Water Content of Hydrated Polymer Brushes Measured by an In Situ Combination of a Quartz Crystal Microbalance with Dissipation Monitoring and Spectroscopic Ellipsometry

摘要

Poly(methacryloyloxy ethyltrimethylammonium chloride) (PMETAC), poly(sulfopropylmethacrylate potassium salt), or poly(N-isopropyl acrylamide) (PNIPAM) brushes are synthesized by means of the atom transfer radical polymerization technique from gold surfaces coated with a monolayer of the initiator ω-mercaptoundecyl bromo isobutyrate. The brush growth is followed in situ and in real time by the combination of quartz crystal microbalance with dissipation technique (QCM-D) and spectroscopic ellipsometry in a single device. The combination of QCM-D and ellipsometry allows for the simultaneous determination of both the acoustic mass, m_acous, comprising the mass of the polymer and the solvent, and the optical mass, m_opt, which corresponds to the polymer mass alone. Brush hydration is calculated from the difference between the values obtained for m_acous and m_opt for each polymer synthesized. Brush hydration is then used to quantify the percentage of water released in the brush during collapse; a 30–40% release of water for PMETAC and PSPM brushes in 1 M NaCl and 80% for PNIPAM brushes when the temperature is increased to values above the lower critical solution temperature is observed.