Comprehensive thermodynamic analysis of mixing of poly(diallyldimethylammonium chloride) (PDADMAC) with water at 25°C has been performed. Isotherms of water sorption with linear and network poly(diallyldimethylammonium chloride) have been measured by means of interval sorption. Enthalpy of dilution of solutions of linear poly(diallyldimethylammonium chloride) and enthalpy of swelling of network poly(diallyldimethylammonium chloride) have been measured over the entire composition range by means of isothermal calorimetry. Concentration dependences of the Gibbs energy of mixing and enthalpy of mixing of poly(diallyldimethylammonium chloride) with water have been computed. It has been shown that these thermodynamic functions are negative over the entire range of composition of the solution and swollen hydrogel. The experimental data have been used in thermodynamic modeling of the interaction process, accounting for different contribution to the thermodynamic functions of mixing of poly(diallyldimethylammonium chloride) with water. It has been shown that the thermodynamic of mixing is predominantly affected, on one hand, by the molecular interaction described in the scope of the Flory–Huggins theory and, on the other hand, by the nonequilibrium disruption of glass structure of the polymer during formation of the solution and swelling of the gel. The modeling has given the values of the Flory–Huggins parameter: –0.05 ± 0.02 for aqueous solution of linear poly(diallyldimethylammonium chloride) and 0.20 ± 0.01 for hydrogel of network poly(diallyldimethylammonium chloride). Basing on the model parameters, individual contributions into the enthalpy, Gibbs energy, and entropy of mixing of poly(diallyldimethylammonium chloride) with water have been calculated.

Методами изотермической сорбции и микрокалориметрии исследована термодинамика взаимодействия полиперфторсульфоновой кислоты Nafion с водой. Определены концентрационные зависимости энергетических и энтропийных параметров смешения водных растворов Nafion и показано, что энергия Гиббса и энтальпия смешения отрицательны, а энтропия смешения положительна во всем диапазоне составов раствора. Экспериментальные изотермы сорбции воды и концентрационные зависимости энтальпии разбавления водных растворов проанализированы с использованием термодинамической модели, учитывающей парные невалентные взаимодействия в растворе, неравновесную стеклообразную структуру полимера и эффекты диссоциации ионогенных сульфогрупп Nafion. Расчетное значение параметра Флори–Хаггинса составило 1.48, а значение его энтальпийной компоненты близко к нулю.

The thermodynamics of interaction between poly(perfluorosulfonic acid) Nafion and water is studied by isothermal sorption and microcalorimetry. The concentration dependences of energy and entropy parameters of mixing of Nafion aqueous solutions are determined. It is shown that the Gibbs energy and the enthalpy of mixing are negative while the entropy of mixing is positive over the entire range of solution compositions. The experimental water sorption isotherms and the concentration dependences of the enthalpy of dilution of aqueous solutions are analyzed in terms of the thermodynamic model allowing for pair nonvalence interactions in solution, nonequilibrium glassy structure of the polymer, and effects of the dissociation of ionic sulfo groups of Nafion. The calculated value of the Flory–Huggins parameter is 1.48, and the value of its enthalpy component is close to zero.

The enthalpies of interactions of various organic compounds with nanocluster molybdenum-containing polyoxometalates have been studied experimentally. Substances with dielectric permittivity varying within a wide range were chosen. The dependence of enthalpy was found to be sign-variable, with a transition from endothermal to exothermal effects in the range of permittivity 15–17. Similar tendencies with an extremum or inflection at permittivity of 15–17 were found for a number of reference physicochemical parameters (boiling and melting points, enthalpies of these processes, enthalpy of formation, viscosity, heat capacity) of a wide range of organic and some inorganic compounds. The general nature of these tendencies may be a basis for further development of modern concepts about the mechanisms of intermolecular interaction.

The enthalpy, Gibbs free energy, and entropy of mixing of polyacrylamide with agarose have been determined using thermodynamic cycles based on microcalorimetry and isothermal equilibrium sorption data. The enthalpies of solution in water have been measured, and water sorption isotherms have been obtained for films of polyacrylamide, agarose, and their mixtures in different ratios. The sorption data have been processed used a sorption model that takes into account the effect of polysaccharide chain stiffness on the change in the chemical potential of water upon the formation of a solution during sorption. The model relationships are shown to be in good agreement with the experimental isotherms over the entire range of variation of the polymer volume fraction and the relative vapor pressure. It has been found that the enthalpy of mixing of polyacrylamide and agarose is negative over the entire range of compositions. Mixtures containing less than 50 wt % agarose are thermodynamically incompatible and are characterized by a positive Gibbs energy of mixing, whereas Gibbs energies are negative for mixtures containing more than 50% agarose. The calculated values of the entropy of mixing are negative in the entire range of agarose to polyacrylamide ratios, thereby indicating ordering in this polymer mixture. The results of studying the thermodynamic compatibility of polyacrylamide and agarose are compared with the swelling behavior and mechanical properties of hydrogels based on semi-interpenetrating networks of these polymers.

Synthesis and study of the physicochemical properties of silsesquioxanes modified with 3-aminopropyl, 2-aminoethyl-3-aminopropyl, and dithiooxamide groups was carried out. The obtained sorbents were characterized by thermal stability, porosity, and a high degree of functionalization; the concentration of groups grafted to the particle surface reached 2.80 mmol g−1. Modified silsesquioxanes were used as an electroactive substance for the development of indicator carbon paste electrodes (CPEs). When using a CPE with a 5% dithiooxamidated silsesquioxane content, the conditions selected for potentiometric titration of aqueous solutions containing silveri were pH 3–4, the titrant was potassium iodide. The designed sensor was successfully tested by analyzing a standard sample and a drug for silver ion content.

Equilibrium isothermal sorption and microcalorimetry are used to study the effect the ratio of units of different nature in the macromolecular network of hydrogels of copolymers of acrylic (AA) and methacrylic (MAA) acids have on the thermodynamic parameters of interaction with water. Isotherms of the sorption of water vapor on dried hydrogels and the concentration dependences of the enthalpy of swelling of partially swollen hydrogels in excess of water are measured experimentally. The values of effective Flory–Huggins integral parameter χ is determined, along with its components χH of enthalpy and χS of entropy. The values of the Flory–Huggins parameter grow naturally upon an increase in the content of MAA units in the copolymers, which indicates weaker interaction with water and is consistent with a reduction in their degree of swelling. In contrast, the values of χH fall as the content of MAA units in the copolymers grows. This suggests that water interacts more energetically with the PMAA network than with PAA, despite the more hydrophilic nature of the latter. The values of χS are positive for all systems, which corresponds to the negative noncombinatorial entropy of gel swelling. Results are discussed in terms of the balance of hydrophilic and hydrophobic hydration in AA and MAA gels.

New data are obtained on the thermodynamics and molecular mechanisms of the interaction between dioxane and nanocluster polyoxomolybdates of the keplerate and toroidal types, with their composites containing water-soluble nonionic polymers—polyvinyl alcohol and polyvinylpyrrolidone, and between the components of such composites. The studies are performed using a gravimetric variant of equilibrium interval sorption with thermodynamic cycle calculations, and by IR spectroscopy. The effect the nature of the sorbates and the sorbents has on the parameters of sorption is analyzed using the constructed sorption isotherms and the concentration dependences of the Gibbs energy, particularly by comparing dioxane to other low-molecular compounds that differ appreciably in polarity and their ability to form hydrogen bonds: methanol, benzene, acetone, and ethyl acetate.

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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.

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The structure and thermodynamic functions of water mixing with polyacrylamide and poly(methacrylic acid) xerogels prepared via drying of chemically crosslinked hydrogels equilibrium swollen in water are studied by methods of scanning electron microscopy, low-temperature nitrogen adsorption, differential scanning calorimetry, isothermal interval sorption of water vapor, and microcalorimetry. The liquid-phase drying in air at 70°C and solid-phase lyophilic drying under vacuum are used. Samples dried by different methods have dissimilar structures, which significantly affects the thermodynamics of the interaction of xerogels with water. The Flory–Huggins parameter of interaction of polyacrylamide and poly(methacrylic acid) with water and also its enthalpy and entropy components are independent of the procedure of xerogel preparation. The influence of the latter component manifests itself only in the thermodynamics of the relaxation of the nonequilibrium glassy structure of polymer.

The effect silver nanoparticles have on the sorption characteristics of perovskite lanthanum manganite relative to methanol, benzene, and hexane vapors is studied by means of gravimetric equilibrium interval sorption. The state of silver particles is investigated using spectroscopic tools. Sorption data are compared to the catalytic activity in deep oxidation reactions of organic compounds over lanthanum manganite-based catalysts.