Rheological Properties Of Cationic And Anionic Surfactant Mixed System

Surfactant mixed system that can form rich microstructures spontaneously,exhibits very complicated phase behavior and unique rheological properties,resulting in a broad application potential in many areas.In this paper,we choose cationic and anionic surfactant mixed system for investigation to explore the influence of complex salt,organic salt and temperature on the phase behavior and rheological properties and aggregate microstructures of the mixed system.1.At 318.15K,the conventional mixing plane of the surfactant ionic total molar fraction x = 0.005 Octadecyl trimethyl ammonium bromide(STAB)/Sodium dodecyl sulfonate(AS)/H2O and x = 0.005 Octadecyl trimethyl ammonium bromide(STAB)/Sodium dodecyl sulfate(SDS)/H2O mixed system as a benchmark,by adding complex salt STA+AS-,STA+DS-and NaBr to change the ratio of inorganic counter ion and corresponding surfactant ion,then as the ratio changes,the influence laws of rheological properties of isotropic single-phase area near the peak viscosity of the mixed system in the pyramid phase diagram were investigated.Experiments show that,based on the conventional mixing plane,for each specified cationic surfactant molar fraction xSTA+ serie,all have a best proportion of inorganic counter ion and corresponding surfactant ion to make the system obtaining the maximum shear viscosity.For the above phenomenons,we can discuss combining with the electrostatic shielding effect of surfactant aggregates,the influence of curvature of surfactant end-cap and the induced worm-like micelles structure transformation which because of the change in ratio of inorganic ion and corresponding surfactant ion.2.The effects of different concentrations of organic salt Sodium salicylate(NaSal)on the phase behavior and rheological properties of 1,10 mmol·kg-1 STAB/H2O and 1,10 mmol kg-1 STAB/SDS mixed system were studied.Experimental results indicate that,when at the lower surfactant concentration,the effects of Sal-in isotropic single-phase of anionic surfactant excess region are not obvious,so the shear viscosity is almost the same.For STAB system and isotropic single-phase region of cationic surfactant excess region of mixed system,with the increase of NaSal concentration,Sal-is adsorbed at the micelles interface,and it can form complexes with STA+,thus electrostatic shielding effect of the system increases,meanwhile,Sal-exhibits a penetration ability,which can insert its benzene ring into STAB ionic headgroups,producing strong hydrophobic interaction,then the surfactant ionic headgroups average area a0 decreases,the critical packing parameter P increases,promoting rod-micelles size becomes longer or grow into threadlike micelles,thus increasing the shear viscosity of the system;when NaSal concentration is increased to a certain degree,and the ratio of NaSal and STAB concentration is optimal,the size of rod-like micelles is longest or threadlike micelles entangle,then the maximum shear viscosity can be obtained;when NaSal concentration continues to increase to excess,with the number of free ions Sal-increased,leading to smaller size rod-like micelles or facilitating entangled threadlike micelles gradually branch,then shear viscosity of the system is reduced.Due to NaSal exhibits specific adsorption and penetration ability,the size of the micelles and aggregate structure will change,therefore,with the NaSal concentration increases to a certain extent,the phase behavior of system will change.3.The influence of temperature(298.15,303.15,308.15,313.15 and 318.15 K)on the phase behavior and rheological behavior of 10 mmol·kg-1 STAB/SDS/H2O and 10 mmol·kg-1 STAB/SDS/5 mmol·kg-1 NaSal mixed systems were explored.It was found that,with the reduction of temperature,the vesicle phase of anionic surfactant excess area disappeares gradually.To cationic surfactant excess area,it will change more complicately on phase behavior,such as it will appear that section area of isotropic single-phase change into vesicle or liquid crystal phase,and the vesicle phase transformed into liquid crystal phase,et al,these are because that,with the decreasing temperature,the ability of counterion binding and the interaction between oppositely charged headgroups strengthen,then the surfactant ionic headgroups average area a0 decreases,the critical packing parameter P increases,promoting rod micelles grow to the vesicle,vesicle continues to pile up to form liquid crystal structure,et al.Meanwhile,as the decrease of temperature,the size of the micelle will grow and aggregate structure will change,thus lead to the surfactant system shear viscosity increases.For 10 mmol·kg-1 STAB/SDS/5 mmol·kg-1 NaSal mixed system,in addition to the above effective factors between the surfactants ionic headgroups,NaSal exhibits specific adsorption and penetration ability,producing electrostatic shielding and strong hydrophobic effect.Due to the mentioned interactions,the phase behavior of mixed system is changed,and its shear viscosity is larger than that of 10 mmol·kg-1 STAB/SDS/H2O mixed system.