The nature of thermodynamic compatibility of components of aqueous solutions of starch and cellulose carboxymethyl derivatives

The Gibbs free energy, enthalpy, and entropy of mixing of starch and carboxymethyl derivatives of starch and cellulose with water were determined by sorption and calorimetry methods at 25°C throughout the entire range of compositions. The contributions due to the equilibrium intermolecular interactions and relaxation of a metastable glassy structure were separated. The relaxation of the metastable structure taking place during physical adsorption of the first portions of water on polymers makes a negative contribution to all thermodynamic functions of mixing. The contribution of equilibrium interactions, which includes pair nonviolent interactions of units and water molecules and electrostatic interactions of ions, is positive for the enthalpy and entropy of mixing. In this case, the positive entropy values exceed those of enthalpy, which is responsible for the thermodynamic compatibility. Thermodynamic analysis of the processes of dissolution of starch, carboxymethyl starch and carboxymethyl cellulose sodium salts showed that, contrary to the popular point of view, the compatibility of polysaccharides and their derivatives with water is based not on the enthalpy, but entropy nature and is strengthened additionally owing to relaxation of the metastable glassy structure of polymers.     

Biodegradable systems: Thermodynamics, rheological properties, and biocorrosion

Systems based on starch and chitosan blends with synthetic polymers and cellulose derivatives (poly(ethylene oxide) and methyl cellulose of various molecular masses, PA, and ethylene-vinyl acetate copolymers containing different amounts of vinyl acetate groups) have been studied. The thermodynamic characteristics of the formation of blends have been determined. The rheological properties characterizing formation of blends from melts have been investigated. The biocorrosion ability of the blends after their use has been estimated by various methods. The concentration dependences of the thermodynamic functions of mixing of components (change in the Gibbs energy, enthalpy, and entropy) change sign in a wide composition range, indicating the complexity of mixing of rigid-chain natural polysaccharides with synthetic polymers. The rheological study of blends in which starch or chitosan plays the role of a biodegradation modifier shows that they are non-Newtonian fluids. The absolute values of viscosity and the activation parameters of melts increase with the content of polysaccharide in the system. The values of viscosity correspond to those typical for commercially processable polymers. The blends under study are biodegradable in a wet and water-soil medium with the content of the natural component being in the range 15–30 wt %.     

Solution and Mixing Thermodynamics of Propranolol and Atenolol in Aqueous Media

Based on the van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs energy, enthalpy, and entropy of dissolution, and of mixing of propranolol (PPN) and atenolol (ATN) in water at pH=11.5, were evaluated from solubility values determined at several temperatures. The equilibrium solubility values obtained for ATN were almost three hundred-fold higher than those for PPN. The enthalpies of dissolution were positive for both drugs, whereas the entropies of dissolution were both negative indicating a greater molecular organization after the drugs’ dissolution processes. Otherwise, the entropies of mixing were also negative in both cases indicating mixing-entropy is driving on drugs dissolution processes. The results were discussed in terms of solute-solvent interactions, especially hydrophobic hydration.     

Solubility of naproxen in several organic solvents at different temperatures

By using the van’t Hoff and Gibbs equations the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, were evaluated from solubility data of naproxen (NAP) determined at several temperatures in octanol, isopropyl myristate, chloroform, and cyclohexane, as pure solvents. The water-saturated organic solvents also were studied except cyclohexane. The excess free energy and the activity coefficients of the solutes, and the mixing and solvation thermodynamic quantities were also determined. The NAP solubilities were higher in chloroform and octanol with respect to those obtained in cyclohexane. In addition, by using literature values for NAP aqueous solubility, the thermodynamic functions relative to transfer of this drug from water to organic solvents were also estimated.     

Thermodynamic features of mixing of chitosan with polyvinyl alcohol and polyethylene oxide

Chitosan-polyvinyl alcohol and chitosan-polyethylene oxide systems were examined by water vapor sorption method. Based on the experimental data, the Gibbs energy, entropy, and enthalpy of the polymer mixing were calculated.     

Ag3PO4溶解热力学函数的晶面效应与温度效应

在室温下制备了立方体{100}、 四面体{111}、 菱形十二面体{110}和块体Ag₃PO₄微晶, 并进行了表征. 测定了其在不同温度下水溶液中的电导率, 结合强电解质溶液和溶解热力学理论, 得到了Ag₃PO₄微晶的溶解热力学函数. 以具有不同晶面的Ag₃PO₄微晶为模型, 研究了纳米材料溶解热力学函数的晶面效应和温度效应. 结果表明, 具有{110}晶面的菱形十二面体Ag₃PO₄的标准摩尔溶解吉布斯自由能()、 标准摩尔溶解焓()和标准摩尔溶解熵()最大, 具有{100}晶面的立方体Ag₃PO₄次之, 具有{111}晶面的四面体Ag₃PO₄最小; 溶解平衡常数(K_{\mathrm{SP}})和随着温度的升高而增大.     

Solution Thermodynamics of Piroxicam in some Ethanol + Water Mixtures and Correlation with the Jouyban–Acree Model

The solubility of piroxicam (PIR) in several ethanol + water mixtures was determined at five temperatures from 293.15 to 313.15 K. The thermodynamic functions; Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these solubility data and the drug properties of fusion by using the van’t Hoff and Gibbs equations. The greatest solubility value was obtained in pure ethanol. A non-linear enthalpy–entropy relationship was observed from a plot of enthalpy versus Gibbs energy of solution. Accordingly, the driving mechanism for PIR solubility in water-rich mixtures is the entropy, probably due to water-structure loss around the drug’s non-polar moieties by ethanol, whereas, in ethanol-rich mixtures the driving mechanism is the enthalpy, probably due to better PIR solvation by the co-solvent molecules. The solubilities and the derived thermodynamic properties in mixed solvents were correlated using the Jouyban–Acree model.     

Solution thermodynamics of nimodipine in some PEG 400 + ethanol mixtures

The solubility of nimodipine (NMD) in several PEG 400 + ethanol mixtures was determined at five temperatures from 293.15 to 313.15 K. The thermodynamic functions of Gibbs energy, enthalpy and entropy of solution and of mixing were obtained by using the van't Hoff and Gibbs equations from these solubility data and drug properties of fusion. The highest solubility value was obtained in PEG 400 and the lowest in ethanol at all temperatures. A non-linear enthalpy–entropy relationship was observed from a plotof enthalpy vs. Gibbs energy of solution. Accordingly, the driving mechanism for NMD solubility in ethanol-rich mixtures is the enthalpy, whereas in PEG 400-rich mixtures thedriving mechanism is the entropy, although the molecular events involved are unclear.     

Effects of Aspartic Acid and Lysine on Thermodynamic Functions of SDS Micellization

Aspartic acid and lysine can promote SDS micellization. The critical micellar concentration of SDS decreases with amino acid concentration, but first does and then increases with temperature. In SDS micellization, the change of standard Gibbs free energy is negative in SDS/H₂O system with or without amino acid. With the increase of amino acid concentration, the changes of mole standard Gibbs free energy and enthalpy decrease, but the change of the system's entropy increases. The effect of lysine is more than that of aspartic acid on the thermodynamic functions.     

The demicellization of alkyltrimethylammonium bromides in 0.1 M sodium chloride solution studied by isothermal titration calorimetry

The demicellization of the cationic detergents dodecyltrimethylammonium bromide, tetradecyltrimetylammonium bromide, and cetyltrimethylammonium bromide was studied at temperatures between 20 and 60 degrees C in 0.1 M NaCl (pH 6.4) using isothermal titration calorimetry (ITC). We determined the critical micellization concentration (cmc) of the cationic detergents which show a minimum at temperatures between 20 and 34 degrees C. In accordance with the lengthening of the hydrophobic tail of the detergents the cmc decreases with increasing alkyl chain length. The thermodynamic parameters describing the changes of enthalpy (DeltaH(demic)), the changes of entropy (DeltaS(demic)) and the Gibbs free energy change (DeltaG(demic)) for demicellization were first obtained using the pseudophase-separation model. The aggregation number n at the cmc as well as the demicellization enthalpy, entropy and Gibbs free energy change were also calculated using a simulation based on the mass-action model. Furthermore, we investigated the demicellization of CTAB in deionized water in comparison to demicellization in sodium chloride solution to determine the influence of counter ion binding on the demicellization.     

Thermodynamics of mixing of polymers

A method of calculating free energy of mixing of two polymers has been proposed. From a study of the sorption of organic solvents vapour by different polymers and their mixtures, Gibbs free energy of mixing for polymer-solvent systems are calculated. The free energy of mixing of two polymers has been calculated by the method proposed. Heats of mixing of polymers have been measured with a Calvet type microcalorimeter. Entropy of mixing has been calculated. Stabilities of polymer-polymer systems have been discussed.     

Solubility and Solution Thermodynamics of Some Sulfonamides in 1-Propanol + Water Mixtures

The solubilities of sulfadiazine (SD), sulfamerazine (SMR) and sulfamethazine (SMT) in some 1-propanol + water co-solvent mixtures were measured at five temperatures from 293.15 to 313.15 K over the polarity range provided by the aqueous solvent mixtures. The mole fraction solubility of all these sulfonamides was maximal in the 0.80 mass fraction of 1-propanol solvent mixture (δ _solv = 28.3 MPa^1/2) and minimal in water (δ = 47.8 MPa^1/2) at all temperatures studied. The apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Apparent thermodynamic quantities of mixing were also calculated by using the ideal solubilities reported in the literature. Nonlinear enthalpy–entropy relationships were observed for these drugs in the plots of enthalpy versus Gibbs energy of mixing. The plot of ?_mix H° versus ?_mix G° shows different trends according to the slopes obtained when the mixture compositions change. Accordingly, the mechanism for the solution process of SD and SMT in water-rich mixtures is enthalpy driven, whereas it is entropy driven for SMR. In a different way, in 1-propanol-rich mixtures the mechanism is enthalpy driven for SD and SMR and entropy driven for SMT. Ultimately, in almost all of the intermediate compositions, the mechanism is enthalpy driven. Nevertheless, the molecular events involved in the solution processes remain unclear.     

Thermodynamics Properties of Oxymatrine in NaCl Solution

The enthalpies of dissolution of oxymatrine in 0.9%NaCl solution were measured using a RD496-2000 Calvet Microcalorimeter at 309.65 K under atmospheric pressure. The differen-tial enthalpy and molar enthalpy of oxymatrine dissolution in the 0.9%NaCl solution of were determined. The corresponding kinetic equation that described the dissolution process was elucidated. Moreover, the half-life, molar entropy, molar enthaply, and Gibbs free energy of the dissolution process were also obtained.     

Thermodynamics of water sorption in acrylic homonetworks and IPNs

The equilibrium thermodynamic properties of poly(hydroxyethyl acrylate) and poly(ethyl acrylate)-i-poly(hydroxyethyl acrylate) hydrogels are investigated starting from the water sorption isotherms of the systems. Partial enthalpy and entropy of the sorbed water in the gel differ markedly from the values of pure water at the lowest water contents, and tend to those of liquid water as saturation is approached. The residual mixing free energy is calculated, as a means of assessing the intensity of the water-polymer interaction. Its small positive magnitude shows that water-polymer hydrogen bonds are labile compared to water-water and polymer-polymer hydrogen bonds, and thus the stability of the gel state is still mainly due to the combinatorial entropic contribution to the mixing free energy. An equation correctly describing the sorption isotherms, when combined with the thermodynamic equations, can deliver the true water-polymer interaction parameter and its dependence on the polymer volume fraction in the gel.     

Thermodynamic quantities relative to solution processes of Naproxen in aqueous media at pH 1.2 and 7.4

Based on van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of naproxen (NAP) in water at pH 1.2 and 7.4, were evaluated from solubility values determined at several temperatures. The solubility at pH 7.4 and 25.0°C was almost 150 times higher with respect to pH 1.2. The enthalpies of solution were positive and greater for pH 1.2, while the entropies of solution were both negative, thereby implying a greater molecular organization at pH 7.4. The results were discussed in terms of solute–solvent interactions.     

Viscous Flow Parameters of Mixed Nonionic Surfactants Microemulsions

The systems investigated were water/sucrose laurate/ethoxylated mono-di-glyceride/oil + ethanol. The oils were R (+)-limonene, isopropylmyristate and caprylic-capric triglyceride. The dynamic viscosity of the systems where the mixing ratio (w/w) of ethanol/oil and that of ethoxylated mono-di-glyceride/sucrose laurate equal unity were measured. Dynamic viscosity was measured as function of temperature at different water volume fractions. The measured viscosities for the samples in all of the systems decrease as the temperature increases. The thermodynamic parameters of viscous flow that include enthalpy, entropy, and Gibbs free energy were estimated. In all of the systems studied, the enthalpy of viscous flow remains constant as function of temperature and varies as the water content in the microemulsions vary. The entropy and the Gibbs free energy vary with both the temperature and the composition of the microemulsions. Linear relationships were observed between the enthalpy and entropy of viscous flow for the systems based on the three oils. The enthalpy-entropy compensation temperatures were determined and found to be 265, 349, and 322 K for the microemulsion systems based on R (+)-limonene, isopropylmyristate and caprylic-capric triglyceride, respectively.     

Solubility of budesonide in {ethanol + water} mixtures from T = (293.2 to 313.2) K: Experimental measurement and mathematical modelling

The solubility of budesonide (BDS) in binary mixtures of ethanol and water at T = (293.2–313.2) K is determined and mathematically represented using two cosolvency models, i.e. Jouyban–Acree model and Jouyban–Acree–van’t Hoff model. The mean relative deviations for fitting the solubility data of BDS in binary mixtures of ethanol + water are 6.6% and 6.5%, respectively. Furthermore, the apparent thermodynamic properties, dissolution enthalpy, dissolution entropy, and Gibbs free energy change of dissolution process of BDS in all the mixed solvents were calculated according to van’t Hoff and Gibbs equations. Dissolution of BDS in these mixed solvents is an endothermic process.     

Solution thermodynamics and preferential solvation of hesperidin in aqueous cosolvent mixtures of ethanol,isopropanol, propylene glycol,and n-propanol

The solubility of hesperidin in some {cosolvent (1) + water (2)} mixtures expressed in mole fraction at temperatures from 293.15 K to 333.15 K reported by Xu et al. has been used to calculate the apparent thermodynamic functions, Gibbs energy, enthalpy, and entropy, of the dissolution processes by means of the van’t Hoff and Gibbs equations. Non-linear enthalpy–entropy relationships were observed for this drug in the plots of enthalpy vs. Gibbs energy of dissolution with positive or negative slopes regarding mixtures composition and/or cosolvent. Moreover, the preferential solvation of hesperidin by the cosolvents was analysed by using the inverse Kirkwood–Buff integrals observing that this drug is preferentially solvated by water in water-rich but preferentially solvated by cosolvents in mixtures 0.20 (or 0.24) ≤ x₁° ≤ 1.00. Furthermore, a new mathematical model was proposed for correlating/predicting the solubility of hesperidin in binary solvent mixtures at various temperatures.     

尺寸效应对氧化锌微/纳体系热力学性质的影响

采用微乳液水热辅助法合成了三种不同尺寸的手榴弹状ZnO 微/纳结构. 通过设计热化学循环, 建立了纳米ZnO与块体ZnO体系热力学性质之间的关系. 并结合微量热技术对不同尺寸ZnO微/纳体系的热力学性质进行了计算. 结果表明, 尺寸效应对微/纳体系热力学性质有显著的影响: 随着反应物尺度的减小, 体系的标准摩尔反应焓、标准摩尔反应Gibbs 自由能、标准摩尔反应熵均降低, 而材料自身的标准摩尔生成焓、标准摩尔生成Gibbs 自由能、标准摩尔熵均增加.