Gaoyong Zhang

Phase Behavior of the APG/Alcohol/Alkane/H2O System

Abstract In this paper, the concentration scanning phase diagram and the fishlike phase diagrams for the quaternary system of alkyl polyglucoside (APG: C8G1.46 or C8/10G1.31)/alcohol/alkane/water mixtures have been studied. By a mass‐balance the mass fractions of APG and alcohol at the interface in the microemulsion (CS and CA) were obtained.The mixing fraction of alcohol at the interface (A S) was also determined by the HLB plane equation based on the geometrical relation of the three‐phase tie triangle in the composition tetrahedron. The net solubilizing power γE is larger for C8/10G1.31 than that for the C8G1.46 microemulsion system. The effect of alcohol on the three‐phase behavior and maximum solubilization was also investigated, which shows that alcohols with short chains have high solubilizing power.

Dynamic surface tension and adsorption mechanism of surfactant benzyltrimethylammonium bromide at the air/water interface

The air‐solution equilibrium tension, γc and dynamic surface tension, γt, of aqueous solutions of a novel ionic surfactant benzyltrimethylammonium bromide (BTAB) were measured by Wilhelmy method and Maximum bubble pressure method (MBPM), respectively. Adsorption equilibrium and mechanism of BTAB at the air‐solution interface were studied. The CMC was determined to be 0.11 mol/L. The results show that at the start, the adsorption process is controlled by a diffusion step. Toward the end, it changes to a mixed kinetic‐diffusion controlled mechanism with the adsorption activation energy of about 11.0 KJ/mol. Effects of temperature, inorganic salts, and alcohols on adsorption kinetics also are discussed.

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.

Adsorption Kinetics of Brij 97 at the Air/Solution Interface

Dynamic surface tension and surface adsorption kinetics at the air/aqueous solution interface of polyoxyethylene‐10‐oleyl ether (Brij®97, C18H35O(CH2CH2O)10H), for application in a drug delivery system, were investigated at different bulk surfactant concentrations and different temperatures. Apparent diffusion coefficients D a , activation barrier ϵ a , and the adsorption kinetic parameters n and t* were obtained from the extended Ward and Tordai approach and Rosens empirical model, respectively. It is shown that Brij 97 solutions follow a mixed diffusion‐activation adsorption mechanism. Results evaluated by the extended Ward and Tordai approach are consistent with those obtained from Rosens empirical model. With increase in bulk concentration from 0.125 to 12.5 CMC, ϵ a increases from 0.151 to 11.0 kJ/mol, and parameter n decreases from 1.57 to 0.711. Increase in temperature results in a decrease in activation barrier ϵ a . This indicates that the diffusion tendency decreases with increase of the interaction between surfactant molecules and the thermo‐motion of molecules favors surface adsorption.

Adsorption of Sulfonated Trioxyethylenated Alcohols at Air/Solution Interface

Abstract Surface properties and adsorption thermodynamics and kinetics at the air/aqueous solution interface of three homologous trioxyethylenated fatty alcohol sulfonates, C12H25(OC2H4)3SO3Na (C12E3S), C14H29(OC2H4)3SO3Na (C14E3S), and C16H33(OC2H4)3SO3Na (C16E3S), have been investigated. Effectiveness and efficiency of the adsorption increase with decreasing temperature. Addition of NaCl to the solutions results in a lower effectiveness and efficiency of the adsorption. Increases in the length of hydrophobic chain results in a higher adsorption efficiency, but has almost no effect on adsorption effectiveness. On the other hand, the adsorption kinetic parameters n and t* increase with increases in hydrophobicity of the surfactants and attractive interaction between the surfactant molecules. Apparent diffusion coefficients obtained from short‐time experimental data and from longer‐time experimental data are in good agreement for the systems investigated, indicating that the adsorption is a process controlled strictly by diffusion of surfactant molecules in the solution. Further more, with increasing length of hydrophobic chain by two –CH2–groups and in the order: C12 → C14 → C16, the change of free energy of adsorption (ΔG ad 0) has been calculated to be −3.1 kJ/mol (C12 → C14) and −2.8 kJ/mol (C14 → C16) per –CH2– group, respectively. The absolute changes are a little bit lesser than the usual value of 3.5 kJ/mol. This may be due to the relative difference of hydrophilicity/hydrophobicity of the polyoxyethylene unit. Finally, modeling of Πcmc has been done by quantitative structure–property relationship (QSPR) methods, and the calculated results are in good agreement with the experimental data.

Study on the Dynamic Surface Tension of Nonionic Surfactant LS45 and LS54 Solutions

The dynamic surface tension (DST) of nonionic surfactants Dodecyl Polyoxyethylene(4) Polyoxypropylene(5) Ether (C12H25O(EO)4(PO)5H, abbr LS45) and Dodecyl Polyoxyethylene(5) Polyoxypropylene(4) Ether (C12H25O(EO)5(PO)4H, abbr LS54), which are short chain polyether surfactants, was measured using the maximum bubble pressure method. The effects of concentration and temperature on DST were investigated systematically, and the parameters (n, t i , t*, t m , γ m , γ 0−γ m , R 1/2) derived from the DST curves were calculated, and the systematic change of the DST parameters with concentration and temperature is discussed. The parameters (p C 20(1S), Δp C 20, C 1s(i)* and C 1s (m)*) of LS54 at 1 second were also measured and the physical meanings of these parameters were analyzed.