The Influence Of Linker And Hydrophobic Group On The Performance Of Sulfate-based Gemini Surfactants

Gemini surfactants are ionic head groups with two amphiphilic molecules that are joined by chemical bonds via linking groups.Due to their unique structure,Gemini surfactants have a much higher surface activity than traditional single-chain surfactants,making them the current research hotspot.From the perspective of molecular design,a series of sulfate Gemini surfactants with different hydrophobic chains and spacer groups were synthesized and the relationship between structure and properties was studied.The main works and conclusions are as follows:A series of sulfate Gemini anionic surfactants were synthesized via etherification,ring-opening and sulfation reactions using epichlorohydrin,fatty alcohol,ethylene glycol and chlorosulfonic acid as the main raw materials;Orthogonal experiments for 1,8-bisalkoxymethylene-3,6-dioxin-1,8-octane disulfate(III1a)were performed on the sulfation reaction to determine the optimal reaction conditions.The structures of the intermediate and final products were characterized by FT-IR,1H-NMR methods.The thermogravimetric results showed that the sulfate Gemini surfactant had good heat resistance;Sulfate Gemini surfactants with a rigid spacer group(the thermal decomposition temperature was in the range of 140-170 ?)had better heat resistance than its with flexible spacer group(the thermal decomposition temperature was in the range of 200?230 ?).The Krafft point and surface properties of eighteen different surfactants with different spacer or hydrophobic groups were measured.The results showed that the eighteen surfactants had lower Krafft points and exhibited good water solubility;When spacer group was-(CH2)2-,with the increase of the carbon chain length from C12 to C14,the micellar concentration(CMC)and surface tension(?cmc)were gradually decreased from 8.23×10-4 mol/L to 7.12X10-4 mol/L and 27.5 mN/m to 26.9 mN/m,respectively;While the value of CMC and ycmc increased slightly when the carbon chain was C16.However,the value of CMC and ycmc are lower than that of the traditional anionic surfactant sodium dodecyl sulfate(SDS)by an order of magnitude and about 10 mN/m.When the spacer group was same,the value of CMC and ycmc decreased first,then increased with increasing the hydrophobic groups;When the hydrophobic groups were same,the value of CMC and ycmc increased first,then decreased with increasing the spacer group.The value of ycmc of the same hydrophobic carbon chain surfactant with a phenylene group(rigid)as a spacer was higher than other flexible spacers,however,The value of CMC of which was lower than other flexible spacers,and the value of ycmc of sulfate Gemini surfactants with a short,hydrophobic,and flexible spacer group(the number of carbon atoms was 2)was minimum.The results of the other surface activity parameters(pC20,?mat,and Amn,)showed that these surfactants had a strong adsorption on the gas-liquid interface and high efficiency in reducing surface tension.Campared to the the same carbon number of 6 flexible chains(III1c,III2c,and III3c),Surfactants(III1f,III2f,and III3f)with phenylene spacer groups had lower adsorption and higher Amin.In addition,emulsifiability was measured by means of recording the time of separating water in emulsion system.There was a corresponding relationship between HLB value and emulsification performance.The results showed that the smaller the HLB value,the better the lipophilicity and the emulsion stability and with the increase of the carbon chain length of the spacer and the hydrophobic group,the emulsifying ability was stronger.The emulsifying properties of the same hydrophobic chain surfactant spacer group as a rigid group were close to the emulsifying properties of the spacer group of-(CH2)6-,and the HLB values of the two were equal.In addition,the wetting time of the surfactant was measured by the method of the sedimentation of canvas.It was found that the wetting time showed a tendency of decreasing first and then increasing with the increase of the carbon chain length of the spacer.Due to the hydrophobic effect,the wetting time became longer with the length of the hydrophobic carbon chain increases.The wettability time of the surfactant with C12 of hydrophobic carbon chain and a spacer group of-(CH2)4-is 14 seconds,and the wetting property is better;The results of calcium soap dispersancy and calcium soap dispersion also indicated that the surfactant had a strong ability to disperse calcium soap.Compared to the traditional surfactant SDS,other surfactants had better wetting properties and calcium soap dispersing ability.The foam properties of the eighteen surfactants were tested by the Waring-Blender method,and the surfactant system with a hydrophobic carbon chain length of C12and C14 was determined to be stable at a concentration of 0.3 wt%to 0.4 Ywt%;When the hydrophobic carbon chain length was C16,there is no foam performance;when the hydrophobic carbon chain was C12 and C14,the foaming volume and the half-life of the solution gradually decrease with the increase of the number of methylene groups of the spacer group;With the hydrophobic carbon chain,the growth,foaming volume and half-life of the solution showed a decreasing trend;The III2a surfactant with C14 hydrophobic carbon chain and-(CH2)2-as the spacer group had the best foaming property and foam stability.Its foaming volume reached to 730 mL and its half-life was 300 s;essentially,the foam performance was influenced by the molecular arrangement at air/water interface.The mixture of III2a,and oleamide amidopropyl betaine(OAB)was selected to optimize the compounding ratio.Finally,0.2 wt%OAB and 0.4 wt%by weight of III2a,were determined to have the best foaming performance with a foaming volume of 800 mL and a half-life of 380 seconds.In this paper,the influence of temperature,rotating speed,and inorganic salt on the foam performance of the compounding system were studied.The results showed that on the condition of the temperature reached to 70 ? and the optimal rotation speed was 5000 rpm.The effect of the concentration of Ca2+ on the foaming performance was greater than that of Na+,and when the concentration of Na+ reached to 2.0×104mg/L,the foaming volume was 650 mL and the half-life was 191 s;when the the concentration of Ca2+ reached to 1.5×103 mg/L,the foaming volume was 600 mL and the half-life was 189 s;the foam performance of the compounded system showed better salt tolerance.This showed that anionic surfactants and amphoteric surfactants form internal salts,and then form a synergistic effect,which can increase the salt tolerance of the system.