De-swelling kinetics of copolymer hydrogels in metallic ion solution

De-swelling kinetics of swollen copolymer hydrogels(AA/AMPS,AA/DMAEMA and AMPS/ DMAEMA) in metallic ion(Ag~+,Cu~(2+),Fe~(3+) and Pb~(2+)) solutions was investigated with gravimetry.The copolymer hydrogels showed responsive volumetric shrinking behavior in Ag~+,Cu~(2+),Fe~(3+) and Pb~(2+) metallic ion solutions,and the extent of de-swelling increased with increasing metallic ion concentration.By using a decaying exponential first-order function,the volume shrinking process of the hydrogels could be well fitted with the correlation coefficient above 0.98.At a fixed concentration of metallic ion,the equilibrium volume shrink ratios(V_∞/V_0) of AA/AMPS,AA/DMAEMA and AMPS/DMAEMA hydrogels were in the order Fe~(3+)Pb~(2+)Cu~(2+)Ag~+,Cu~(2+)Fe~(3+)Pb~(2+)Ag~+,and Pb~(2+)Fe~(3+)Cu~(2+)Ag~+,respectively,and so did the de-swelling rate constant.In addition,a mechanism,"lone pairs of electrons-unoccupied orbitals"was proposed for the gel volume shrinking process,in which the energy of activation values of AA/AMPS-Fe~(3+),AA/DMAEMA-Cu~(2+),and AMPS/DMAEMA-Pb~(2+) system were 3.081,1.86,and 1.917 kJ·mol~(-1),respectively.