A possible mechanism for the substrate effect on hydrogel formation

A possible mechanism for the formation of the substrate-induced interface d uring the gelation, which leads to heterogeneous polymerization, is propose d. According to this mechanism, a surface polymer deplete layer would be fo rmed during the polymerization due to the high interfacial energy between t he hydrophobic substrate and the aqueous polymerizing solution. When the po lymer concentration attains the critical value at which an extensive entang lement occurs, and/or a chemical network forms, the thickness of the deplet e layer increases dramatically to a macroscopic level to give an interface, due to the weak elasticity of the network. Theoretical model describing re lations between the substrate surface tension, the increment in the surf ac e tension of the solution upon polymerization, and the predicted position o f the interface show a resonable agreement with the experimental data.