Preparation and electrical sensitive behavior of poly (N-vinylpyrrolidone-co-acrylic acid) hydrogel with flexible chain nature

On the basis of the existing knowledge of reactions and properties of poly (N-vinylpyrrolidone) (PVP) and poly (acrylic acid) (PAA), a novel pH- and electrical-sensitive poly (N-vinylpyrrolidone-co-acrylic acid) [poly (NVP-co-AA)] hydrogel was formulated and prepared from linear poly (NVP-co-AA). Gelation reaction was initiated by potassium persulfate (KPS) used as a radical initiator, and the mechanism of crosslinking reaction was investigated by FTIR and solid-state CP/MAS NMR techniques. The morphology of hydrogel with flexible chain nature and large free volume was verified by measurement of scanning electron microscope. The swelling behavior and bending phenomenon of the hydrogel were investigated. In the electric field, the gel bent toward cathode independently of the pH of buffer solution, applied voltage, crosslinking extent and polyion content in the backbone of gel. But the deflection and speed of the bending depended on them. Bending of poly (NVP-co-AA) gel was reinterpreted by bending theory of polyelectrolyte gel based upon the change of osmotic pressure, which is due to the difference of ion concentration between the sides facing anode and cathode.