CONTROLLING BILAYER COMPOSITION AND SURFACE WETTABILITY OF SEQUENTIALLY ADSORBED MULTILAYERS OF WEAK POLYELECTROLYTES

Variations in the linear charge density of a weak polyacid brought abo ut by controlling solution pH in a layer-by-layer sequential adsorptio n process were used to systematically control the layer thickness, lev el of layer interpenetration, and surface wettability of sequentially adsorbed layers of poly(acrylic acid) (PAA) and poly(allylamine) (PAH) . The thickness contributed by an individual polyion layer was found t o depend primarily on the pH of the polymer's dipping solution and, wi thin the pH range examined, was not influenced by the thickness or lev el of interpenetration of the previously adsorbed layer. Contact angle and methylene blue adsorption measurements revealed that the deposite d layers are typically highly interpenetrated and that the deposition process is a surface charge dominated adsorption process. Using this s imple molecular-level blending approach, it is possible to create surf aces with advancing water contact angles that vary from essentially ze ro (completely wettable surfaces) to as high as 50 degrees, all using the same simple polycation/polyanion combination.