Kinetically Controlled Mesoporous Silica Films for Quasi-3D Nanoconfinement of Semicrystalline Polymers below Their Lamellae Dimensions.

Abstract

Mesoporous silica thin films are candidates for next-generation dielectric materials due to their potential for control over their texture, high surface area, and good dielectric properties. Further, their dielectric response can potentially be further modified by infiltrating a second phase such as a polymer to produce thin film nanocomposite dielectrics. Despite their potential, uptake of mesoporous silica thin films has been hindered by difficulties in controlling the nanoscale structure and silica texture. We employ advanced characterization and kinetic Monte Carlo modeling to identify critical synthesis parameters governing the mesoporous silica texture. Different degrees of pore ordering can be achieved from quasi-random to highly ordered, eliminating the trial-and-error typically associated with achieving a targeted nanostructure. We then infiltrate semicrystalline poly(vinylidene fluoride) and polypropylene into the sub-10 nm pores to completely suppress the formation of crystalline domains in the polymers and produce nanocomposite dielectrics. Polypropylene nanocomposite dielectrics exhibit dielectric constants ∼20% higher than silica and 125% greater than those of polypropylene. Poly(vinylidene fluoride) nanocomposites exhibit relaxor ferroelectric behavior. These dielectric materials are enabled by controlled, hierarchical design that spans the self-assembly of the silica matrix, tuning of the pore surface chemistry, and modification of the polymer conformations through the resulting quasi-3D nanoconfinement. We believe that these nanocomposites represent a powerful platform for the study of polymers under extreme levels of confinement, as well as a potential platform for next-generation dielectric materials.