Solvent Content in Thin Spin-Coated Polystyrene Homopolymer Films

The solvent content of thin polystyrene (PS) films, spin-coated from protonated and deuterated toluene onto silicon substrates, is investigated. Neutron reflectometry (NR) is used to probe the total remaining solvent inside the PS films in a nondestructive and noninvasive way. In freshly prepared films, the investigated parameters are the molecular weight of PS and the total film thickness. Moreover, the effect of postproduction treatment by annealing at temperatures below and above the glass transition of PS as well as long-term storage over 2 years are examined to deduce the reduction of the remaining solvent. The remaining solvent content increases with increasing molecular weight and with increasing film thickness. An enrichment of toluene at the Si/polymer interface is found. Under the different annealing and storage conditions tested, the remaining solvent is not totally removed. The observed behavior is discussed in the framework of polymer thin films and compared with results obtained by alternative experimental approaches.