Edible CO2-Responsive Wormlike Micelles with Docosahexaenoic Acid

Due to their unique microstructure and modifiable rheological properties, wormlike micelles that respond to environmental stimulation have garnered significant interest in recent years. Among them, CO2-responsive wormlike micelles have the advantages of simple preparation and controllable properties, which have significant development potential in the food chemistry field of thickeners. In this study, CO2-responsive wormlike micelles were prepared using docosahexaenoic acid (DHA), pyridoxamine (PA), and glucosamine (GA); the stimulus-responsive behaviors and mechanisms of the two systems, namely, NaDHA/PA and NaDHA/GA, were investigated using dynamic light scattering (DLS) and cryo-transmission electron microscopy (Cryo-TEM). The nearly unaltered viscosity of the systems confirmed the cyclic reversibility of the CO2 response of the two systems when the two mixed solutions were converted back to aqueous liquids 10 times. The preparation and properties of DHA-based CO2-responsive wormlike micelles are expected to advance fundamental research and establish the theoretical groundwork for their practical application in controllable thickening agents in food chemistry.

Pickering Emulsions and Viscoelastic Solutions Constructed by a Rosin-Based CO2-Responsive Surfactant

Designing stimulus-switch viscoelastic solutions and Pickering emulsions with reversible CO2-responsive behavior remains a challenge. A rosin-based CO2-responsive surfactant, N-cetyl-maleimidepimaric acid N,N-dimethylenediamide (C16MPAN), was synthesized and used to prepare CO2-triggered viscoelastic solutions and Pickering emulsions. This surfactant exhibited excellent CO2-responsive performance in water and formed a viscoelastic solution. This viscoelastic system was investigated by dynamic light scattering (DLS), rheology, and cryogenic transmission electron microscopy (Cory-TEM). The shear viscosity of the system increased by 3-4 orders of magnitude after bubbling with CO2 and a large number of elongated, flexible, tubular wormlike micelles were observed. Further, Pickering emulsions were prepared by C16MPAN+ synergistically with cellulose nanocrystals (CNCs), whose stability and switchability were investigated via adsorption isotherm, droplet size, contact angle, and macroscopic photographs. C16MPAN+ was adsorbed with CNCs to form mechanical barriers at the oil-water interface, making the emulsion stable for at least three months, and desorption from CNCs enabled emulsion breaking. The cycle could be switched reversibly multiple times and the particle size distribution of emulsion was basically the same. This work enriches the application of biomass resources in intelligent responsive materials.

Investigation of Polymer-Assisted CO2 Flooding to Enhance Oil Recovery in Low-Permeability Reservoirs

CO2 flooding is a favorable technical means for the efficient development of low-permeability reservoirs, and it can also contribute to the realization of net-zero CO2 emissions. However, due to the unfavorable viscosity ratio and gravity overriding effect, CO2 channeling will inevitably occur, seriously affecting its storage and displacement effects. This paper conducts a systematic study on the application of polymer-assisted CO2 flooding in low-permeability reservoirs. Firstly, the polymer agent suitable for low-permeability reservoirs is optimized through the viscosity-increasing, rheological, and temperature- and salt-resistant properties of the solution. Then, the injectivity performance, resistance-increasing ability, and profile-improving effect of the polymer solution were evaluated through core experiments, and the optimum concentration was optimized. Finally, the enhanced oil recovery (EOR) effects of polymer-assisted and water-assisted CO2 flooding were compared. The results show that the temperature-resistant polymer surfactant (TRPS) has a certain viscosity-increasing performance, good temperature resistance performance, and can react with CO2 to increase the solution viscosity significantly. Meanwhile, TRPS has good injection performance and resistance-increasing effect. The resistance increasing factor (η and η') of TRPS-assisted CO2 flooding increases with increased permeability, the concentration of TRPS solution, and injection rounds. Considering η' and the profile improvement effect comprehensively, the application concentration of TRPS should be 1000 mg/L. The EOR effect of TRPS-assisted CO2 flooding is 8.21% higher than that of water-assisted CO2 flooding. The main effective period is in the first and second rounds, and the best injection round is three. The research content of this paper can provide data support for the field application of polymer-assisted CO2 flooding in low-permeability reservoirs.

Developing aerogel surfaces via switchable-hydrophilicity tertiary amidine coating for improved oil recovery

Blanket aerogels (i.e., Cabot™ Thermal Wrap® (TW) and Aspen™ Spaceloft® (SL)) with surfaces that have controllable wettability are promising advanced materials for oil recovery applications, where high oil uptake during deployment could be coupled with high oil release to enable reusability of recovered oil. The study presented here details the preparation of CO₂-switchable aerogel surfaces through the application of switchable tertiary amidine (i.e., tributylpentanamidine (TBPA)) onto aerogel surfaces using drop casting, dip coating, and physical vapor deposition techniques. TBPA is synthesized via two step processes: (1) synthesis of N, N-dibutylpentanamide, (2) synthesis of N, N-tributylpentanamidine. The deposition of TBPA is confirmed by X-ray photoelectron spectroscopy. Our experiments revealed that surface coating of TBPA onto aerogel blankets was partially successful within limited set of process conditions (e.g., 290 ppm CO₂ and 5500 ppm humidity for PVD, 106 ppm CO₂ and 700 ppm humidity for drop casting and dip coating), but that the post-aerogel modification strategies yielded poor, heterogeneous reproducibility. Overall, more than 40 samples were tested for their switchability in the presence of CO₂ and water vapor, respectively, and the success rate was 6.25 %, 11.7 % and 18 % for PVD, drop casting, and dip coating, respectively. The most likely reasons for unsuccessful coating onto aerogel surfaces are: (1) the heterogeneous fiber structure of the aerogel blankets, (2) poor distribution of the TBPA over the aerogel blanket surface.

Application of Recently used Green Solvents in Sample Preparation Techniques: A Comprehensive Review of Existing Trends, Challenges, and Future Opportunities

Green solvents (GSs) has gained significant attention in recent years due to their potential as safer and more sustainable alternatives to traditional organic solvents. Solvents are used in a wide range of applications, from industrial processes to everyday products. Solvent emissions and losses can have a significant impact on the environment and human health, which is why many initiatives are being undertaken to get rid of or switch to eco-friendly alternatives. A key area of green chemistry that led to the concept of "green" solvents is the development of alternative solvents that are less toxic and more environmentally friendly than traditional organic solvents. The advantages of using green solvents over conventional ones are their environmental friendliness, biocompatibility, biodegradability, and simplicity of preparation. Different sample preparation techniques have successfully utilized green solvents to offer a sustainable separation media for the extraction of a variety of inorganic and organic compounds which are crucial for research in environmental samples. Recent developments in green analytical chemistry (GAC) have focused on how to prepare and use samples using environmentally sustainable solvents. The current study covers the advance and currently used green solvents with an emphasis on environmentally friendly sample preparation methods. This review aims to briefly summarize the current state of knowledge about the use of green solvents particularly ionic liquids, deep eutectic solvents and switchable solvents (SSs) with the perspective of GAC in sample preparation methods.

Advances in CO2-switchable surfactants towards the fabrication and application of responsive colloids

CO₂-switchable surfactants have selective surface-activity, which can be activated or deactivated either by adding or removing CO₂ from the solution. This feature enables us to use them in the fabrication of responsive colloids, a group of dispersed systems that can be controlled by changing the environmental conditions. In chemical processes, including extraction, reaction, or heterogeneous catalysis, colloids are required in some specific steps of the processes, in which maximum contact area between immiscible phases or reactants is desired. Afterward, the colloids must be broken for the postprocessing of products, solvents, and agents, which can be facilitated by using CO₂-switchable surfactants in surfactant-stabilized colloids. These surfactants are mainly cationic and can be activated by the protonation of a nitrogen-containing group upon sparging CO₂ gas. Also, CO₂-switchable superamphiphiles can be formed by non-covalent bonding between components at least one of which is CO₂-switchable. So far, CO₂-switchable surfactants have been used in CO₂-switchable spherical and wormlike micelles, vesicles, emulsions, foams, and Pickering emulsions. Here, we review the fabrication procedure, chemical structure, switching scheme, stability, environmental conditions, and design philosophy of such responsive colloids. Their fields of application are wide, including emulsion polymerization, catalysis, soil washing, drug delivery, extraction, viscosity control, and oil transportation. We also emphasize their application for the CO₂-assisted enhanced oil recovery (EOR) process as a promising approach for carbon capture, utilization, and storage to combat climate change.

CO2-triggered switchable solvent for lipid extraction from microalgal biomass

This study proposed a novel and energy-efficient method using switchable polarity solvents for lipid recovery from microalgae. Different from the existing methods, use of switchable polarity solvents does not require the fractional distillation for separation of lipid and solvent by only converting the polarity of the solvent after lipid extraction. When a non-polar amine solvent reacts with CO₂, amino group (NH) can be transformed to a polar form, i.e. carbamate (NHCOO^-). Nuclear magnetic resonance (NMR) spectrum indicated that only secondary amines are convertible to a polar compound of carbamate after CO₂ treatment. The polarity switching potential of each amine candidate was quantitatively evaluated by normalized polarity energy (E_T^N). Dipropylamine (DPA) showed the greatest change in E_T^N from 0.452 to 0.789 kcal/mol (E_T^N of water = 1.0 kcal/mol) before and after CO₂ treatment. DPA is a potential polarity switchable solvent capable of achieving an excellent lipid extraction yield of 7.51% from tested microalgal biomass (Chlorella vulgaris) with 9.16% of total lipid content and 95.5% fatty acid methyl esters (FAMEs) content. Furthermore, the used solvent could be recovered at the high efficiency of 84.0%. With a significant polarity switchability from nonpolar amine to carbamate in the presence of CO₂, DPA, a secondary amine, could be suggested as a suitable solvent used for both extraction of lipids with a higher FAMEs content from microalgae and separation of lipid by only adding CO₂.

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).

Diol responsive viscosity increase in a cetyltrimethylammonium bromide/sodium salicylate/3-fluorophenylboronic acid micelle system

We report a novel smart micellar system utilising a phenylboronic acid (PBA) derivative whose viscosity increases on adding diol compounds such as sugar or sugar alcohol. We prepared a typical worm-like micelle (WLM) system in 100 mM cetyltrimethylammonium bromide (CTAB)/70 mM sodium salicylate (NaSal), which showed high zero-shear viscosity (η 0). Upon the addition of 20 mM 3-fluorophenylboronic acid (3FPBA) to the WLM system, η 0 decreased by 1/300 that of the system without 3FPBA. Furthermore, upon the addition of 1.12 M fructose (Fru) and 1.12 M sorbitol (Sor) to the CTAB/NaSal/3FPBA system, η 0 increased by 50-fold and 30-fold, respectively. 19F NMR spectral results of the systems using 4-fluorosalicylic acid (FSal) instead of NaSal demonstrated that the FSal/3FPBA-complex interacts with CTAB. Moreover, the addition of sugar or sugar alcohol to the micellar system leads to a decrease in the amount of FSal/3FPBA-complex interacting with CTA+ and an increase in the amount of 3FPBA/Fru or Sor-complex, which does not interact with CTA+. These changes in molecular interactions induce the elongation of the WLMs and increase the viscosity of the system. This system utilises the competitive cyclic ester bond between the NaSal/3FPBA and 3FPBA/sugar or sugar alcohol to induce viscosity changes.

A pH, thermal and light triple-stimuli responsive micellar solution formed by a cationic surfactant and trans-o-hydroxycinnamic acid

Controlling the viscoelastic characteristics of wormlike micelles is of great significance to both basic theory and practical applications. In this article, a novel multi-stimuli responsive wormlike micellar solution was prepared by mixing cationic surfactant 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R₁₆HTAB) with trans-o-hydroxycinnamic acid (OHCA). Rheological studies, nuclear magnetic resonance (¹H-NMR) spectroscopy, UV-vis spectroscopy, and cryogenic-transmission electron microscopy (cryo-TEM) were utilized to investigate the wormlike micellar system's multi-responsive activity. The results showed that the self-assembled structure and viscoelasticity of the mixed system could be regulated by pH, temperature, and light irradiation. With the increasing trans-OHCA concentration, η₀ of the mixed solution increases first and then decreases and the turning point is presented at 30 mM trans-OHCA, indicating the transformation of spherical micelles to wormlike micelles, and then to short micelles. The microstructure of the mixed systems could be reversibly altered by adjusting the pH between 6.41 and 3.90, which was ascertained by cryogenic-transmission electron microscopy (cryo-TEM). The relationship of temperature and η₀ obeys the Arrhenius law, attributed to the decreasing micellar contour length. η₀ of a 40 mM R₁₆HTAB/15 mM OHCA solution sharply increases after UV irradiation, mainly because the cis-isomer could insert into the micelle more easily, and the transition mechanism was studied by UV-vis and ¹H NMR. The multi-responsive self-assembled system may open a new vista for building multi-functional aggregates to adapt to various environmental changes.

Behavior of Smart Surfactants in Stabilizing pH-Responsive Emulsions

Newly structured pH-responsive smart surfactants (N⁺ -(n)-N, n=14, 16) from alkyl trimethylammonium bromides are reported. In neutral and alkaline media N⁺ -(n)-N behaves as a normal cationic surfactant and stabilizes conventional emulsions alone, as well as Pickering emulsions and oil-in-dispersion emulsions together with oppositely and similarly charged nanoparticles, respectively. In acidic media N⁺ -(n)-N becomes a hydrophilic Bola-type surfactant, N⁺ -(n)-NH⁺ , and is an inferior emulsifier either when used alone or together with charged nanoparticles, resulting in demulsification. N⁺ -(n)-NH⁺ returns to the aqueous phase alone or together with nanoparticles after demulsification without contaminating the oil phase, and the aqueous phase can be recycled when triggered by pH change. This protocol is a green process and leads to preparation of various temporarily stable emulsions which are often used in emulsion polymerization, heterogeneous catalysis, and oil transportation.

Dual CO2 Responsiveness of an Oil-In-Water Emulsion by Using Sodium Oleate and Water-Soluble Tertiary Amines

Two kinds of water-soluble tertiary amines (TAs), triethylamine (TEA, monoamine), and tetramethyltrimethylenediamine (TMA, diamine) were introduced into a NaOA stable oil-water (O/W) emulsion, respectively, and their dual reactivity to carbon dioxide was studied. TA was converted into bicarbonate after bubbling of CO₂, which induced the increase of ionic strength of the aqueous phase, and formed ion pair with NaOA through electrostatic interaction. NaOA itself can also be protonated into oleic acid, which can be reverently deprotonated by alternating bubbles of CO₂ at 25 °C and N₂ at 50 °C, thus affecting the stability and demulsification process of the emulsion. In order to demonstrate TA's and NaOA's synergistic effect on CO₂ responsiveness, gas chromatography-mass spectrometry, ζ potential, electrical conductivity, pH value, ¹H nuclear magnetic resonance, morphological evolution, and interfacial tension were used to study the contributions of the single component and two components of NaOA, TEA, and TMA to emulsion stability and CO₂ responsiveness, respectively. Combined with the composition distribution under different pH conditions, it was further proved that TAs had an effect on the stability and CO₂ responsiveness of the NaOA emulsion.

A CO2-responsive smart fluid based on supramolecular assembly structures varying reversibly from vesicles to wormlike micelles

CO2-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO2-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles. Firstly, oleic acid and 3-dimethylaminopropylamine reacted to form a single-chain weak cationic surfactant with a tertiary amine head group, N-[3-(dimethylamino)propyl]oleamide (NDPO). Then, 1,3-dibromopropane was used as the spacer to react with NDPO to form a gemini cationic surfactant, trimethylene α,ω-bis(oleate amide propyl dimethyl ammonium bromide) (GCS). By controlling the feed ratio of 1,3-dibromopropane and NDPO, we found that the mixtures of GCS and NDPO with the molar ratio of 7 : 3 approximately could form vesicles in aqueous solution by supramolecular self-assembly. After bubbling CO2, the tertiary amine of NDPO was protonated. The packing parameter of the mixed surfactants reduced accordingly, accompanied by the transition of aggregates from vesicles to wormlike micelles. As a result, the zero-shear viscosity of the solution increased by more than four orders in magnitude. When the solid content of GCS/NPDO mixtures was higher than 5 wt% in solution, the sample treated by CO2 behaved as a gel over a wide frequency range with shear-thinning and self-healing properties. In addition, the sol-gel transition could be repeatedly and reversibly switched by cyclically bubbling CO2 and N2. Our effort may provide a new strategy for the design of CO2-responsive smart fluids, fostering their use in a range of applications such as in enhanced oil recovery.

Diblock, Triblock and Cyclic Amphiphilic Copolymers with CO2 Switchability: Effects of Topology

The combination of topology and CO2 switchability could provide new options for amphiphilic copolymers. Cyclic molecules supply novel topologies, and CO2 switching provides stimulus responsiveness. Cyclic poly(2-(diethylamino)ethyl methacrylate)-b-poly(ethylene oxide) and their corresponding block copolymers were prepared from poly(ethylene oxide) and 2-(diethylamino)ethyl methacrylate via atom transfer radical polymerization and Keck allylation with a Hoveyda-Grubbs catalyst. Changes in conductivity, surface activity, and hydrodynamic size were examined to illustrate the switchability of the produced amphiphilic copolymers upon contact with CO2 in the presence of water. The reversible emulsification and switchable viscosity behaviors of the copolymers were also demonstrated.

Different strategies of foam stabilization in the use of foam as a fracturing fluid

An attractive alternative to mitigate the adverse effects of conventional water-based fluids on the efficiency of hydraulic fracturing is to inject foam-based fracking fluids into reservoirs. The efficiency of foaming fluids in subsurface applications largely depends on the stability and transportation of foam bubbles in harsh environments with high temperature, pressure and salinity, all of which inevitably lead to poor foam properties and thus limit fracturing efficiency. The aim of this paper is to elaborate popular strategies of foam stabilization under reservoir conditions. Specifically, this review first discusses three major mechanisms governing foam decay and summarizes recent progress in research on these phenomena. Since surfactants, polymers, nanoparticles and their composites are popular options for foam stabilization, their stabilizing effects, especially the synergies in composites, are also reviewed. In addition to reporting experimental results, the paper also reports recent advances in interfacial properties via molecular dynamical simulation, which provide new insights into gas/liquid interfacial properties under the influence of surfactants at molecular scale. The results of both experiments and simulations indicate that foam additives play an essential role in foam stability and the synergic effects of surfactants and nanoparticles exhibit more favorable performance.

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.

Controllable CO2-Responsiveness of an Oil-in-Water Emulsion by Varying the Number of Tertiary Amine Groups or the Position of the Hydroxyl Group of Tertiary Amine

A series of water-soluble tertiary amines (TAs) are introduced into an oil-in-water (O/W) emulsion stabilized by sodium oleate (NaOA). TAs convert into bicarbonate salts upon bubbling of CO₂, which could induce the increase of ionic strength of the aqueous phase, form ion pairs with NaOA by electrostatic interaction, and finally result in demulsification. ζ-Potential, conductivity, pH value, ¹H NMR, separation rate, and interfacial tension are applied to figure out the effects of number of tertiary amine groups and different positions of the hydroxyl group. TA with an increasing number of tertiary amine groups can further stabilize the O/W emulsion and accelerate the process of demulsification by bubbling CO₂. More tertiary amine groups bring about a more stable emulsion and faster demulsification by bubbling CO₂. The position of the hydroxyl group is a key factor affecting the solubility of the corresponding ion pair formed with NaOA. The better the water solubility, the slower the demulsification. The worse the water solubility of the ion pair, the more perfect the demulsification is. More importantly, water-soluble TA, with proper structure, could bring about perfect demulsification.

Depletion driven self-assembly of block copolymer solutions by homopolymers

The addition of a non-adsorbing homopolymer to a block copolymer solution provides a convenient strategy for regulating its self-assembly. We systematically investigate the depletion effect from a homopolymer on the morphologies of AB diblock and BAB triblock copolymers in selective solvents. Increasing the homopolymer content results in larger spherical micelles, and the curvature of micelles is proportional to the square of homopolymer concentrations. A high enough homopolymer concentration may transfer micelles into vesicles. A deep analysis shows that the depletion effect produces attractive interaction between hydrophilic B blocks as well as their contraction on the micellar surface. The size of triblock copolymer micelles is not affected by homopolymers significantly, and spherical-to-wormlike micelle transition occurs at high homopolymer contents. These results have important applications for the precise design of self-assembled nanostructures of copolymer systems.

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.

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.

Light and CO2/N2 dual stimuli-responsive wormlike micelles based on a zwitterionic surfactant and an azobenzene surfactant

Stimulus-responsive surfactant wormlike micelles have been widely investigated in the past decade. In this article, we report light and CO₂/N₂ dual stimuli-responsive wormlike micelles using a zwitterionic surfactant (SDAP) and an azobenzene surfactant (C₄AzoC₆N). In contrast to traditional amine-containing wormlike micelles, a fast and reversible CO₂-triggered thinning behavior was observed. The system can also be reversibly switched by UV irradiation. The dual stimuli-responsive wormlike micelles (C₄AzoC₆N-SDAP) may have applications in the development of functional materials for microfluidics and analytical chemistry.

CO2-Switchable Membranes Prepared by Immobilization of CO2-Breathing Microgels

Herein, we report the development of a novel CO₂-responsive membrane system through immobilization of CO₂-responsive microgels into commercially available microfiltration membranes using a method of dynamic adsorption. The microgels, prepared from soap-free emulsion polymerization of CO₂-responsive monomer 2-(diethylamino)ethyl methacrylate (DEA), can be reversibly expanded and shrunken upon CO₂/N₂ alternation. When incorporated into the membranes, this switching behavior was preserved and further led to transformation between microfiltration and ultrafiltration membranes, as indicated from the dramatic changes on water flux and BSA rejection results. This CO₂-regulated performance switching of membranes was caused by the changes of water transportation channel, as revealed from the dynamic water contact angle tests and SEM observation. This work represents a simple yet versatile strategy for making CO₂-responsive membranes.

UV and NIR dual-responsive self-assembly systems based on a novel coumarin derivative surfactant

Controllable self-assembly systems have attracted increasing attention in both the academic and industrial fields recently. Herein, we designed and synthesized a new photo-degradable anionic surfactant (PAS) with a coumarin group which could be degraded by both UV and NIR light. Thus, the micelles that are formed by sodium salts of PAS (PAS-Na) could be broken controllably under UV or NIR irradiation. Surface tension measurements, DLS, and Cryo-TEM were adopted to investigate the formation and disruption of PAS-Na micelles. PAS could also form wormlike micelles and vesicles when they co-assembled with common surfactant tetradecyldimethylamine oxide (C₁₄DMAO). These wormlike micelles and vesicles could be degraded by UV and NIR irradiation due to the participation of PAS. Accordingly, the rheology properties of the wormlike micelles and vesicles were also changed significantly. Finally, the stimulus-responsive system was used to control the diffusion of hydrophobic and hydrophilic molecules. And it has shown controllable release effects on both the hydrophobic and hydrophilic molecules.

Responsive, switchable wormlike micelles for CO2/N2 and redox dual stimuli based on selenium-containing surfactants

A dual-stimuli responsive, wormlike micelle system was developed using a switchable selenium-containing surfactant, dihendecylcarboxylic acid sodium selenide (C₁₁-Se-C₁₁), and a commercially available surfactant, cetyltrimethyl ammonium bromide (CTAB). The solution showed a viscoelastic characteristic at low shear frequencies, and the synergism was significant when the concentrations of CTAB and C₁₁-Se-C₁₁ were 145 mM and 25 mM, respectively. Additionally, the system was fast and reversibly responded to CO₂ and redox dual stimuli, and it showed a circulatory gel/sol transition, which reflected changes in the self-assembly from entangled worms to rodlike micelles. Moreover, these transitions were switchable at least three times. The dual responsiveness of the solution allowed for precise control of the wormlike micelles, and these micelles will have a wide range of applications in the development of functional materials for pharmaceutical or biomedical materials.