An electrowetting optical device includes a conductive liquid, a non-conductive liquid, and a substrate. The conductive liquid is buffered to an acidic pH. The conductive liquid and the non-conductive liquid are immiscible. The substrate includes a dielectric topcoat. The conductive liquid and the non-conductive liquid are in contact with the dielectric topcoat. The dielectric topcoat is a plasma-deposited organosilane precursor having the molecular formula SiOxCyHz.