Syntheses Of C02-swithable Surfactants And Their Regulation For Emulsion And Vesicle

Emulsions, which are liquid-liquid dispersion systems mainly stabilized by surfactants, are important in the fields of oil recovery, manufacturing, cleaning and others. Vesicles, which are spherical bilayers formed by the self-assembly of surfactants, are similar to the structure of cell membrane and widely studied in the field of life science. Switchable surfactants can reversibly possess or lose surface activity by changing the external environment. The use of these switchable surfactants may regulate the properties of emulsion or vesicle, consequently generate smart applicational effect. Among various switchable surfactants, CO2-switchable surfactant, which has the advantage of mild and efficient regulation, is a novel class of switchable surfactants and rarely reported at present. Therefore, it is of significance in theory and practice to do the research on how to regulate the emulsion or vesicles formed by CO2-switchable surfactants.In this dissertation, four N’-alkyl-N,N-dimethylacetamidines which have different carbon chains of decyl, dodecyl, tetradecyl and hexadecyl are synthesized. Then, the four N’-alkyl-N,N-dimethylacetamidines react with CO2to generate a kind of cationic surfactants, N’-alkyl-N’N-dimethylacetamidinium bicarbonates (DAB, DDAB, TDAB and HDAB). With the increase of carbon chains, the cmc and ycmc both decline and the surface activity enhances.7%(wt%) of DDAB aqueous solution can reversibly and repeatedly emulsify-demulsify water and alkane (dodecane or hexadecane) three times. In addition, DDAB shows a significant switchable performance on emulsification-demulsification to crude oil from Daqing No.2Factory.By dynamic light scattering (DLS) and transmission electron microscopy (TEM), it is shown that mixing DDAB and SDBS aqueous solution can spontaneously form vesicles at various concentration (1×10-3～1×10-2mol·L-1) and mole fraction (X1=0.1～0.9, not including X1=0.5). The radius of vesicle varies from50nm to120nm depending on the concentration and mole fraction. Due to the high pKa of DDAB, the radius of vesicle cannot be adjusted only by removal or addition of CO2. The pH increase by addition of NaOH solution can facilitate SDBS/DDAB vesicles expanding obviously in DAB-rich. The DDAB solution can also form vesicles at a suitable pH value (between11.2and11.8) by the addition of NaOH aqueous solution.Four2-alkyl-1-hydroxyethylimidazolines are synthesized by reaction of N-(2-hydroxyethyl)ethanediamine with dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids. Then the imidazoline compounds react with CO2to produce imidazolinium bicarbonates (UHIB, THIB, PHIB and HHIB). The cmc decreases with the increase of carbon chains.1%(wt%) of THIB aqueous solution can stabilize the emulsion of water/alkane (the alkane is octane, decane or dodecane, and volume ratio of water to alkane is1:1) more than one day.Vesicles are formed in0.01mol·L-1N-decylimidazole (NDI) aqueous solution at pH5.8～6.2by HCl/NaOH adjustment. The vesicle radius increases from73.8nm to100.8nm as the increase of pH from5.8to6.2. By CO2/Ar adjustment, the vesicles can be also formed in0.01mol·L-1N-decylimidazole aqueous solution at pH5.8～6.2; The vesicle radius is152.4nm with narrow distribution when pH is6.0. Compared with the HCl/NaOH adjusted NDI system, the CO2/Ar tuned NDI vesicles can be better repeated with stable vesicle size because of little change of salinity and concentration.