Theme 1 Electrostatic Effects in Polymers and Soft Matter: Electrostatic interactions are ubiquitous in soft materials and biological systems. The long-range nature of electrostatic interactions leads to rich, interesting, and often counterintuitive phenomena. In our group, we use theory and computer simulation to study a variety of charged polymer and soft matter systems, with a particular focus on the role of electrostatic correlations. Current projects include: chain conformation and phase transitions in polyelectrolyte solutions; image charge effects on electrical double layer structure and forces; polyelectrolyte adsorption on surfaces and polyelectrolyte-mediated interactions between surfaces; structure and dynamics of room temperature ionic liquids.
Theme 2 Nucleation or Barrier Crossing: The formation of a more stable phase from a metastable state requires overcoming a free energy barrier. Examples include precipitation of minerals in a supersaturated solution, or boiling of water from a superheated state, or less obviously, translocation of particles through a lipid membrane. We develop novel density functional theories and self-consistent-field theories that can accurately describe the inhomogeneous structures, such as liquid-vapor interfaces, and combine with the string method, to study the nucleation/barrier crossing in a number of soft-matter and polymer systems, such as bubble nucleation in polymer foaming with high-pressure gases, or nucleation of periodically ordered structures from the disordered state of block copolymers.
Theme 3 Dynamics and Rheology of Associating Polymers: Polymers with associating groups can form physically crosslinked gel networks with unique dynamic and rheological properties. In collaboration with Prof. David Tirrell’s group, we are studying how polymers diffuse in the network. We are also investigating how the networks break and reform under large/rapid deformation and how this structural rearrangement in turn affects their rheological behavior. Recently, we have been collaborating with Prof. John Brady’s group to study the use of active particles as an internal source of energy to control the structure and dynamics in gels. A closely related problem is entangled polymer melts and solutions, where we are studying how polymers disentangle when subjected to large/rapid flow deformations.