Studies On Dilatational Viscoelasticity Of Liguid/Air Interface Of Natural Surfactants

So far, many achievements have been accomplished on typical surfactants at home and abroad, but studies on the interfacial viscoelastic properties of natural surfactants are few. Chitosan is one natural sugar surfactant with biodegradable, good film forming properties, biocompatibility, anti-bacterial and anti-tumor properties. Saponins are rich in Pu Tizi aril plants, which have good foaming and cleaning performance and anti-bacterial and other biological activities. So the amount of chitosan and Pu Tizi saponins in the pharmaceutical, food, cosmetics, detergent and other industries as wetting agents, dispersants, emulsifiers and detergents, etc is growing.The interfacial stability of chitosan and saponin solution can be affected by interfacial dilational viscoelasticity, the molecular interfacial viscoelastic parameters reflect on some micro-interfacial information, such as interfacial molecular adsorption, diffusion, orientation, configuration conversion and other microscopic relaxation processes. So research on the interfacial dilational viscoelasticity of natural surfactants is a very meaningful topic.The topic is mainly completed with the dilatational rheological method by JMP2000A interfacial rheological instrument. The research measures the gas-liquid interfacial dilational viscoelastic properties of chitosan and Pu Tizi saponins solution, and explores the influences of various experimental conditions (such as temperature, frequency, solution concentration, NaCl,MgCl2,AICI3 three kinds of inorganic salts and nano Mg(OH)2 particle) on the two dilatational systerms'viscoelasticity. We get their relaxation amplitude, dilatational modulus |ε|, dilatational elasticityεd dilatational viscosityηd, phade angleθand other dilatational viscoelastictic coefficients. In addition, the work further characterizes the structure of materials and the nature of systems, combined with other characterization methods (such as infrared spectra, uv-vis spectrophotometer etc). The results show:(1) The size of chitosan molecules in the 1 g/L solution is determinated by nano-particle analyzer, which found that the molecular size in the solution increases after placing 48 h. Uv-vis spectroscopy is maeasured in the newly 1 g/L,48 h,72 h,5 days- later chitosan solution respectively, which shows that the UV absorption intensity decreased with the extension of storage time. The surface tension of chitosan solution is maeasured by the maximum continuous bubble method. All of these results indicate that chitosan molecules in the solution gather with each other. The gas-linquid interfacial dilatational viscoelasticity of 1 g/L chitosan solution show that: the interfacial change is different from that of typical cationic surfactant CTAB. The dilatational modulus increases gradually, and then reaches stability with the experiment going on. But the dilatational modules of CTAB do not change with time. We speculate that chitosan molecules also interacte with each other on the surface. When the solution is shocked or heated and then cooled, the aggregation abates. This indicates that the interaction between interfacial moleculers is weak and reversible. Besides, the greater concentration of chitosan (0.01 g/L～2 g/L) is, the bigger the interfacial dilatational modulus|ε|, the elasticityεd, the viscosityηd are.(2) Instrument frequency, concentration and temperature have a certain influence on the gas-liquid interfacial viscoelastic parameters, |ε|,ε1 andηd change presentablely with working frequency (0.033 Hz～0.1 Hz), and decrease with the increase of concentration (0.05%～0.5%) and temperature (10℃～30℃).(3) inorganic salts(0.1 g/100 mL～1.5 g/100 mL) can reduce the interfacial dilatational modulus|ε|, the elasticityεd, the viscosityηd of the two natural surfactants, and the parameter|ε|,εd,ηd decrease with the increase of the metal ion concentration. When add 0.7 g/100 mL NaCl,MgCl2,AlCl3, the reduce of the viscoelastic parameters are embodied as AlCl3>MgCl2>NaCl.(4) The interfacial dilatational modulus|ε|, the elasticityεd, the viscosityηd of Pu Tizi saponins solution significantly reduce and then increase with content of nano Mg(OH)2 particle increasing, and decreases with the surfactant concentration(0.05%～0.5%) increasing.