Effect of temperature and composition on density, viscosity, surface tension and refractive index for 2-HEAA + CPAc, 2-HEAA + HEAPe, and CPAc + HEAPe binary mixtures at atmospheric pressure
Year: 2026
Type: preprint
Abstract: Density and dynamic viscosity were measured for binary mixtures of 2-hydroxyethanaminium acetate (2-HEAA), 2-hydroxyethanaminium pentanoate (HEAPe), and caprolactam acetate (CPAc) from 293.15 to 373.15 K at 101.3 kPa. Surface tension was measured from 293.15 to 343.15 K, and refractive index from 293.15 to 353.15 K. The three systems were 2-HEAA + CPAc, 2-HEAA + HEAPe, and CPAc + HEAPe. Excess molar volume and deviations in viscosity, surface tension, and refractive index were calculated and correlated with the Redlich–Kister equation. Excess molar volumes were predominantly negative, consistent with contraction relative to ideal mixing. Viscosity deviations changed sign in the first two systems and were negative throughout the measured interior compositions of CPAc + HEAPe. Refractive-index deviations were mostly positive; for CPAc + HEAPe they reached 0.017, indicating a positive excess molar refraction of about 3% that is attributed to the accommodation of flexible pentanoate chains and hydrogen-bond donors around the rigid lactam rings. Surface-tension deviations were predominantly negative for the two 2-HEAA systems, with positive values only in the dilute region of 2-HEAA + CPAc, and positive at all 54 interior points of CPAc + HEAPe, reaching + 11.92 mN·m⁻¹. An Eyring–NRTL correlation reproduced the viscosities of 2-HEAA + HEAPe with an average absolute relative deviation of 0.92%, whereas the corresponding deviations were 12.76% and 6.23% for 2-HEAA + CPAc and CPAc + HEAPe. These data provide thermophysical properties and mixing information for the three ionic-liquid pairs at atmospheric pressure.
Source: Research Square
Institutions: Universidade Federal do Ceará, Embrapa
Language: English
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223952704