Adsorption Kinetics of Ultrathin Polymer Films in the Melt Probed by Dielectric Spectroscopy and Second-Harmonic Generation

作者：Cinzia Rotella, Simone Napolitano, Stefaan Vandendriessche, Ventsislav Kolev Valev, Thierry Verbiest, Maria Larkowska, Stanisław A. Kucharski, Michael Wübbenhorst · 发表于：Langmuir · 年份：2011 · DOI：10.1021/la2027779 · 被引用次数：85 · 研究领域：Spectroscopy and Quantum Chemical Studies、Analytical Chemistry and Sensors、Advanced Fluorescence Microscopy Techniques

We studied the adsorption kinetics of supported ultrathin films of dye-labeled polystyrene (l-PS) by combining dielectric spectroscopy (DS) and the interface-specific nonlinear optical second harmonic generation (SHG) technique. While DS is sensitive to the fraction of mobile dye moieties (chromophores), the SHG signal probes their anisotropic orientation. Time-resolved measurements were performed above the glass transition temperature on two different sample geometries. In one configuration, the l-PS layer is placed in contact with the aluminum surface, while in the other one, the deposition is done on a strongly adsorbed layer of neat PS. From the time dependence of the dielectric strength and SHG signal of the l-PS layer in contact with the metal, we detected two different kinetics regimes. We interpret these regimes in terms of the interplay between adsorption and orientation of the adsorbing labeling moieties. At early times, dye moieties get adsorbed adopting an orientation parallel to the surface. When adsorption proceeds to completeness, the kinetics slows down and the dye moieties progressively orient normal to the surface. Conversely, when the layer of l-PS layer is deposited on the strongly adsorbed layer of neat PS, both the dielectric strength and the SHG signal do not show any variation with time. This means that no adsorption takes place.