The Study of Interfacial Adsorption Behavior for Hydroxyl-Substituted Alkylbenzene Sulfonates by Interfacial Tension Relaxation Method

In order to explore the interface adsorption mechanism of hydroxyl-substituted alkylbenzene sulfonates, the interfacial tension relaxation method was used to investigate the dilational rheology properties of sodium 2-hydroxy-3-octyl-5-octylbenzene sulfonate (C(8)C(8)OHphSO(3)Na) and sodium 2-hydroxy-3-octyl-5-decylbenzene sulfonate (C(8)C(10)OHphSO(3)Na) at the gas–liquid interface and oil–water interface. The effect of the length of the hydroxyl para-alkyl chain on the interfacial behavior of the surfactant molecules was investigated, and the main controlling factors of the interfacial film properties under different conditions were obtained. The experimental results show that for the gas–liquid interface, the long-chain alkyl groups adjacent to the hydroxyl group in the hydroxyl-substituted alkylbenzene sulfonate molecules tend to extend along the interface, showing strong intermolecular interaction, which is the main reason why the dilational viscoelasticity of the surface film is higher than that of ordinary alkylbenzene sulfonates. The length of the para-alkyl chain has little effect on the viscoelastic modulus. With the increase in surfactant concentration, the adjacent alkyl chain also began to extend into the air, and the factors controlling the properties of the interfacial film changed from interfacial rearrangement to diffusion exchange. For the oil–water interface, the presence of oil molecules will hinder the interface tiling of the hydroxyl-protic alkyl, and the dilational viscoelasticity of C(8)C(8) and C(8)C(10) will be greatly reduced relative to the surface. The main factor controlling the properties of the interfacial film is the diffusion exchange of surfactant molecules between the bulk phase and the interface from the beginning.