Wei Xi-lian

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.

A Highly Viscoelastic Anionic Wormlike Micellar System

The rheological behavior of carboxylate gemini surfactant O,Oʹ-bis(sodium 2- tetradecylcarboxylate)-p-dibenzenediol (referred to as C14ϕ2C14) with a concentration of 140 mmol·L - 1 in aqueous solution in the presence of 100 mmol·L - 1

Effect of Sodium Salicylate on the Formation and Properties of Wormlike Micelles in Aqueous Cationic Gemini Surfactant Solutions

The effect of sodium salicylate (NaSal) on the formation and properties of wormlike micelles in aqueous solutions of 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3(OH)-12) and propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3-12) at a surfactant concentration of 50 mmol·L - 1 was investigated using steady-state and frequency sweep rheological measurements. In the absence of a salt, 12-3(OH)-12 or 12-3-12 only produced spherical or small rod-like micelles at 50 mmol· L - 1 . The addition of NaSal promoted micellar growth yielding wormlike micelles in both systems. 12-3 (OH)-12 showed a more sensitive response to the added NaSal compared with 12-3-12 and formed wormlike micelles at relatively lower salt concentrations. Moreover, the wormlike micelles formed by 12-3 (OH)-12 were longer than those formed by 12-3-12, resulting in higher viscosity for the former solution. These were attributed to the hydrogen bonding interactions between the hydroxyl substituted spacers in the 12-3(OH)-12 system, which increased hydration on the aggregate surface and stimulated the dissociation of counterions. The higher charge on the 12-3(OH)-12 micellar surface was strongly associated with Sal - , which led to a tighter packing of the surfactant molecules in the micelles and thus strengthened the intermolecular hydrogen bonding interactions and effectively reinforced the growth of the (Article)

Research on colored lyotropic liquid crystals

Splendidly colored lyotropic liquid crystals formed in the ternary system of a novel cationic surfactant, 3-p-nonylphenoxy-2-hydroxypropyl trimethyl ammonium bromide (NPTAB)-n-butanol-water system, had been observed under polarized light microscope. Small-angle X-ray scattering (SAXS), 2H (deuterium) quadrupolar splitting (2H NMR) were employed to confirm the structures of these liquid crystals. The structural transformation of these special lyotropic liquid crystals had been confirmed by differential scanning calorimetry (DSC). The influences of liquid crystal film thickness, temperature and conserving time on the color of liquid crystals have been investigated. It is also theoretically discussed for forming and changing of liquid crystal color.

Host-Guest Complexation of Cyclodextrin with a Series of New Kind of Surfactants

The association of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) with sodium polyoxyethylene dodecyl sulfonate (C12EnS, n=1, 3) was studied by means of isothermal titration calorimetry and 1H NMR measurements in aqueous solution at 298.15 K. The results indicated that the binding processes of β-CD with the surfactants were characterized by both enthalpy favorable and entropy favorable, while those of α-CD with the surfactants were mainly entropy driven. The stoichiometry of β-CD binding with the surfactants varied with numbers of oxyethyl groups in surfactant molecules, while that of α-CD binding with the surfactants made no difference. The 1H NMR spectra revealed that chemical shift data of all protons in α-CD and β-CD molecules moved to high field in the presence of C12EnS, which could be regarded as a microscopic evidence of the occurrence of inclusion interaction.

Study on Dynamic Interfacial Tension of 3‐Dodecyloxy‐2‐hydroxypropyl Trimethyl Ammonium Chloride at n‐Decane/Water Interface

Dynamic interfacial tension (DIT) and interface adsorption kinetics at the n‐decane/water interface of 3‐dodecyloxy‐2‐hydroxypropyl trimethyl ammonium chloride (R12TAC) were measured using spinning drop method. The effects of RnTAC concentration and temperature on DIT have been investigated, the reason of the change of DIT with time has been discussed. The effective diffusion coefficient, D a, and the adsorption barrier, ϵa, have been obtained with extended Word‐Tordai equation. The results show that the higher the concentration of surfactants is, and the smaller will be the DIT and the lower will be the curve of the DIT, and the R12TAC solutions follow a mixed diffusion‐activation adsorption mechanism in this investigation. With increase of concentration in bulk solution of R12TAC from 8×10−4 mol · dm−3 to 4×10−3 mol · dm−3, D a decreases from 2.02×10−10 m−2 · s−1 to 1.4×10−11 m−2 · s−1 and ϵ a increases from 2.60 kJ · mol−1 to 9.32 kJ · mol−1, while with increase of temperature from 30°C to 50°C, D a increases from 2.02×10−10 m−2 · s−1 to 5.86×10−10 m−2 · s−1 and εa decreases from 2.60 kJ · mol−1 to 0.73 kJ · mol−1. This indicates that the diffusion tendency becomes weak with increase strength of the interaction between surfactant molecules and that the thermo‐motion of molecules favors interface adsorption.

Solubilization and Transfer Free Energy of Some Organic Compounds from Bulk Aqueous Phase to Micelle of a New Type of Surfactant

A new type of surfactant, 3‐alkoxyl‐2‐hydroxylpropyltrimethyl ammonium bromide (CnH2n+1OCH2CH(OH)CH2N(CH3)3 +Br−, abbreviated as RnTAB, n=8, 12, 14, 16) was synthesized. The solubilization of n‐pentanol, n‐hexanol, n‐heptanol, benzyl alcohol, n‐hexane, benzene, toluene, heptane, and carbon tetrachloride in aqueous solutions of RnTAB, sodium dodecyl sulfonic(R12SO3Na), and in the mixed solution of R16TAB/R12SO3Na have been studied by the microtitration method. The experimental results show that the solubilized amounts of the organic compounds increase with the growing of the hydrocarbon chain of RnTAB, and the solubilizing ability of the binary system is lower for polar substances than for a mono‐surfactant aqueous solution. “V” isothermal curves of the solubilized amount of polar substances have been observed, and the minimum solubilized amount is at the molar ratio 1∶1 of R16TAB/R12SO3Na. However, the solubilizing ability of mixed surfactants for non polar substances is higher than that for a mono‐surfactant solution, the solubilizing isotherm curves present a “saddle” shape, and the maximum solubilized amount is at the molar ratio 1∶1 of R16TAB/R12SO3Na too. The length of hydrophobic chains of surfactant and the polarity of the organic compound affect the transfer free energy from aqueous to micelle phase. The longer the hydrophobic chain of RnTAB and the lower the polarity of the organic compound, the more easily will the compound transfer from aqueous phase to micelle phase.