Solutions Of Zwitterionic Surfactants Research Articles

Synergisms between Surfactants, Polymers, and Alcohols to Improve the Foamability of Mixed Systems

In order to produce detergents with improved performance and good market acceptability, it is crucial to develop formulations with improved foamability and cleaning performance. The use of a delicate balance of surfactants and additives is an appealing strategy to obtain good results and enables a reduction in the amount of chemicals used in formulations. Mixtures of hydrophobically modified linear polymers and surfactants, as well as balanced mixtures with co-surfactants and/or hydrotropes, are the most effective parameters to control foamability and foam stability. In the present study, the effect of the addition of hydrophobically modified linear polymers, nonionic co-surfactants and hydrotropes, and their mixtures to anionic and zwitterionic surfactant aqueous solutions was evaluated. It was found that the presence of the hydrophobically modified polymer (HM-P) prevented the bubbles from bursting, resulting in better stability of the foam formed using zwitterionic surfactant solutions. Also, the surfactant packing was inferred to be relevant to obtaining foamability. Mixtures of surfactants, in the presence of a co-surfactant or hydrotrope led, tendentially, to an increase in the critical packing parameter (CPP), resulting in higher foam volumes and lower surface tension for most of the studied systems. Additionally, it was observed that the good cleaning efficiency of the developed surfactant formulations obtained a higher level of fat solubilization compared to a widely used brand of commercial dishwashing detergent.

Promote or inhibit turbulence drag reduction behavior of surfactant solutions with different micelle structures by certain nanoparticle addition

The micelle structure of surfactant is easy to be destroyed in the flow process resulting in a decrease in its drag reduction (DR) efficiency; therefore, how to strengthen the stability of the micelle structure during the flow process and thus improve the drag reduction efficiency deserves intensive research. In this work, by comparing a variety of nanoparticles, hydrophobic silica nanoparticles were selected as the best additive to enhance the turbulence drag reduction efficiency of surfactant solution with spherical micelle structure. The experimental results also demonstrated that the hydrophobic silica nanoparticles had a reinforcing effect on anionic, cationic, nonionic, and zwitterionic surfactant solutions with the same concentration (dominated by spherical micelles), and the optimal nanoparticle addition concentration and maximum drag reduction rate were obtained. Meanwhile, the effect of silica nanoparticles on the turbulence drag reduction efficiency of surfactant solutions with different micelle structures was evaluated by inducing the surfactant micelle structure change. It was shown that the hydrophobic silica nanoparticles had a strengthening effect on the turbulence drag reduction performance of surfactant solutions with spherical micelle structure, while they had an inhibiting effect on the turbulence drag reduction performance of surfactant solutions with worm-like micelle structure. The change in solution viscoelasticity indicated that the decrease in viscoelasticity was the main reason for the decrease in drag reduction efficiency of surfactant solution with worm-like micelle structure when silica nanoparticles were added. A mechanism for the interaction of hydrophilic/hydrophobic silica nanoparticles with spherical micelles and wormlike micelle structures was finally discussed and proposed.

Analytical modeling of micelle growth. 5. Molecular thermodynamics of micelles from zwitterionic surfactants

HypothesisThe critical micelle concentration, aggregation number, shape and length of spherocylindrical micelles in solutions of zwitterionic surfactants can be predicted by knowing the molecular parameters and surfactant concentrations. This can be achieved by upgrading the quantitative molecular thermodynamic model with expressions for the electrostatic interaction energy between the zwitterionic dipoles and micellar hydrophobic cores of spherical and cylindrical shapes. TheoryThe correct prediction of the mean micellar aggregation numbers requires precise calculations of the free energy per molecule in the micelles. New analytical expressions for the dipole electrostatic interaction energy are derived based on the exact solutions of the electrostatic problem for a single charge close to a boundary of spherical and cylindrical dielectric media. The obtained general theory is valid for arbitrary ratios between dielectric constants, radii of spheres and cylinders, positions, and orientations of dipoles. FindingsThe detailed numerical results show quantitatively the effects of the micelle curvature and dielectric properties of the continuum media on the decrease of the dipole electrostatic interaction energy. Excellent agreement was achieved between the theoretical predictions and experimental data for the critical micelle concentration, size and aggregation number of zwitterionic surfactant micelles. This study can be extended to mixed micelles of zwitterionic and ionic surfactants in the presence of salt to interpret and predict the synergistic effect on the rheology of solutions.

Coarsening reduction strategies to stabilize CO2-foam formed with a zwitterionic surfactant in porous media

Micromodel experiments at high-pressure high-temperature conditions were performed to evaluate the impact of different coarsening reduction strategies on CO2-foams stabilized with a zwitterionic surfactant, using silica nanoparticles in small concentration and mixing CO2 with a less water-soluble gas (nitrogen). The CO2-foam stabilized only by the surfactant showed poor behavior in the porous media, while an improvement in both foam texture (bubble density at the inlet of the micromodel) and gas trapping was qualitatively seen in the experiments using a nanofluid containing silica nanoparticles. The strong adsorption of the nanoparticles at the gas-water interface allowed to reduce the coarsening mechanism, reaching a minimum pressure gradient for strong foam generation throughout the micromodel chip. The use of a small concentration of nanoparticles in combination with the zwitterionic surfactant proved to be effective in reducing gas mobility without significant increase in pressure drop, which could be used as a strategy to control the mobility of injected CO2 in high permeability porous media, with reduced loss of injectivity. Coarsening was also reduced by using a mixture of CO2 and N2 as foaming gas, with an even greater gas mobility reduction, achieving a pressure drop 7.6 times higher compared to the CO2-foam stabilized only by surfactant. Furthermore, larger areas with trapped gas were visualized along the micromodel when co-injecting the mixture of gases and the zwitterionic surfactant solution. The large decrease in gas mobility seen for this strategy suggests that using a gas mixture would be suitable to control gas mobility in high-permeability channels and to block thief zones. The combination of using a gas mixture and a nanofluid to decrease CO2-foam destruction in porous media yielded a slight reduction in gas mobility, similar to that obtained with CO2-foam in the presence of nanoparticles, for they had similar pressure-drop values at same injection flow rate. The results obtained in this work demonstrated the importance of interfacial phenomena for tuning of coarsening and coalescence mechanisms associated with CO2-foam stability to the desired pore-scale application.

Inducing pH control over the critical micelle concentration of zwitterionic surfactants via polyacids adsorption: Effect of chain length and structure

HypothesisThe critical concentration above which micelles form from zwitterionic surfactant solutions and their thermodynamic stability is affected by the interaction with weak Brønsted polyacid chains (An) via the formation of charged hydrogen bonds between the latter and anionic moieties. ExperimentsThe interaction between zwitterionic micelles and polyacids capable of forming hydrogen bonds, and its dependence on the environmental pH and polymer structure, has been studied with constant–pH simulations and a restricted primitive model for all electrolytes. FindingsAt low pH, the formation of polyacid/micelle complexes is witnessed independently of the polymer size or structure, so that the concentration above which micelles form is substantially decreased compared to polyacid–free cases. Upon rising pH, polymer desorption takes place within a narrow range of pH values, its location markedly depending on the size and structure of polyacids, and on the relative disposition between headgroup charged moieties. Thus, the desorption onset for long linear polyacids (A60) interacting with sulphobetainic headgroups is roughly two pH units higher than for six decameric chains (6A10) adsorbed onto micelles bearing phosphorylcholinic headgroups. This effect, together with the preferential desorption of chain ends at intermediate pH, may be exploited for drug delivery purposes or building advanced metamaterials.

IFT or wettability alteration: What is more important for oil recovery in oil-wet formation?

Several researchers have investigated the dominant recovery mechanisms among the wettability alteration and interfacial tension (IFT) reduction during surfactant flooding in unconventional, oil-wet reservoirs. Most of the previous studies carried out using spontaneous imbibition fail to answer the dominance of prominent mechanisms, especially with respect to time and location. In this paper, these research gaps are addressed through physico-chemical interactions, and microfluidic studies carried out using zwitterionic surfactant solutions of varying alkyl length and salinity. Based on the IFT and zeta potential values, three surfactant formulations (F1, F2 and F3) are chosen for representative carbonate microfluidic studies. The observations of microfluidic studies are significant to emphasize that at early time F2 and F3 formulation corresponded to higher imbibition rate than F1 formulation due to its higher ability to alter the rock wettability from oil-wet to water-wet. As the front propagates to far location, F1 with ultra-low IFT begins to outperform F3 by providing better microscopic displacement and quicker frontal propagation throughout. In the water-wet media, F1 formulation with the lowest IFT outperforms other formulations at all the time. The results of the study signify that while significant IFT reduction is sufficient for the complete oil displacement in water-wet media, significant IFT reduction at later stage and good wettability alteration at the early stage are needed during surfactant flooding in oil-wet formation.

A Novel Supercritical CO2 Foam System Stabilized With a Mixture of Zwitterionic Surfactant and Silica Nanoparticles for Enhanced Oil Recovery.

In order to improve the CO2 foam stability at high temperature and salinity, hydrophilic silica nanoparticles (NPs) were added into a dilute zwitterionic surfactant solution to stabilize supercritical CO2 (SC-CO2) foam. In the present paper, the foaming capacity and stability of SC-CO2 foam were investigated as a function of NP concentration at elevated temperatures and pressures. It was observed that the drainage rate of SC-CO2 foam was initially fast and then became slower with NPs adsorption at the gas-liquid interface. The improved foam stability at high temperature was attributed to the enhanced disjoining pressure with addition of NPs. Furthermore, an obvious increase in the foam stability was noticed with the increasing salinity due to the screening of NP charges at the interface. The rheological characteristics including apparent viscosity and surface elasticity, resistance factor, and microstructures of SC-CO2 foam were also analyzed at high temperature and pressure. With addition of 0.7% NPs, SC-CO2 foam was stabilized with apparent viscosity increased up to 80 mPa·s and resistance factor up to 200. Based on the stochastic bubble population (SBP) model, the resistance factor of SC-CO2 foam was simulated by considering the foam generation rate and maximum bubble density. The microstructural characteristics of SC-CO2 foam were detected by optical microscopy. It was found that the effluent bubble size ranged between 20 and 30 μm and the coalescence rate of SC-CO2 foam became slow with the increasing NP concentration. Oscillation measurements revealed that the NPs enhanced surface elasticity between CO2 and foam agents for resisting external disturbances, thus resulting in enhanced film stability and excellent rheological properties.

Foaming in aqueous solutions of zwitterionic surfactant in presence of monovalent salts: The specific ion effect

The specific ion effect on foamability and foam stability was investigated. The foams were prepared from the aqueous solutions of a zwitterionic surfactant [i.e. N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS)] in the presence of three monovalent salts (i.e. LiCl, NaCl, and CsCl). Addition of salt to the DDAPS solution increased the adsorption of surfactant at the interface and decreased the CMC. The efficiency of these salts in decreasing the surface and interfacial tension followed the order: CsCl > NaCl > LiCl. Similarly, the efficiency of these salts in decreasing the foam stability followed the above-mentioned order. The zeta potential at the hexane–water interface was measured. The efficiency of the salts in making the zeta potential more negative followed the same order. The hydrated radii of the ions played a significant role in the foaming properties of the surfactant solutions.

ПРОТОЛІТИЧНІ РІВНОВАГИ3-(ТРИФЛУОРОАЦЕТИЛ)ІМІДАЗО[1,2-a]ПІРИМІДИНУ В МІЦЕЛЯРНИХ РОЗЧИНАХ АНІОННОЇ ТА ЦВІТЕР-ІОННОЇ ПАР

Мета роботи. Дослідження протолітичних властивостей та спектральних характеристик протигрибкової субстанції 3-(трифлуороацетил)імідазо[1,2-a]піримідину в міцелярних розчинах аніонної та цвітер-іонної поверхнево-активних речовин.
 Матеріали та методи дослідження. У роботі використано стандартну спектрофотометричну методику з потенціометричним контролем рН водної фази.
 Результати і обговорення. У водних розчинах 3-(трифлуоро­ацетил)імідазо[1,2-a]піримідину існують дві протолітичні рівноваги: в лужних розчинах спостерігається молекулярна депротонована форма R; форма HR+ існує в діапазоні рН від 7 до 4, дикатіон H2R2+ існує у середовищі з рН < 1.
 У роботі досліджено кислотно-основні властивості та спектральні характеристики 3-(трифлуороацетил)імідазо[1,2-a]піримідину у міцелярних розчинах поверхнево-активних речовин (ПАР): аніонної ПАР – натрій н-додецилсульфаті (н-C12H25OSO3Na, ККМ ~ 8´10–3 М) та цвітер-іонної ПАР – цетилдиметиламонійпропансульфонаті (C16H33N(CH3)2(CH2)3SO3-, ККМ ~ 5´10–5 М).
 Розраховано константи ступінчастої дисоціації речовини у воді та «уявні» («apparent») константи ступінчастої дисоціації в міцелярних системах.
 Результати показали, що в міцелярних розчинах аніонної ПАР константи дисоціації збільшуються порівняно з водними розчинами через додатковий внесок електростатичної складової міцелярної поверхні, якою зв’язується субстрат. У міцелярних розчинах цвітер-іонної ПАР значення констант дисоціації досліджуваної речовини незначно змінюються порівняно з водними розчинами, що свідчить про низький розподіл речовини між водною фазою та міцелярною псевдофазою, унаслідок нейтральної поверхні міцел цвітер-іонної ПАР.
 Висновки. Досліджено кислотно-основні та спектральні характеристики вперше синтезованої субстанції 3-(трифлуороацетил)імідазо[1,2-a]піриміди­ну протигрибкової дії у воді та у міцелярних розчинах аніонної та цвітер-іонної ПАР. Розраховано константи ступінчастої дисоціації речовини у всіх досліджуваних системах.

Effect of electrostatic correlations on micelle formation

Micellization phenomena are fundamental to countless biological and chemical processes. Salts can dramatically change the micellization, depending on the kind of electrolyte and its concentration. Traditional approaches to model and describe these phenomena do not take into account electrostatic correlation interactions. Those interactions are essential when modeling surfactant solutions containing multivalent and/or highly concentrated electrolytes. Therefore, the development of a theory that is able to correctly predict the behavior of surfactant solutions with salts is a key to improve the application of surfactants in industrial processes. Here, we propose a simple methodology that uses a mean field approach to include electrostatic correlation effects and we coupled it with the well-established molecular thermodynamics approach to describe the micellization phenomena. From the proposed model, we can obtain the critical micelle concentration (CMC) of ionic and zwitterionic surfactant solutions and information about the size and shape of the micelles. We also propose an approach to take into account the binding of cations and anions on the surface of zwitterionic surfactants. To validate the model we compared our results with experimental data of CMC and counterion binding for different surfactants. We obtained very good agreement with the experimental data with a completely predictive model.

Using temperature-responsive zwitterionic surfactant to enhance the enzymatic hydrolysis of lignocelluloses and recover cellulase by cooling

Some zwitterionic surfactants exhibit upper critical solution temperature (UCST) in aqueous solutions. For the zwitterionic surfactant solution mixed with cellulase, when its temperature is below UCST, the cellulase can be recovered by coprecipitation with zwitterionic surfactant. In this work, 3-(Hexadecyldimethylammonio) propanesulfonate (SB3-16) was selected to enhance the enzymatic hydrolysis of lignocelluloses and recover the cellulase. After adding 2mmol/L of SB3-16, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) and by sulfite (Eu-SPORL) increased from 27.9% and 35.1% to 72.6% and 89.7%, respectively. The results showed that SB3-16 could reduce the non-productive adsorption of cellulase on hydrophobic interface, while it did not significantly inhibit the activity of cellulase. For the solution contained 1wt% SB3-16 and 200mg protein/L CTec2 cellulase, 55.2% of protein could be recovered by cooling. The filter paper activity of the recovered cellulase was 1.93FPU/mg protein, which was 95.8% of its initial activity.

Mechanical Properties of PM CNT-Dispersed Cu Composite

Microstructural and mechanical properties of powder metallurgy (PM) with carbon nanotube (CNTs) dispersed copper (Cu) composites were investigated in detail. Pure copper powder was coated with un-bundled CNTs by using the zwitterionic surfactant solution containing CNTs. The powder rolling process was applied to increase the powder surface area to be coated with CNTs. The total rolling reduction of Cu-CNT composite powder by 5 steps rolling was about 75%. With increasing the number of rolling steps, the content of CNTs coated on the Cu powder surface increased because of the increment of the flat surface area of flaky Cu rolled powder. As a result, the CNT content was 0.67mass% after 5 steps powder rolling. It was about twice as that of as-coated Cu-CNT composite powder without rolling. The grain size of PM extruded Cu-CNT composite was about one fifth of that of the extruded monolithic Cu material without CNT. Yield stress of the extruded Cu-CNT composite via the rolling process was 192 MPa, which is about twice that of the extruded monolithic Cu material (88 MPa). CNTs distributed at primary particle boundaries were effective to prevent the grain coarsening by their pinning effects, and this grain refinement was the main strengthening factor of the Cu-CNT composite via rolling process.

Foaming in aqueous solutions of zwitterionic surfactant: Effects of oil and salts

ABSTRACTThis paper reports a study on the stability of foams generated from the aqueous solutions of the zwitterionic surfactant, N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, in presence of NaCl, CaCl2 and AlCl3. The effect of oil (i.e. n-hexane) on foam was also studied. The surface and interfacial tensions were measured. These tensions and the CMC decreased upon salt addition, signifying an increased adsorption of the surfactant molecules at the interface. The quantity of salt required for reducing the surface tension and CMC was in the sequence: NaCl > CaCl2 > AlCl3. The salts had a pronounced effect on the foaming characteristics, i.e. they reduced the initial foam volume. The effectiveness of salts in reducing the foam stability followed the sequence: AlCl3 > CaCl2 > NaCl. However, the foam collapse rate was reduced in the presence of salt. The presence of oil decreased the foam volume and reduced its stability. The entering, bridging, and spreading coefficients were calculated, which explained the stability of foams in presence of oil.

カーボンナノチューブ分散純銅基複合材料の組織変化と力学特性

Microstructural and mechanical properties of powder metallurgy (PM) copper (Cu) composites dispersed with carbon nanotube (CNTs) were investigated in detail. A pure copper powder was coated with un-bundled CNTs by using the zwitterionic surfactant solution containing CNTs. The powder rolling process was applied to increase the powder surface area to be coated with CNTs. The total rolling reduction of Cu-CNT composite powder by 5 times rolling was about 75%. With increasing the rolling number, the content of CNTs coated on the Cu powder surface increased because of the increment of the flat surface area of flaky Cu rolled powder. As a result, the CNT content was 0.67 mass% after 5 times powder rolling. It was about twice as that of as-coated Cu-CNT composite powder without rolling process. The grain size of PM extruded Cu-CNT composite powder material was about 1/5 of that of the extruded monolithic Cu material without CNT. Yield stress of the extruded material of CuCNT composite via the rolling processing was 192 MPa, and about twice compared to the extruded monolithic Cu material (88 MPa). CNTs distributed at primary particle boundaries were effective to prevent the grain coarsening by their pinning effects, and this grain refinement was a main strengthening factor of the Cu-CNT composite material via rolling process.

Wettability of a PTFE surface by aqueous solutions of zwitterionic surfactants: Effect of molecular structure

Abstract Advancing contact angle (θ) for aqueous solutions of the zwitterionic surfactants, hexadecanol glycidyl ether glycine Betaine (C16PB), guerbet alcohol hexadecyl glycidyl ether glycine Betaine (C16GPB), hexadecanol polyoxyethylene (3), glycidyl ether glycine Betaine (C16(EO)3PB) and guerbet alcohol hexadecyl polyoxyethylene (3), glycidyl ether glycine Betaine (C16G(EO)3PB), were measured on the polytetrafluoroethylene (PTFE) surface by the sessile drop analysis. The obtained results indicate that a sharp decrease of θ appears only when the bulk concentration is higher than critical micelle concentration (CMC). Both branched chains and the introduction of polyoxyethylene (EO) units decrease the contact angle significantly. Similar, both branched chains and the EO units appear to cause a significant increase in adhesional tension on PTFE-water interface. Moreover, there are two adsorption equilibrium stages on PTFE surface. At the first equilibrium stage, the surfactant molecules mostly form a monolayer on PTFE surfaces for four zwitterionic surfactants. For C16PB and C16GPB, the adsorptions at PTFE-water interface are much smaller than at water–air interface. However, it is more easier to absorb onto solid interface for C16(EO)3PB and C16G(EO)3PB surfactants because of intermolecular hydrogen bonding by EO units. In the second saturated stage, the adsorbed molecules may become oriented more and more perpendicular to the PTFE interface with hydrophilic heads oriented toward the water for C16PB and C16GPB. In the case of C16(EO)3PB and C16G(EO)3PB, the hemimicelle formed on the PTFE surface will enhance ionic head density and result in lower PTFE-water interfacial tension.

Rheological Properties of Zwitterionic Wormlike Micelle in Presence of Solvents and Cosurfactant at High Temperature

Rheological properties of wormlike micelle solutions of zwitterionic surfactant were studied as a function of cosurfactant, organic salt, and solvents at high temperature. Addition of cosurfactant and organic salt increases the viscoelasticity at high temperature. Addition of isopropanol as solvent shifts the maximum viscosity of wormlike micelle to lower temperature. Addition of propylene glycol as solvent has less effect on the viscoelasticity of the wormlike micelle solution. An analysis based on the polarity of the solvent and phase behavior in concentrate region explains the effect of solvents on worm-like micelle.

Multi-Walled Carbon Nanotubes Reinforced Titanium Composites via Powder Metallurgy Process

Un-bundled multi-walled carbon nanotubes (MWCNTs) were coated on titanium powder surface by using zwitterionic surfactant solution and mixing process, and their CNT/Ti composite powders were consolidated into full-dense materials by spark plasma sintering and the following hot extrusion process in solid-state. Wrought titanium powder metallurgy (PM) composites containing CNTs revealed extreme increment of yield stress and tensile strength of 85% and 50%, respectively, compared to conventional PM titanium with no reinforcement, while they had enough high ductility. The mechanical improvement was mainly due to dispersion strengthening effect of CNTs and in-situ formed TiC fine particles and a small mount of carbon solid solution into Ti matrix. In addition, the control of grain growth was promoted by TiC dispersoids during SPS, and contributed to their strengthening behavior. Furthermore, high-temperature tensile strength less than 673K of PM pure titanium materials was also obviously improved by the pinning effect of TiC particles dispersed at grain boundaries. In this paper, microstructural and mechanical properties of powder metallurgy titanium composites would be introduced in detail.

High-temperature properties of extruded titanium composites fabricated from carbon nanotubes coated titanium powder by spark plasma sintering and hot extrusion

Pure titanium matrix composite reinforced with carbon nanotubes (CNTs) was prepared by spark plasma sintering and hot extrusion via powder metallurgy process. Titanium (Ti) powders were coated with CNTs via a wet process using a zwitterionic surfactant solution containing 1.0, 2.0 and 3.0wt.% of CNTs. In situ TiC formation via reaction of CNTs with titanium occurred during sintering, and TiC particles were uniformly dispersed in the matrix. As-extruded Ti/TiCs composite rods were annealed at 473K for 3.6ks to reduce the residual stress during processing. After annealing process, the tensile properties of the composites were evaluated at room temperature, 473, 573 and 673K, respectively. Hardness test was also performed at room temperature up to 573K with a step of 50K. The mechanical properties of extruded Ti/CNTs composites at elevated temperature were remarkably improved by adding a small amount of CNTs, compared to extruded Ti matrix. These were due to the TiC dispersoids originated from CNTs effectively stabilized the microstructure of extruded Ti composites by their pinning effect. Moreover, the coarsening and growth of Ti grain never occurred even though they were annealed at 573, 673K for 36ks and 673K for 360ks, respectively.

Ionic-Liquid-Induced Changes in the Properties of Aqueous Zwitterionic Surfactant Solution: Solvent and Rotational Relaxation Studies

In the recent past, the chameleon-like nature of zwitterionic micelles has been utilized for performing electrophilic, nucleophilic, base, and acid catalyzed reactions. But the use of simple salts to induce the zwitterionic character limits the variation to inorganic cations and anions only. To overcome this problem, we have used room temperature ionic liquids (RTILs), which can be tailored according to need. More precisely, we have shown the effect of added RTILs on the nature of water molecules in the palisade layer of a zwitterionic (N-hexadecyl-N,N-dimethylammonio-1-propanesulfonate (SB-16)) micelle using solvation and rotational relaxation studies of C-153 dye. We have carried out a comparative study of changes in the solvent and rotational relaxation parameters of C-153 in an aqueous solution of SB-16 upon addition of three different ionic liquids (ILs): 1-ethyl-3-methylimidazolium ethyl sulfate [C(2)mim][C(2)SO(4)], 1-ethyl-3-methylimidazolium n-butyl sulfate [C(2)mim][C(4)SO(4)], and 1-ethyl-3-methylimidazolium n-hexyl sulfate [C(2)mim][C(6)SO(4)]. It has been observed that in the presence of added RTILs the solvation dynamics become faster and the change in solvation dynamics is more pronounced in the case of [C(2)mim][C(6)SO(4)] compared to that for [C(2)mim][C(4)SO(4)] and [C(2)mim][C(2)SO(4)]. This can be accounted for by considering the increased water penetration (increased microfluidity) with the addition of ILs. In accordance with solvation dynamics results, fluorescence anisotropy studies also indicate an increase in microfluidity of the palisade layer of the SB-16 micelle with the added RTILs. The average rotational relaxation time in 28 mM SB-16 was found to be 1.12 ns. With the addition of 800 mM [C(2)mim][C(2)SO(4)], the average rotational relaxation time remains the same (1.12 ns), whereas with the addition of 800 mM [C(2)mim][C(6)SO(4)] it decreases to 0.40 ns. This observation is in agreement with our earlier report on the microfluidity of SB-16 solution with the addition of [C(2)mim][C(2)SO(4)] and [C(2)mim][C(6)SO(4)] (Rao, V. G.; Ghatak, C.; Ghosh, S.; Mandal, S.; Sarkar, N. Chem. Phys. Chem. DOI: 10.1002/cphc.201100866).

粉末冶金法を用いたカーボンナノチューブ分散Cu-Ti合金の組織と機械的および電気的特性

Microstructural and electrical properties of copper alloy (Cu-Ti) with carbon nanotubes (CNTs) prepared by powder metallurgy (P/M) process have been investigated. The Cu-0.5 mass% Ti pre-alloyed powder was made by water atomization process. The powders coated with un-bundled CNTs by using the zwitterionic surfactant solution containing CNTs were consolidated at 1223 K in vacuum by spark plasma sintering, and then extruded at 1073 K. The P/M Cu-Ti alloy without CNTs (monolithic alloy) had 202 MPa yield stress (YS) and 42.5 International-Anneld-Cupper-Standard % (IACS%) conductivity. The extruded Cu-Ti composite alloy containing CNTs revealed small decreased of YS compared to the monolithic Cu-Ti alloy. On the other hand, the composites revealed a higher electrical conductivity than that of the monolithic alloy. For example, Cu-Ti with 0.19 mass% CNTs showed 175.8 MPa YS and 83.5 IACS% conductivity. In the case of the Cu-Ti composite with CNTs, intermetallic compounds such as Cu4Ti and TiC were observed around CNTs by TEM-EDS analysis. The amount of the titanium solid solution in the above Cu-Ti composite alloy matrix was 10 % of the monolithic Cu-Ti alloy, and resulted in the remarkable increment of its electrical conductivity.