Permeation and diffusion of nutrient ions in poly (vinyl alcohol) hydrogel membrane

Abstract

Poly (vinyl alcohol) (PVA) hydrogel membrane has transport properties because of their cross-linked network structure, which had been used in soilless cultivation of plants. This work revealed the permeability and diffusion ability of nutrient ions in the PVA hydrogel membrane, such as K+, Na+, Ca2+, and Mg2+, which were based on the solution–diffusion model and free volume theory. The microstructure of the membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy. From experimental results, the process of ion diffusion was a steady-state diffusion. With the increase in temperature and concentration, ion permeability was enhanced. However, compared with divalent ions, permeability increase for monovalent ions is more pronounced due to its smaller hydrated radius. At the concentration of 0.01 mol/L, the permeability coefficient of K+ was 3.5 × 10−7 cm2/s at 30 °C, which was nearly three times of Mg2+. The nutrient ion permeability coefficient was more strongly dependent on the temperature than the ion concentration. For the permeability of K+, the temperature increases from 20 to 50 °C, the permeability coefficient changes from 1.54 to 8.64 × 10−7 cm2/s, and when the concentration increases from 0.01 to 0.08 mol/L, the permeability coefficient changes from 4.53 to 6.8 × 10−7 cm2/s.