Studies On Dilatational Rheological Viscoelasticity Of Interface (Surfacial) Of Surface Active Substance

Because of surfactant's 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. So surfactant is often called the "MSG of industry".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. The information of microscopic process of interface and surface can be derived through the research of dilatational viscoelaticity of interface or surface. In recent more than 30 years, lots of theoretical models have been derived to illuminate the relaxation. But the research of two-dimension dilatational viscoelaticity of gas-liquid surface and liquid-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 2-Naphthalenesulfonic acid Sodium Salt, Ethylnaphthalenesulfonic acid Sodium Salt, TritonX-100, Cocoamidopropyl Betaine (CAB-30), TritonX-100/CTAB, CAB-30/TritonX-100 and CAB-30/CTAB etc., by the interfacial dilatational viscoelasticity meter (JMP2000A ), which is prepared by our laboratory and developed by Shanghai Powereach Co. Ltd. We get some informations of the dilatational modulus |ε| , dilatational elasticity ε_d , dilatational viscosity η_d , phase angleθ and other dilatational rheological viscoelasticity coefficients with Sine wave movement methods, the same speed movement methods and interfacial tension relaxation methods and the influence of temperature , concentration, inorganic salt and pH value to these coefficients. The results of experiments indicate:(1) Dilatational modulus|ε|, dilatational elasticity ε_d, dilatational viscosity η_d, phase angle θ of 2-Naphthalenesulfonic acid Sodium Salt, Ethylnaphthalenesulfonic acid Sodium Salt, oil/water, TritonX-100, Cocoamidopropyl Betaine (CAB-30), TritonX-100/CTAB, CAB-30/TritonX-100 and CAB-30/CTAB systems are regularly changing with the change of dilatational frequency.(2) The concentration of surfactant effect on the dilatational modulus, the relaxation processes and the hysteresis circle area: the dilatational modulus greater at first stage then minishing; relaxation processes gradually increased; the hysteresis circle area was greater with the concentration when the concentration was lower the CMC with the increasing the concentration of surfactant.(3) The dilatational rheological viscoelasticity coefficients are greatly influenced by the experiment temperature.With the increasing of the temperature dilatational modulus, dilatational elasticity and dilatational viscosity were decreaced; but phase angle have complex change.(4) With the increacing of the concentration of sodium chloride, the dilatational modulus of anionic surfactant become greater at first stage then decreacd; the dilatational modulus of amphoteric surfactant minished at first stage then increacd ; the dilatational modulus of nonionic surfactant didn't change.(5) The dilatational rheological viscoelasticity coefficients of Cocoamidopropyl Betaine and TritonX-100 are greatly influenced by the pH value. The coefficients will fall when the pH value is very big or very small.(6) Ethylnaphthalenesulfonic acid Sodium Salt has better viscoelasticity properties than 2-Naphthalenesulfonic acid Sodium Salt, because of their different structure. The value of dilatational rheological viscoelasticity coefficients at Oil-water interface are more stable than gas-water interface, but it is hard to explain the microscopic relaxation model , because oil and water maybe produce new substance at Oil-water interface. (7) We have the same result by Sine wave movement methods, the same speed movement methods and interfacial tension relaxation methods.(8) The mix system are similar with the single system, but coefficients of dilatational rheological viscoelasticity properties are increased more or less compared with single system.