Solvent Retention in Thin Spin-Coated Polystyrene and Poly(methyl methacrylate) Homopolymer Films Studied By Neutron Reflectometry

We utilize neutron reflectometry (NR) to probe the amount of residual solvent in thin polystyrene (PS) and poly(methyl methacrylate) (PMMA) films spin-coated from deuterated toluene solutions onto silicon substrates. The effect of thermal treatment at temperatures below and above the glass transition of PS and PMMA are examined to determine how these treatments affect the residual solvent. The parameters investigated include the total film thickness and molecular mass for PS and only thickness for PMMA. We find that the volume fraction of solvent in PMMA films is less than a few percentages, while no residual solvent was detected in PS films. The residual solvent content of the PMMA films had a slight dependence on thickness. These results are corroborated utilizing Fourier Transform infrared (FTIR) spectroscopy. We discuss these observations in the context of a large body of seemingly conflicting literature on residual solvent in polymer thin films.