A pH-responsive wormlike micellar system of a noncovalent interaction-based surfactant with a tunable molecular structure

Self-Assembled Viscoelastic Surfactant Micelles with pH-Responsive Behavior: A New Fracturing-Displacement Integrated Working Fluid for Unconventional Reservoirs

The integrated fracturing and oil recovery strategy is a new paradigm for achieving sustainable and cost-effective development of unconventional reservoirs. However, a single type of working fluid cannot simultaneously meet the different needs of fracturing and oil displacement processes. Here, we develop a pH-responsive fracturing-displacement integrated working fluid based on the self-assembled micelles of N,N-dimethyl oleoamine propylamine (DOAPA) and succinic acid (SA). By adjusting the pH of the working fluid, the DOAPA and SA molecules can be switched repeatedly between highly viscoelastic wormlike micelles and aqueous low-viscosity spherical micelles. The zero-shear viscosity of the working fluid enriched the wormlike micelles can reach more than 93,100 mPa·s, showing excellent viscoelasticity and sand-carrying properties. The working fluid is easy to gel-break when it encounters oil, generating a low-viscosity liquid without residue. In addition, the system has strong interfacial activity, which can greatly reduce the oil-water interfacial tension to form emulsions and can achieve reversible demulsification and re-emulsification by adjusting pH. Through the designed and fabricated microfluidic chip, it can be visualized that under the synergistic effect of viscoelasticity and interfacial activity DOAPA/SA can effectively expand the swept volume of tight fractured formations, promote pore wetting reversal and crude oil emulsification, and improve the displacement efficiency. The DOAPA/SA meets the design requirements of the fracturing-displacement integrated working fluids and provides a novel method and idea for constructing the integrated working fluids suitable for fracturing and displacement in unconventional reservoirs.

pH- and temperature-responsive supramolecular assemblies with highly adjustable viscoelasticity: a multi-stimuli binary system

Stimuli-responsive materials are increasingly needed for the development of smart electronic, mechanical, and biological devices and systems relying on switchable, tunable, and adaptable properties. Herein, we report a novel pH- and temperature-responsive binary supramolecular assembly involving a long-chain hydroxyamino amide (HAA) and an inorganic hydrotrope, boric acid, with highly tunable viscous and viscoelastic properties. The system under investigation demonstrates a high degree of control over its viscosity, with the capacity to achieve over four orders of magnitude of control through the concomitant manipulation of pH and temperature. In addition, the transformation from non-Maxwellian to Maxwellian fluid behavior could also be induced by changing the pH and temperature. Switchable rheological properties were ascribed to the morphological transformation between spherical vesicles, aggregated/fused spherical vesicles, and bicontinuous gyroid structures revealed by cryo-TEM studies. The observed transitions are attributed to the modulation of the head group spacing between HAA molecules under different pH conditions. Specifically, acidic conditions induce electrostatic repulsion between the protonated amino head groups, leading to an increased spacing. Conversely, under basic conditions, the HAA head group spacing is reduced due to the intercalation of tetrahydroxyborate, facilitated by hydrogen bonding.

Development of CO2-Sensitive Viscoelastic Fracturing Fluid for Low Permeability Reservoirs: A Review

There are economic and technical challenges to overcome when increasing resource recovery from low permeability reservoirs. For such reservoirs, the hydraulic fracturing plan with the development of clean and less expensive fracturing fluid plays a vital aspect in meeting the energy supply chain. Numerous recent published studies have indicated that research on worm-like micelles (WLMs) based on viscoelastic surfactant (VES) fluid has progressed substantially. This study looks at the development of CO2-sensitive viscoelastic fracturing fluid (CO2-SVFF), its applications, benefits, limitations, and drawbacks of conventional fracturing fluids. The switchable viscoelasticity of CO2-SVFF system signifies how reusing of this fluid is attained. Compared to conventional surfactants, the CO2-SVFF system can be switched to high viscosity (to fracture formation and transporting proppants) and low viscosity (easy removal after causing fracture). The effect of pH, conductivity, temperature, and rheological behaviors of CO2-SVFFs are also highlighted. Further, the aid of Gemini surfactants and nanoparticles (NPs) with low concentrations in CO2-SVFF can improve viscoelasticity and extended stability to withstand high shear rates and temperatures during the fracturing process. These studies provide insight into future knowledge that might lead to a more environmentally friendly and successful CO2-SVFFs in low-permeability reservoirs. Despite the increased application of CO2-SVFFs, there are still several challenges (i.e., formation with high-temperature range, pressure, and salinity).

Advances of supramolecular interaction systems for improved oil recovery (IOR)

Improved oil recovery (IOR) includes enhanced oil recovery (EOR) and other technologies (i.e. fracturing, water injection optimization, etc.), have become important methods to increase the oil/gas production in petroleum industry. However, conventional flooding systems always encounter the problems of low efficiency, high cost and complicated synthetic procedures for harsh reservoirs conditions. In recent decades, the supramolecular interactions are introduced into IOR processes to simplify the synthetic procedures, alter their structures and properties with bespoke functionalities and responsiveness suitable for different conditions. Herein, we primarily review the fundamentals of several supramolecular interactions, including hydrophobic association, hydrogen bond, electrostatic interaction, host-guest recognition, metal-ligand coordination and dynamic covalent bond from intrinsic principles and extrinsic functions. Then, the descriptions of supramolecular interactions in IOR processes from categories and advances are focused on the following variables: polymer, surfactant, surfactant/polymer (SP) complex for EOR and viscoelasticity surfactant (VES) for clean hydraulic fracturing aspects. Finally, the field applications, challenges and prospects for supramolecular interactions in IOR processes are involved and systematically addressed. The development of supramolecular interactions can open the way toward adaptive and evolutive IOR technology, a further step towards the cost-effective production of petroleum industry.

On the effects of organic-acids isomers on temperature-responsiveness in wormlike micelles (WLMs) systems

Responsive wormlike micelles (WLMs) consisted of cationic surfactants and organic-acids are fascinating due to their reversible molecular recognition properties. However, it is unknown how the structure of organic-acids alters the stimuli-responsiveness of WLMs systems. Herein, the peculiar nature of temperature-responsive behaviors in three WLMs systems were systematically investigated. These were manufactured by combining N-erucamidopropyl-N,N-dimethylamine (UC₂₂AMPM) with isomers of organic-acids: o-phthalic acid (o-PA), m-phthalic acid (m-PA) and p-phthalic acid (p-PA) at molar ratio of 2:1 (named as o-EAPA, m-EAPA and p-EAPA respectively). The phase behaviors, macro- and micro-rheology, as well as the mechanism of temperature-responsiveness were explored by visual inspection, rheological and optical methods. The results showed that the three systems exhibited different responsiveness with increase of temperature. Among them, the viscosity and viscoelasticity of o-EAPA were gradually decreased with temperature increase from 30 °C to 90 °C. On the other hand, those of p-EAPA were firstly increased and subsequently decreased, exhibiting the highest viscosity during the heating process. This peculiar phenomenon was attributed to the hydrophilic difference of organic-acids isomers, leading to variations of micelle transitions upon temperature increase. This study is the first report of aromatic-acids isomers inducing different on temperature-responsiveness, and finding beneficial for the development of responsive WLMs for different applications.

pH-responsive viscoelastic supramolecular viscosifiers based on dynamic complexation of zwitterionic octadecylamidopropyl betaine and triamine for hydraulic fracturing applications

Viscosity modifying agents are one of the most critical components of hydraulic fracturing fluids, ensuring the efficient transport and deposition of proppant into fissures. To improve the productivity index of hydraulic fracturing processes, better viscosifiers with a higher proppant carrying capacity and a lower potential of formation damage are needed. In this work, we report the development of a novel viscoelastic system relying on the complexation of zwitterionic octadecylamidopropyl betaine (OAPB) and diethylenetriamine (DTA) in water. At a concentration of 2 wt%, the zwitterionic complex fluid had a static viscosity of 9 to 200 poise, which could be reversibly adjusted by changing the suspension pH. The degree of pH-responsiveness ranged from 10 to 27 depending on the shear rate. At a given concentration and optimum pH value, the zwitterionic viscosifiers showed a two-orders-of-magnitude reduction in settling velocity of proppant compared to polyacrylamide solution (slickwater). By adjusting the pH between 4 and 8, the networked structure of the gel could be fully assembled and disassembled. The lack of macromolecular residues at the dissembled state can be beneficial for hydraulic fracturing application in avoiding the permeation damage issues encountered in polymer and linear-gel-based fracturing fluids. The reusability and the unnecessary permanent breakers are other important characteristics of these zwitterionic viscosifiers.

Viscosity modifying agents are one of the most critical components of hydraulic fracturing fluids, ensuring the efficient transport and deposition of proppant into fissures.

pH-Responsive aggregates transition from spherical micelles to WLMs induced by hydrotropes based on the dynamic imine bond

In recent years, the use of dynamic chemical bonds to construct stimulus-responsive micelle systems has received increasing attention. However, current reports focus on the construction of dynamic covalent bond surfactants using dynamic chemical bonds, and the method of applying dynamic covalent bonds to hydrotropes has not been reported yet. In this study, a novel pH-responsive worm-like micelle system was constructed by mixing cetyltrimethylammonium bromide (CTAB), 4-hydroxybenzaldehyde (HB) and p-toluidine (MB) at the molar ratio of 60 mM : 40 mM : 40 mM. The formation mechanism of the dynamic covalent bond hydrotropes and the rheological behavior of the micelles were investigated via rheology, 1H-NMR spectroscopy and Cryo-TEM. The results show that as the pH increases, the viscosity of the solution first decreases and then increases rapidly. The microscopic aggregates in the solution transition from spherical micelles to worm-like micelles (WLMs), and the solution changes from a water-like fluid without viscosity to a gel system that can withstand its own weight. The transformation of the aggregates and their rheology can be attributed to the formation of MB-HB-, which is a type of hydrotrope with dynamic covalent bonds. Moreover, the transition from spherical micelles to worm-like micelles in this system is reversible.

pH-Responsive Wormlike Micelles Formed by an Anionic Surfactant Derived from Rosin

A novel pH-responsive wormlike micellar viscoelastic solution was constructed by a rosin-based anionic surfactant (Na-MPA-AZO-Na) in the presence of cetyltrimethylammonium bromide (CTAB). The viscoelasticity, aggregate morphology, and pH-responsiveness of the pH-responsive wormlike micelles have been investigated through the method of rheology and cryogenic-transmission electron microscopy. Its corresponding mechanism has been studied using ¹H NMR and ¹H-¹H 2D NOESY HNMR. The zero-shear viscosity (η₀) of the wormlike micellar solution rapidly decreases by 3 orders of magnitude as the pH increases from 5.21 to 9.56. The viscoelastic fluids and water-like solutions can be converted by tuning the pH between 3.62 and 12.00, and the corresponding aggregates also transform between wormlike micelles and spherical micelles. In addition, the wormlike micellar cross-sectional diameter is approximately 10 nm, which is remarkably larger than that of the common wormlike micelles. The phenomenon can be attributed to the large steric volume of the rosin rigid skeleton. When the pH is 12.00, a "pseudo" Gemini surfactant is constructed by Na-MPA-AZO-Na and CTAB through the electrostatic interactions. Wormlike micelles also can be formed with the increasing concentrations. The η₀ of the wormlike micellar system shows strong dependence on concentration with an exponent of 9.6 (η₀ ∝ C^9.6). This work further promotes new applications of forest resources.

Experimental Investigation and Performance Evaluation of Modified Viscoelastic Surfactant (VES) as a New Thickening Fracturing Fluid

In hydraulic fracturing, fracturing fluids are used to create fractures in a hydrocarbon reservoir throughout transported proppant into the fractures. The application of many fields proves that conventional fracturing fluid has the disadvantages of residue(s), which causes serious clogging of the reservoir’s formations and, thus, leads to reduce the permeability in these hydrocarbon reservoirs. The development of clean (and cost-effective) fracturing fluid is a main driver of the hydraulic fracturing process. Presently, viscoelastic surfactant (VES)-fluid is one of the most widely used fracturing fluids in the hydraulic fracturing development of unconventional reservoirs, due to its non-residue(s) characteristics. However, conventional single-chain VES-fluid has a low temperature and shear resistance. In this study, two modified VES-fluid are developed as new thickening fracturing fluids, which consist of more single-chain coupled by hydrotropes (i.e., ionic organic salts) through non-covalent interaction. This new development is achieved by the formulation of mixing long chain cationic surfactant cetyltrimethylammonium bromide (CTAB) with organic acids, which are citric acid (CA) and maleic acid (MA) at a molar ratio of (3:1) and (2:1), respectively. As an innovative approach CTAB and CA are combined to obtain a solution (i.e., CTAB-based VES-fluid) with optimal properties for fracturing and this behaviour of the CTAB-based VES-fluid is experimentally corroborated. A rheometer was used to evaluate the visco-elasticity and shear rate & temperature resistance, while sand-carrying suspension capability was investigated by measuring the settling velocity of the transported proppant in the fluid. Moreover, the gel breaking capability was investigated by determining the viscosity of broken VES-fluid after mixing with ethanol, and the degree of core damage (i.e., permeability performance) caused by VES-fluid was evaluated while using core-flooding test. The experimental results show that, at pH-value (6.17), 30 (mM) VES-fluid (i.e., CTAB-CA) possesses the highest visco-elasticity as the apparent viscosity at zero shear-rate reached nearly to 106 (mPa·s). Moreover, the apparent viscosity of the 30 (mM) CTAB-CA VES-fluid remains 60 (mPa·s) at (90 ∘C) and 170 (s−1) after shearing for 2-h, indicating that CTAB-CA fluid has excellent temperature and shear resistance. Furthermore, excellent sand suspension and gel breaking ability of 30 (mM) CTAB-CA VES-fluid at 90 (∘C) was shown; as the sand suspension velocity is 1.67 (mm/s) and complete gel breaking was achieved within 2 h after mixing with the ethanol at the ratio of 10:1. The core flooding experiments indicate that the core damage rate caused by the CTAB-CA VES-fluid is (7.99%), which indicate that it does not cause much damage. Based on the experimental results, it is expected that CTAB-CA VES-fluid under high-temperature will make the proposed new VES-fluid an attractive thickening fracturing fluid.

Effects of sodium chloride on rheological behaviour of the gemini-like surfactants

The gemini-like surfactants have been constructed by compounding N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA), and are denoted as o-EAPA, m-EAPA, and p-EAPA, respectively. It is well known that inorganic salts have significant effects on surfactant aggregates, and herein the effects of sodium chloride (NaCl) on gemini-like surfactants is explored by rheological and dynamic light scattering measurements, and cryo-TEM. It is found that the viscoelasticity of the EAPA systems first increases and then decreases with an increase of the NaCl concentration. And the optimal NaCl concentrations for these three systems are in the order of o-EAPA < m-EAPA < p-EAPA due to different spacer distances between the two carboxyl groups in the phthalic acid. Similar trends in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, or p-PA systems were also observed. The results show that an appropriate NaCl concentration will promote gemini-like surfactants to form wormlike micelles (WLMs). Upon further increasing the NaCl concentration, the WLMs transform into vesicles. Excessive NaCl concentration will cause the surfactant systems to reach their cloud point and make the surfactants precipitate out. The mechanism of the effects of NaCl is that Cl- reduces the electrostatic repulsion between the headgroups of the surfactants. This work is helpful in understanding the effects of inorganic salts on the surfactants and this study is useful for exploring the practical applications of gemini-like surfactants.

A new interpretation of the mechanism of wormlike micelle formation involving a cationic surfactant and salicylate

HYPOTHESIS

When tetradecyltrimethylammonium bromide, TTAB, is added to aqueous solution of sodium salicylate, NaSal, the threading of the aromatic anion into the micellar palisade leads to the formation of wormlike micelles. Based on the calorimetric titration of NaSal with TTAB, and on the lifetime of fluorescence of salicylate, we propose that the aggregation of the two components directly leads to the formation of wormlike micelles, without any pre-aggregation.

EXPERIMENTS

By using an isothermal titration calorimeter, aliquots of TTAB were added to a dilute solution of NaSal. The energy involved in each addition was then integrated and the variation of enthalpy was determined. In the same range of concentrations and molar ratios, the surface tensiometry and time-resolved emission spectroscopy experiments were performed.

FINDINGS

A very characteristic calorimetric signal associated with wormlike micelle formation was obtained, being the enthalpy variation of this process, Δ_WLMH₂₉₈⁰ < 0. When 1.2 mmol L^-1 of NaSal is titrated with 11.0 mmol L^-1 of TTAB at 298.15 K, Δ_fH₂₉₈⁰ = -10.31 kJ per mol of injectant. By adding TTAB to NaSal solution, two fluorescence lifetimes of salicylate were observed solely after wormlike micelle being formed. The correspondent lifetime values of 4.0 ns and 7.2 ns are respectively associated with the free and associated species of salicylate. The new results demonstrated that wormlike micelles are the first aggregate formed when TTAB is added to salicylate. This aspect is relevant for understanding the mechanism of wormlike micelles formation.

pH-Switchable IFT variations and emulsions based on the dynamic noncovalent surfactant/salt assembly at the water/oil interface

Additional HCl can facilely control the dynamic noncovalent interaction between anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and additional organic matter, 4,4'-oxydianiline (ODA), at the water/oil interface. At low HCl concentration (ODA/HCl molar ratio (r) = 1 : 1.5, [ODA] = 250 mg L-1), the ODA+ ions effectively enhanced the SDBS ability to reduce the water/oil interfacial tension (IFT) by about two orders of magnitude, while the (SDBS)2/ODA2+ gemini-like surfactants could be constructed at a relatively high HCl concentration (r = 1 : 4, [ODA] = 250 mg L-1), which could largely reduce the IFT to 1.19 × 10-3 mN m-1. Molecular simulation was employed to explore the interfacial activity of ODAn+ (ODA+/ODA2+) ions and the SDBS/ODAn+ interaction. The control experiments used another three surfactants to verify the proposed model. The pH-switchable gradual protonation of amino groups in ODA molecules determined the SDBS/ODA interfacial assembly, which was responsible for the reversal of IFT variations and the related emulsion behaviors.

Study on the effect of the organic acid structure on the rheological behavior and aggregate transformation of a pH-responsive wormlike micelle system

A worm-like micelle (WLM) system can be obtained by mixing long-chain cationic surfactants and polybasic organic acids in an aqueous solution. However, the effect of different organic acid structures on the rheological behavior of WLM systems has not been researched. Herein, a novel pH-responsive wormlike micelle system (EATA) was constructed by the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and benzene tricarboxylic acid (TA) at a molar ratio of 3 : 1. UC22AMPM/citric acid (EACA) was also prepared to perform a comparison. The rheological behavior, aggregate transformation and thickening mechanism of EATA solutions were investigated by using rheological measurements, cryo-TEM, DLS, surface tension and 1H NMR. The results show that, at low pH, spherical micelles were formed and the EATA solution exhibited a lower viscosity than the EACA system due to the strong hydrophobicity of the phenyl groups of TA molecules, but the viscosity reaches 106 mP s at pH 4.80. Because of the lower pKa value of TA than CA, the viscosity of the EATA system drops sharply with the appearance of precipitates caused by the isoelectric point when the pH is greater than 4.80. In addition, by circularly changing the pH value several times, the wormlike micelles could maintain their original viscoelasticity without being weakened in the slightest.

Photoresponsive Behavior of Wormlike Micelles Constructed by Gemini Surfactant 12-3-12·2Br- and Different Cinnamate Derivatives

The photoresponsive wormlike micelles constructed by Gemini surfactants and cinnamate derivatives play a great role in the field of smart materials. However, how the structure of cinnamate derivatives affects the photoresponsive behavior of micelles is still a hotspot for scientists to research. Here, three kinds of aromatic salts with different ortho-substituted groups including trans- o-methoxy cinnamate ( trans-OMCA), trans- o-hydroxy cinnamate ( trans-OHCA), and trans-cinnamate ( trans-CA) were introduced into Gemini surfactant 12-3-12·2Br^- aqueous solutions to construct photoresponsive wormlike micelles through their noncovalent interactions. Their properties were researched using the rheological method, cryo-transmission electron microscopy, and ¹H NMR and two-dimensional nuclear Overhauser effect spectra. The results show that these cinnamate derivatives could well construct wormlike micelles with 12-3-12·2Br^-. Furthermore, subtle differences in the ortho substituents' structure have a significant effect on the photoresponsive behavior of formed wormlike micelles. Specifically, the zero viscosity (η₀) of 40 mM 12-3-12·2Br^-/24 mM trans-OHCA mixed solution decreases from 26.72 to 2.6 Pa·s with the shortening of the length of wormlike micelles after UV irradiation. Correspondingly, the η₀ for the same ratio of 12-3-12·2Br^-/ trans-OMCA decreases from 2.42 to 0.06 Pa·s and the wormlike micelles are transited into rodlike micelles and even spherical micelles after the same UV irradiation time. However, the variation of wormlike micelles in the 12-3-12·2Br^-/ trans-CA system induced by UV light is not obvious with η₀ being maintained at around 2.89 Pa·s. This study will help us better understand the effects of chemical groups on macrophenomena and microinteraction for micellar systems. It provides a theoretical basis for the construction of photoresponsive micelles, thus widening their application in the field of soft materials.

Responsive morphology transition from micelles to vesicles based on dynamic covalent surfactants

A dynamic covalent bond is widely used to fabricate stimuli responsive systems due to its reversible molecular recognition properties. In this study, we developed a pH-responsive morphology transition system based on a mixture of a cationic surfactant CTAB and two nonamphiphilic precursors, 4-hydroxybenzaldehyde (HB) and octylamine (OA), at a molar ratio of 100 : 60 : 60 (CTAB/HB/OA). The morphology transition of CTAB/HB/OA was characterized by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, macroscopic appearance observation, dynamic light scattering, and rheological and cryo-TEM measurements. The phase behavior of CTAB/HB/OA solutions underwent transition from a water-like fluid to a transparent gel-like solution and then converted into a turbid low-viscosity solution upon increasing the pH. Upon increasing the pH from 4.93 to 7.99, the morphology was transformed from spherical micelles to wormlike micelles. Upon further increasing the pH to 12.02, the wormlike micelles gradually disappeared with the formation of vesicles. Thus, a morphology transition from micelles to vesicles can be triggered by varying the pH of CTAB/HB/OA solutions. This drastic variation in morphology behavior was attributed to the pH dependent ionization and formation of the anionic surfactant HB-OA-. Besides, over 3 cycles of morphological alternation among spherical micelles, wormlike micelles and vesicles of the CTAB/HB/OA solutions can be obtained by adjusting the pH.

Enhanced stability and high temperature-tolerance of CO2 foam based on a long-chain viscoelastic surfactant for CO2 foam flooding

CO₂ switchable foams have gained increasing attention recently for their smart properties. However, their performance at high temperature and high pressure has been less documented. In this study, a long-chain viscoelastic surfactant, N1-(3-aminopropyl)-N3-octadecylpropane-1,3-diamine bicarbonate (ODPTA) has been studied as a CO₂ foam agent for its application in CO₂ flooding in complex and harsh reservoir conditions, and the foam performance under static and dynamic conditions was tested up to 160 °C and 10.5 MPa using a visualized foam-meter and in sand-pack flooding experiments. The viscosity of the ODPTA and conventional surfactant solutions saturated with dissolved CO₂ was measured using a long coiled-tube viscometer at HTHP, and its effect on the high temperature-tolerance of CO₂ foams has been analyzed. The experimental results show that CO₂ foam generated using ODPTA is much more stable than the conventional surfactants (such as SDS and alkylphenol ethoxylates) and has high temperature-tolerance up to 160 °C, and has also exhibited excellent mobility control in CO₂ flooding experiments. The viscosity of the ODPTA–CO₂ bulk phase can be maintained as high as 12 mPa s under 160 °C and 10.5 MPa, which is much higher than that of the conventional surfactant solutions (similar to water). ODPTA's good foam performance with extremely high temperature-tolerance can be attributed to its high bulk phase viscosity in the brine water saturated with CO₂.

CO₂ switchable foams have gained increasing attention recently for their smart properties.

Ion-selective molecular inclusion of organic dyes into pH-responsive gel assemblies of zwitterionic surfactants

The pH-Responsive sol–gel transition of a surfactant gel took place along with ion-selective capture and release of dye molecules.

Investigation of Active-Inactive Material Interdigitated Aggregates Formed by Wormlike Micelles and Cellulose Nanofiber

In this work, a novel active-inactive material interdigitated aggregates (AIMIAs) structure was constructed by self-assembled wormlike micelles (WLMs) and one-dimensional cellulose nanofiber (CNF). The rheological behaviors and microstructures of the AIMIA systems with different CNF concentrations were investigated by rheometer, cryogenic transmission electron microscopy, and environmental scanning electron microscope. Some key parameters, including zero-shear viscosity (η₀), relaxing time (τ_R), and contour length ( L), were calculated to analyze the changes in the properties of different systems. Meanwhile, a proper mechanism describing the interaction between CNF and WLMs was proposed. Through this work, we expect to deepen the understanding of the AIMIAs structure and widen its application.

UV-Responsive Behavior of Multistate and Multiscale Self-Assemblies Constructed by Gemini Surfactant 12-3-12·2Br- and trans- o-Methoxy-cinnamate

Photoresponsive systems with adjustable self-assembly morphologies and tunable rheological properties have aroused widespread concern of researchers in recent years because of their prospect applications in controlled release, microfluidics, sensors, and so forth. In this paper, we combine a cationic Gemini surfactant 12-3-12·2Br^- and trans-2-methoxy-cinnamate ( trans-OMCA) together to create a representative UV-responsive self-assembly system. The system displays abundant self-assembly behaviors, and the self-assemblies with different states and different scales including wormlike micelles, vesicles, and lyotropic liquid crystals (LCs) as well as an aqueous two-phase system (ATPS) are observed even at lower surfactant concentration. The UV-responsive behavior of the formed self-assemblies is investigated systematically. The results have shown that the photoisomerization of OMCA from trans form to cis form under UV light irradiation alters the hydrophobicity and steric hindrance effect of OMCA and thus affects the molecular packing at the micellar interface and further leads to the transformation of assembly morphologies. The long wormlike micelles can gradually transform into much shorter rodlike micelles under UV irradiation and companied by the decrease of solution viscosity by 2 orders of magnitude. In addition, the vesicles can evolve into multistate self-assembly structures including the ATPS, wormlike micelles, rod-like micelles, and small spherical micelles depending on the UV irradiation time. The ATPS and its adjacent anisotropic LC phase can respectively combine into a single phase and separate into ATPS under UV irradiation. The morphologies of assemblies in the 12-3-12·2Br^-/ trans-OMCA mixed system can be tailored by adjusting the system composition and duration of UV light irradiation on purpose. The photoresponsive system with abundant self-assembly behaviors and tunable rheological properties has wide application prospect in numerous fields such as drug delivery, materials science, smart fluids, and so forth, and the macroscopic phase separation and combination provide novel strategies for effective separation and purification of certain substances.

A responsive anionic wormlike micelle using pH-directed release of stored sodium based on polybasic acids

Responsive wormlike micelles are very useful in a number of applications, whereas it is still challenging to create dramatic viscosity changes in anionic surfactant systems. Here a differential pH-responsive wormlike micelle based on sulfonic surfactants was developed, which is formed by mixing sodium dodecyl trioxyethylene sulphate (SDES) and ethylenediaminetetraacetic acid tetrasodium (EDTA4-·4Na+) at the molar ratio of 1 : 1. The phase behavior, aggregate microstructure and viscoelasticity of the SDES/EDTA4-·4Na+ solution were investigated via macroscopic observation, cryo-TEM and rheological measurements. It was found that the phase behavior of the SDES/EDTA4-·4Na+ solution undergoes transitions from a water-like fluid to viscoelastic upon decreasing the pH. On decreasing the pH from 12.01 to 3.27 by adding HCl, the viscosity of the transparent solutions with wormlike micelles was increased rapidly and reached ∼3100 mPa s. Furthermore, on increasing the pH by adding NaOH, the viscosity was slightly increased due to the addition of Na+. However, the increase in the concentration of Na+ is much smaller than the theoretical addition. The same phenomenon was noted in the sodium citrate solution, but does not exist in the sodium formate system. The viscosity of the micellar solution has a sensitive response to inorganic acids and tolerance to inorganic bases due to the characteristics of polybasic acids.

Rheological behavior and mechanism of pH-responsive wormlike micelle variations induced by isomers of phthalic acid

Responsive wormlike micelles (WLMs) constructed by different carboxylic acids are fascinating. However, it is unknown how the position of the carboxylic groups alters the stimuli-response of wormlike micellar systems. Herein, three pH-responsive WLMs based on Gemini-like surfactants (named o-EAPA, m-EAPA, and p-EAPA) were formed and studied through the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA) at the molar ratio of 2 : 1. The viscoelasticity, phase behavior and aggregate microstructure were separately explored by rheological, appearance observation and cryo-TEM methods. The results show that all phthalic acids can protonate UC22AMPM, thereby forming WLMs. However, with the shorter spacer distance between two carboxyl groups in phthalic acid, o-EAPA exhibits the longer length scale of aggregates and a more efficient thickening ability compared to the other two systems. Similar results in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, and p-PA systems further verify the applicability of this mechanism. Furthermore, the phthalic acid based WLMs are found to exhibit intriguing reversible pH-responsive behaviors, which include promptly switching between a high elastic system and a low viscosity fluid by pH control. The o-EAPA system possesses a larger viscosity maximum, which produces more precipitous viscosity changes as the pH varies. This study is beneficial for the formation of pH-responsive WLMs and to determine their advantages for applications.

Growth of wormlike micelles in nonionic surfactant solutions: Quantitative theory vs. experiment

Despite the considerable advances of molecular-thermodynamic theory of micelle growth, agreement between theory and experiment has been achieved only in isolated cases. A general theory that can provide self-consistent quantitative description of the growth of wormlike micelles in mixed surfactant solutions, including the experimentally observed high peaks in viscosity and aggregation number, is still missing. As a step toward the creation of such theory, here we consider the simplest system - nonionic wormlike surfactant micelles from polyoxyethylene alkyl ethers, C_iE_j. Our goal is to construct a molecular-thermodynamic model that is in agreement with the available experimental data. For this goal, we systematized data for the micelle mean mass aggregation number, from which the micelle growth parameter was determined at various temperatures. None of the available models can give a quantitative description of these data. We constructed a new model, which is based on theoretical expressions for the interfacial-tension, headgroup-steric and chain-conformation components of micelle free energy, along with appropriate expressions for the parameters of the model, including their temperature and curvature dependencies. Special attention was paid to the surfactant chain-conformation free energy, for which a new more general formula was derived. As a result, relatively simple theoretical expressions are obtained. All parameters that enter these expressions are known, which facilitates the theoretical modeling of micelle growth for various nonionic surfactants in excellent agreement with the experiment. The constructed model can serve as a basis that can be further upgraded to obtain quantitative description of micelle growth in more complicated systems, including binary and ternary mixtures of nonionic, ionic and zwitterionic surfactants, which determines the viscosity and stability of various formulations in personal-care and house-hold detergency.

Reversibly Switching Wormlike Micelles Formed by a Selenium-Containing Surfactant and Benzyl Tertiary Amine Using CO2/N2 and Redox Reaction

Multiresponsive wormlike micelles (WLMs) remain a significant challenge in the construction of smart soft materials based on surfactants. Herein, we report the preparation of a viscoelastic wormlike micellar solution based on a new redox-responsive surfactant, sodium dodecylselanylpropyl sulfate (SDSePS), and commercially available benzyl tertiary amine (BTA) in the presence of CO₂. In this system, SDSePS can be reversibly switched on (selenide) and off (selenoxide) by a redox reaction, akin to that previously reported for benzylselanyl or phenylselanyl surfactants. By alternately adding H₂O₂ and N₂H₄·H₂O, WLMs can be reversibly broken and formed because of the transformation of the hydrophilic headgroup of SDSePS, originating from the reversible formation of selenoxide. Moreover, WLMs can also be switched on and off by cyclically bubbling CO₂ and N₂ because of the variation of the binding interaction between SDSePS and BTA, resulting from the reversible protonation of BTA. This interesting and unique multiresponsive behavior makes the current WLMs a potential candidate for smart control of the "sol-gel" transition or substantial thickening of solutions.

A gemini surfactant-containing system with abundant self-assembly morphology and rheological behaviors tunable by photoinduction

The photoisomerization of OMCA affects the degree of OMCA participation in the formation of mixed micelles and results in the transformation of micellar morphologies.

pH-Responsive self-assembly of cationic surfactants with a star-shaped tetra-carboxylate acid and the solubilization of hydrophobic drugs

This work involved the construction of pH-responsive self-assembly systems from a pH-sensitive four-arm carboxylate acid (4EOCOOH) and either the cationic single chain surfactant dodecyl trimethyl ammonium bromide (DTAB) or the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12). It was found that the constructed oligomeric-like structures from the mixtures of 4EOCOOH with DTAB or 12-6-12 greatly enhance the aggregation ability of the mixtures, thus improving the pH-responsivity. In particular, surfactant concentrations significantly affect the pH-responsivity at a fixed 4EOCOOH concentration. At higher surfactant concentrations, the pH-responsivity is suppressed, while at lower surfactant concentrations, the mixed aggregates gradually change from micelles to unstable large spherical aggregates or vesicles, and then to stable spherical aggregates, with decreasing pH. Moreover, the surfactant/4EOCOOH systems have different solubilization abilities for three hydrophobic drugs. For quercetin and baicalein, the systems support much better solubilization at lower pH values, while for indomethacin, the systems show better solubilization at higher pH values. In particular, compared with DTAB, 12-6-12 is more efficient in constructing pH-responsive systems, and the 12-6-12/4EOCOOH mixture shows better ability for solubilizing hydrophobic drugs. This work will be helpful in the design of high-efficiency, pH-responsive surfactant systems for solubilizing hydrophobic drugs by simply mixing pH-sensitive molecules with surfactants.

The N-allyl substituted effect on wormlike micelles and salt tolerance of a C22-tailed cationic surfactant

Wormlike micelles (WLMs) have been observed in a wide variety of cationic surfactants. Here we developed WLMs based on an N-allyl substituted cationic surfactant with an unsaturated C₂₂-tail, N-erucamidopropyl-N,N-dimethyl-N-allyl-ammonium bromide (EDAA), and compared them with UC₂₂AMPM at the same concentration. The viscoelasticity, aggregate microstructure and salt tolerance of EDAA solutions were investigated by rheology, surface tension and Cryo-TEM measurements. It was found that EDAA exhibited a higher viscosity and a high salt tolerance. Upon increasing the concentration of NaCl, the viscosity of wormlike micelles in the solutions continuously increased and reached ∼1.10 × 10⁶ mP s at 200 mM. On further increasing the NaCl concentration to 2000 mM, the viscosity remained at ∼10⁶ mP s without any reduction. But the viscosity of UC₂₂AMPM solutions showed a drastic change with the increase of NaCl concentration. This drastic variation in rheological behavior is attributed to the presence of the N-allyl substituent. Besides, the EDAA also shows some advantages such as low overlapping concentration(∼2.2 mM) and stable viscosity over the whole pH range.

Understanding the temperature–resistance performance of a borate cross-linked hydroxypropyl guar gum fracturing fluid based on a facile evaluation method

A facile procedure has been proposed to evaluate the temperature–resistance performance of fracturing fluids, which was used to understand the temperature–tolerance performance of a borate cross-linked hydroxypropyl guar gum fracturing fluid.

pH-Responsive wormlike micelles based on microstructural transition in a C22-tailed cationic surfactant–aromatic dibasic acid system

pH-Responsive wormlike micelles based on microstructural transition have been developed by a C₂₂-tailed cationic surfactant and aromatic dibasic acid.