Microcalorimetric study of poly(ethylene oxide) in water and in water-ethanol mixed solvent

Abstract

Intermediate heats of dilution, heats of mixing, and heat capacities have been measured in the dilute and intermediate concentration ranges for the polyethylene oxide) (PEO)-water and PEOwater-ethanol systems. Heats of dilution are exothermic for all systems and pass through a minimum at 50% by weight of ethanol. Heats of fusion of PEO in water and in 50% water-ethanol calculated from the combined heat of dilution and heat of mixing results are 9564 and 10 224 J basemol"1, respectively. Apparent basemolar heat capacity (CPi0) has been determined for PEO. In water, results show that CPi# decreases with increasing concentration and that Cp¿ at infinite dilution decreases with decreasing molecular weight. The value of 0" increases with increasing temperature. Values of CPi0 in water-ethanol go through a minimum at 30% by weight of ethanol. The results do not support very strongly the existence of an ordered structure for PEO in solution in water. However, they are in very good agreement with the conclusion of a recent light scattering study of the same system assuming that aggregates coexist with molecularly dispersed PEO.

Volumetric and calorimetric properties of aqueous ionene solutions

“…This is because the strong solute-water electrostatic interactions induce the distortion of the water structure around the solute and break hydrogen bonds, while the presence of a non-polar solute orders the hydration water [31, 42, 43]. Such picture is consistent with the results for the polyelectrolytes where C p ,Φ decreases with the increasing degree of ionization (increasing charge density) of polyacids [34, 38, 39]. Another classification was proposed by Makhatadze and Privalov [29] who classified the amino acid side chains as hydrophobic or hydrophilic according to the sign of the temperature derivative of the apparent molar heat capacity (for hydrophobic amino acids, ∂ C p ,Φ /∂ T < 0, and for hydrophilic ∂ C p ,Φ /∂ T > 0).…”

“…Indices 1 and 2 stand for the solvent and the solute, respectively. Assuming the ideal behaviour of the solvent, i. e. ${\overline{C}}_{p1}=C_{p1}^{\ast }$ (molar heat capacity of pure solvent), we can write $C_p=n_1{C}_{p1}^{\ast }+n_2{C}_{p,\mathrm{\Phi }}$, where C p ,Φ denotes the apparent molar heat capacity of the solute and represents a formal contribution of the solute to the total heat capacity of the solute-solvent system [38, 39]. …”

Excess molar volumes and excess molar heat capacities of (polyethylene glycols + water) at temperatures betweenT=278 K andT=328 K

“…With an increase in temperature, hydrogen bonds are weakened, thus favouring the progressive dehydration of oxygen ethers and the release of the water structure. However, this effect is counterbalanced by an increase of hydrophobic interactions (5) leading to more compact conformations, and the growth of aggregates into microgels (2,7) is enhanced until the cloud point is reached. This results in less negative excess volumes and increasing positive excess heat capacities as the temperature increases.…”

Capacité calorifique de polyélectrolytes en solution

“…Les donnCes expCrimentales sont disponibles sur demande.4 Les rCsultats indiquent une diminution de C,.+ lorsque la concentration augmente dans le cas des deux polyacides faibles. Des rksultats similaires ont ete obtenus pour le polyoxyCthylkne dans l'eau (12). L'augmentation de la concentration intensifie I'enchevCtrement des chaines, ce qui reduit leur mobilitC ou leur rnouvement de reptation et cela se reflete dans la valeur de Cp,+.…”

“…Les difftrents polyrneres utilisks dans cc travail sont: un tchantillon d'acide polyrnCthacrylique (HPMA) dCj8 dtcrit aillxrs (10) (12). L'erreur estimCe sur le calcul de C,,+ diminue sensiblernent lorsque la concentration augmente.…”