Zhongni Wang

Ionic liquid crystals of quaternary ammonium salts with a 2-hydroxypropoxy insertion group

A 2-hydroxypropoxy group was inserted at the junction between the headgroup and the alkyl chain of quaternary ammonium salts. This group promotes a bent configuration for the alkyl chain relative to the ammonium headgroup, as compared to those without the 2-hydroxypropoxy group. At the same time, the insertion of this group weakens the N+–X− ionic interactions and hydrogen bonding interactions within the ionic layers and, therefore, allows the compounds to have a wide temperature range of mesophase. The molecular structures were determined by single crystal X-ray diffraction, in order to have a better understanding of the influence of the 2-hydroxypropoxy group on the packing arrangement and the mesomorphic properties. Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray powder diffraction and rheological measurements. Its important to note that anions have a profound effect on the phase properties of these liquid-crystalline compounds, such as phase transition temperatures, crystallisation rate, layer spacing and structural strength.

Phase behavior of new aqueous two-phase systems: 1-Butyl-3-methylimidazolium tetrafluoroborate + anionic surfactants + water

The aqueous mixtures of an anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) and an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim]BF4) within a certain range of compositions can spontaneously separate into two immiscible aqueous phases (ATPS): one surfactant-rich and the other ionic liquid-rich. The phase diagrams of the ternary system of the SDBS/[Bmim]BF4/water were drawn based on experimental data determined at 10.0, 20.0 and 30.0 °C, respectively. The borderlines of the different specific regions in the diagrams were determined using turbidity titration method. The narrow two-phase region aqueous were found to be close to the water - [Bmim]BF4 side. The formation conditions, compositions, and physicochemical properties of the aqueous two phases have been studied. The effects of temperature, surfactant and ionic liquid content on the phase separation time and phase volume ratio of the ATPS were also investigated. This phase separation phenomenon was found to be likely due to the existence of micelle aggregates with quite large size obtained by Transmission Electron Microscopy (TEM) and Steady-state Fluorescence Quenching Measurements (SFQM) methods.

Phase and rheological behavior of a gemini cationic surfactant aqueous system

The phase behavior of aqueous system of a gemini-type cationic surfactant, N,N′-dodecyl-2-hydroxyl-N,N,N′,N′-tetramethyl diammonium dichloride (simply written as 12-3(OH)-12(2Cl)), has been investigated by various complementary methods. A micellar solution region, a hexagonal liquid crystal phase region and two transition regions in the phase diagram are confirmed by SAXS and polarizing microscopy. Over the concentration range, 10–40 (wt%) of 12-3(OH)-12(2Cl), the viscoelastic properties of 12-3(OH)-12(2Cl) solutions at different temperatures have been determined using steady state and frequency sweep rheological measurements. The results from the FF-TEM study are in good agreement with the predictions from steady shear and dynamic rheology in which the large difference in the rheological behavior between 12-3(OH)-12(2Cl) and 12-3(OH)-12(2Br) at the same conditions might be mainly attributed to the role of the intermolecular hydrogen bonding which occurred between the hydroxyl substituted spacers and chloride counter ion and crystallization water molecule.

Curcumin-Encapsulated Hexagonal Liquid Crystalline Formed by Brij 97/NaDC Mixtures

The phase diagram of a five-components Brij 97-NaDC/IPM-PEG 400/H2O system was determined at 25°C. The hexagonal liquid crystalline phase (H1) was found in this system. By use of small-angle x-ray scattering (SAXS), polarization microscopy, and rheology techniques, the influence of composition, temperature, and addition of curcumin on H1 phase was studied. It is shown that: 1) the investigated hexagonal liquid crystals exhibit a strong shear thinning behavior and viscoelasticity and the strength of the network of H1 phase becomes weaker with increasing oil content; 2) the frequency-dependent moduli of H1 samples decreases as the temperature increases and the steady-state limiting viscosity of the hexagonal samples shows an Arrhenius-like dependence on temperature; and 3) samples in H1 phase containing curcumin retained their organized hexagonal structure. The SAXS results show that the curcumin molecules may be solubilized both into the apolar core of cylinders together with IPM and in the polar domain coexisting with PEG 400 between the cylinders. When curcumin is encapsulated in samples with low oil content, there is a significant decrease in the frequency-dependent moduli. The tendency of frequency behavior for samples incorporating curcumin as a function of temperature is weakened.

Phase Behavior and Rheological Properties of Concentrated Lecithin Aqueous Solutions with Additives

The phase behavior and rheological properties of the concentrated lecithin aqueous solutions were investigated at 37°C. When adding Isopropyl myristate (IPM) to lecithin solutions, besides an anisotropic liquid crystal (LC) phase, an isotropic liquid (L2) region and an isotropic viscous (I) phase are found. By continuously adding Brij 97, the LC region shifts towards higher water content and the L2 region is extended to the area of lower IPM concentration, meanwhile the I phase disappears. By analyzing the shear rate (ηγ=0.1) and yield stress (σ0), adding IPM to lecithin solutions increases the values of ηγ=0.1 and σ0, and after further adding Brij 97, the ηγ=0.1 and σ0 decrease dramatically. Notably, different from the lecithin/DDAB/water system studied by Youssry and Montalvo, in lecithin/Brij 97/IPM/H2O system, at the relatively higher water content area of the LC phase, the water content has little effect on the critical stress. It is also found that the change of dynamic storage modulus (G′) is similar with that of ηγ=0.1 and σ0 parameters when adding IPM and Brij 97. Maxwell model fitting results show that in the LC phase, the relaxation of the water molecule is prolonged by adding IPM and Brij 97 to lecithin solutions.

Lamellar Liquid Crystals Formed in Ternary DEP/Oil/Water Systems

Lamellar liquid crystals of the nonionic surfactant dodecyl polyoxyethylene (4) polyoxypropylene (5) ether (DEP) were investigated by means of phase diagram and rheological technique at 25°C in the presence of different solvents. The aqueous medium includes pure water, physiological saline and 20% sucrose solution, and the oil phase includes isopropyl myristate (IPM), oleic acid, and geraniol, which are all pharmaceutically accepted chemicals. The steady and dynamic rheological property analyses of the lamellar liquid crystals formed in DEP/H2O/IPM system indicate that the lamellar samples constructed by this special surfactant behave as pseudo-plastic fluid with relatively high elasticity and possess defects in their assembled structure. Also in this system, the elastic character gets decreased with increase in the water content. Furthermore, the comparison investigations show that the relatively high polar oil component increases the network strength of the lamellar phase, while increase in the polarity of water phase enhances the structure defects.

Studies in the phase behavior of the microemulsions formed by mixed cationic and nonionic surfactants

The middle-phase behavior for the systems of cetyltrimethylammonium bromide (CTAB)/poly-ethyleneglycol-9-monododecyl ether (AEO9)/alcohol/oil/brine and CTAB/octylphenolpolyoxyethylene-10-ether (Triton X-100)/alcohol/oil/brine have been studied with ɛ-β fishlike phase diagram method. The interfacial layer composition was determined, and some significant physicochemical parameters are derived from the hydrophilic-lipophilic balance plane equation. The effects of different alcohols, oils, temperature and inorganic salt (NaCl) on the middle-phase behavior of microemulsion formed by composite CTAB/AEO9 systems were also investigated systematically. The effects of different factors on the phase behavior of microemulsions formed by CTAB/AEO9 and CTAB/TX-100 systems were compared. The results suggest that the solubilization of CTAB/AEO9 microemulsion is higher than that of CTAB/TX-100 system under the same conditions.

Lyotropic Liquid Crystals Formed by Brij 97/PEO‐PPO‐PEO Mixtures

The phase diagrams of Brij 97/(PEO)m(PPO)n(PEO)m/water/IPM quaternary systems (A L‐64: m=13, n=30; A L‐62: m=7, n=32; A L‐61: m=3.5, n=31) were determined at 25°C. The liquid crystalline phases (lamellar Lαand hexagonal H1) were investigated by means of small angle x‐ray scattering (SAXS) and rheological techniques, with comparison of composition and component effects. The lamellar phases formed in Brij 97/A L‐64 and Brij 97/A L‐62 systems array more orderly than that of Brij 97/A L‐61 system, indicated by the stronger intensity of the second reflection peak in the SAXS patterns and the higher moduli (G′ and G″) in the dynamic rheograms. In Brij 97/A L‐64/water/IPM system, all Lα phases exhibit elastic rheograms, moreover the viscous property get increased with increase in water content. On the other hand, with this change, the H1 phases show Maxwell and gel‐like rheograms in order, in which the latter shows mechanical and relaxation spectra typical of highly structured materials.

Studies on Dynamic Surface Tension of an Outstanding Microemulsifier in Supercritical CO2 and Its Wetting Performance

Dodecyl polyoxyethylene(4) polyoxypropylene(5) ether (LS45) is an outstanding microemulsifier in supercritical CO2. The dynamic surface tension (DST) of this nonionic surfactant was investigated by using the maximum bubble pressure instrument. The effects of concentration and temperature on DST parameters (n, ti, t*, tm, and R1/2) and its adsorption mechanism were discussed by Rosens empirical equation and the asymptotic Ward and Tordai equation for the LS45 solution system. Finally, the parameters at 1 s related to Dravess wetting performance, pC20(1s), C1s (i)*, and C1s*, analyzed. The results showed that were with increase of bulk concentration and temperature, dynamic surface activity increased. Parameters at 1 s indicated that LS45 is of high surface activity and a very good wetting agent. One‐second related parameters, C1s (i)* and C1s*, are valuable in the treatment of practical applications of surfactants. Optimum wetting can be expected at the concentration of 4.8×10−4 mol/dm3 for LS45 solution.

Surface Properties and Solubility of Simvastatin in the Micelles of Polyglycerol Diisostearate Ethoxylates

A series of polyglycerol diisostearate ethoxylates with two hydrophobic chains were prepared by the reaction of polyglycerol diisostearate with ethylene oxide. Surface properties including water solubility, cloud temperature, critical micelle concentration, emulsification, and the solubilizing capacity of polyglycerol diisostearate ethoxylates for simvastatin were investigated in comparison with those of Tween‐80. The critical micelle concentrations of all polyglycerol diisostearate ethoxylates are less than 0.01 mmol l−1, which is one order of magnitude lower than that of Tween‐80. Polyglycerol diisostearate ethoxylates show better emulsification than Tween‐80. For enhancing the solubility of simvastatin in micelles, polyglycerol diisostearate ethoxylates also are superior to Tween‐80.