Interaction of aerosil nanoparticles with networks of polyacrylamide, poly(acrylic acid), and poly(methacrylic acid) hydrogels

For hydrogels based on rarely crosslinked matrices of polyacrylamide, poly(acrylic acid), and poly(methacrylic acid) filled with aerosil, the equilibrium degrees of swelling are measured as functions of the filler contents. The differences in the behaviors of gels are analyzed in terms of the competitive intermolecular interaction in three-component systems. For this purpose, the enthalpies of swelling for preliminarily dried and partially hydrated gels are measured via isothermal microcalorimetry. On the basis of concentration dependences of the enthalpy of swelling, the values of the enthalpy Flory-Huggins parameter for polymer matrices filled and unfilled with water, the parameters of structural changes in the polymers in filled hydrogels, and the enthalpies of adhesion and adsorption interactions of polymer matrixes with the surface area of aerosil are estimated. It is shown that there is a linear correlation between the change in the Flory-Huggins parameter and the enthalpy of adsorption of subchains on the surface of aerosil particles that assumes negative values in the case of poly(acrylic acid) and positive values in the case of poly(methacrylic acid) and polyacrylamide.