Rheological Behavior of Viscoelastic Wormlike Micelles in CTAB/SSS/H2O Systems

The effect of the addition of sodium 4-styrenesulfonate (SSS) and KNO3 as well as temperature and shear rate on the structural transition of aqueous micellar solutions of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) was studied by viscosity. The effect of hydrocarbons on viscoelastic CTAB solutions was also examined. Possible mechanism for formation of CTAB wormlike micelles in the presence of sodium 4-styrenesulfonate (SSS) and KNO3 was discussed. The rapid increase in the apparent viscosity of CTAB solutions on the addition of SSS and KNO3 was due to the transition in micellar shape from spheres to wormlike ones. The rheological properties of CTAB solutions fit Maxwell model at low shear frequency. AFM image indicated a structure of transient network of CTAB/SSS/KNO3/H2O solution.     

疏水缔合聚丙烯酸与蠕虫状胶束的协同作用

从宏观流变性和介观尺度方面, 研究了疏水缔合聚丙烯酸(HMPA)与油酸钠(NaOA)构筑的蠕虫状胶束的协同作用. 考察HMPA对蠕虫状胶束溶液流变性和表观粘度的影响, 结果表明, 极少量HMPA的引入导致蠕虫状胶束溶液体系动态模量明显增加; 其表观粘度随HMPA浓度的增加先增强后减弱. 另一方面, 通过耗散颗粒动力学(DPD)分子模拟方法研究了混合体系中溶液组成对HMPA分子链的均方根末端距的影响. 结果表明,随着NaOA浓度增加, HMPA的均方根末端距会出现峰值; HMPA的伸展程度受其自身浓度变化制约, 相对于纯HMPA体系, NaOA胶束的存在对高浓度区的HMPA伸展程度影响更明显. 结合流变实验和分子模拟结果,初步解释了聚合物与蠕虫状胶束的协同作用机制.     

TBAB/KCl对构筑阴离子蠕虫状胶束的影响

采用流变测试技术考察了两种阴离子表面活性剂油酸钠(NaOA)和芥酸钠(NaOEr)在四丁基溴化铵(TBAB)和KCl诱导下构筑蠕虫状胶束的行为.随着KCl浓度增加, NaOA水溶液粘度增加,而加入TBAB使NaOA-KCl样品的粘度持续降低.与之相反, TBAB浓度的增加却使NaOEr-KCl样品的粘度大幅度增强.此外, NaOEr分子比NaOA表现出更强的形成胶束的能力,构成粘弹性蠕虫状胶束所需表面活性剂浓度和盐浓度更少.本文采用TBAB和KCl两种盐协同诱导NaOEr,制备了具有强粘弹性的阴离子蠕虫状胶束,探讨了盐TBAB/KCl对长链阴离子表面活性剂构筑蠕虫状胶束的影响机理.     

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.     

Photoinduced reversible change of fluid viscosity

We report a reversible photoinduced fluid viscosity change. A small amount of a "photoswitchable" azobenzene-modified cationic surfactant (4-butylazobenzene-4'-(oxyethyl)trimethylammonium bromide, AZTMA) was added to a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal). The trans-AZTMA solution had a remarkably high viscosity as a result of the entangled network of wormlike micelles. UV light irradiation on the trans-AZTMA solution remarkably decreased the viscosity of the solution because the bulky structure of cis-AZTMA is likely to disrupt the network structure of wormlike micelles. This photoinduced viscosity change is perfectly reversible between the trans- and cis-AZTMA solutions.     

Control of viscoelasticity using redox reaction

The viscoelasticity of a fluid was tuned with the Faradaic reaction of (11-ferrocenylundecyl)trimethylammonium bromide (FTMA), a "redox-switchable" surfactant. An aqueous solution of the reduced form of FTMA exhibited a remarkable viscoelasticity in the presence of sodium salicylate (NaSal) because of the formation of three-dimensional entanglement of wormlike micelles. Electrolytic oxidation of FTMA caused the viscosity of the system to dramatically decrease and the elasticity to disappear. This drastic decrease in viscoelasticity arose from the disruption of wormlike micelles. This novel electrorheological phenomenon is expected to be applicable to ink for inkjet printers, the electrochemically controlled release of substances entrapped in wormlike micelles of FTMA, and fluid flow rate control using electric signals.     

CO2 responsive wormlike micelles based on sodium oleate,potassium chloride and N,N-dimethylethanolamine

The anionic surfactant sodium oleate (NaOA) can self-assemble in aqueous solution in the presence of counter-ion inorganic salts to form wormlike micelles (WLMs), which exhibited viscoelastic behavior. In this paper, KCl was used to induce the formation of wormlike micelles with sodium oleate. In this process, we found that the addition of N, N-dimethylethanolamine (DMEA) can destroy the structure of WLMs leading significant decrease of viscosity. However, after introducing CO₂ into the ternary solution (KCl-NaOA-DMEA), the WLMs can be regenerated due to the electrostatic interaction between the protonated DMEA and the anionic surfactants. The addition of sodium hydroxide (NaOH) causes the electrostatic interaction between OA^- and DMEAH⁺ be destroyed, which results in the wormlike micelles becoming spherical micelles of lower viscosity. The transition of WLMs with high viscosity and low viscosity spherical micelles can be repeated several times by using CO₂ and NaOH.     

阴离子疏水缔合共聚物/阳离子蠕虫状胶束协同增粘自组装网络

将阴离子疏水缔合丙烯酰胺共聚物P(NaAMC14S-b-AM)与阳离子蠕虫状胶束十六烷基三甲基溴化铵/水杨酸钠(CTAB/NaSal)在水溶液中自组装制备了新型的缔合增粘体. 由稳态剪切和动态流变实验结果得出: 自组装体系在80 ℃下仍具有显著的协同增粘效应, 其流变行为符合Maxwell模型. 同蠕虫状胶束相比, 自组装体系的稳态模量G0、力学松弛时间τR和缠结点密度ν都有增加, 由此分析缔合体系中两组分间形成了相互缠结的网络结构, 在链缠结处共聚物主链上的疏水侧链嵌入到了蠕虫状胶束的内核.     

Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge

The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow.     

A new reverse wormlike micellar system: mixtures of bile salt and lecithin in organic liquids

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.     

疏水缔合和静电作用调控P(DTAB-co-AM)与蠕虫状胶束自组装网络

由新型的阳离子疏水单体二甲基十四烷基(3-丙烯酰胺基丙基)溴化铵(DTAB)与丙烯酰胺(AM)共聚合成了阳离子型疏水缔合共聚物P(DTAB-co-AM),研究了该共聚物与蠕虫状胶束自组装后的协同增黏效应,及改变疏水单体含量对自组装体系黏度的调控作用.制备了十八烷基三甲基氯化铵(CTAC)/水杨酸钠和芥酸钾/三羟乙基苄基氯化铵两类稳定的黏度较大的蠕虫状胶束体系.共聚物P(DTAB-co-AM)与芥酸钾/三羟乙基苄基氯化铵蠕虫状胶束在疏水缔合和静电吸引双重作用下自组装可形成协同增黏的缔合体系,而与CTAC/水杨酸钠阳离子蠕虫状胶束进行自组装由于只有疏水缔合作用,增黏效果不及前者.表观黏度研究表明,随着疏水单体含量的增加,P(DTAB-co-AM)与芥酸钾/三羟乙基苄基氯化铵缔合体系的黏度先增加后降低,当疏水单体含量为0.15 mol%时,缔合体系黏度达到极大值;当疏水单体含量为0.3 mol%时,缔合体系黏度反而低于与阳离子蠕虫状胶束缔合后的黏度.对于共聚物与CTAC/水杨酸钠蠕虫状胶束缔合体系,随着疏水单体含量增加,由于疏水缔合作用与静电排斥作用的相互抵消,致使体系黏度有所下降.由此说明改变疏水单体含量可以达到调控自组装体系黏度的目的.     

Rheological behavior of viscoelastic wormlike micelles in mixed sodium dodecyl trioxyethylene sulfate–monolaurin aqueous system

Rheological behavior of viscoelastic wormlike micelles in an aqueous system of mixed sodium dodecyl trioxyethylene sulfate (SDES)–monolaurin (ML) is presented. Dilute aqueous solution of SDES has a high fluidity and follows Newtonian liquid-like behavior due to formation of small globular type of micellar structure. Addition of lipophilic nonionic cosurfactant ML to dilute or semidilute solution of SDES decreases the interfacial curvature of the aggregates favoring one dimensional micellar growth, and hence, viscosity increases. After a certain concentration of ML, the elongated micelles get entangled with each other leading to the formation of viscoelastic wormlike micelles. The viscoelastic solution follows Maxwell model of a single stress relaxation mode at low-frequency region. Further addition of ML decreases the viscosity of the solution due to formation of micellar joints in the network structure. The viscosity of the viscoelastic wormlike micelles decreases upon heating, and the system with poor viscoelastic character is observed at higher temperatures.     

Adsorption of SDBS and Its Effect on Rheology of Preformed Particle Gels

The adsorption of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) onto preformed particle gels (PPGs) and the effect of SDBS on the swelling ratio and rheology of PPGs were investigated. SDBS molecules can adsorb onto PPGs because of the hydrophobic association with the chain of PPGs at low concentration and the association of the SDBS micelles with the chains of PPGs at high concentration. PPGs contract and the shear stress of PPGs decreases after adsorption of SDBS. In addition, the storage modulus decreases first and then increases with increasing SDBS concentration.     

Pickering Emulsion Stabilized by Self-Assembled Micelles of Amphiphilic Random Copolymer P(St-co-DM)

Self-assembled polymeric micelles can be used as efficient particulate emulsifiers. Styrene (St) and dimethylaminoethyl methacrylate (DM) were used to synthesize the amphiphilic random copolymer P(St-co-DM). This copolymer self-assembles into spherical polymeric micelles. The polymeric micelles show surface activity and pH sensitivity for producing Pickering emulsion. The experiment shows that the stability of the emulsion increases with the micelle concentration. The emulsion can only be formed when the salt concentration is below a certain limiting value. Using the white oil as the oil phase, polymeric micelles have emulsification in a large pH range. The emulsifying performance of the polymeric micelles could be enhanced by raising the water/oil volume ratio.      

Rheological properties of wormlike micelles formed in the sodium oleate/trisodium phosphate aqueous solution

Aqueous solution of anionic surfactant,sodium oleate（NaOA）,was studied by means of steady-state shear rheology and dynamic oscillatory technique.The system of NaOA/Na3PO4 showed high viscosity,strong viscoelasticity and good ability of countering Ca^2＋,Mg^2＋.The Maxwell model and Cole-Cole plot were applied to study the dynamic viscoelasticity of wormlike micelles.The microstructures of the wormlike micelles were characterized by FF-TEM.     

Small-Angle Neutron Scattering Study of Nonionic Surfactant Micelles and Phase Transitions in w/o Microemulsion

The structure of micelles formed by a four component water-in-oil nonionic microemulsion surfactant polyoxyethene (20) sorbitan monoleate (Tween 80), sorbitan monolaurate (Span 20) at ethyl oleate and deuterated water interface have been probed by small-angle neutron scattering (SANS). The total surfactant concentration in each of the samples studied (Tween 80: Span 20) is fixed at 3:2. The deuterated water content is variable at 5–60% w/w. The experimental SANS data from all the seven samples are fit well by spherical micelles interacting with hard sphere potential. Increased deuterated water leads to spherical to lamellar and rod-like micelle geometry featured in the SANS scattering data. The observed change in micelle geometry supports the characterization of phase transition between the self-assembled micelles of the nonionic microemulsion.