Nonmonotonic Impact of Statistical Copolymer Composition on the Kinetics of Capillary Rise Infiltration

Infiltration dynamics of poly(styrene-stat-2-vinylpyridine) (PS-stat-P2VP) statistical copolymers (StCPs) undergoing capillary rise infiltration into the interstices of silica nanoparticle (SiO2 NP) packings are investigated by in situ spectroscopic ellipsometry with varying ratios of strongly interacting 2-vinylpyridine (2VP) and weakly interacting styrene (S) repeat units. As the fraction of 2VP (fP2VP) increases, a nonmonotonic dependence is observed in the time required to fully fill the interstices of the SiO2 NP packings (tinf) and the effective viscosity (ηeff). To understand the mechanism behind the nonmonotonic trend in infiltration dynamics, polymer properties such as zero-shear viscosity (η0) and glass transition temperature (Tg) are considered; however, these factors fail to explain the trend. When the strong interactions between 2VP and SiO2 are suppressed by modifying the surface of SiO2 NPs with the epoxide group, the infiltration dynamics no longer show strong dependence on fP2VP. This result indicates the important role played by the 2VP unit in the anomalous slowdown observed in StCPs, possibly by controlling its conformation on the pore surface and the interactions between the surface-adsorbed chains and chains that are translated through the pores.