Tunable Wetting of Polymer Nanocomposite Films

Surfaces with controlled wettability are of growing technological importance. In this study, nanoparticles (NPs) with tunable spacing were assembled on poly(styrene-\textit{ran}-acrylic acid), S-$r$-AA, films to manipulate the composite films' wetting properties. Amine-modified silica NPs (15-200 nm) were covalently grafted to the AA moieties on the surface of the S-$r$-AA films, in which the S phase imparts mechanical stability and the AA domains swell, increasing the roughness and surface area. By controlling surface roughness and reaction time, NP coverage ranged from 1{\%}-70{\%}. These films displayed NP-coverage-dependent water contact angles between 60$^{\circ}$and 120$^{\circ}$. The enhanced hydrophobicity is attributed to capillary climbing of S-$r$-AA chains to cover the previously hydrophilic NP surface. Upon increasing NP diameter, the contact angle was found to increase at a fixed total coverage. This increase in attributed to the increase in effective surface area with increasing particle size. This system is utilized as a platform to create Janus particles with unique optical properties and templates for investigating molecular motors.