Formation of hydrated layers in PMMA thin films in aqueous solution

Abstract

Neutron reflectometry (NR) measurements have been made on thin (70–150Å) poly(methylmethacrylate) (PMMA) films on Si/SiOx substrates in aqueous conditions, and compared with parameters measured using ellipsometry and X-Ray reflectometry (XRR) on dry films. All techniques show that the thin films prepared using spin-coating techniques were uniform and had low roughness at both the silicon and subphase interfaces, and similar surface energetics to thicker PMMA films. In aqueous solution, NR measurements at 25°C showed that PMMA forms a partially hydrated layer at the SiOx interface 10Å under the film, while the bulk film remains intact and contains around 4% water. Both the PMMA film layer and the sublayer showed minimal swelling over a period of 24h. At 50°C, PMMA films in aqueous solution roughen and swell, without loss of PMMA material at the surface. After cooling back to 25°C, swelling and roughening increases further, with loss of material from the PMMA layer.