Studies On Dilatational Rheological Viscoelasticity Of Surfactant Film At Gas-Liquid Surface

The importance of monomolecular film in both fundamental investigation and applied research has been realized long time ago. But because of the restriction of the analytic instruments and methods in old days, only recently is the dilatational rheological viscoelasticity of the surface monomolecular film becoming the hot spot and a kind of science which can be concerned with many other subjects.Surfactant is a kind of valuable products in the field of chemical industry, Because of its unique properties, such as wetness, osmosis, emulsification, demulsification, froth, defoamer, dispersal, flocculation, washing and so on, it is of great importance in improving manufacturing technology, perfecting product quality, economizing energy sources, reducing cost, increasing productivity and so on. Surfactant is often called the "MSG of industry" because many self-assembled structures formed by surfactants such as foam and emulsion are widely used in industry, agriculture, biology, medicine and family life on account of the stability of surfactants.The properties of interfacial or surface film determine the stability of emulsion and foam. The dilatational viscoelasticity of interfacial film is one of the most essential properties of gas-liquid surface and liquid-liquid interface, which will show the resistance ability of interfacial film to dilatational distortion. Compared with shear viscoelasticity properties of interfacial film, the properties of dilation are several multitudes larger than the properties of shear. So the research on the dilatational viscoelasticity of interface or surface is significant to the research of the stability of emulsion and foam.Surface microscopic relaxation process on the interface or surface is the base of the formation of the dilatational rheological viscoelasticity properties of interface or surface. In recent 30 years, lots of theoretical models have been derived to illuminate the relaxation. The information of microscopic process of interface and surface can be derived through the research of dilatational viscoelaticity of interface or surface. But the research of two-dimension dilatational viscoelaticity of gas-liquid surface andliquid-liquid interface monomolecular film has not been developed perfectly. Viscoelasticity data derived from different methods are profoundly different and not theoretical in agreement. Only qualitative inference or model description is derived under certain frequency. So improving accuracy of the present determination techniques and applicability and developing viscoelasticity theory applicable to two-dimension film are of great importance in monomolecular film research.This paper is mainly concerned with the research of dilatational rheological viscoelasticity properties of interface or surface film of different kinds of surfactants, including Sodium Dodecyl Benzene Sulphonate (SDBS), Sodium dodecyl sulphonate (SDS), Sodium laurate, OP, etc., by the interfacial dilatational viscoelasticity meter (JMP2000A), which is prepared by our laboratory and developed by ShanghaiPowereach Co. Ltd. We get some informations of the dilatational modulus |ε|,dilatational elasticity εd, dilatational viscosity ηd, phase angle θ and other dilatationalrheological viscoelasticity coefficients and the influence of temperature and concentration to these coefficients. We also get the microscopic relaxation model of these systems. Furthermore, the influences of the concentration of metal cations and the structure of surfactants to the property of dilatational viscoelasticity have also been discussed. The results of experiments indicate:(1) Dilatational modulus|ε|, dilatational elasticity εd, dilatational viscosity ηd, phase angle θ of SDBS and OP systems are regularly changing with the change of dilatational frequency. The double logarithmic curve with s and dilatationalfrequency are an approximate linear, and both of the linear fit parameters are above 0.98. The slopes of linear fit curves infer that the microscopic relaxations of the SDBS and OP systems are diffusion-c...