Layer-by-layer assembly of poly (N-acryloyl-N'-propylpiperazine) and poly (acrylic acid): Effect of pH and temperature

Layer-by-layer assembly technique was applied to fabricate multilayer films of poly(N-acryloyl-N'-propylpiperazine) (PAcrNPP) and poly(acrylic acid). The film buildup was followed by Quartz Crystal Microbalance, and the effect of temperature and pH on the layer-by-layer assembly was investigated. Below the lower critical solution temperature of PAcrNPP, the adsorption amount increased with increase of temperature. As the pH of dipping solutions was systematically varied from 2.0 to 7.5, adsorption amount of polymers initially increased and then decreased. The relationship between adsorption amount and degree of ionization of polymers was discussed. When an eight-bilayer film was alternately exposed to HCl aqueous solution (pH = 3.5) and neutral water (pH = 6.5), the film showed pH-response, which could be the result of polymer rearrangement.