Thermal and pH dual stimulated wormlike micelle in aqueous N-cetyl-N-methylpyrrolidinium bromide cationic surfactant-aromatic dibasic acid system

pH and light dual stimuli-responses of mixed system of 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecyl ammonium bromide) and trans-ortho-hydroxyl cinnamic acid

Stimuli-responsive smart supramolecular self-assembly with controllable morphology and adjustable rheological property has attracted widespread concern of scientists in recent years due to the great potential application in microfluidics, controlled release, biosensors and so on. In this study, a pH and UV light dual stimuli-responsive system was constructed by combining Gemini surfactant 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecyl ammonium bromide) (12-3(OH)-12·2Br^-) with trans-ortho-hydroxyl cinnamic acid (trans-OHCA) in aqueous solution. The phase behavior and stimuli-responsive behavior of the system including the microstructural transition, rheological property, intermolecular interaction, and isomerization reaction were explored by various experiment techniques such as rheometer, UV-vis spectrum, polarized optical microscopy (POM), transmission electron microscopy (TEM), dynamic light scattering (DLS) as well as theoretical calculation. The system displays abundant phase behaviors that supramolecular self-assemblies of different morphologies in different states such as spherical micelle, wormlike micelle, lamellar liquid crystal, and aqueous two phase system (ATPS) were observed even at lower concentration, which provide the research basis on the abundant stimuli-responsiveness of the system. The results prove that the multiple ionization and the photo-isomerization of trans-OHCA endow the system with plentiful responses to pH and UV light stimuli. It is expected that this study on the dual stimuli-responsive system with abundant self-assembly behaviors and adjustable rheological behaviors would be of theoretical and practical importance, which would provide essential guidance in designing and constructing smart materials with multiple stimuli-responses.

Imparting pH and temperature dual-responsiveness in a micellar solution of cationic surfactants by introducing a hydrotrope

Over the recent years, intelligent, multi-responsive micelles have received considerable attention due to their promising application in a variety of fields, including biomedical technology, drug delivery, separation, and catalysis. However, the design of such systems with controlled self-assembly is challenging both experimentally and theoretically and is still in the nascent stage. In this study, a novel dual-stimuli triggered wormlike micellar solution is prepared by mixing cationic surfactants 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R₁₆HTAB) and sodium hydrogen phthalate (SHP). The viscoelasticity, aggregate morphology, and pH- and thermo-responsive behavior of the micellar solution are examined by rheological measurements, cryogenic-transmission electron microscopy (cryo-TEM), nuclear magnetic resonance (¹H NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The dual-sensitive fluid can be switched between a water-like state and a gel-like state by adjusting the pH and temperature. The variations in the flowing behavior are ascribed to the microstructural transition between wormlike micelles, short cylindrical micelles, and spherical micelles. Furthermore, based on the experimental results, dual-responsive behavior of the mixed solution is attributed to the different binding modes between SHP and the surfactant with the variation in the pH and temperature. We hope that the proposed system provides a new route for developing multi-stimuli-responsive materials that are capable of adapting to local environmental variations.

pH and Redox Dual-Stimulated Wormlike Micelles Based on Cystamine and Conventional Anionic Surfactant

Redox-responsive soft materials have attracted considerable concerns throughout the last few decades. Herein, we report the preparation of dual-stimulated wormlike micelles (WLMs) based on N,N,N',N'-tetramethylcystamine dihydrochloride (TMCDD) and a conventional anionic surfactant, sodium dodecyl sulfate (SDS). The WLMs can be reversibly switched on and off by adjusting pH, resulting from the reversible protonation of TMCDD. Moreover, the WLMs can be destroyed by a redox reaction after addition of dithiothreitol (DTT), originating from the cleavage of the disulfide bonds in TMCDD. The dual responsiveness of the WLMs allowed for the smart control of the "sol-gel" transition or thickening of viscoelastic solutions, and the micelles will have a wider range of applications in the development of functional materials for pharmaceutical or biomedical materials.

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.

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.

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.

Smart worm-like micelles responsive to CO2/N2 and light dual stimuli

CO₂/N₂ and light dual stimuli-responsive worm-like micelles (WLMs) were obtained by addition of a relatively small amount of a switchable surfactant, 4-butyl-4'-(4-N,N-dimethylhexyloxy-amine) azobenzene bicarbonate (AZO-B6-CO₂), sensitive to the same triggers to a binary aqueous solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal).

Rheological characterizations and molecular dynamics simulations of self-assembly in an anionic/cationic surfactant mixture

The formation of self-assemblies in mixed amino acid-based anionic N-hexadecanoylglutamic acid (HGA) and cationic benzyldimethyl hexadecylammonium chloride (HDBAC) surfactants in aqueous solutions has been characterized. With rheological analysis, the viscoelastic properties of the mixed system are found to be completely dependent on the concentration of HDBAC. Molecular dynamics simulation results suggest that the morphology of self-assembly can be regulated from spherical micelles to wormlike micelles by the addition of HDBAC. The aromatic group of HDBAC adsorption provides a "charge-neutral" function to the micelle corona; the repulsive interactions within the head group of HGA are progressively screened and closely packed. In addition, the dynamic processes and formation mechanisms of self-assembly were analyzed in detail with molecular simulation techniques.