Flory–Huggins Parameters of Guar Gum, Xanthan Gum, Agarose, and Gellan Gum in Aqueous Solutions

The thermodynamics of the interaction of guar gum, xanthan gum, agarose, and gellan gum with water has been investigated. The isotherms of water sorption by the polysaccharides have been obtained using the isothermal interval sorption at 25°C, which have an S-shape typical of glassy polymers. Values of Gibbs energy of mixing polysaccharides with water determined from the isotherms obtained are negative. The calculated Flory–Huggins parameters for polysaccharide solutions are almost the same and equal on average to 0.82. The concentration dependences of the enthalpy of dilution of aqueous solutions of polysaccharides are measured by isothermal microcalorimetry. The values of the enthalpy Flory–Huggins parameter found from them are close to zero for all polysaccharides. At the same time, the integral enthalpy of dissolution shows large negative values, which are entirely due to the relaxation of the glassy state of the polymers upon dissolution. The calculated entropy Flory–Huggins parameter exhibits large positive values. This indicates the ordering of polysaccharides in solutions, which is manifested by a strong aggregation of macromolecules.