Comparison of the swelling kinetics of a partially neutralized poly(acrylic acid) hydrogel in distilled water and physiological solution

Abstract

The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in distilled water and physiological solution at temperatures ranging from 20 to 40 ºC were determined. The possibility of applying both the Fick’s kinetics model and kinetics model of the first order chemical reaction to the swelling kinetics of the PAA hydrogel in distilled water and physiological solution were examined. It was found that the possibilities of applying these models were limited. The new model of the kinetics of swelling in distilled water and physiological solution was established. The kinetic parameters (Ea, ln A) for the swelling in distilled water and physiological solution were determined. The decrease of the equilibrium degree of swelling and the saturation swelling rate of the swelling of the PAA hydrogel in physiological solution compared to swelling in distilled water could be explained by the decreased differences in the ionic osmotic pressures between the hydrogel and the swelling medium. The increase of the initial swelling rate in the physiological solution might be caused by an increased density of charges at the network and by an increased affinity of the network towards the water molecules. The increase of the activation energy of the swelling of the PAA hydrogel in the physiological solution is a consequence of its additional "ionic crosslinking".

U radu su ispitivane izotermalne kinetičke krive bubrenja hidrogela delimično neutralisane poli(akrilne) kiseline u destilovanoj vodi i fiziološkom rastvoru u temperaturnom opsegu od 20 do 40 °C. Ispitivana je mogućnost primene Fikovog kinetičkog modela kao i kinetike i reda hemijskih reakcija na kinetiku bubrenja poliakrilnog hidrogela.Utvrđeno je da su mogućnosti za njihovu primenu vrlo ograničene. Iz tih razloga primenjen je novi model kinetike bubrenja. Određeni su kinetički parametri (Ea, lnA) za procese bubrenja u destilovanoj vodi i fiziološkom rastvoru. Smanjenje ravnotežnog stepena bubrenja i saturacione brzine bubrenja hidrogela delimično neutralisane poli(akrilne) kiseline u fiziološkom rastvoru u odnosu na destilovanu vodu može se objasniti smanjenjem razlike u jonskom osmotskom pritisku između hidrogela i medijuma za bubrenje. Povećanje inicijalne brzine bubrenja u fiziološkom rastvoru u odnosu na destilovanu vodu prouzrokovano je povećanjem gustine naelektrisanja na polimernoj mreži i povećanim afinitetom prema molekulima vode. Povećanje energije aktivacije hidrogela delimično neutralisane poli(akrilne) kiseline pri bubrenju u fiziološkom rastvoru se objašnjava dodatnim "jonskim umreženjem" hidrogela u fiziološkom rastvoru.