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This work focuses on the formation of multilayers by layer-by-layer deposition of weak polyelectrolytes, poly (allylamine hydrochloride) and poly (acrylic acid). These multilayers were built on smooth surfaces (silicon wafer) and rough surfaces (Millipore membrane, clay-coated paper). The effect of concentrations, pH of the depositing polyelectrolyte solutions and drying between the absorption steps were investigated in films deposited on Si wafers. These films were characterized using ellipsometry, contact angle and AFM. In the pH ranges investigated in the study (2.5-4.5), at concentrations of 10-2 M and 10-1 M, the layer-by-layer deposition proceeds in a linear manner, with pH influencing the thickness of the bilayers. Thickness of the films increased with increase in the solution pH. The films deposited at higher concentrations showed higher thickness and roughness. Drying in all cases, lead to thinner and rougher films. Contact angle studies showed that the wettability of the polyelectrolyte multilayers is likely dependent upon the interpenetration of the underlying layer and can change with the pH of the solution. Drying had a significant effect when films were deposited at lower concentration but no effect when films were deposited at higher concentrations. Polyelectrolytes were also deposited on Millipore membranes and clay- coated papers. USAXS data on coated Millipore membranes showed that coating densified the fibers and also reduced the pore and solid chords. Permeation studies in coated Millipore membranes showed that bilayers increase the selectivity for CO2. Permeation studies in coated clay-coated paper showed that bilayers reduce water vapor permeability. |
