ASSEMBLY, STRUCTURAL CHARACTERIZATION, AND THERMAL-BEHAVIOR OF LAYER-BY-LAYER DEPOSITED ULTRATHIN FILMS OF POLY(VINYL SULFATE) AND POLY(ALLYLAMINE)

We have recently introduced a new method of creating homogeneous ultrathin films on solid supports, which is based on the electrostatic attraction between opposite charges. Consecutively alternating adsorption of anionic and cationic polyelectrolytes from their aqueous solution leads to the formation of multilayer assemblies. The multilayer buildup is easily monitored by small angle X-ray scattering (SAXS) and a linear increase of the film thickness with the number of adsorbed layers is observed. In the present study we concentrate on the polyelectrolytes poly(vinyl sulfate) (PVS) and poly(allylamine) (PAH), discussing especially the influence of the adsorption conditions of PVS on the growth and the properties of the resulting films. A stable film growth was found to depend on two prerequisites for the PVS deposition: an adsorption time of at least 15 min and a maximum concentration of added sodium chloride of 0.2 mol/L. In the regime of stable growth the multilayer film is able to smooth the surface roughness of the underlying glass substrate from 18 A to a value of 4.5 A. The addition of small amounts of electrolyte to the PVS solution leads to an increase of the thickness of one layer pair from 13 A (at 0.0 mol of NaCl/L) to 34 angstrom (at 0.9 mol of NaCl/L). This behavior is similar to the well-known ''rod-to-coil'' transition of polyelectrolytes in solution and due to screening of electrostatic charges on the polymer chain. The films are stable up to temperatures of at least 160-degrees-C but seem to lose trapped water above 60-degrees-C.