AbstractExperimental results were presented dealing with the water permeance and diffusion rate in two‐phase membranes consisting of hydrophilic domains of polyacrylic acid chemically bound by grafting to hydrophobic matrices: these are either rigid crystalline (polypropylene) or elastomeric amorphous (EPDM). Permeance is higher in rigid matrices: this is attributed to the wide net of microfractures originated from swelling of the hydrophilic domains whose formation is only possible in the case of a rigid matrix. A calculation method was proposed, which allows the evaluation of the apparent diffusion coefficient of both water and salt, starting from dilatometric measurements of membranes contacted with water and salt water. The apparent diffusion coefficient of water in rigid membranes is of the order of 10‐8cm2sec‐1, whereas in elastomeric membranes it appeared about 100 times lower. The apparent diffusion coefficient of salt is of the order of 10‐12cm2sec‐1for both rigid‐matrix and elastomeric membranes when previou
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