Effect of curing strategies on porosity in silane-modified silica colloidal coatings

Suspensions of silica (20 nm) in propoxyethanol were used to make porous silica coatings. A silane coupling agent, glycidoxypropyltrimethoxysilane (GPS), was added as a binder to increase coating durability and prevent cracking. GPS addition prevented crack formation but only when added in large amounts (GPS to silica weight ratio 0.5 to 1) such that porosity was filled by a GPS-based siloxane polymer. Attempts to enhance the fracture toughness of porous coatings through UV curing and glycol additions failed to lead to improvements in the critical cracking thickness (CCT). However, addition of triethylenetetramine resulted in a 3-fold increase in the CCT. Wear resistance increased for both the UV-cured and amine-cured coatings.