Correlation between temperature-dependent dissolution of poly(N-vinylcaprolactam)/poly(N-l-(1-hydroxymethyl)propylmethacrylamide) layer-by-layer films and cloud point of mixed solutions of the two polymers in the presence of chloride salts

We studied the effect of chloride salts on the dissolution behavior of layer-by-layer (LbL) films of two thermosensitive polymers. Poly(N-vinylcaprolactam) (PVCL) and poly(N-l-(1-hydroxymethyl)propylmethacrylamide) (P(l-HMPMAm)) were used to assemble a LbL film in water at 33 °C. We found that the dissolution temperature (Td) of the LbL film in a solution of 0.5 M chloride salts was lower than that in water. Furthermore, the effect of chloride salts on the Td of films was positively correlated with the effect of chloride salts on the cloud points of the mixed solutions. These experimental results indicate that the stability of the LbL films of two thermosensitive homopolymers can be increased in chloride salt solutions. Other researchers have found that some polyelectrolyte LbL films are stable in water but dissolve in a solution containing high concentrations of salts. The effect of salts on polyelectrolyte LbL films and the effect of salts on LbL films of the thermosensitive polymers are opposite. The opposite effects could be attributed to the different characteristics – some films are ionic and the others are non-ionic. These dissolvable films of non-ionic polymers could have potential for biological applications.