Template polymerization to fabricate hydrogen-bonded poly(acrylic acid)/Poly(vinylpyrrolidone) hollow microcapsules with a pH-Mediated swelling-deswelling property

Hydrogen-bonded hollow microcapsules with a lightly cross-linked shell structure were fabricated by polymerization of acrylic acid in a Solution containing surface-modified silica particles and poly(vinylpyrrolidone) and a subsequent core removal with HF. By further incorporating additional cross-linkers, a highly cross-linked shell structure was produced, which endows the microcapsules with better stability against large pH fluctuations. The hollow and intact microcapsules in both wet and dry states were characterized and confirmed by TEM, SEM, AFM, and CLSM. The chemical compositions of the microcapsules and hydrogen bonding in the shells were determined by elemental analysis and FTIR spectroscopy, respectively. The continuous shells of the lightly cross-linked microcapsules on the silica particles are composed of PVP and PAA with an equal molar ratio of AA to VP. Alkaline treatment cannot separate PVP from PAA, which dernonstrates the strong interactions between PAA and PVP. The lightly cross-linked and highly cross-linked microcapsules could increase their sizes along with the pH increase, following a sigmoidal regime. The capsule swelling-shrinking process is completely reversible at high and low pH values, respectively.