Ultra-fine polyelectrolyte hydrogel fibres from poly(acrylic acid)/poly(vinyl alcohol)

Ultra-fine fibrous membranes were prepared by electrospinning of aqueous mixtures of poly(acrylic acid) and poly(vinyl alcohol) at 17%-83% PAA or 0.14-3.5 COOH/OH molar ratios and cross-linked by heat-induced (140 degrees C, 5 min) esterification. The fibre diameters increased from 270 to 450 nm with increasing PAA contents. The swelling ratio of the fibrous hydrogels increased up to 31 times their dry weight with increasing pH from 2 to 7, and most significantly between pH 4 and pH 5. The liquid uptake of the fibrous hydrogels was attributed to both the liquid diffused into the fibres and that held in the inter-fibre pores. About 53%, 35%, 43% and 37% of the swelling was contributed by the liquid in the inter-fibre pores when the fibrous hydrogels were swollen at pH 2, 4, 5 and 7, respectively. The fully swollen fibrous membranes could be triggered by an applied electric field to swell further. Such additional swelling was dependent upon the polymer compositions, strength of electric field and pH, and was reversible.