A Study Of The Interaction Of Molecules With Different Structures At Oil-water Interfaces

As a typical colloidal dispersion system,emulsion is widely used in medicine,food,cosmetics,petrochemical and other industries for carrying lipophilic bioactive drugs and oil mining and transportation.Zeta potential test based on electrophoretic measurement of the colloidal particles can obtain the potential at the slip surface of the interface electric double layer.Second Harmonic Generation(SHG)spectroscopy with interface selectivity detects the interfacial molecular information.In this paper,these two techniques are used to detect the emulsion interface in real time and study the interaction of molecules with different structures at the oil-water interfaces.In this thesis,surfactant-free emulsion was prepared by using hexadecane and water to compare the ionic strength dependent Zeta potential curves after sodium n-alkyl sulfate molecules absorbed at the oil-water interface.The experimental results show that,the maximum value in the zeta potential curve disappears as the length of the hydrophobic chain in sodium n-alkyl sulfate decreases.This confirmed the chain-chain interaction between the tails of the interfacial surfactant molecules and demonstrated that this chain-chain interaction decreases as the number of carbon atoms decreases.By comparing the ionic strength dependent zeta potential and the SHG spectroscopy results,we obtained that there is also an increased intermolecular ?-? interaction between dye molecules with the increasing of total electrolyte concentration in the emulison system.It is possible that MG molecules have a greater degree of anti-parallel arrangement at the interface than under high electrolyte concentration.In order to understand the interaction between interfacial molecules more comprehensively,the molecular interactions at the benzene-water interface were also investigated.The experimental results are similar to those at the hexadecane-water interface.This indicates that the type of interface has little effect on the intermolecular interaction.The above studies confirmed that the maximal effect of the ionic strength dependent zeta potential at the oil-water interface is induced by further adsorption caused by interfacial interaction,indicating that the interaction of surfactant molecules at the interface decreases with the decrease of chain length.At the same time,the ?-? interaction of the two dye molecules at the interface is revealed.This study provides direct experimental evidence for understanding the dynamics behavior of interface molecules and the stability of oil-water emulsions.