The Study Of Formation And Rheological Properties Of Polyhedral Vesicle Gels

As one kind of the important materials,surfactant gels consisting vesicles have attracted much attention recently because they own the dual advantages of gels and vesicles.Although spherical vesicle gels have been obtained in limited surfactant systems,polyhedral vesicle gels have been barely reported.Therefore,an anionic surfactant-perfluorocarboxylic acid with simple structure and different chain length was selected?7-11?were mixed with one cationic hydrocarbon surfactant,tetradecyltrimethylammonium hydroxide?TTAOH?,to construct a surfactant gel to explore the conditions and regularity of polyhedral vesicle gel formation.And the effects of external conditions such as temperature and ionic strength on the microstructure and rheological properties of the obtained gel were investigated.When different fluorinated fatty acid surfactants were mixed with TTAOH in water solution,different phase behaviors were observed.For the C₇F₁₅COOH/TTAOH/H₂O system,it can be seen no gel phase was formed.For the other four systems,it all can be seen gel-phase regions.Under the studied concentration and mixed ratio conditions,the gel area formed by the C₁₀F₂₁COOH/TTAOH/H₂O system is large,while with the increase of fluorocarbon chain,the gel areas decrease.From the FF-TEM images,it can be seen that the gel is consisting of close-packed polyhedral vesicles with a polydisperse size.Besides,the length of the fluorocarbon chains has a certain influence on the viscoelasticity of the gel.The longer the anionic surfactant fluorocarbon chain,the higher the viscoelasticity of the gel is.Temperature is an important factor which affects the structure and rheological properties of aggregates.Therefore,a representative system,the C₁₀F₂₁COOH/TTAOH/H₂O system,has been selected to study the effect of temperature on the formation,structure and rheological properties of the gel.It is found that with the increase of temperature,the microstructure of polyhedral vesicle gel formed by C₁₀F₂₁COOH/TTAOH/H₂O system changes from close-packed monolayer polyhedral vesicles to polydisperse spherical vesicles,and the vesicle size increases.In addition,when the temperature is lower than the phase transition temperature of the vesicle gel,the viscoelasticity of the gel increases with increasing temperature;when the temperature rises above its phase transition temperature,the viscoelasticity of the gel decreases,then it turns into solution.The effect of ionic strength on the rheological properties of the gel formed by the C₁₀F₂₁COOH/TTAOH/H₂O system is also studied.It is found that salt-free anionic surfactant mixed system gradually changed to the anion-cationic surfactant system containing counterions after adding the 1-1 NaCl,and the viscoelasticity of the gel is decreased.After adding a small amount of high valence metal ions MgCl₂,the complex system precipitates rapidly and has a significant destruction on the gels.Besides,the effect sodium salicylate on the vesicle gel is studied,it is found that with the increasing concentration of sodium salicylate,the viscoelasticity of the gel is first increased and then decreased,and finally the vesicle structure disappears into a clear and transparent solution.