Chemical Engineering Seminar

Motivated by the significant recent interest in using block copolymers to create solvent-free, mechanically robust battery electrolytes, we use statistical mechanical theory and simulations to study the structure and dynamics of model copolymers.  Of particular interest are AB diblock copolymers that microphase separate into various ordered phases, where A is soft and facilitates ion transport while B provides mechanical strength.  Bicontinuous phases such as the double gyroid are desired for mechanical and transport properties but can be difficult to access, expeically at high molecular weights.  In recent SCFT calculations, we showed that linear tapered copolymers, composed of blocks of pure A and B separated by a middle "tapered" block with mixed composition that linearly varies from pure A to pure B (or from B to A for an inverse taper), prefer the gyroid phase over a wider region of the phase diagram than typical diblocks.  Currently, we employ fluids density functional theory (fDFT) and molecular dynamics (MD) simulations together to better capture monomer scale packing effects, especially important when the system includes ions.  The fDFT results allow us to efficiently determine the nanostructure and ensure the appropriate equilibrim state will be formed in the MD simulations.  Tapering widens the interfacial region and lowers the overall domain spacing, however, the dynamics cannot be predicted via a simple correlations with these structural changes.  Since a tapered system's polymer diffusion is not the same as the analogous diblock with a similar density profile, tapering could allow for separate adjustment of a material's dynamics and structure.