Novel Polymer Nanocomposite Structures Created by Nanoparticle Jamming and Polymer Infiltration*

Understanding the fundamental polymer science that govern structure-property relationships in polymer nanocomposites (PNCs) remains a key challenge. Herein, we discuss two new directions for controlling PNC morphologies and their resultant properties by (1) arresting nanoparticle (NP) dynamics and (2) infiltrating polymer into scaffolds.  First, the interplay between surface enrichment, phase separation, and wetting in PNC films and resulting unique morphologies are investigated using a system of poly(methyl methacrylate) grafted NP (PMMA-NP) in a poly(styrene-ran-acrylonitrile) (SAN) matrix. For PNC films annealed in the one-phase region, surface enrichment of the lower surface energy component (PMMA-NP) occurs, with a homogeneous distribution of NPs remaining in the bulk of the film. In the two-phase region, wetting and phase separation occur simultaneously leading to a tri-layer structure, with two symmetrical PMMA-NP rich wetting layers sandwiching a SAN rich phase containing PMMA-NP pillars that span the two wetting layers.  The ‘jammed’ morphologies lead to enhanced mechanical properties and increased thermal stability of the films. Second, a high-filler PNC is created 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 upon heating PS (P2VP) above its glass transition temperature (Tg). PS and P2VP, having different affinities to the gold scaffold, exhibit different segmental dynamics inside the confined pores as measured through their Tg. The more attractive P2VP shows a 20°C increase in Tg while PS shows only a 6°C increase at comparable molecular weight. Two new approaches are presented that achieve precise control of the structure-property relationships in PNCs and have potential to lead to improved performance for solid polymer electrolytes and gas transport membranes.