Anomalous Slow Down in the Kinetics of Capillary Rise Infiltration of Random Copolymers into Packings of Nanoparticles

Capillary rise infiltration (CaRI) has recently emerged as a versatile technique for fabricating highly filled polymer nanocomposite films with extremely high nanoparticle fractions. 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 this study, we investigate the CaRI involving random copolymer infiltrating random packings of silica nanoparticles using in situ ellipsometry. To examine the effect of varying degrees of polymer-silica surface interactions, we use poly(styrene-co-2-vinylpyridine) (S-co-2VP) random copolymers with different ratio of the two monomers: strongly interacting, 2VP and weakly interacting, S. We observe that these random copolymers exhibit significantly slower infiltration rates compared to PS and P2VP homopolymers of the same molecular weight. We believe that the conformation of surface-bound polymers including tails and loops and the enhanced entanglements of chains near the surface may be responsible for the observed trends.