Temperature dependence of self-diffusion of THO in copolymer hydrogels

Abstract

The self-diffusion experiment of THO was performed across a series of copolymer hydrogels at different temperatures. Copolymer hydrogels were prepared by copolymerizing 2-hydroxyethyl methacrylate(HEMA) and 2-aminoethyl methacrylate(AEMA) in the presence of the solvent and the crosslinker ethylene glycol dimethacrylate (EGDMA). By changing the crosslinker content and the ratio of HEMA and AEMA monomer, two series of copolymer hydrogel were synthesized. The tagging material was THO and efflux of THO was counted on a Liquid Scintillation Counter. The experimental data show that the permeability decreases as the amount of EGDMA and the mole fraction of HEMA increase, and the permeability is proportional to the temperature. The partition coefficient shows a parallel trend except in the temperature. The partition coefficient is inversely proportional to the temperature. So the self-diffusion coefficient show a parallel trend with the permeability. Using the relationship between viscosity and diffusivity derived from Eyring``s absolute rate theory, the corresponding viscosity of water within the membrane was obtained. The results derived from the relationship between temperature and viscosity show that the viscosity of water within the membrane may have the same value with those of supercooling water whose temperature ranges from $25.0\,^\circ\!C$ to $-32.42\,^\circ\!C$. From the diffusivities, Arrhenius plots were performed and show the activation energy for self-diffusion of water through the membrane. The results show that the activation energy ranges from 6.93 Kcal/mole to 10.58 Kcal/mole.