Salt-induced erosion of hydrogen-bonded layer-by-layer assembled films

Hydrogen-bonded layer-by-layer assembled films from poly(vinyl pyrrolidone) (PVPON) and poly(acrylic acid) (PAA) were fabricated. Fabry-Perot fringes were used as a simple but efficient method for studying the structure changes in the films during salt treatment. Results indicate that these films are very sensitive to salt when incubated in water. A brief treatment in salt solution of low concentration results in microphase separation in the films, the extent of which increases with increasing pH and salt concentration. The microphase separation in PVPON-PAA films is explained by the enhanced dissociation of PAA, which partially breaks the hydrogen bonds in the films. More importantly, the erosion of the PVPON-PAA films accelerates greatly in salt solution. Morphology changes during the erosion suggest a dewetting process of the films, which facilitates their dissolution. Finally, salt-triggered, rapid release of ibuprofen was achieved by the quick, salt-induced erosion of the hydrogen-bonded films.