Surface grafted agents with various molecular lengths and photochemically active benzophenone moieties

Abstract

Homologues of benzophenone silane, a covalently graftable, photochemically active surface functionalizing agent, are investigated as surface functionalization agents for both small particles and planar substrates. In these homologues, a chlorosilane functional group and a photochemically active benzophenone oxo moiety are separated with an aliphatic spacer of varying length. The species obtained are first investigated by surface grafting on substrates (Si wafers, glass plates, and indium tin oxide coated glass plates). Si wafer samples are investigated with ellipsometry clearly indicating monolayer formation. The monolayer thickness can be controlled by the size of the aliphatic spacer group and also by the doping concentration of the solution used in the spin-casting step. The functionalized surfaces are further investigated by measuring the contact angle of a suitable organic fluid, a nematic liquid crystal. Photo exposure of these samples results in a drastically varied contact angle: The surface grafted species are still photochemically active and photo exposure leads to the addition of a nearby organic molecule (from the liquid crystalline phase) to each activated surface agent molecule. The synthesized species are then investigated as (covalently binding) surfactants in the wet planetary ball milling process aimed to fabricate solid–liquid dispersions (of Fe doped lithium niobate particles). It was found that the use of species with higher molecular length results in dispersions of small particles, functionalized with photochemically active surface agents. Indeed, they show better performance than conventional surfactants.