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bcBuilding a connection between the variations in interfacial tension and the microstructure of the oil-water interface is still very challenging. Here, we employ a molecular dynamics method to study the effect of monovalent ions on the decane-water interfacial tension and reveal the relationship between ionic hydration and the variation of interfacial tension. Our results indicate that interfacial tension presents a non-monotonic dependence on the ionic concentrations owing to the distinctive adsorption characteristics of ions. At low ionic concentrations, the hydration of the discrete ions at the interface causes an enhancement in the virial term of the interfacial tension, resulting in an increase of the interfacial tension with increasing ionic concentrations. At high ionic concentrations, the ion pairs at the interface weaken the ionic hydration, thus the virial term of the interfacial tension decreases and the interfacial tension decreases slightly. In addition, the kinetic energy term of interfacial tension increases only with increasing temperature, while the virial term decreases with an increase in either temperature or pressure on account of the weakening ionic hydration; therefore, the increase of temperature and pressure induces different degrees of the decrease in the interfacial tension owing to the major contribution of the virial term, particularly at high ionic concentrations.

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Experimental results on the coalescence of a dissipative structure "droplet cluster" obtained by means of high-speed thermal imaging are presented. It is found out that coalescence of a single cluster droplet with a liquid layer can generate a capillary wave on the interphase, and propagation of this wave causes coalescence of the whole cluster during several thousandths of a second. Cluster coalescence is accompanied by a temperature jump on the interphase. With cluster restoration, the surface temperature of a liquid layer returns gradually to the initial level. The interphase temperature under the droplet cluster can be both lower and higher than the interphase temperature without this cluster, i.e., the cluster can not only initiate both heat and mass transfer between liquid and gas, but also deteriorate it.