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

Fabrication and Enzymatic Disorganization of Multiresponse Worm-Like Micelles

How to fabricate multiresponse worm-like micelles (WLMs) and the corresponding green disposal is still challenging. A strategy of fabricating the surfactant-based WLMs that can respond simultaneously to light, heat, and pH was developed by using triple-response sodium (E)-2-(4-(phenyldiazenyl)phenoxy) acetate (AzoNa) and butyrylcholinesterase (BChE)-hydrolyzable palmitoylcholine bromide (PCB). Under the optimal molar ratio of AzoNa to PCB (∼0.5), the PCB-AzoNa WLMs formed with a maximum zero-shear viscosity (η0) value of about 2.1 × 105 mPa·s and an average diameter (D) of 4.1 ± 0.6 nm under conditions of 37 °C and pH 7.4. After irradiated with 365 nm UV light for 80 min, AzoNa underwent the trans-to-cis transition, by which the PCB-AzoNa WLMs was destroyed; however, the PCB-AzoNa WLMs could be reformed upon the irradiation of 455 nm blue light for 18 h or heating at 70 °C for 45 min due to the cis-to-trans isomerization of AzoNa. When pH changed from 7.4 to 2.0, the PCB-AzoNa WLMs was destroyed rapidly because of the conversion of AzoNa to the acid form of AzoH, whereas the PCB-AzoNa WLMs could be reformed after pH was restored to 7.4. The multiple responsiveness of the PCB-AzoNa WLMs was reversible due to the reversible trans-cis isomerization or protonation of AzoNa. Besides, the average D values of light, heat, and pH-regenerated PCB-AzoNa WLMs were 4.2 ± 0.7, 4.0 ± 0.7, and 4.0 ± 0.6 nm, respectively. Finally, the PCB-AzoNa WLMs could be enzymatically disorganized under conditions of 37 °C and pH 7.4 due to the BChE-catalyzed hydrolysis of PCB. We hope that the fabrication and enzymatic disorganization strategies for PCB-based multiresponse WLMs presented here will find potential applications in the formulation of antimicrobial household and personal care products containing PCB and in the green disposal of viscous waste containing PCB.

Stimuli-responsive viscosity modifiers

Stimuli responsive viscosity modifiers entail an important class of materials which allow for smart material formation utilizing various stimuli for switching such as pH, temperature, light and salinity. They have seen applications in the biomedical space including tissue engineering and drug delivery, wherein stimuli responsive hydrogels and polymeric vessels have been extensively applied. Applications have also been seen in other domains like the energy sector and automobile industry, in technologies such as enhanced oil recovery. The chemistry and microstructural arrangements of the aqueous morphologies of dissolved materials are usually sensitive to the aforementioned stimuli which subsequently results in rheological sensitivity as well. Herein, we overview different structures capable of viscosity modification as well as go over the rheological theory associated with classical systems studied in literature. A detailed analysis allows us to explore correlations between commonly discussed models such as molecular packing parameter, tube reptation and stress relaxation with structural and rheological changes. We then present five primary mechanisms corresponding to stimuli responsive viscosity modification: (i) packing parameter modification via functional group conditioning and (ii) via dynamic bond formation, (iii) mesh formation by interlinking of network nodes, (iv) viscosity modification by chain conformation changes and (v) viscosity modification by particle jamming. We also overview several recent examples from literature that employ the concepts discussed to create novel classes of intriguing stimuli responsive structures and their corresponding rheological properties. Furthermore, we also explore systems that are responsive to multiple stimuli which can provide enhanced functionality and versatility by providing multi-level and precise actuation. Such systems have been used for programmed site-specific drug delivery.

Unusual Increasing Viscoelasticity of Wormlike Micelles Composed of Imidazolium Gemini Surfactants with Temperature

The viscoelasticity of wormlike micelles composed of ionic surfactants typically shows an exponential decrease with increasing temperature, which limits their application in relatively high-temperature (>90.0 °C) oilfields and the synthesis of functional materials as supramolecular templates at high temperatures. In this work, a series of imidazolium gemini surfactants, 1,9-(ethane-1,2-diyl)bis(3-alkyl-1H-imidazol-3-ium) bromide ([C_n-2-C_nim]Br₂, n = 12, 14, 16, 18, 20), were synthesized. Their surface activities and aggregation behaviors in water were studied by electrical conductivity, rheology, polarization optical microscopy, small-angle X-ray scattering, ζ potential, and hydrogen nuclear magnetic resonance measurements. [C₁₂-2-C₁₂im]Br₂ and [C₁₄-2-C₁₄im]Br₂ mainly precipitate in water. [C_n-2-C_nim]Br₂ (n = 16, 18, 20) forms lamellar liquid crystals over a large range of concentrations at low temperatures. With the increase of temperature, the lamellar liquid crystals transit to wormlike micelles. Interestingly, the viscoelasticity of the three wormlike micelles first increases to the maximum and then decreases with increasing temperature. These wormlike micelles without additives retain high viscoelasticity up to 90.0 °C or above. With the increase of the alkyl chain length of the surfactants, the transition temperature of lamellar liquid crystal to wormlike micelles and the disintegration temperature of wormlike micelles increase. The unusual increase of the viscoelasticity of wormlike micelles was due to the desorption of weakly bound counterions and the extension of the long hydrophobic chains of surfactants at high temperatures.

Gradual transformation of anionic/zwitterionic wormlike micelles from viscous to elastic domains: Unravelling the effect of anionic surfactant chain length

HYPOTHESIS

Ultra-long tailed zwitterionic surfactants often form aqueous wormlike elastic micelles, whereas the shorter ones mainly exhibit spherical viscous micelles. Anionic surfactants are widely used to tune the micellar morphology from spherical into wormlike. Systematic investigations in the molecular level are insightful to understand the viscoelasticity regulative mechanism.

EXPERIMENTS

Anionic/zwitterionic hybrid wormlike micelles are composed of sodium alkylsulfate (SAS) homologues and dodecyl dimethyl amidopropyl hydroxyl sulfobetaine (DHSB). The formation of wormlike micelles was studied by employing rheometer, cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering (SAXS) techniques. The effects of surfactant concentration, molar ratio, anionic surfactant chain length and temperature were investigated systematically.

FINDINGS

SAS promoted the formation of SAS/DHSB hybrid wormlike micelles. The increase in both chain length and molar ratio (x_SAS) of SAS are advantageous in the enhancement of viscosity. Interestingly, sodium hexadecylsulfate (SHS) endowed elastic wormlike micelles with thermally insensitive viscosity below its Krafft temperature (T_k), which was distinguished from the viscous ones formed by sodium octylsulfate (SOS). SAXS results showed that the size of SAS/DHSB wormlike micelles was primarily determinate by surfactants with longer hydrophobic tails.

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.

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.