Rheological Properties of Mixed Aqueous Solutions of Geminis (12‐3‐12,2Br−) and SDS

The rheological properties of surfactant solutions are the main parameter that affects the surfactant application. In this work, the rheology of the mixed system 12‐3‐12,2Br^?/SDS/H₂O was discussed particularly. The relationship between the microstructure of surfactant aggregates and rheology of mixed solutions was explored. It is shown that the rheological properties of solutions have different behaviors at different molar ratio of two surfactants under given total concentration. With the increase of molar ratio (12‐3‐12,2Br^?/SDS), the solution change from Newtonian liquid into positive thixotropy then to negative thixotropy, at last turn to positive thixotropy again, and ATPS becomes the dividing line. The difference of rheological properties is the embodiment of difference for surfactant aggregates' microstructures. The cryo‐TEM results shown that the solutions containing aggregates with big size, such as rodlike micelles, multilamellar micelles, show positive thixotropy. However, the solutions containing lamellar micelles or liquid crystal will show negative thixotropy. The positive thixotropy endows the mixied system a potential application in enhanced oil recovery.     

Rheological Properties of a Novel Photosensitive Micelle Composed of Cationic Gemini Surfactant and 4-Phenylazo Benzoic Acid

A new and simple reversible photorhelogical (PR) micelle system was investigated, which is composed of the cationic Gemini surfactant propylene-(dimethyldioctadecylammonium chloride) (18-3-18) and the photoresponsive counter ion, trans-4-phenylazo benzoic acid (trans-ACA). Before UV irradiation, the 18-3-18/trans-ACA mixtures with proper compositions formed highly viscoelastic fluids, showing good viscoelasticity, thixotropy, and shear thinning properties. After UV irradiation, the rheological properties of 18-3-18/ACA micelles changed obviously, exhibiting UV photothinning properties, because the trans-ACA was isomerized to cis-ACA. For the 18-3-18/ACA (8 mM/10 mM) micelle system, after 1 hour UV irradiation at 365 nm, the reduction percentage of the relative viscosity of the micelle was nearly 90%, and its thixotropy loop disappeared. It was revealed that the rheological properties of micelles changed gradually during the process of UV irradiation. In addition, the rheological properties of UV-irradiated micelles can recover after visible light irradiation. The proposed mechanism was validated by ultraviolet-visible (UV-vis) spectra of 18-3-18/ACA micelles.     

A dually effective inorganic salt at inducing obvious viscoelastic behavior of both cationic and anionic surfactant solutions

Hydrazine nitrate (HN), an inorganic salt, was first found to have dual effects on inducing obvious viscoelasticity of both cationic and anionic surfactant solutions. It was interesting that the surfactant solutions exhibited characteristic wormlike micelle features with strong viscoelastic properties upon the addition of this inorganic salt. The rheological properties of the surfactant solutions have been measured and discussed. The apparent viscosity of the solutions showed a volcano change with an increase of the HN concentration. Correspondingly, the microstructures of the micelles in the solutions changed with the apparent viscosity. First, wormlike micelles began to form and grew with an increase of the HN concentration. Subsequently, the systems exhibited linear viscoelasticity with characteristics of a Maxwell fluid in the intermediate mass fraction range, which originated from a 3D entangled network of wormlike micelles. Finally, a transition from linear micelles to branched ones probably took place at higher HN contents. In addition, the origin of the dual effects brought by HN addition on inducing viscoelasticity in both cationic and anionic surfactant solutions was investigated.     

Formation of rodlike micelles of dimethyloleylamine oxide in aqueous solutions: effects of addition of HCl and NaCl on the micelle size and the intermicellar interaction

Angular dependence of light scattering has been measured for aqueous solutions of dimethyloleylamine oxide in the presence of HCl and NaCl. In micellar solutions more concentrated than 0.1×10^–2 g cm^–3, rodlike micelles are dominantly formed, and their properties are strongly reflected in the characteristics of the solutions. The aggregation number, radius of gyration and even flexibility of the rodlike micelles increase with the addition of HCl as well as NaCl. The increase of HCl concentration up to 10^–3 N makes the aggregation number of rodlike micelles as large as 58,000, when 0.01 M NaCl is present. The large micelle size would be stabilized by the dehydration of the amine oxide group and the hydrogen bonding between nonprotonated and protonated molecules in a micelle.In aqueous solutions without HCl and NaCl or in their presence at very low concentrations, the light scattering is subject to the effects of both external and internal interferences. The effect of external interference can be separated from the effect of internal interference by applying the Zernike-Prins equation to the observed angular dependence of light scattering. Then the second virial coefficient and the pair interaction potential of rodlike micelles can be derived by means of certain approximate methods. The addition of HCl to 10^–3 N makes both repulsive and attractive forces stronger and the resulting potential well deeper, but the addition of NaCl depresses such an effect of HCl considerably.     

季铵盐Gemini表面活性剂胶团水溶液的流变性质

用毛细管振荡剪切流动法研究联接基团为聚亚甲基链的季铵盐型Gemini表面活性剂C_12-s-C₁₂·2Br(s=2,4,8)的流变性质,并用动态光散射技术测定胶团生长过程中的胶团形状和大小的变化规律,探索联接基团长度对胶团形状、大小以及溶液流变性质的影响.实验结果表明,胶团形状和大小与联接基团长度有关,而溶液的流变性质主要由胶团的大小和形状所决定,球形和棒状(长椭球体)胶团溶液的流变性质以纯粘度为主,而线性胶团溶液则显示粘弹性质.此外,增加电解质浓度和降低温度均使溶液的粘度增大.     

Rheology and rheokinetics of triethanolamine modified carboxymethyl hydroxyethyl cellulose

To meet requirements of fracturing fluid thickener, triethanolamine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain product called T-CMHEC of high viscosity. Rheological properties of CMHEC and T-CMHEC solutions were investigated to compare its structure and rheological performance, including viscosity, flow curve, thixotropy, and viscoelasticity. Viscosities of CMHEC and T-CMHEC solutions are, respectively, 19.0 and 63.2?mPa?·?s for the same concentration of 0.3%. Viscosity of T-CMHEC solutions is 3.3 times of CMHEC ones. Besides, the thixotropy and viscoelasticity of T-CMHEC system are both getting stronger than before. In summary, the T-CMHEC system shows better rheological performance after modification. Crosslinking process of T-CMHEC system is investigated under steady shear under different conditions, containing shear rates, concentrations of crosslinking agent, concentrations of pH adjuster, and temperature. Viscosity curves changing with time are obtained during crosslinking process. Four-parameter crosslinking rheokinetics equation is suitable to fit the viscosity curves under different conditions. Study on crosslinking process of T-CMHEC solutions is helpful to deepen the understanding on gel formation, and provides a theoretical basis for its application.     

Mg-Al-MMH-高岭土分散体系触变性研究

触变性是分散体系流变学研究的重要内容之一,在外切力作用下,若体系的粘度随时间下降,静止后又恢复,即具有时间因素的切稀现象,称为正触变性（positive thixotropy);反之,若体系的粘度或切力上升,静止后又恢复,即具有时间因素的切稠现象,称之为负触变性（Negative thixotropy)^[1],若在外切力作用下,某个特定体系的粘度或切力随时间先后呈现出正触变性和负触变性特征,则称之为复合触变性（Complex thixotropy)^[2,3],目前,对各种触变性机理的认识尚不统一。     

Characteristics of rodlike micelles of cetyltrimethylammonium chloride in aqueous NaCl solutions: Their flexibility and the scaling laws in dilute and semidilute regimes

Static light scattering has been measured for aqueous NaCl solutions of cetyltrimethylammonium chloride (CTAC) at 25 °C. While spherical micelles are formed above the critical micelle concentration for 0–1.5 M NaCl solutions, rodlike micelles are formed at NaCl concentrations higher than 1.18 M.The aggregation number of rodlike micelles increases markedly with increasing NaCl concentration, and it is as large as 11400 in 4.0 M NaCl. Long rodlike micelles are semiflexible and behave like wormlike chains. Their contour length and persistence length have been calculated as 630 and 46.4 nm, respectively, in 4.0 M NaCl.Rodlike micelles overlap and entangle together to form a network in semidilute solutions above a threshold micelle concentration. The radius of gyration of the blob can be scaled for its molecular weight with the exponent, 0.55, coinciding with that for isolated rodlike micelles in dilute solutions. The scaling laws for the reciprocal envelope of light scattered in the semidilute regime and for the molecular weight and the radius of gyration of the blob are also discussed with reference to the micelle concentration.     

The viscoelasticity of spinnable solutions of alkyltrimethylammonium salicylates

The viscoelasticity has been measured for aqueous solutions of tetradecyl-and hexadecyltrimethylammonium salicylates (C₁₄TASal, C₁₆TASal). The aqueous solutions of C₁₄TASal without salt displayed the gel-like behavior at 10.0×10^–2 g cm^–3, but those more dilute than 3.2×10^–2 g cm^–3 presented the viscoelasticity similar to that of a Maxwell liquid. The Maxwell-like behavior was converted to the polymer-like one on the addition of (0.1–0.2) M NaBr or (0.02–0.2) M NaSal. The gel-like viscoelasticity can be connected with the spinnability of cohesive fracture failure, and the Maxwell-like and polymer-like viscoelasticities are concerned with the spinnability of ductile failure. The gel-like and Maxwell-like viscoelasticities originate in the pseudo-network formed by the pseudo-linkages between rodlike micelles, while the polymer-like viscoelasticity is caused by the entanglement of long rodlike micelles in semidilute and concentrated solutions. The aqueous solutions of C₁₆TASal behaved very similar to those of C₁₄TASal.     

Rheological properties of wormlike micelles in sodium oleate solution induced by sodium ion

Aqueous solutions of anionic surfactant, sodium oleate (NaOA), have been studied by means of steady-state shear rheology and dynamic oscillatory technique. The micellar structure can be changed upon the addition of NaCl, Na₂CO₃ and NaCl/NaOH while NaOA concentration is maintained at 0.060 M. These systems except NaOA/NaCl show high viscosity and strong viscoelasticity. The hydroxide ion is very important for the formation of wormlike micelles. The anions of salts also have effect on the rheological properties of wormlike micelles. Three parameters: intersection frequency ω_i, plateau modulus G₀ and relaxation time τ are also discussed. The Maxwell model and Cole-Cole plot are applied to investigate the dynamic viscoelasticity of wormlike micelles. Variation in surfactant packing parameter R_P can be used to explain the change of rheology and microstructure of the micelles.     

Rheology and high-temperature stability of novel viscoelastic gemini micelle solutions

To broaden the application of clean fracturing fluid based on surfactant, a gemini cationic C₂₅-tailed surfactant, called FL-25, was synthesized. FL-25 can form a wormlike viscoelastic fluid in aqueous solution without adding any organic or inorganic salts. The rheological properties and thermal stability of the novel gemini micelle solutions were further investigated. The results show that the gemini micelle solution possesses viscoelasticity, thixotropy, and shear-thinning properties. The apparent viscosity of the viscoelastic gemini micelle solution at a shear rate of 170?s^?1 remains approximately 69?mPa?·?s at 110°C for 90 minutes, showing good high-temperature-resistance property. FL-25 may be a novel gemini surfactant applied in clean viscoelastic surfactant fracturing fluids in the oil and gas field.     

Rheology and Rheokinetics of Photosensitive Micelle Composed of 3-Chloro-2-Hydroxypropyl Oleyl Dimethyl Ammonium Acetate and trans-4-Phenylazo Benzoic Acid

A novel rheological reversible photosensitive micelle composed of 3-chloro-2-hydroxypropyl oleyl dimethyl ammonium acetate (ODAA) and trans-4-phenylazo benzoic acid (trans-ACA) was investigated. The mixed micelle system under a suitable molar ratio (ODAA:ACA = 1.25:1) shows great viscoelastic property. Before UV irradiation, the ODAA/ACA micelle system exhibits high viscosity and good viscoelasticity. Upon irradiation by UV light (365 nm), ACA undergoes a photoisomerization from its trans to its cis form, causing a change of the molecular structure, which leads to viscosity decreases obviously; thixotropy and viscoelasticity almost disappear. The above changes of rheological properties can be reversible by exposing to visible light. Furthermore, the rheokinetics process of ODAA/ACA micelle system during UV irradiation was studied and rheokinetics equation was established, which can well describe the changing processes of viscosity and viscoelasticity. The viscoelasticity process is divided into two sections to be simulated by rheokinetics equation. In addition, these photosensitive phenomena are repeatable easily and the mechanism can be validated by UV-vis spectra.     

Rheological Properties of Anionic Surfactant Solutions in the Presence of Al3+ Counterion

Aqueous solutions of ionic surfactants with strongly binding counterions exhibit wormlike or network properties. The properties of anionic micelles of sodium dodecyltrioxyethylene sulfate (AES) in the presence of multivalent counterion Al³⁺ were investigated by dynamic rheological methods. The steady-shear viscosity and stress, the zero-shear viscosity, the complex viscosity, and the dynamic shear modulus have been determined as a function of the surfactant and salt concentrations. Some interesting and noticeable results have been obtained, which can express the micellar growth and structure. The formation of wormlike micelles or network structure in surfactant solutions becomes much easier with increasing surfactant and salt concentrations. The Cox-Merz rule and the Cole-Cole plot are not applicable perfectly to the systems studied. The nonlinear viscoelasticity and non-Newtonian behavior can be found in all solutions according to the comparison with the simple Maxwell model. The technique of freeze-fracture transmission electron microscopy (FF-TEM) was also applied to confirm the formation of these interesting structures.     

Co-solvent effects on drag reduction, rheological properties and micelle microstructures of cationic surfactants

Some quaternary cationic surfactants, when mixed with a counterion, are known to self-assemble into threadlike micelles in water. Such behavior causes drastic changes in rheological properties of even very dilute solutions, allowing them to be used as drag reducing agents (DRA) in turbulent pipe flow circulating systems, such as district cooling/heating systems. Surfactant self-assembly is a physicochemical phenomenon whose character depends on surfactant nature and concentration, nature of the solvent, temperature and type and concentration of counterions. This study investigates drag reduction (DR) and rheological properties of two cationic surfactants, Ethoquad O/12 (oleyl bis(hydroxyethyl)methylammonium chloride) and Ethoquad O/13 (oleyl tris(hydroxyethyl) ammonium acetate), with excess salicylate counterion (NaSal), in mixed solvents containing 0 to 28 wt% ethylene glycol (EG) and water. The addition of EG to the solvent had greater effects on solutions' DR ability, shear viscosity, apparent extensional viscosity and viscoelasticity at 25 degrees C than at approximately 0 degrees C. Cryo-TEM images show threadlike micelle in these systems. DR at low temperatures in solutions containing moderate amount of EG can be utilized in a new approach to energy saving in district cooling systems using EG-water based mixtures as the cooling fluids.     

Rodlike micelles of dimethyloleylamine oxide in aqueous NaCl solutions,and their flexibility and size distribution

Angular dependence of light scattering from aqueous NaCl solutions of dimethyloleylamine oxide has been measured in the presence of NaCl from 5×10^–4 M to 10^–1 M at 25 °C. The molecular weight and radius of gyration of micelles increase with increasing micelle concentration and reach constant values, suggesting occurrence of the sphere-rod equilibrium dependent on the micelle concentration. With increasing NaCl concentration, rodlike micelles are larger in molecular weight and become longer. The micelles formed at NaCl concentrations higher than 10^–3 M are nearly monodisperse when the micelle concentration is high.Rodlike micelles of dimethyloleylamine oxide in 10^–2 M and 5 × 10^–2 M NaCl solutions have molecular weights of 4,760,000 and 6,900,000, respectively, and behave as semi-flexible or wormlike chains. In 5×10^–2 M NaCl they have a contour length of 5750 Å and a persistence length of 1760 Å. These micelle parameters correspond to the end-to-end distance of 3780 Å and the number of Kuhn's statistical segments of 1.64. The large aggregation number of the rodlike micelles is induced by the strong cohesion of long hydrocarbon chains in solution, and their flexibility is caused by the hydration of amine oxide groups.     

The influence of salt concentration on negative thixotropy in solutions of partially hydrolyzed polyacrylamide

The influence of NaCl concentration on negative thixotropy in aqueous glycerol solutions of partially hydrolyzed polyacrylamide have been investigated. It was found that negative thixotropy type I (a slow increase in viscosity with time of shearing) sets in at higher critical shear rates when the salt is present. On the other hand, critical shear rates for negative thixotropy type II (a rapid increase in viscosity followed by viscosity oscillation) did not depend on the salt addition. Using the critical shear stress as a hydrodynamic criterion for the occurrence of negative thixotropy, a possible explanation of the behavior is proposed.     

Rheological Properties and Crosslinking Rheo-Kinetics of CMHEC/CTAB Synergistic Systems

Aiming at synergistic interaction between carboxymethyl hydroxyethyl cellulose (CMHEC) and cetyltrimethyl ammonium bromide (CTAB), mixtures of CMHEC and CTAB solutions were investigated, employing relative viscosity and rheological measurements. The effects of mass ratio of CMHEC and CTAB solutions, temperature, and polysaccharide concentration on relative viscosities of CMHEC/CTAB systems were studied. Rheological method was used to study rheo-kinetics of the isothermal crosslinking process for CMHEC/CTAB synergistic fracturing fluid, and the novel crosslinking rheo-kinetics equation was established. The results showed the strong synergism between CMHEC and CTAB, resulting in a higher relative viscosity, storage modulus G′, and loss modulus G″ than that of separate ones. CMHEC/CTAB systems behave as pseudoplastic fluids with considerable thixotropy and viscoelasticity, and the flow behavior can be well described by Carreau?Williamson model. The crosslinking rheo-kinetics equation can well describe the isothermal crosslinking process at different shear rates. The model parameters are well-defined and reasonable.     

Rheological properties of modified xanthan and their influence on printing performances on cotton with reactive dyes in screen printing

In this study, various modified xanthan gums (MXG) were prepared by deacetylation under alkali treatment at certain temperature. The molecular weight of xanthan gum decreased after alkali modification. Rheological properties such as flowability, thixotropy and viscoelasticity were investigated via steady-shear, transient and dynamic oscillatory tests. The results showed that the flowability and viscous effect of MXG increased, while the structural viscosity and elastic effect decreased with increasing degrees of modification. Compared to xanthan gum, printing performances using MXG as a thickener were improved, especially the screenability, color yield and penetration. In addition, the quantitative interpretation of the rheological parameters, which are strongly associated with the quality-determining parameters, was obtained using rheological models (the power-law and Friedrich-Braun models). Excellent printing performances were achieved by applying MXG under the appropriate modification conditions. These thickeners, which have better flowability, more viscous behavior and smaller structural viscosity, might be good pastes to meet the the requirements of cotton printing with reactive dyes.     

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 behavior of an elongated micellar solution at low and high salt concentrations

 The aim of this experimen-tal work is to investigate the mechanism responsible of the decrease of the zero shear viscosity at high inorganic salt content. We report the linear and some nonlinear rheological properties of aqueous worm-like micellar solutions of CTAB containing NaNO₃ salt. The zero-shear viscosity η₀ curve versus salt concentration exhibits a well-defined maximum. We choose two salt concentrations (low and high) having the same zero-shear viscosity, and carefully explore the rheological characteristics and their evolutions in (and around) these two situations. The experimental results presented here, without excluding the possibility of the connections, suggest the possibility that the decreasing of η₀ is a result of the reduction in size of the worm-like micelles. Received: 16 February Accepted: 8 June 1998