Heat capacity measurements in carboxylic polyelectrolyte solutions

Abstract

Apparent molal heat capacities as a function of the degree of neutralization have been determined for dilute aqueous solutions of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), copoly(maleic acid‐ethylene) (MAEt), and copoly(maleic acid‐styrene) (MASt) using direct flow microcalorimetry. Apparent molal volumes were measured as well. Both molal heat capacity and molal volume decrease with increasing ionization of the polymer. The effect of the hydrophobic interactions of the methyl group or phenyl group was obtained from the difference in the molal quantities of PMA and PAA, or MASt and MAEt. No evidence of hydrophobic effects, as determined from the heat capacity, was found for the conformational transition of PMA, but the hydration of the phenyl groups in MASt was found to be changed significantly at a degree of neutralization of 0.4.

Volumetric and calorimetric properties of aqueous ionene solutions

“…In all cases the heat capacities increase from 3,3 to 6,9–ionene, that is, with the decreasing charge density. The finding is in agreement with the previous results of polyelectrolytes [34, 38]. …”

“…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).…”

“…The water molecules around the polyion rearrange under the influence of charged and hydrophobic groups. The charged groups strongly attract (electrostrict) the neighbouring water molecules, increasing the local density of the solvent, leading to the reduction in partial molar volumes of the polyelectrolyte [34, 35]. The electrostriction of water by the counterions should also be taken into account [25, 26].…”

“…The electrostriction of water by the counterions should also be taken into account [25, 26]. Hydrophobic hydration usually leads to an increase in the partial molar volume of the solute [34]. Although Durchschlag and Zipper [36] or Gianni and Lepori [37] have used empirical procedures to account for partial molar volumes (all these authors give additivity rules to calculate partial molar volumes of solutes at infinite dilution), up to date, no theory of partial (apparent) molar volumes of polyelectrolyte solutions, capable of considering all types of interactions, exists.…”

Temperature Dependence of Viscosities and Potentiometric Titration Behavior of Aqueous Poly(acrylic acid) and Poly(methacrylic acid) Solutions

“…Yamashita and Kwak, 6 however, have concluded from their precise heat capacity measurements that there is no evidence of the hydrophobic interactions in the conformational transition behavior of PMA. Recently, on the basis of the fluorescence studies, Bednar et a/.…”