Equilibrium and Dynamic Surface Tension of Carboxymethylchitosan and Alkyl Trimethylammonium Bromide Mixtures

A water-soluble derivative of chitosan, carboxymethylchitosan (CMCH), was mixed with alkyltrimethylammoniumbromides (C_mTAB) and was studied on the adsorption at air/water interface using equilibrium and dynamic surface tension method. The effects of surfactant and polymer concentrations, surfactant chain length, as well as pH of solution were investigated. Addition of the surfactants remarkably promotes the polymer adsorption. Increasing any one of surfactant concentration, surfactant chain length, and pH will facilitate the adsorption of the mixture whereas little effects of polymer concentration were observed. The results are explained in terms of the interaction between CMCH and C_mTAB under different conditions.     

Dynamic Surface Elasticity of Polyelectrolyte/Surfactant Adsorption Films at the Air/Water Interface: Carboxylmethylchitosan and Cetyltrimethylammonium Bromide

The dynamic surface elasticity of the solution of carboxymethylchitosan (CMCH) and cetyltrimethylammonium bromide (C₁₆TAB) was measured as a function of the surfactant concentration and the surface age by the oscillating drop method. The results showed that the surface layer of the CMCH/C₁₆TAB solution transformed from loose to structured with the increase in the surfactant concentration. The surface elasticity versus the surface pressure curve during the adsorption showed different features at different surfactant concentration ranges, which was connected with the structural transformation of the surface layer. Our results show that the measurement of dynamic surface dilational properties is a powerful tool for studying the surface kinetics, which is helpful for dealing non-equilibrium systems in industry.     

Salinity Controlled Vesicle Formation and Growth in Aqueous Mixture of Aerosol OT/Triton X‐100

Mixed vesicles can be formed spontaneously from aqueous mixture of the double‐tailed anionic surfactant sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) and the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X‐100) under the inducement of salt, the formation mechanism of which should be attributed to the compression of salt on the electric bilayers of the head groups. The stability and the polydispersity of the vesicles are superior to single‐component AOT vesicles, which can be proved by the TEM image and visual observation. The vesicle region was presented in a pseudo‐ternary diagram of AOT/TX‐100/brine. The size of the vesicle was measured using dynamic light scattering. It is found that the vesicle size increases with the salinity but decreases with the content of TX‐100 in the mixture at the same salinity. Especially, the vesicle size is independent of the surfactant concentration at fixed salinity.     

Clouding and Hydrodynamic Behavior of Pluronic-Surfactant Interaction in Aqueous Salt Solutions

Clouding behavior of PEO-PPO-PEO and PPO-PEO-PPO block copolymers were studied in presence of sodium dodecyl sulfate (SDS) and NaCl. Extensive study of Pluronic P84 (EO₁₉PO₄₃EO₁₉) with different salts and ionic surfactants, were carried out using cloud point, viscosity and dynamic light scattering (DLS) measurements. The change in cloud point, as well as the size of P84 micelles in aqueous salt solution obeys the Hofmeister lyotropic series. Results on P84-ionic surfactant mixture indicate stronger interaction in case of SDS compared to those in presence of dodecyl trimethylammonium chloride (DTAC); here interaction seems to diminish in the presence of salts.     

Dispersed Structure of Ethanol‐Gasoline Fuel According to Dynamic Light Scattering Method

The dispersed structures of mixtures of five different gasolines with anhydrous ethanol were investigated by the dynamic light scattering (DLS) method. The aim of the work was to find whether these blends are colloid systems. Influence of different parameters was investigated to verify the results of this research. Ethanol‐gasoline blends were found to be colloid systems with the drop size of 20–150 nm.     

Rheological Properties of Model and Crude Oil Systems when Wax Precipitate under Quiescent and Flowing Conditions

Wax precipitation and deposition is a recurring challenge in transportation of crude oil, and increased knowledge about the behavior of such systems is necessary. Microscopy and differential scanning calorimetry were used to follow the crystallisation of wax for two model systems. The amount of solid was also determined by the latter method as well. The flow and viscoelastic behavior were investigated around the wax precipitation temperature, and the yield stress was determined both after dynamic and static cooling. Interpretation of the results was carried out in view of crystal growth and microstructure of the wax crystals. The variables that were studied were wax composition, amount of wax and thermal and shear history.     

Skin Constituents as Cosmetic Ingredients. Part II: A Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Dynamic Mode

This work aims at presenting the viscoelastic behavior of bio‐mimetic monoglycerides used as emulsifier in a mixture made of two non‐miscible liquids, squalene and water. The measurement of the interfacial tension, carried out by the “pendant drop” method in “dynamic” mode, made it possible to characterize these amphiphilic molecules according to the value of their elastic modulus, ?, as well as their relaxation time, τ_R.

The analysis of these parameters, as well as those developed in the previous publication [L. Blasco et al. (2006) Skin constituents as cosmetic ingredients. Part I: A Study of bio‐mimetic monoglyceride behavior at the squalene‐water interface by the “pendant drop” method in a static mode. J. Dispers. Sci. Technol., 27(6).] shows that the hydrocarbon chain structure, such as its length, the presence of one or more unsaturations, hydroxyl function, affects the behavior of surfactant molecules at the squalene/water interface.     

Solution Behavior of Poly(n-Isopropylacrylamide) in Water: Effect of Additives

The effect of different kinds of additives (electrolytes, nonelectrolytes, hydrotropes, and surfactants) on the cloud point (CP) of low molecular weight and narrow dispersed poly(n-isopropylacrylamide) (PNIPAM) synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization was examined. The CP showed a concentration dependent variation and it is greatly modified in the presence of additives. The size of the random polymer coil at 30°C obtained from dynamic light scattering (DLS) measurements is often influenced by the presence of additives. We have explained the effects of different additives on PNIPAM in terms of their interaction with polymer and resultant changes in the coil structure.     

人类谷胱甘肽硫转移酶家族等位基因蛋白B与抑制剂作用模型的理论研究

采用分子动力学模拟方法系统地研究了谷胱甘肽硫转移酶家族(Glutathione S-transferases,GSTs)的等位基因蛋白B(GSTP1*B)与抑制剂利尿酸(EA)以及EA的谷胱甘肽(GSH)共轭物EAG(I),EAG(O)的具体结合方式.抑制剂及其谷胱甘肽共轭物与蛋白的相互作用能计算结果及分子动力学轨迹的统计分析结果表明,GSTP1*B与EA的谷胱甘肽共轭物的结合能力优于其与EA的结合能力,Phe8,Arg13,Trp38和Tyr108是作用过程中的关键残基,对稳定抑制剂及其谷胱甘肽共轭物在GSTP1*B的G和H位点的构象具有重要的作用.通过对构象的统计分析发现,残基Phe8和Tyr108与GSTP1*B酶对抑制剂的选择性密切相关.     

Photoinduced phase transitions

Employing actinic light to alter/stabilise a particular thermodynamic phase via the photo-isomerisation of the constituent molecules is an interesting tool to investigate soft matter from a new dimension. This article focuses on our recent results on several aspects of these non-equilibrium phase transitions, which are isothermal in nature. We specifically discuss (i) the influence of different parameters, such as confinement, applied electric field, pressure etc., on the dynamics associated with both the photochemical transition driving the equilibrium nematic to the non-equilibrium isotropic phase and the thermal back relaxation recovering the nematic phase, (ii) unique light-driven disorder–order transition in a reentrant system, (iii) dynamic self-assembly of the smectic A phase, which is stabilised only in the presence of actinic light, (iv) novel temperature-intensity phase diagrams and an example of primary and secondary photo-ferroelectric effects in an antiferroelectric smectic C system. These results highlight the fact that the actinic light can be used as a new tool to study phase transitions and the associated critical phenomena that could also bring about effects that are not seen in equilibrium situations.