Suppress polystyrene thin film dewetting by modifying substrate surface with aminopropyltriethoxysilane

Aminofunctional organosilanes, such as 3-aminopropyltriethoxysilane (APTES), have been widely utilized as adhesion promoters, and have also been found to have the ability to prevent dewetting of polymer thin films from substrates. The APTES molecule contains an active terminal amino group that can hydrogen bond with the multiple hydroxylated head groups in itself and hydroxyl groups on a substrate, thus forming cyclic structures and a complex loose network at ambient conditions. Upon heating, the hydrogen bond can be broken, allowing more silanol groups to condense with each other and form siloxane linkages, hence tightening the three-dimensional network. When a polymer thin film is in contact with the APTES layer during the thermal process, the polymer chains can diffuse/penetrate into the APTES network while the network is being tightened by the additional crosslinking. The penetrated and subsequently anchored chains could help to stabilize the thin film on the substrate. This hypothesis was verified by dewetting studies of thin films of polystyrene (PS), having molecular weights above and below the entanglement molecular weight (Me), from APTES and control surfaces when the systems were subjected to various treatments. Dewetting suppression was observed for PS/APTES that was thermally treated at ∼80 °C or 120 °C prior to the annealing of the thin film at higher temperatures. Much stronger suppression was noticed for PS having a molecular weight higher than Me. When PS thin films were deposited onto a precured APTES network, no dewetting suppression was observed.