Study on the oscillating phenomena of electrical potential across a liquid membrane

The electrical oscillations across a liquid membrane in water/oil/water system was studied with octanol as oil phase by introducing two opposite charged surfactants in oil and aqueous phase, respectively. The sustained and rhythmic oscillation was observed. To a certain extent, the features of the oscillation (e.g. induction time, frequency, life time and orientation of the pulse pikes) strongly depend on the property of surfactant, dissolved in octanol. The mechanism may be explained by the formation and destruction of dual-ion surfactant membrane accompanying with emulsification at the interface and considering the coupling effect of diffusion and associated reaction in the vicinity of the interface.     

Studies on Middle-Phase Microemulsions of Green Surfactant n-Dodecyl Polyglucoside C12G1.46

The three-phases behavior in the quaternary stsem of n-dodecyl polyglucoside C12G1.46/1-butanol/cyclohexane/water has been studied at 40℃ in terms of the variables γ and δ.Increasing δ at constant γcauses a phase inversion from an oil-in-water microemulsion in contact with excess oil(winsor I or 2) to a water-in-oil microemulsion in contact with excess water (winsor Ⅱor 2)via a middle-phase microemulsion in contact with excess oil and water(winsor Ⅲor 3).By taking into account the different solubilities of alkyl polyglucoside and 1-butanol in the oil phase,the composition of the hydrophile-lipophile balanced interfacial film in the middle of the three-phase body can be calculated.The effects of different oils and aqueous media on the phase behavior and on the composition of the interfacial film and the efficiency for alkyl polyglucoside to make equal weights of water and oil to a single phase were investigated.It was found that the oil molecules with small molecular volumes can improve the solubilizing efficiency of the surfactant to form single-phase microemulsion.In inorganic salt(NaCl) and acid(HCl) solutions,less 1-butanol is needed than that in alkali(NaOH) solution to form middle-phase microemulsion.     

青霉素G钾盐对SDS水溶液物理化学性质的影响及其在SDS/n-C5H11OH/H2O体系中的释放

The effects of penicillin potassium salt （PenK） on the solubility, Krafft temperature TK, critical micelle concentration CMC of SDS micelle and the phase behavior of SDS/n-C5H11OH/H2O system were studied. The partial phase diagrams of SDS/PenK/H2O system at different temperatures were determined. The release amounts of PenK in SDS/n-C5H11OH/H2O system and the distribution coefficient of PenK between micelle and water were measured by UV-Vis spectroscopy. The results show that in the presence of PenK, the CMC of SDS was decreased while the TK of SDS was increased and the solubility of SDS in both water and SDS/n-C5H11OH/H2O oil in water （O/W） microemulsion was decreased, but increased in water in oil （W/O） microemulsion. SDS micelles and SDS/n- C5H11OH/H20 O/W microemulsion could accelerate the release rate of PenK. The addition of SDS and water could both increase the release rate of PenK, whereas the presence of n-C5H11OH reduced the release rate of PenK. The above results were related to the electrostatic repulsion between PenK and SDS.     

Dielectric Behavior of Middle Phase Microemulsion

l ntroductionMicroemulsiolls are transparent and nuid systems composed of water, oil andamphiphilic molecules. They form spontaneously with simple mixing. Microemulsionsmay be water- or oil- continuous and bicontinuous under some conditions of temperatureor composition. Middle phase microemulsions(MPME) is called the 'bicontinuousstate' which is considered to be a sponge-like random netWork. Owing to its ultralowinterfacial tellsiolls against the excess water and oil phase with which they ar…     

Location of ethanol in sodium dodecyl sulfate aggregates

The hexagonal liquid crystalline phase of SDS (Sodium dode-cyl sulfate)/H2O system changes into lamellar liquid crystal and the effective length of surfactant molecule d0/2 in the lamellar liquid crystal decreases with the addition of ethanol. The micellar aggregation number N of SDS decreases and the micellar diffusion coefficient increases with the added ethanol. Under a constant concentration of SDS, the molecule number ratio of ethanol to SDS in the micelle increases with the concentration of ethanol and even exceeds 10 when ethanol concentration is 1. 085 mol/L. All these results show that ethanol, even though a short chain alcohol and soluble in water, can partly exist in the interphase of the amphiphilic aggregates showing some properties of co-surfactant.     

The Catalysis of Sodium Dodecyl Sulfate／1-Pentanol／Water W／O Microemulsion on the Photoisomerization of trans-Stilbene

The photoisomerization of trans-stilbene was studied in the water in oil (W/O) microemulsion formed by SDS (sodium dodeeyl sulfate), n-C5H11OH (1-pentanol) and H2O. The experimental results show that after 2-minute UV-irradiation, the yield of cis-stilbene is higher in W/O mieroemulsion than in homogeneous solvent-n-C5H11OH.     

Molecular dynamics simulation for surface melting and self-preservation effect of methane hydrate

The surface melting process of structure sI methane hydrate is simulated at T = 240, 260, 280, and 300 K using NVT molecular dynamics method. The simulation results show that a quasi-liquid layer will be formed during the melting process. The density distribution, translation, orientation, and dynamic properties of water molecules in the quasi-liquid layer are calculated as a function of the distance normal to the interface, which indicates the performance of quasi-liquid layer exhibits a continuous change from crystal-like to liquid-like. The quasi-liquid layer plays as a resistance of mass transfer restraining the diffusion of water and methane molecules during the melting process. The resistance of quasi-liquid layer will restrain methane molecules diffuse from hydrate phase to gas phase and slow the melting process, which can be considered as a possible mechanism of self-preservation effect. The performance of quasi-liquid layer is more crystal-like when the temperature is lower than the melt- ing-point of water, which will exhibit an obvious self-preservation. The self-preservation will weaken while the temperature is higher than the melting-point of water because of the liquid-like performance of the quasi-liquid layer.     

SOME ASPECTS OF MORPHOLOGIES AND INTERFACES IN COPOLYMER/HOMOPOLYMER BLENDS

Based on a series of morphological studies of blends of homopolymer (Homo) and a variety of block and graft copolymers (Cop), the nature of phase separation, interface, emulsification and inner morphology of copolymer-dispersed phase etc. in the blends are discussed. In the cases of Cop AB/Homo A/Homo B systems, in which one homopolymer forms matrix, it is observed that the dispersed homopolymer phase is exclusively associated with Cop AB, i.e. no Homo A-Homo B interface exists. This phenomenon is believed to be caused by minimizing the interfacial energy of the systems. Meanwhile, preferential solubilization or anchoring of the like chains of copolymer into homopolymer matrix leads to stabilization of the dispersed phase in the matrix. In addition, regular variation of the inner morphology of the dispersed copolymer phase with the composition and molecular parameters of the component polymers is observed. When the two components have comparable proportions, alternating concentric shells are the most common feature which is associated with minimizing the interfacial energy in the Cop/Homo systems.     

Phase behavior and structure analysis of the middle mixed layer for ASP flooding system at low surfactant concentration

The phase behavior and interfacial tension of alkali/surfactant/polymer (ASP) flooding system and simulative crude oil were investigated, and the size distribution and structure analysis of the middle mixed layer (MML) were also studied by size analyzer and freeze-fracture TEM. It was found that there were some rules between the volume of MML and the concentration of each component, and the interfacial tension between MML and the oil phase or water phase could reach an ultra-low value. Especially, the freeze-fracture TEM micrographs of MML were firstly obtained, and the new viewpoint was put forward that there coexist the structures of micelle, microemulsions and emulsions in MML and the structure of microemulsion is dominant. This would make an important effect on the research of surfactant theory and ASP flooding mechanism.     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) intensity of PA6/PS/(SMA-CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient(NTC) effect was eliminated.The electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

A novel method to quantify the amount of surfactant at the oil/water interface and to determine total interfacial area of emulsions

We present a methodology to quantitatively determine the fraction of sodium dodecyl sulfate (SDS) that partitions to the oil/water interface in oil-in-water macroemulsions and calculate the total interfacial area (TIA) through the novel use of filtration through nanoporous membranes. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS (as monomers and micelles) that is in the bulk water phase (i.e., not at the interface) could pass through. The concentration of SDS in the filtrate was determined and used to calculate the TIA for each system. The mean droplet diameter of the emulsions was measured by light scattering. We analyzed the effects of total SDS concentration and oil chain length on the amount of SDS that partitions to the interface, the TIA, and the droplet diameter. The results showed that partitioning of SDS to the oil/water interface increases with increasing total SDS concentration in emulsion systems (i.e., the more SDS we add to the bulk solution, the more SDS partitions to the oil/water interface). However, the surface-to-bulk partition coefficient (i.e., the SDS concentration at the interface divided by the SDS concentration in the aqueous phase) remains the same over the entire concentration range (8-200 mM). The results showed a chain-length compatibility effect in that the minimum amount of SDS partitioned to the interface for C(12) oil. The droplet size measurements revealed a maximum size of droplets for C(12) oil. Penetration of oil molecules into SDS film at the interface has been proposed to account for the maximum droplet size and minimum partitioning of SDS at the oil/water interface for C(12) oil+SDS emulsion system. The TIA, as determined from our ultrafiltration method, was consistently two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.     

Effect of long-chain alcohols on SDS partitioning to the oil/water interface of emulsions and on droplet size

The effect of long-chain alcohols (C(n)OH for n=8, 10, 12, 14, 16, 18) on the partitioning of sodium dodecyl sulfate (SDS) to the oil/water interface in oil-in-water macroemulsions was investigated and related to emulsion droplet size and total interfacial area (TIA) contributed by SDS. Alcohols were solubilized in hexadecane and emulsified in SDS solutions. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS that is in the bulk water phase as monomers or micelles (i.e., not at the interface) could pass through. The results showed a chain-length compatibility effect; the maximum amount of SDS partitioned to the interface when dodecanol (C(12)OH) was added to the oil. The results also showed that partitioning of SDS is affected only when dodecanol is added. All other alcohols had no significant influence on SDS partitioning to the oil/water interface. Droplet size measurements revealed a minimum in droplet size for emulsions with added C(12)OH. In order to explain the results, it was proposed that the penetration of alcohol molecules into the interfacial film occur at the interface, resulting in more cohesive molecular packing at the interface, and the minimum droplet size and maximum partitioning of SDS at the oil/water interface for C(12)OH/SDS emulsion system. The TIA provided by the SDS molecules, as determined from our ultrafiltration method, was two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.     

A Visible Spectroscopic Study of Microstructure of O/W Microemulsions of Anionic Surfactants: Effect of Cosurfactant

The microstructure of o/w microemulsions, stabilized by sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) with different cosurfactants, has been studied by partitioning of a dye, phenol red, between the oil‐water interface and bulk water. The cosurfactants used are propan‐1‐ol, propan‐2‐ol, butan‐1‐ol, butan‐2‐ol, pentane‐1‐ol, pentane‐2‐ol, and pentan‐3‐ol. The effects of changing the oil volume fraction and surfactant‐cosurfactant w/w ratio on the oil‐water interface and droplet size have also been discussed. Larger droplet size was predicted for SDS than SDBS. The predicted droplet radius increased with increase in the oil fraction, decrease in the surfactant concentration, increase in the C‐number of the linear cosurfactant, and decrease in branching of the cosurfactant. Surfactant‐cosurfactant ratio and pH did not affect the droplet size significantly. The minimum concentrations of surfactants with which microemulsions were formed were found to be higher for larger oil fraction, smaller C‐number of the alcohol, more branching of the alcohol, and higher pH.     

Partition and water/oil adsorption of some surfactants

Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a series of three tetraalkylammonium dodecylsulfate (TEADS, TPADS, and TBADS) in water/CH 2Cl 2. Interfacial tension measurements performed at the water/air and water/oil interfaces provided all the necessary information for the determination of the adsorption parameters by taking partition into account. These measurements also allowed the comparison of the adsorption properties at both interfaces which showed an increase of the adsorption equilibrium constant and a decrease of the maximum surface concentration at the water/oil interface compared to water/air. The values of the critical aggregation concentration showed, in all cases, that only the surfactant dissolved in the aqueous phase contribute to the decrease of the water/oil interfacial tension. In the case of the four ionic surfactants, the critical aggregation concentration obtained in biphasic conditions were lowered because of the formation of mixed surfactant-CH 2Cl 2 aggregates.     

Fluorescence Quenching of Anthracene by N,N-Diethylaniline in the Sodium Dodecyl Sulfate/Benzyl Alcohol/Water System

Photoinduced electron-transfer reaction of anthracene with N,N-diethylaniline (DEA) was studied in the SDS (sodium dodecyl sulfate)/BA (benzyl alcohol)/H₂O system. In an oil/water microemulsion, only the excited anthracene located at the interface can be quenched by DEA. In a water/oil microemulsion, this quenching reaction occurs in the BA continuous phase. Besides being the quencher of the excited anthracene, DEA could also change the system's structure.     

Adsorption kinetics of some carotenoids at the oil/water interface

The kinetic analysis of the adsorption of two carotenoids (i.e., ethyl ester of β-apo-8′-carotenoic acid and β-carotene, all trans-isomers) from n-hexane solutions at the oil/water interface is presented for several carotenoid concentrations in the oil phase. A new kinetic approach is developed and it addresses the diffusion adsorption associated with a reversible interfacial reaction, which describes the reorientation of surfactant molecules between two conformations. This approach leads to a general analytical expression that contains four physical parameters and describes with high accuracy the experimental dynamic interfacial tensions for the two carotenoids, which independently adsorb from n-hexane phase to the n-hexane/water interface. The calculations give the characteristic times for the carotenoid adsorption at the oil/water interface in terms of diffusion relaxation and kinetic relaxation times. The results explain the long time effects on the adsorption of these carotenoids at the oil/water interface. The data are in substantial agreement with the molecular structure of these carotenoids and with the earlier data recorded for cholesterol adsorption at the n-heptane/water interface. Based on these findings, we propose a molecular mechanism for the interfacial transformation of carotenoid molecules at a hydrophobic/hydrophilic interface.     

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (～2.0?×?10^?3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50?=?25.04?µm) and was well emulsified with crude oil after the mechanical oscillation (D50?=?4.27?µm).     

Self-aggregation of the SDS surfactant at a solid-liquid interface

Molecular dynamics simulations of sodium dodecyl sulfate (SDS) molecules on a graphite surface are presented. The simulations were conducted at low and high surface coverage to study aggregation at the water/graphite interface. Results showed that at low surface coverage, the SDS molecules form hemicylindrical aggregates, in agreement with AFM experiments, whereas at high surface coverage, the surfactants form full cylinders. The latter aggregates have not been reported in systems of SDS on hydrophobic substrates, such as graphite. The unexpected results are explained in terms of a water layer adsorbed at the solid surface which was the responsible for the formation of these aggregates. Moreover, the SDS tails in the full cylindrical configuration became straighter than those of the hemicylindrical aggregate. Hydrogen bond formation between water and surfactant head groups was also studied, and it was found that they did not depend on the surfactant concentration.     

Electrically driven motion of an air bubble on hemispherical oil/water interface by three-phase boundary reactions

Our electrochemical cell consisted of a ferrocene-included hemispherical nitrobenzene (NB) droplet on the glassy carbon (GC) electrode which was immersed in the aqueous solution including sodium sulfate and sodium dodecyl sulfate (SDS). When an air bubble was injected near the boundary between the oil and the aqueous phase, it stayed at the top of the hemisphere on the boundary so that the lower half of the bubble was put in oil and the other half was in water. From the force balance of surface tension and buoyancy of the bubble, the bubble took an energetic minimum at the interface. It sank into the oil phase when ferrocene in the oil was electrochemically oxidized through the GC electrode by the three-phase boundary reaction. The electrochemical reduction caused the bubble to move back toward the aqueous phase. The motion of the bubble was synchronized with the redox reaction of ferrocene. The potential step oxidation showed such a rapid response that the motion could not be attributed to diffusion of ferricenium ion from the three-phase boundary to the bubble. Our idea of explaining the rapidity was the translational motion of the SDS layer along the boundary, which was driven by the difference in the surface concentration of SDS caused by the electrochemical generation of the ferricenium ion. The motion of the SDS layer was demonstrated by the shrinkage of the oil layer spread on the water surface when SDS solution was dropped on the oil layer. The spreading velocity was close to the velocity of propagating the oxidation of ferrocene to the bubble.     

Analytical investigation of the self-desorption of the oligomers of mixtures of a polydisperse ethoxylated surfactant with sodium dodecylsulfate from a silica/water interface

The adsorption isotherms onto a hydrophilic silica of mixtures of sodium dodecylsulfate (SDS) and of all the oligomers of a polydisperse nonylethylene glycol n-dodecyl ether (C(12)E(9)) surfactant were determined using a high-performance liquid chromatography (HPLC) technique. Incorporation of the anionic surfactant to the negatively charged silica surface is favored by the adsorption of the nonionic surfactant. Comparison between the adsorption isotherms of mixtures of SDS with a monodisperse C(12)E(9) and a polydisperse C(12)E(9) shows that the adsorption of SDS at the silica/water interface is stronger with the latter material than with the former in a large surface coverage domain. The composition of the surface aggregates and the variation of the oligomer distribution in these aggregates were determined. The previously described phenomena called self-desorption which was observed for the global C(12)E(9) and SDS surfactant mixtures was confirmed: increasing the total concentration at a fixed surfactant ratio induces at high concentration a desorption of the anionic surfactant and all of the less polar oligomers from the solid/water interface. An interpretation scheme is proposed which assumes that the interaction of SDS is larger with the less polar oligomers than with the polar ones. The self-desorption effect could then be considered as the consequence of the polydispersity of the nonionic surfactant and to the net repulsion interaction between SDS and the silica surface as the mole fraction of SDS in the surfactant mixture increases.