In the framework of the quantum chemical semiempirical PM3 method thermodynamic and structural parameters of the formation and clusterization of aliphatic alcohols C(n)H(2n+1)OH (n(OH) = 8-16) at 298 K at the water/alkane vapor C(n)H(2n+2), (n(CH(3)) = 6-16) interface were calculated. The dependencies of enthalpy, entropy and Gibbs' energy of clusterization per one monomer molecule of 2D films on the alkyl chain length of corresponding alcohols and alkanes, the molar fraction of alkanes in the monolayers and the immersion degree of alcohol molecules into the water phase were shown to be linear or stepwise. The threshold of spontaneous clusterization of aliphatic alcohols at the water/alkane vapor interface was 10-11 carbon atoms at 298 K which is in line with experimental data at the air/water interface. It is shown that the presence of alkane vapor does not influence the process of alcohol monolayer formation. The structure of these monolayers is analogous to those obtained at the air/water interface in agreement with experimental data. The inclusion of alkane molecules into the amphiphilic monolayer at the water/alkane vapor interface is possible for amphiphiles with the spontaneous clusterization threshold at the air/water interface (n(s)(0)) of at least 16 methylene units in the alkyl chain, and it does not depend on the molar fraction of alkanes in the corresponding monolayer. The inclusion of alkanes from the vapor phase into the amphiphilic monolayer also requires that the difference between the alkyl chain lengths of alcohols and alkanes is not larger than n(s)(0) - 15 and n(s)(0) - 14 for the 2D film 1 and 2D film 2, respectively.
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Adv Colloid Interface Sci
May 2020
Department of Physics, Technische Universität Darmstadt, Darmstadt 64289, Germany. Electronic address:
The theoretical description of the adsorption of surfactants at interfaces between aqueous solutions and oil was based over a very long time on models derived for the solution/air interface. Thus, most of the experimentally observed peculiarities could not be specifically considered but were merely interpreted in terms of a penetration of oil molecules into the alkyl chain layer of the adsorbed surfactant molecules. These penetrating oil molecules enhance the surfactant adsorption as compared to the water/air interface.
View Article and Find Full Text PDFSci Rep
January 2018
Department of Earth Sciences, Durham University, South Road, Durham, DH1 3LE, United Kingdom.
In this study, classical molecular dynamic simulations have been used to examine the molecular properties of the water-alkane interface at various NaCl salt concentrations (up to 3.0 mol/kg). A variety of different force field combinations have been compared against experimental surface/interfacial tension values for the water-vapour, decane-vapour and water-decane interfaces.
View Article and Find Full Text PDFJ Chem Phys
August 2017
Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005-1827, USA.
Experiments show that at 298 K and 1 atm pressure, the transfer free energy, μ, of water from its vapor to liquid normal alkanes CH (n=5…12) is negative. Earlier it was found that with the united-atom TraPPE model for alkanes and the SPC/E model for water, one had to artificially enhance the attractive alkane-water cross interaction to capture this behavior. Here we revisit the calculation of μ using the polarizable AMOEBA and the non-polarizable Charmm General (CGenFF) forcefields.
View Article and Find Full Text PDFSoft Matter
September 2014
Donetsk Medical University, 16 Ilych Avenue, Donetsk 83003, Ukraine.
On the basis of experimental data for the homologous series of alkyltrimethylammonium bromides (CnTAB) the equilibrium surface tension isotherms at three types of liquid-fluid interfaces are discussed: solution/air, solution/alkane vapor and solution/liquid alkane interfaces. It is shown that the adsorption characteristics can be described at all three interfaces by the same thermodynamic approach. In the presence of alkane molecules (in the liquid alkane phase or in the alkane vapor phase) the CnTAB adsorption layers can be best described by a co-adsorption of the alkane molecules.
View Article and Find Full Text PDFLangmuir
November 2013
Donetsk Medical University, 16 Ilych Avenue, 83003 Donetsk, Ukraine.
The adsorption of members of the homologous series of alkyl trimethylammonium bromides (C(n)TAB) is studied at water/alkane interfaces by drop profile analysis tensiometry. The results are discussed in terms of a competitive adsorption process of alkane and surfactant molecules. A thermodynamic model, derived originally for the adsorption of surfactant mixtures, is adapted such that it describes a competitive adsorption of the surfactant molecules from the aqueous phase and alkane molecules from the oil phase.
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