Temperature dependences of the molecular area of surfactant 2D monolayers at the air/water interface
L.M. Litvinenko Institute of Physical Organic and Coal Chemistry
Abstract: The dependences of the molecular area (Ac) at the onset of the transition from the liquid-expanded to liquid-condensed (LE-LC) phase for 2D surfactant monolayer on the temperature and chain length are considered for seven surfactant classes at the air/water interface. A thermodynamic model of the amphiphilic monolayer behavior (taking into account the nonideality of mixing entropy) is used to evaluate Ac, as well as a quantum chemical approach that allows an assessment of the thermodynamic and structural parameters of surfactant associates. The calculated Ac values adequately reflect the experimental temperature dependence for the considered phase transition: the temperature increase leads to a decrease of the area per surfactant molecule with the fixed chain length and vice versa lengthening of the surfactant carbon chain at a fixed temperature results to the Ac value increase. The average values of the slope in the Ac = f(T) dependences for the regarded surfactant classes are in the range of 0,57-1,32 Å2/°C. The estimation of the (dAc/dn)T value shows that the best agreement of the calculated and available experimental data is achieved for saturated carboxylic acids and dialkyl-substituted melamine. The obtained results demonstrate applicability of the proposed approach for predictive purposes.
Keywords: 2D monolayer, clusterization Gibbs energy, unit cell, phase transition, thermodynamic model
- Elena S. Kartashynska – Dr. Sc., Researcher of Supramolecular Chemistry Department, L.M. Litvinenko Institute of Physical Organic and Coal Chemistry
Kartashynska, E.S. Temperature dependences of the molecular area of surfactant 2D monolayers at the air/water interface / E.S. Kartashynska // Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials. — 2022. — I. 14. — P. 408-418. DOI: 10.26456/pcascnn/2022.14.408. (In Russian).
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