Calorimetry of aqueous solutions

WOOD and smith-magowan Calorimetry of Aqueous Solutions 579... 

Hvidt, S Jorgensen, EB Brown, W Schillen, K, Micellization and Gelation of Aqueous Solutions of a Triblock Copolymer Studied by Rheological Techniques and Scanning Calorimetry, Journal of Physical Chemistry 98, 12320, 1994. 

Previous works reported on the study of the freezing process of aqueous solutions of ethanol in relation with the phase diagram. They were focused on the identification of different stable or metastable ethanol-hydrate structures using X-ray diffraction and differential scanning calorimetry (DSC). They also mentioned the formation of clathrate hydrates. In spite of the familiarity of alcohol-water systems and their importance in many fields of chemistry, cryobiology, astrophysics, there are still significant discrepancies in the literature with uncertainties concerning the composition and the structure of the stable or metastable eutectic or peritectic hydrates. ... 

GAN Gan, L.-H., Cai, W., and Tam, K.C., Studies of phase transition of aqueous solutions of poly(V,V-diethylacrylamide-co-acryhc add) by differential scatming calorimetry and spectrophotometry, Eur. Polym. J., 37,1773,2001. 

In calorimetry, not only is the degree of solubility and degree of dissociation important, but the slow rate of dissolution of many electrolytes in organic solvents must also be considered. It is advisable to make an initial study of the nature of the system by first observing the dissolution rate of the solute and then determining the degree of dissociation by conductance measurements. Much time can be saved by these preliminary examinations. The slow rate of solution of many salts may also pose problems in solubility measurements. It is advisable, as in the case of aqueous solutions, that solubility studies be conducted from both super- and under-saturation to ensure that equilibration has been attained. 

NIN Ninni, L., Meirelles, A.J.A., and Maurer, G., Thermodynamic properties of aqueous solutions of maltodextrins from laser-light scattering, calorimetry and isopiestic investigations. Carbohydrate Polym., 59,289,2005. 

MOH Mohite, L.V. and Juvekar, V.A., Quantification of thermodynamics of aqueous solutions of poly(ethylene glycols) Role of calorimetry. Fluid Phase Equil, 278, 41, 2009. 

Hvidt, S., Jorgensen, E. B., Brown, W., Sehillen, K. (1994). Micellization and gelation of aqueous-solutions of a triblock copolymer studied by rheological techniques and seanning calorimetry. Journal of Physical Chemistry, 98, 12320-12328. 

The enthalpies of dilution at 25°C of binary and tertiary aqueous solutions containing the isomeric disaccharides cellobiose, maltose, and trehalose, were investigated, and an empirical relationship between saccharide solvation and solute solute interactions was deduced. The thermochemical properties of aqueous solutions of small carbohydrates as glasses and rubbers at sub-zero temperatures have been measured by differential scanning calorimetry (DSC), and the thermodynamic properties of alcohols and monosaccharides in aqueous biuret solution at 25 C have been determined by flow microcalorimetry. By use of DTG... 

In this section, the focus is on the surface-active properties of aqueous solutions of MEGA and MELA surfactants. Their surface properties and micelle formation have been studied by light scattering [25,53], spectro-fluorimetry, ultrasonic absorption and time resolved fluorescence quenching [30], differential scanning calorimetry (DSC) [54], and measurements of aqueous solution densities [27] and surface tensions [24,49,55]. The results can be summarized as follows ... 

Fig. 6.30 Dilution of aqueous solution of (dodecyldimethylammonio) butanoate (C12N3C) and its adsorption onto Spherosil XOB015 (Sbet = 25m g ) at 298 K (a) enthalpy of dilution, (b) adsorption isotherm, (c) differential molar enthalpy of displacement. In both types of titration calorimetry experiment, a 0.3 mol kg C12N3C solution in pure H2O was used...

Table 5 Transition temperature of aqueous solutions of PVME (determined by differential scanning calorimetry (DSC), dr/df=5Kmin 4.0gM), rvPT(

If one considers the use of subzero temperature differential scanning calorimetry (SZT-DSC) as an analytical tool, a striking fact becomes evident whereas this technique has been used extensively for the study of aqueous solutions of polymers, biopolymers, and other organic compounds such as phospholipids, only a little attention has been given to the investigation of amphiphilic systems. Even less attention has been paid to the study of ternary (water + surfactant + oil) and quaternary (water -I- surfactant -l- cosurfactant + oil) systems. 

Wadsd I 1994 MIcrocalorlmetry of aqueous and biological systems Solution Calorimetry, Experimental Thermodynamics vol IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

Studies on metal-pyrazole complexes in solution are few. The enthalpy and entropy of association of Co(II), Ni(II), Cu(II) and Zn(II) with pyrazole in aqueous solution have been determined by direct calorimetry (81MI40406). The nature of the nitrogen atom, pyridinic or pyrrolic, involved in the coordination with the metal cannot be determined from the available thermodynamic data. However, other experiments in solution (Section 4.04.1.3.3(i)) prove conclusively that only the N-2 atom has coordinating capabilities. 

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

Zhu, C., Streng, W. H. Investigation of drug self-association in aqueous solution using calorimetry, conductivity, and osmometry. Int. I. Pharm. 1996, 130, 159-158. 

A drum of 30% solution in water exploded an hour after filling at 50°C, despite having a vent. Calorimetry demonstrated an exothermic, autocatalytic hydrolysis to ammoniacal potassium bicarbonate. In theory, a pressure exceeding 30 bar is obtainable. Aqueous solutions are unstable even at room temperature. Similar hydrolysis may account for an explosive product with Gold(III) chloride. 

The physical properties of the anhydrate form and two polymorphic monohydrates of niclosamide have been reported [61], The anhydrate form exhibited the highest solubility in water and the fastest intrinsic dissolution rate, while the two monohydrates exhibited significantly lower aqueous solubilities. In a subsequent study, the 1 1 solvates of niclosamide with methanol, diethyl ether, dimethyl sulfoxide, N,/V -dimethyl formamide, and tetrahydrofuran, and the 2 1 solvate with tetraethylene glycol, were studied [62], The relative stability of the different solvatomorphs was established using desolvation activation energies, solution calorimetry, and aqueous solubilities. It was found that although the nonaqueous solvates exhibited higher solubilities and dissolution rates, they were unstable in aqueous media and rapidly transformed to one of the monohydrates. 

Another area where titration calorimetry has found intensive application, and where the importance of heat flow versus isoperibol calorimetry has been growing, is the energetics of metal-ligand complexation. Morss, Nash, and Ensor [225], for example, used potenciometric titrations and heat flow isothermal titration calorimetry to study the complexation of UO "1" and trivalent lanthanide cations by tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA), in aqueous solution. Their general goal was to investigate the potential application of THFTCA for actinide and lanthanide separation, and nuclear fuels processing. The obtained results (table 11.1) indicated that the 1 1 complexes formed in the reaction (M = La, Nd, Eu, Dy, andTm)... 

Effects of solvent mixtures can be seen in biochemical systems. Ligand binding to myoglobin in aqueous solution involves two kinetic components, one extramolecular and one intramolecular, which have been interpreted in terms of two sequential kinetic barriers. In mixed solvents and subzero temperatures, the outer barrier increases and the inner barrier splits into several components, giving rise to fast intramolecular recombination. Measurements of the corresponding solvent structural relaxation rates by frequency resolved calorimetry allows the discrimination between solvent composition and viscosity-related effects. The inner barrier and its coupling to structural relaxation appear to be independent of viscosity but change with solvent composition (Kleinert et al., 1998). 

---