Study Of The Properties And Phase Behaviors Of Mixed Cationic-anionic Surfactants As Well As The Template Function In Mesoporous Material Synthesis

As one kind of the mixed surfactants,cationic-anionic surfactant has stronger synergies than single surfactant because of the cooperative formation mechanism.Searies of orderd structures including micelle,vesicle,and liquid crystal(LC)can be easily formed by adjust the molar ratio of cationic and anionic surfactant in aqueous solution.These specific aggregates have much application value in nanomaterial synthesis,bioactive compounds extraction and drug capsulation and releas e.Firstly,the phase behavior of aqueous solutions of mixed sodium dodecyle sulphate(SDS)and alkyl trimethyl ammonium bromide(CnTAB)with different carbon chain length(n=12-18)has been systematically investigated.It has been found that in the persudo diagrams of SDS/CnTAB/H2O mixed system,the liquid crystal phase with cationic surfactant in abcess(LCc)would move to the CnTAB solution apex with the increase of the chain length of cationic surfactant.It is probably because the discrepancy of SDS and CnTAB chain length caused the generation of vacancy or chain curve in the hydrophobic area of the aggregates,the only way to reduce the vacancy or curve is increasing the relative content of cationic surfactant.Fuether experience conpared the liquid crystal phase with anionic surfactant in abcess(LCa)in aqueous solutions of mixed CTAB and sodium alkyl sulfate with 12 and 18 carbon atoms.LCa phase moved to the SDS solution apex proved the speculation.Secondly,the effect of linear medium chain alcohols on phase behavior of SDS/CTAB/H2O mixed system has been explored in detail.The result demonstrated that the medium chain alcohols,especially the 1-hexanol can insert into the surfactant fence and weaken the electrostatic interaction between polar head group of surfactant,hence the phase area of LC can be remarkably expand as well as the precipitates were dissolved into vesicle.Thirdly,the effect of organic pore-enlarging agent(PEA)including 1-octane and mesitylene on the LC phase behavior of octadecyl sulfate sodium(SOS)/CTAB/H2O mixed system has been studied systematically.The result indicated that the PEA would successfully dissolved in the hydrophobic area of the LC and kept the lamellar structure unchanged when the concentrations of PEA was within certain limits.In addition,the lamellar structure was heat instability as the system temperature risen brings about the“cloud point”property with the presence of PEA.Finally,accroding to the result about the influence of 1-hexanol on the SDS/CTAB/H2O and PEA on the SOS/CTAB/H2O mixed systems,we investigaged the synthesis of mesoporous silica(MS)by using liquid crystal which were formed by SDS/CTAB/Hexanol/H2O and SOS/CTAB/PEA/H2O as template,respectively.In this part,the effet of SDS/CTAB ratio,reaction temperature and the concentration of PEA on the micro structure of mesoporous silica were systematically studied.The high specific surface area of MS indicated that 1-hexanol play a positive role in the synthetic process.However,the instability of the template with PEA in presence ad versed to the micro stucture ordered of MS.