The effect of poly-l-lysine structure on the pH response of polygalacturonic acid-based multilayers

The effect of poly-l-lysine (PLL) molecular weight and structure on pH stability of polygalacturonic acid (PGaLA)-based multilayer films is studied over a pH cycle 7.0–1.6–7.0. The multilayer assembled with the lowest molecular weight PLL (1 kDa) showed the largest pH response. Only 12% of the mass remained and a preferential loss of PLL was observed. Extensive structural reorganisation of the layer as the pH was increased was due to the PGaLA reionisation leading to extensive net loss of hydrated mass. The multilayers assembled with the higher molecular weight linear PLLs (10 kDa, 200 kDa) showed loss of about 50% of their initial polymer mass. The multilayer assembled with the dendrimer (22 kDa) showed a stronger response to pH compared to the linear higher molecular weight PLLs. Over the pH cycle a loss of about 60% polymer mass and a decrease in the film thickness was observed. Despite having a reduced density at pH 1.6, the density substantially recovered to 0.54 g mL−1 on return to pH 7.0.