两性/阴离子表面活性剂形成具有耐盐性能的蠕虫状胶束

利用流变学方法研究了两性表面活性剂十四烷基磺基甜菜碱(TDAPS)和阴离子表面活性剂十二烷基硫酸钠(SDS)混合体系中蠕虫状胶束的耐盐性能, 分析了二价金属离子对蠕虫状胶束微观结构的影响. 结果表明, 在加入MgCl₂和CaCl₂使Mg^2＋和Ca^2＋总浓度达到0～1900 mg/L的情况下, TDAPS/SDS体系中形成的蠕虫状胶束的粘弹性能和耐剪切能力不仅没有损失而且增强. 对静态流变和动态流变结果进一步分析表明体系中同时存在两种可区分尺寸的蠕虫状胶束. 加入二价金属离子, 体系的微观结构发生了由小尺寸蠕虫状胶束向大尺寸蠕虫状胶束转变, 同时, 大尺寸蠕虫状胶束线性增长并发生枝化. 两性表面活性剂头基上的正电荷中心减小了蠕虫状胶束的反离子结合程度, 抑制了线性生长到枝化生长的过程, 使体系表现出优异的耐盐性能.     

十六烷基三甲基溴化铵/油酸钠混合体系蠕虫状胶束流变性研究

阴、阳离子表面活性剂之间强烈的相互作用利于形成自由弯曲的蠕虫状胶束。本文利用阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)和阴离子表面活性剂油酸钠(Na OA)制备了CTAB/Na OA蠕虫状胶束,研究了两表面活性剂的混合比和表面活性剂总浓度的变化对蠕虫状胶束体系稳态流变性及动态粘弹性的影响。结果表明,蠕虫状胶束在剪切过程中的解缠、拟网状结构的破坏以及最终沿剪切速度方向取向等是蠕虫状胶束产生剪切稀释特性的原因。两表面活性剂的混合比和表面活性剂总浓度的变化导致表面活性剂之间的静电作用、疏水作用发生较大的变化,最终引起体系内部表面活性剂聚集体形态的差异。体系内蠕虫状胶束长度、体系结构复杂程度、蠕虫状胶束形成的网络结构的致密度等都影响着体系的流变行为。在混合比R=3.6、总浓度CT=0.24mol/L时,体系中蠕虫状胶束最长,网络结构最为紧密,体系的零剪切粘度达到最大值。表面活性剂浓度一定时,混合比的提高有助于蠕虫状胶束的定向生长,弛豫时间τR和储能模量高频区平台模量G0提高,R=3.6时两者皆达到极大值,此后由于蠕虫状胶束的分枝化及(或)胶束破裂导致τR及G0下降。在表面活性剂混合比一定(R=3.6)时,表面活性剂浓度的提高利于蠕虫状胶束的增长或者分枝化,增加了胶束网络结构缠绕(融合)点的密度,导致G0逐渐增大。Cole-Cole图证实本文研究的蠕虫状胶束体系是符合Maxwell模型的线性粘弹性流体。     

光和热双重响应性rod-coil两亲分子的合成与溶液自组装行为

本文合成了一种单链的非离子型rod-coil两亲分子TriBAzoEO,分子中的偶氮苯基团和聚氧乙烯醚头基分别赋予其对光和热的响应性. TriBAzoEO降低表面张力的能力有限,但在水溶液中会形成蠕虫状胶束.其浓度越高,蠕虫状胶束越长,体系的黏度越大.紫外光激发可将TriBAzoEO中的偶氮苯从反式变为顺式构型,诱导蠕虫状胶束向球形胶束的转变,但可见光激发不能实现逆转变过程,这可能与聚集体中顺式TriBAzoEO分子间存在较强的π-π相互作用及较大的空间位阻有关. TriBAzoEO水溶液具备热增稠现象,这种热可逆转变由聚氧乙烯醚头基与水分子间氢键作用的变化所引起.升温会削弱氢键而降低TriBAzoEO的亲水性,促进更大结构蠕虫状胶束的形成而导致热增稠;降温后TriBAzoEO的亲水性增强,蠕虫状胶束结构恢复,体系的黏度降低.     

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.     

水杨酸钠对阳离子Gemini表面活性剂水溶液中蠕虫状胶束形成和性质的影响

用稳态和震荡剪切实验研究了水杨酸钠(NaSal)对50 mmol·L^-1阳离子Gemini表面活性剂2-羟基-(三亚甲基-α,ω-双十二烷基三甲基溴化铵和三亚甲基-α,ω-双十二烷基三甲基溴化铵, 简写为12-3(OH)-12和12-3-12)水溶液中形成蠕虫状胶束及其性质的影响. 在无盐状态下, 50 mmol·L^-1的12-3(OH)-12或12-3-12在水溶液中仅形成球状或棒状胶束. NaSal可促进上述两体系胶束的生长, 生成蠕虫状胶束. 比较而言, 12- 3(OH)-12对NaSal更敏感, 可以在低盐浓度下生成蠕虫状胶束. 而且与12-3-12体系相比, 12-3(OH)-12生成了更长的蠕虫状胶束. 这些差别在于12-3(OH)-12体系中存在羟基连接链之间的氢键作用, 这增加了12- 3(OH)-12头基的亲水性, 促进了反离子的解离, 增大的胶束表面电荷密度更强烈地结合水杨酸根反离子, 减小了头基间的静电斥力, 反过来又增强了分子间氢键, 致使 12-3(OH)-12胶束迅速生长.     

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.     

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.     

阳离子表面活性剂R16HTAB及其复配体系的流变性能

用稳态和动态流变学方法研究了3-十六烷氧基-2-羟丙基三甲基溴化铵（R16HTAB）单纯以及水杨酸钠（NaSal）存在下溶液的流变特性．无盐体系中,在测定的浓度范围内,表面活性剂与零剪切黏度呈指数关系（η0∝c^2．53）．水杨酸钠的加入促进了体系由球状向蠕虫状胶束转化．Cox—Merz规则和Cole-Cole图证明,混合体系生成了蠕虫状胶束．与传统的CTAB比较,无论水杨酸钠存在与否,R16HTAB水溶液的流变性能均较好,这主要归因于羟丙基基团的插入,使得R16HTAB和NaSal分子之间形成氢键连接,生成了更加稳定的三维网络结构．应用冷冻蚀刻电子显微镜技术进一步证实了体系中蠕虫状胶柬的存在．     

粘弹性蠕虫状胶束及其应用

介绍了粘弹性蠕虫状胶束的形成、类型、基本性质及其应用情况.粘弹性蠕虫状胶束具有重要的微观结构,因其特殊的流变性能而在不同领域具有重要应用.最近,蠕虫状胶束的结构和动态性质的研究已经延伸到不同类型的表面活性剂,如阴离子、两性离子和聚合物表面活性剂.目前,其应用领域已经拓展到油田、社区冷热流体的减阻、个人护理和家庭清洁产品的增稠剂等方面.     

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.     

Wormlike micelles and microemulsions in aqueous mixtures of sucrose esters and nonionic cosurfactants

A study of the phase and rheological behavior of sucrose hexadecanoate (C16SE)/cosurfactant/water systems in the presence of solubilized oil, using complementary techniques such as dynamic light scattering and small angle X-ray scattering, is presented. Viscoelastic wormlike micellar solutions are found when a nonionic lipophilic cosurfactant is added to C16SE aqueous systems. Contrary to previous reports, the effect of oil solubilization on these wormlike micelles is not unique and depends on several factors. Linear alkyl chain oils that tend to solubilize in the micellar core have a disrupting effect, decreasing the relaxation time and the viscosity of the systems. This effect is larger as the molecular volume of oil increases and as the solubility of the cosurfactant in oil increases. On the other hand, oils that penetrate in the palisade layer, such as p-xylene, induce micellar growth and have a thickening effect at a given micellar composition. Thermodynamic considerations are used to explain the experimental results.     

Microfluidic flows of wormlike micellar solutions

The widespread use of wormlike micellar solutions is commonly found in household items such as cosmetic products, industrial fluids used in enhanced oil recovery and as drag reducing agents, and in biological applications such as drug delivery and biosensors. Despite their extensive use, there are still many details about the microscopic micellar structure and the mechanisms by which wormlike micelles form under flow that are not clearly understood. Microfluidic devices provide a versatile platform to study wormlike micellar solutions under various flow conditions and confined geometries. A review of recent investigations using microfluidics to study the flow of wormlike micelles is presented here with an emphasis on three different flow types: shear, elongation, and complex flow fields. In particular, we focus on the use of shear flows to study shear banding, elastic instabilities of wormlike micellar solutions in extensional flow (including stagnation and contraction flow field), and the use of contraction geometries to measure the elongational viscosity of wormlike micellar solutions. Finally, we showcase the use of complex flow fields in microfluidics to generate a stable and nanoporous flow-induced structured phase (FISP) from wormlike micellar solutions. This review shows that the influence of spatial confinement and moderate hydrodynamic forces present in the microfluidic device can give rise to a host of possibilities of microstructural rearrangements and interesting flow phenomena.     

Rheology of wormlike micelles in aqueous systems of a mixed amino acid-based anionic surfactant and cationic surfactant

Amino acid-based anionic surfactant, N-dodecanoylglutamic acid, after neutralizing by 2, 2′, 2″-nitrilotriethanol forms micellar solution at 25 °C. Addition of cationic cosurfactants hexadecyltrimethylammonium chloride (CTAC), hexadecylpyridinium chloride (CPC), and hexadecylpyridinium bromide (CPB) to the semi-dilute solution of anionic surfactant micellar solutions favor the micellar growth and after a certain concentration, entangled rigid network of wormlike micelles are formed. Viscosity increases enormously ～4th order of magnitude compared with water. With further addition of the cosurfactants, viscosity declines and phase separation to liquid crystal occurs. The wormlike micelles showed a viscoelastic behavior and described by Maxwell model with a single stress-relaxation mode. The position of viscosity maximum in the zero-shear viscosity curve shifts towards lower concentration upon changing cosurfactant from CPB to CTAC via CPC; however, the maximum viscosity is highest in the CPB system showing the formation of highly rigid network structure of wormlike micelles. In all the systems, viscosity decays exponentially with temperature following Arrhenius type behavior.     

Polymerization of anionic wormlike micelles

Polymerizable anionic wormlike micelles are obtained upon mixing the hydrotropic salt p-toluidine hydrochloride (PTHC) with the reactive anionic surfactant sodium 4-(8-methacryloyloxyoctyl)oxybenzene sulfonate (MOBS). Polymerization captures the cross-sectional radius of the micelles (approximately 2 nm), induces micellar growth, and leads to the formation of a stable single-phase dispersion of wormlike micellar polymers. The unpolymerized and polymerized micelles were characterized using static and dynamic laser light scattering, small-angle neutron scattering, 1H NMR, and stopped-flow light scattering. Stopped-flow light scattering was also used to measure the average lifetime of the unpolymerized wormlike micelles. A comparison of the average lifetime of unpolymerized wormlike micelles with the surfactant monomer propagation rate was used to elucidate the mechanism of polymerization. There is a significant correlation between the ratio of the average lifetime to the monomer propagation rate and the average aggregation number of the polymerized wormlike micelles.     

Enhanced rheological properties and performance of viscoelastic surfactant fluids with embedded nanoparticles

A combination of viscoelastic surfactants with nanoparticles gives a new class of functional self-assembled materials promising for a large variety of applications. Nanoparticles improve the rheological properties of these systems because of the incorporation into the network of entangled wormlike micelles by linking to micellar end-caps, thus leading to elongation or cross-linking of the micelles. The present article reviews recent studies of these hybrid systems. Mechanisms of the interaction of nanoparticles with wormlike surfactant micelles as well as factors favoring the enhancement of rheological properties of viscoelastic surfactants by added nanoparticles are discussed, providing ways for proper design of such systems in the future. It is shown that viscoelastic surfactants modified with nanoparticles display very attractive features for practical applications, in particular, for fracturing fluids in oil recovery.     

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.     

Salt-induced viscoelastic wormlike micelles formed in surface active ionic liquid aqueous solution

The growth and structure of the aqueous micellar solutions of a surface active ionic liquid, 1-hexadecyl-3-methylimidazolium bromide (C16mimBr), in the presence of an organic salt sodium tosylate (NaTos), were investigated by rheological measurements and freeze-fracture transmission electron microscopy at room temperature (298 K). As in some conventional ionic surfactant/salt aqueous systems, wormlike micelles and network structures could be formed in the C16mimBr/NaTos aqueous solutions, according to measurements of the zero-shear viscosity, the entanglement length, the average contour length, as well as application of the Cox-Merz empirical rule and Cole-Cole plots. FF-TEM images further confirmed that wormlike micelles were formed in these aqueous solutions. The wormlike micelles presented here would expand potential applications of ionic liquids in home care products, oilfield stimulation fluids, and nanobiotechnology.     

The effect of alkane tail length of CiE8 surfactants on transport to the silicone oil-water interface

The phase behavior and rheological properties of an anionic surfactant, bis(2-ethylhexyl) sulfosuccinate (AOT), mixed with a zwitterionic tetradecyldimethylamine oxide (C(14)DMAO) in aqueous solutions, were studied at different ratios, R=w(AOT)/(w(C(14)DMAO + w(AOT)). When R=1, the 6.0 wt% AOT solution is two-phase with dense vesicles as the lower phase. With an increase of C(14)DMAO fraction (decreasing R) at a total concentration of 6.0 wt%, the lower vesicle-phase (L(αv)-phase) extends to generate a single L(αv)-phase. Then the L(αv)-phase turns into a viscoelastic wormlike micellar phase and finally rod-like or spherical C(14)DMAO micelles. The wormlike micellar solutions (from R=0.3 to 0.2) are highly viscoelastic, indicating the formation of rigid network structures. The rheological properties of the viscoelastic solutions exhibit a typical Maxwell characteristic at low and intermediate oscillatory frequencies. A pronounced temperature effect on the wormlike micellar structures can be observed by rheological studies. With an increase in temperature, the samples become less structured due to shortening of the micelles. After introducing certain additives, e.g., octanol and divalent metal ions, a transition from wormlike micellar phases to birefringent L(αv)-phases was observed.     

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.