoparticles, a free-volume theory predicts that crowding by nanoparticles can modify polymer conformations, with biological relevance for protein and RNA folding.