| Abstract: |
Polymer nanocomposites have proven as versatile materials for numerous applications, blending the optimal properties of the inorganic filler and matrix polymer. Such composites are often fabricated through the addition of inorganic nanofillers to a polymer matrix.Achieving a high volume fraction of filler proves difficult in such a method due to particle aggregation. Our experimental collaborators, Weiwei Kong and Russell Composto, create highly-loaded (50 vol% filler) composites by infiltrating polystyrene (PS) or poly(2-vinylpyridine) (P2VP) into a nanoporous gold scaffold exhibiting a bicontinuous structure with nanoscale pores. Infiltration occurs through capillary forces by heating the above its glass transition temperature. If infiltration is dictated by reptation, the infiltration time should scale with the molecular weight of the polymer as t ~ MW^3.4. However, our previous work found that polystyrene infiltration time is faster than expected, scaling as t ~ MW^1.4. Molecular dynamics simulations reveal that the reduced dependence of MW and the enhanced kinetics of infiltration are attributed to a reduction in chain entanglement density during infiltration and a reduction in polymer–wall friction with increasing polymer molecular weight.
We have also observed that P2VP, which has a stronger affinity to the gold surface than PS, infiltrates at a slower rate when compared at a similar MW as PS. The first research objective of this Discover ACCESS allocation is to use molecular dynamics simulations of polymer capillary rise into bicontinuous nanoporous structures to elucidate the mechanism behind the infiltration kinetics observed experimentally for entangled polymers with a strong affinity for the gold surface. LAMMPS on TACC's Stampede3 will be used to perform these simulations.
Along the same theme, we plan to investigate the kinetics of capillary rise infiltration into nanoparticle packings. Capillary rise infiltration (CaRI) is a method through which numerous polymer architectures, such as block or random copolymers, can be infiltrated into a highly confined random close-packed nanoparticle packing. Most previous studies on CaRI have focused homopolymers to investigate the influence of confinement on infiltration kinetics and the mechanical properties of resulting composite films. In contrast to the capillary rise infiltration kinetics of homopolymers, the microphase separation of block copolymers becomes a factor. In addition, preferential wetting of one monomer type to the nanoparticle surface will alter the infiltration kinetics of both block and random copolymers. Our experimental collaborators, Taeyoung Heo and Daeyeon Lee, investigate the CaRI of random and block copolymer infiltrating random packings of silica nanoparticles using in situ ellipsometry. To examine the effect of varying degrees of polymer-silica surface interactions, they use poly(styrene-co-2-vinylpyridine) (S-co-2VP) random and block copolymers with different ratio of the two monomers: strongly interacting, 2VP and weakly interacting, S.
The second research objective of this Discover ACCESS allocation is to use molecular dynamics simulations of block and random copolymer capillary rise into nanoparticle packings to elucidate the mechanism behind the infiltration kinetics observed experimentally. LAMMPS on TACC's Stampede3 will be used to perform these simulations. |
0000-0002-2315-9546