Effect Of Additives On The Self-assembly Behavior Of Gemini Surfactants Containing Hydroxyl Groups

Currently,Gemini surfactants have received widely attention in revent years due to their ability in forming novel aggregates.The distance between the two head groups of the Gemini surfactant molecule can be effectively modulated by the spacer that is introduced at or near the head groups.The head groups are necessarily more sensitive to the counterions in the solution.In this paper,three organic salt isomers and a series of anioic surfactants were selected as the additives.The effect of the molecular structure of the organic salts and the anionic surfactants on the formation and growth of wormlike micelles formed by the Gemini surfactants was studied systematically.The results of this study have important scientific significance for understanding the self-assembly of Gemini surfactants.The main results are summarized as follows:1.The effects of three organic salts???2-hydroxybenzoic monosodium salt(o-ph-ONa),3-hydroxybenzoic monosodium salt(m-ph-ONa)and 4-hydroxybenzoic monosodium salt(p-ph-ONa)on the formation and growth of wormlike micelles in aqueous solutions of 2-hydroxyl-propanediyl-?,?-bis(dimethyldodecylammonium bromide)(12-3(OH)-12)were investigated by using steady-state and dynamic frequency-sweep rheological means.The manner and degree of interaction between the organic salts and 12-3(OH)-12 was verified by the surface tension method and the 1H-1H 2D NOESY.The results showed that three organic salts all interacted with 12-3(OH)-12 and promoted effectively the formation of wormlike micelles in 12-3(OH)-12 solution.The viscosities of the solutions are tremendously affected by the position of the hydroxyl group of the organic salts.Among them,o-ph-ONa was more likely to promote 12-3(OH)-12 molecules to form wormlike micelles,followed by m-ph-ONa.The effect of p-ph-ONa is the weakest.2.A series of novel carboxylate anionic Gemini surfactants SL-n-SL(n=3,6,10)were synthesized and their structures were confirmed by MS,1H NMR and IR.The surface active properties of SL-n-SL(n=3,6,10)were determined by Py fluorescence probe method and surface tension method at 25 °C.The cmc values of SL-n-SL(n=3,6,10)were 0.29 mmol·L-1,0.058 mmol·L-1 and 0.012 mmol·L-1,respectively,increasing with the increase of the spacer length.The ?cmc values were 31.96 m N?m-(16),36.18 mN?m-(16)and 36.27 mN?m-(16),respectively.SL-3-SL had the strongest ability to reduce the surface tension of water.The minimum cross-sectional area of the adsorbed molecules Amin were 0.295 nm2,0.347 nm2 and 0.569 nm2,respectively.This indicates that the surfactant with shorter spacer length has the smaller occupation area at the interface.3.The influence of the spacer length on the viscoelasticity in aqueous solution of 12-3(OH)-12 was studied using the carboxylate anionic Gemini surfactant SL-n-SL(n=3,6,10).The results showed that the 12-3(OH)-12/SL-n-SL systems showed the strongest viscoelasticity.The zero shear viscosity of the mixed solution reached the maximum(94.7 Pa?s)at ?=0.06(? is the molar ratio of SL-n-SL and 12-3(OH)-12).When the spacer length was increased to 6,the maximum zero shear viscosity(75 Pa?s)occured at ?=0.056.The maximum zero shear viscosity remained constant(74.9 Pa?s)when the spacer length was increased to 10.This indicated that the length of the spacer had an important effect on the formation and growth of micelles in the mixed surfactant systems.