The effect of molecular branching on surface tension of liquid alkanes

Abstract

HypothesisPrevious experimental evidence suggests surface tension of branched isomers of n-alkanes is lower than the linear isomer. This finding is significant as it has implications for various interfacial processes. However, a clear definition of the degree of branching, its relationship to surface tension, and its structural origins are lacking, which will be determined in this study. SimulationsWe simulated linear alkane (triacontane, C30H62) and three of its branched isomers (2,6,13,17-tetrapropyloctadecane, 2,5,7,8,11,12,15-heptaethylhexadecane and 2,3,6,7,10,11-hexapropyldodecane), as well as linear tetracosane (C24H50) for comparison. Surface tensions, interfacial stresses, and structural properties were determined and analysed. FindingsOur simulations yielded surface tensions within 9 % of experimental data for linear triacontane and tetracosane. We found that the branched isomers of triacontane exhibited lower surface tensions, which decreased linearly with increasing the degree of branching. By analyzing the molecular structures and resolving stresses at the nanoscale, we discovered that the increased branching led to higher normal (σ┴) and tangential (σ||) interfacial stresses due to increased dispersion forces. However, the rate of increase in σ┴ was higher, resulting in a decrease in surface tension as the degree of branching increased. These findings have implications for designing customized molecular structures to control surface tension.