Effect of molecular size on the W-shaped excess heat capacities: oxaalkane–alkane systems

Abstract

Excess molar heat capacities, Cz , throughout the entire concentration range have been determined at 25 "C for the following oxaalkanealkane systems : 2,5,8,11,14-pentaoxapentadecane (tetraglyme) with decane, nonane, octane and hexane ; 2,5,8,11-tetraoxadodecane (triglyme) with hexadecane, pentadecane, tetradecane, dodecane, decane and hexane; 2,5,8-trioxanonane (diglyme) with 2,6,10,15,19,23-hexamethyltetracosane (squalane), 2,6,10,14-tetramethylpentadecane (pristane), hexadecane and decane ; 23-dioxahexane (monoglyme) with squalane, pristane, decane and heptane ; and 1,4-dioxacycIohexane @-dioxane) with cyclohexane. For all these tures CE has a W-shaped concentration dependence (two minima separated by a maximum). By increasing the molecular size of either component, the maximum in Ck is enhanced and displaced towards high concentrations of the smaller component. C; behaviour correlates with degrees of non-randomness in the mixtures as quantified by the concentration-concentration correlation function S, , which is calculated using the Flory-Huggins theory with a group-interaction model and assuming interaction between molecular surfaces.

Temperature and Pressure Dependences of Thermophysical Properties of Some Ethylene Glycol Dimethyl Ethers from Ultrasonic Measurements

“…Similarly, in order to obtain heat capacities at atmospheric pressure, literature values [27][28][29][30][31][32] were fitted to a second-order polynomial function:…”

Temperature dependence of the volumetric properties of binary mixtures containing oxaalkane + c-hexane

“…8 as a function of the temperature, using eq. [2] and the coefficients Bij in Table 7. An almost linear increase of the excess volume with the temperature can be observed.…”

Analysis of temperature dependence of some physical properties of (n-nonane+ tetraethylene glycol dimethyl ether)

“…The excess molar volumes were compared with those measured by Trejo et al (6) and Tovar et al (7) at T = 298.15 K. The miscibility gap showed by this mixture at a fixed temperature and composition is remarkable. For its determination, the (liquid + liquid) equilibrium (l.l.e.)…”

“…Excess molar volumes at T = 298.15 K were measured by Treszczanowicz et al (15) Other researchers determined that excess molar heat capacities for (alkane + glyme) mixtures show a W-shaped concentration dependence at several temperatures. Besides, Trejo et al (6) and Tovar et al (7) determined heat capacities of (n-nonane + tetraglyme). The aim of this work is a better characterisation of this mixture by means of studying more physical properties.…”