Synthese And Properties Of Alkoxymethyl Choline Surfactants

Two kinds of choline-derived cationic surfactants, with different structure of hydrophobic chains, weresynthesized, which were tetradecyloxymethyl-(2-hydroxyethyl)-dimethyl ammonium salts (RX) andhexadecyl-(2-hydroxyethyl)-dimethylammonium salts (CnOX)(X=Cl, BF4, NO3; n=12,14,16). Theproperties of RX and CnOX have been herein conducted by the methods of conductometry, drop-volumemethod, fluorimetry, thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC),Ubbelohde viscometer methods and so on. The effect of three aspects—the structure of hydrophobic chain,different counter ion and the length of hydrophobic chain—on the properties of choline-derived quaternaryammonium surfactants was studied.The properties of tetradecyloxymethyl-(2-hydroxyethyl)-dimethyl ammonium chloride (RCl) andhexadecyl-(2-hydroxyethyl)-dimethylammonium chloride (C14OCl) were studied. They have the equallength of carbon chain, the same counter ion but the different structure of hydrophobic chain. As theintroduction of the polar group-O-, the CMC value of C14OCl is larger than that of RCl, higher ability toreduce surface tension, but reduces the efficiency of the surface tension. At the same time, such structuremakes C14OCl have the poor thermal stability, the lower melting point and the smaller aggregation number.Counter ion can be adjusted to the balance of the repulsive force between the cations and theattraction between the alkyl chain and the cation which promote the aggregation of the surfactant. Theeffect of different counter-ions on the nature of the surfactant is different. In this work, the affect of threekinds of counter ions, which were Cl, BF4and NO3, on the properties of RX and C14OX (X=Cl, BF4, NO3)was explored. The larger hydraulic radius of counter ion (Cl-<NO-3<BF-4), the smaller CMC values of RXand C14OX, the more easily micelles formed, the more efficiently surface tension reduced. In addition tothe hydraulic radius of counterions, the structure and polarity of the counter ions can also influence thenature of the surfactants. The structure and polarity of NO-3makes the aggregation number of C14ONO3larger than that of C14OCl and C14OBF4, but the order of the micellar aggregation number of RX followedbelow: RCl> RNO3> RBF4. Secondly, the larger hydraulic radius of counter ion, the greater the volume ofcounter ion, the more difficult the counter ion binded to the micelle surface, the larger the degree ofionization of the micelle α, the more negative the standard free energy of adsorption and aggregation of surfactants. And the negative of the standard free energy of adsorption and aggregation indicated that theprocesses—the formed process of micelle and the adsorption process at the interface—were spontaneous.The value of the the standard free energy of aggregation ΔG0micwas larger than the value of the standardfree energy of adsorption ΔG0ads, which illustrates that the process of aggregation more happened than theprocess of adsorption. In addition, the morphology of the liquid crystal at concentrated concentration wasobtained by the polarization experiments POM. RX and C14OX (X=Cl, BF4, NO3) can form a variety ofliquid crystal pattern-cross pattern, fan-shaped pattern, the pattern of oil-like pattern and granite, and theliquid crystal texture types formed by RCl and C14OCl were most. SAXS verify the results of POM.In this work, the relatively long quaternary ammonium cationic surfactants CnOBF4(n=12,14,16)were studied. With the growth of the carbon chain, the CMC values of CnOBF4decreases, the more formmicelles, the more effectively the surface tension reduced, the degree of ionization decreases, the morenegative ΔG0mic. Meanwhile, the higher the temperature, the more difficult to form micelles, the largerCMC value, the larger α, the more negative ΔG0mic. But the thermal stability of CnOBF4was less effectedby the length of the carbon chain. Growth of carbon chain length, so that the driving force of micelleformation CnOBF4changed. As the value of TΔS0micof C14OBF4and C12OBF4was larger than that of ΔH0mic,the formed process of their micelles was an entropy-driven process, but the formed process of C16OBF4micelles was an enthalpy-driven process because that the value of TΔS0micwas smaller than that of ΔH0mic.In addition, at higher concentrations CnOBF4solution, C12OBF4and C14OBF4appeared viscous illiquidphenomenon, but C16OBF4precipitation in aqueous solution. The solubility C16OBF4changed withtemperature was measured by Krafft point. The Krafft point of C16OBF4is30℃and only above thistemperature C16OBF4can fully play its surface activity. The plots of reduced viscosity vs the massconcentration speculated that C12OBF4and C14OBF4can form different structure micelles under differentmass concentration. TEM and Cryo-TEM respectively demonstrated the presence of mesh and wormlikeaggregates at high concentrations of C12OBF4and C14OBF4.