Surface pattern in thin poly(styrene–maleic anhydride) films

Abstract

Monodispersed poly(styrene–maleic anhydride) alternating copolymer (SMA) is synthesized through radical polymerization, and characterized by GPC, DSC, FT-IR and 1H NMR spectra. The mole fraction, χ, of styrene in the copolymer is 0.51, determined from integrated 1H NMR spectrum, this value is consistent with the alternating structure. FT-IR spectra show that maleic anhydride moieties on the backbone chains hydrolyze in a THF solution containing water, and HCl can accelerate the hydrolysis process. Atomic force microscopy reveals that well-arrayed and uniform-sized holes formed in thin SMA films on single crystal silicon wafer substrates spin-cast from the THF solutions containing HCl. HCl can also influence hydrogen bonding between the carboxylic acid groups in the THF solution, which is crucial for the formation of holes in the thin films. The volatilization process in the spin-casting is divided into two stages, THF and water volatilization. The formation of holes is interpreted as the trace of water droplets emulsified by the hydrolyzed SMA in the second stage, i.e. water volatilization. Results also indicate that there are both mobile and bound water populations in the solution, and that the bound water is responsible for the hole or valley pattern of these thin films.