Characterization of Titanium Alkoxide- Based Sol-Gel Systems and their Behavior in Icephobic Coatings

Abstract

New coatings have been developed that display resistance to the nucleation and adhesion of ice and are therefore termed 'icephobic'. These coatings are comprised of sub-micron sized phase domains of a hydrophobic matrix and a multi-component melt-point depressant. The melt-point depresssant complex consists of a titanium alkoxide-based sol-gel system designed to facilitate the slow-release of tripropylene glycol (TPG) and glycerol to the coating surface. The presence of these compounds is necessary for effective prevention of the nucleation and adhesion of ice; however, their concentrations are depleted with time and exposure to water. Thus, the rate at which TPG and glycerol are released to the surface is critical to both the coating's performance and its lifetime.

The morphology of the coating was verified using SEM, EDS and AFM techniques. Mass loss kinetics were studied over the temperature range, 30 to 90°C ,for two coating formulations and indicated that the rate at which TPG and glycerol are released to the surface is limited by diffusion through the coating matrix. Additives can also be used to control the mass loss behavior in these coatings. Similar studies performed on the isolated melt-point depressant complex combined with chemical analyses from FT-IR, NMR and TGA techniques indicate mass loss in the melt-point depressant is controlled by diffusion of TPG through the sol-gel network. TPG is the only species released through sol-gel reactions; glycerol remains bound to the network. The chemistry of the sol-gel network was altered by changing the reaction conditions. This had only minimal effects on the mass loss kinetics, which were affected primarily by changes in the diffusion environment rather than by reaction kinetics.

The original design of this coating was based on the assumption that the kinetics of the sol-gel reaction would control the rate at which TPG was released to the coating surface. This study found that the release of TPG is controlled by diffusion rather than by chemical reaction kinetics. Nevertheless, this coating was still found to be effective for preventing the nucleation and adhesion of ice.