Li Ganzuo

A study of the microstructure of CTAB/1-butanol/octane/water system by PGSE-NMR, conductivity and cryo-TEM

Abstract A quaternary microemulsion system of a cationic surfactant (cetyltrimethylammonium bromide, CTAB), octane, water, and 1-butanol has been investigated using conductivity, pulsed field gradient spin-echo NMR measurements, and electron microscopy (Cryo-TEM and freeze fracture electron microscopy (FFEM)). The conductivity behavior has a distinct percolative phenomenon and a bell-shaped curve as a function of water contents. This indicates that the single-phase microemulsion is changed continuously from oil-in water structure via a bicontinuous structure to water-in oil structure. This result is consistent with those of the PGSE-NMR, Cryo-TEM, and FFEM. In the w/o region, the self-diffusion coefficient of water is relatively high (2–7×10−10 m2 s−1) due to the higher solubility of water in the continuous phase which consisted of octane(10 wt.%) and 1-butanol. The penetration of a large amount of octane molecules between surfactant chains results in the self-diffusion coefficient of octane being much lower (1–8×10−10 m2 s−1) in the w/o region.

Nonaqueous Lyotropic Liquid Crystals from Lecithin and Nonionic Surfactants

Abstract Lyotropic liquid crystals were prepared from mixtures of lecithin and nonionic surfactants with the general formula polyethylene glycol dodecyl ethers with no low molecular solvents being added. The repeat distance in the structure was reduced with increased amount of the nonionic surfactant showing complete penetration of the surfactants between the lecithin molecules.

Spontaneous vesicle formation in aqueous solution of zwitterionic and anionic surfactant mixture

Abstract Vesicles form spontaneously in the aqueous mixtures of dodecyl sulfonate betaine (DSB) and sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT (AOT)) at certain mixing ratios, which has been demonstrated by microcalorimeter, negative-staining transmission electronic microscopy (TEM) and quasi-elastic light scattering (QELS) methods. The addition of NaCl will expand the range of vesicle formation, and monodispersed vesicles are obtained in the solution from the salinity of 0.03 to 0.09 M at the mixing molar ratio of 7/3 (DSB/AOT, mol/mol), with the polydispersity of the system lower than 0.1. To learn more about the structural change in the mixture, ultrasonic was employed finally. Meanwhile analysis was made from the viewpoint of molecular geometry structure.

THE ALKALINE HYDROLYSIS OF ETHYL ACETATE AND ETHYL PROPIONATE IN SINGLE AND MIXED MICELLAR SOLUTIONS

ABSTRACT The effect of mixed micelles (polyethylene glycol-CTAB cationic surfactant, shortchain alcohol-SDS anionic surfactant) on the alkaline hydrolysis of normal aliphatic esters has been studied at 20 and 30°C with the method of difference of thermogram-area of thermokinetics in this paper. The results indicate that this reaction is inhibited by the single and mixed micelles. The mixed micelles of PEG and CTAB exhibit a greater effect of inhibition on the reaction than those do in single PEG or CTAB systems. The extent of inhibition for the reaction in the mixed micelles of SDS and alcohol is less than that in single SDS micellar solutions. The critical micellar concentrations of the corresponding systems have also been measured with the conductivity method in this paper.

THE EFFECT OF CATIONIC, ANIONIC, AND NONIONIC SURFACTANT MICELLES ON THE ALKALINE HYDROLYSIS OF ESTERS

ABSTRACT The alkaline hydrolysis of aromatic and normal aliphatic acid esters has been studied at 25°C in micellar solutions of surfactants (DTAB, TTAB, CTAB, SDS, Brij 35 and Triton X—100) with UV spectrophotometry and the method of thermokinetics in this paper. The rate constants of the alkaline hydrolysis of esters in micellar pseudophase, k1m and K2m have been calculated, respectively. The ratios of k2m to k2w or k1w to k1w indicate that the alkaline hydrolysis of esters arc inhibited by all of the surfactants investigated. It was supposed that such inhibition is mostly in relation to the micropolarity of micellar surface. The critical micellar concentrations of the corresponding systems have also been measured with the conductivity method and UV spectrophometry in this paper.

STUDIES ON THERMOKINETICS(XVI) THE KINETICS OF THE POLYMERIZATION OF ACRYLAMIDE IN MICELLAR SOLUTION

ABSTRACT The kinetics of the polymerization of acrylamide in aqueous solution and CTAB micellar solution initiated by sodium sulfite has been investigated with the theory and method of thermokinetics for n order reactions with equal concentration in this paper. The influence of initiator and CTAB concetrations on molecular weight of polyacrylamide has been discussed.The second—order rate constants of this reaction at 30 and 40°C in aqueous solution are 0. 112and 0. 0262dm3 mol-1s_1, respectively. The activation energy,based on measurements at these two temperatures,is 66. -4kJ mol-1. The ratio k2√n in CTAB micellar solution is smaller than that in aqueous solution. The rate of forming radical in micellar solution has been decreased.

Solubilization in Non-Aqueous Lyotropic Liquid Crystals

Abstract The solubilization of a hydrocarbon and two alcohols in a non-aqueous lamellar liquid crystal of lecithin and ethylene glycol was investigated determining the phase region of the liquid crystal and the geometrical dimension of the latter by low angle X-ray diffractometry. The results indicated the solubilized molecules to be located both in the polar solvent between the lecithin layers in the liquid crystal and between the individual molecules. The hydrocarbon was mainly localized between the hydrophobic end surfaces of the amphiphile and the methanol showed a balanced partition. The solubilization of long chain alcohols caused a reduction of the interlayer distance presumably due to enhanced penetration of the ethylene glycol after solubilization of the alcohol.

Studies on Lyotropic Liquid Crystal Formation in the Ternary Systems of a Type of New Cationic Surfactant/n‐Butanol/Water by 2H Quadrupolar Splitting and X‐Ray Diffraction

A new phenomenon, lyotropic liquid crystals appearing in different colors, has been observed under polarized light microscopy in the ternary systems of a cationic surfactant, 3‐alkoxy‐2‐hydroxypropyltrimethyl ammonium bromide/n‐butanol/water. Some florid multicolor photographs clearly showing texture structure of liquid crystal have been obtained using a polarizing‐light microscope. The structural transformation of these special lyotropic liquid crystals has been confirmed by differential scanning calorimeter (DSC). Small‐angle X‐ray scattering and 2H nuclear magnetic resonance (2H NMR) were employed to confirm the structure of these liquid crystals.

FLUORESCENCE PROBE STUDIES ON THE SECOND CRITICAL MICELLE CONCENTRATION OF SEVERAL KINDS OF SURFACTANTS

ABSTRACT The fluorescence intenstiy ratios (F2/F1) of excimer (F2) to monomer (F1) of probe (pyrene) were measured as a function of the concentration of the surfactant in several systems, which consist of sodium hexadecyl sulfonate (C16As)-anionic surfactant, cetyltrimethylammonium bromide (CTAB)-cationic surfactant and pentaoxyethylene decyl ether (C10E5)-nonionic surfactant. The second CMC values were obtained according to F2/F1 ~ surfactant concentration curve break. In addition, we also studied the variation of second CMC vs NaCl concentration. It was found that the second CMC values of C16A5 and CTAB decreased with the increase of NaCl concentration. But the present of NaCl had no influence on the second CMC value of C10E5. Results showed that sphere-shaped micelles turn into rod-like micelle at the second CMC. The results were interpreted in terms of diffusion of pyrene molecules and the distribution of pyrene among micelles.

STUDIES ON THERMOKINETICS(X IV) THE ALKALINE HYDROLYSIS OF ASPIRIN IN MICELIAR SOLUTION

ABSTRACT The alkaline hydrolysis of aspirin has been studied in CTAB micellar solution with the method of thermokinetics for the pseudo-first-order reactions in this paper. The second-order-rate constants of this reaction at 30 and 35°C in the absence of CTAB are 0. 0394 and 0. 0628 dm3 mol−1 s−1,respectively. The rates of this reaction in CTAB micellar solutions at 30 and Z5V have decreased as the increased of CTAB concentration at the considerable values of [OH−]- This reaction has been found to be inhibited by CTAB micelles.