title: Adsorption kinetics of ultrathin polymer films in the melt probed by dielectric spectroscopy and second-harmonic generation.
abstract: 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.
authors.affiliation: Laboratory of Acoustic and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium. cinzia.rotella@fys.kuleuven.be
authors.forename: Cinzia
authors.initials: C
authors.lastname: Rotella
authors.forename: Simone
authors.initials: S
authors.lastname: Napolitano
authors.forename: Stefaan
authors.initials: S
authors.lastname: Vandendriessche
authors.forename: Ventsislav K
authors.initials: VK
authors.lastname: Valev
authors.forename: Thierry
authors.initials: T
authors.lastname: Verbiest
authors.forename: Maria
authors.initials: M
authors.lastname: Larkowska
authors.forename: Stanislaw
authors.initials: S
authors.lastname: Kucharski
authors.forename: Michael
authors.initials: M
authors.lastname: Wübbenhorst
mesh_terms: D000327:Adsorption; D058266:Dielectric Spectroscopy / Q000379:methods*; D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers