The Effect of Molecular Branching on Surface Tension of Liquid Alkanes

The study investigates the impact of molecular branching on the liquid-vapour surface tension of alkanes through molecular dynamics simulations. Specifically, linear alkane, triacontane (C30H62), and three of its branched isomers 2,6,13,17, tetrapropyloctadecane, 2,6,9,10,13,17, hexaethyloctadecane, and 2,3,6,7,10,11, hexapropyldodecane are simulated to examine the effect of the degree of branching on surface tension. Additionally, linear tetracosane (C24H50) is studied to assess the impact of molecular weight and provide a benchmark for the results. Long-range truncation correction is applied to the calculated values, resulting in surface tensions within 9% of experimental data available in the literature, with triacontane exhibiting higher surface tension. The branched systems display lower surface tensions, which decrease linearly with the degree of branching. Through structural analysis and the resolution of stresses at the nanoscale, it has been demonstrated that due to increased dispersion forces, both normal (σ┴) and tangential (σ||) interfacial stresses escalate with higher branching. Nevertheless, the rate of increase in σ┴ is comparatively larger, which results in a decrease in surface tension as the degree of branching increases. These findings can aid in developing customized molecular structures to fine-tune surface tension.