Wormlike Micellar System Research Articles

PH-responsive wormlike micelles formed by an anionic surfactant derived from erucic acid

An erucic acid-based anionic surfactant, AdEr, was synthesized by a simple neutralization reaction, and AdEr constructed a novel pH-responsive wormlike micellar viscoelastic system in the presence of potassium chloride (KCl). The viscoelasticity and pH-responsiveness of the pH-responsive wormlike micelles have been investigated using rheology, and its corresponding mechanism has been analyzed by Fourier transform infrared (FT-IR) spectra. The zero-shear viscosity (η0) of the AdEr/KCl system dramatically increases by 5 orders of magnitude as the pH increases from 6 to 10. The viscoelastic fluids and dispersion system with white precipitate can be converted by tuning the pH between 10.46 and 6.03, and the corresponding aggregates also transform between wormlike micelles and spherical micelles. Furthermore, by directly adding acid and alkali, the AdEr/KCl system can be precisely reversibly controlled in the pH range 6–10, and the viscosity stays unchanged after three reversible cycles, exhibiting strong pH reversibility. The pH-responsive behavior can be attributed to the manipulation of carboxylic acid protonation. This study promotes new applications of erucic acid resources in smart viscoelastic solutions.

Origin of steady state stress fluctuations in a shear-thinning worm-like micellar system

Large, irregular stress fluctuations under a constant applied shear rate are observed during the flow of dilute worm-like micellar solutions even at low Reynolds numbers. Statistical properties of such fluctuations showing signatures of chaos and elastic turbulence have been studied extensively. Although the mechanisms like boundary slippage, dynamics of shear band interface, time-dependent secondary flows, and inertio-elastic effects are conceived as the possible factors for such striking flow properties, their contributions in different non-linear flow regimes remain poorly understood. Here, we study the Taylor–Couette flow of a well-characterized aqueous worm-like micellar system formed by 2 wt. % cetyltrimethylammonium tosylate and 100 mM sodium chloride (2 wt. % CTAT + 100 mM NaCl). For a fixed applied shear-rate just beyond the onset of shear-thinning, high-speed optical imaging in the flow-gradient plane reveals spatiotemporally varying velocity gradients in the system. In this regime, the magnitude of stress fluctuations remains insignificant. However, the fluctuation becomes substantial beyond a critical shear rate deep inside the non-linear regime of the flow curve when significant free-surface undulations, sustained stick-slip, and elastic recoil events are observed. Imaging in the flow-vorticity and the gradient-vorticity plane indicates that such dynamics are primarily driven by the elasticity-induced turbulent flows in the system. Furthermore, in this regime, we find that the characteristic persistent time of stress fluctuations matches well with the time scales of the stick-slip events, as well as the micellar breaking time, indicating a possible connection between the striking stress dynamics and the micellar kinetics.

Wormlike reverse micelles loaded with aqueous extracts of Psidium guajava leaves: Performance evaluation by rheology and Raman microscopy methods

Phenolic compounds are molecules that provide health benefits. However, they present problems for their use. The use of wormlike reverse micelles to load aqueous extracts of Psidium guajava (guava) was carried out. Different solutions (i.e., content variation of canola oil, oleic acid, soy lecithin; stirring time, stirring speed) were obtained by incorporation of water by ultrasound and centrifugation. The behavior of the wormlike micelles was evaluated with optical microscopy, simple shear tests, and Raman microscopy with and without aqueous extract of guava leaves. The wormlike reverse micelles solution were adjusted to the Carreau-Yasuda model. Influence of the aqueous extracts of guava leaves were observed in the parameters of Carreau-Yasuda model, related with changes in the packing of the hydroxyl groups and high order of packing in wormlike reverse micellar system.

Cellulose nanocrystals enhanced viscoelasticity and temperature-resistance of rosin-based wormlike micelles: Inducing the formation of hydrogels

Wormlike micelles are attractive soft materials, their further combinations with nanoparticles providing a novel kind of functional materials in various applications. Using rosin as the starting materials, a biobased surfactant (CMPA2Na) was synthesized. Its structure was characterized using 1H NMR, FT-IR and MS. Viscoelastic wormlike micelles were prepared using CMPA2Na with cetyltrimethylammonium bromide (CTAB). Wormlike micellar system enchanced by cellulose nanocrystals (CNCs) was further constructed. The viscoelasticity, microstructure and interaction mechanism of the CMPA2Na/CTAB/CNCs system were comprhesively investigated using FT-IR, rheology and Cryo-TEM. The viscoelasticity monotonously increased with increasing addition amount of CNCs. And the viscoelastic solutions transformed into hydrogels as the addition amount of CNCs was larger than 0.5 %. Unexpectedly, a dramatical increase of 67 times in viscosity and 10 times in elasticity were obtained, surpassing the reported wormlike micelles combined with nanoparticles. In addition, the wormlike micelles enhanced with CNCs could maintain the excellent viscoelasticity under high temperature. The network of the wormlike micelles was prominently strengthened by the strong hydrogen bonds and electrostatic interactions between the wormlike micelles and CNCs. The study provided a biobased wormlike micelle modified by nanoparticles with high viscoelasticity and excellent temperature-resistance, facilitating the applications of biomass resources in the petroleum industry.

Light-Modulated Rheological Properties in Green Innovative Formulations

The addition of azorubine to a viscoelastic aqueous dispersion of sodium oleate (NaOL, 0.43 M, 13% w/w) and KCl (up to 4% w/w) leads to a green gel-like system whose rheological behavior can be efficiently and reversibly triggered from remote by using UV light. Rheology, Differential Scanning Calorimetry (DSC) measurements and phase behavior studies indicate that the original texture of the NaOL dispersion is significantly hardened upon UV irradiation for 8 hours in the presence of azorubine, showing a seven hundred-fold increase in viscosity. The UV treatment brings about the trans to cis isomerization of azorubine, which modifies the structure of the NaOL wormlike micellar system, leading to a more entangled, close-textured network. The cooperative effect of KCl on the fluid viscosity is found to be concentration-dependent. The system slowly reverts to its original rheological behaviour after standing for about 1 day. These results are relevant for the development of stimuli-responsive innovative systems based on biocompatible, non expensive and commercially available materials that can be used in a wide range of applications, such as in drug delivery or enhanced oil recovery, where a quick change in the physico-chemical features of the system is required but difficult to be performed.

Study on a Two-dimensional nanomaterial reinforced wormlike micellar system

A two-dimensional nanomaterial reinforced wormlike micellar system was constructed by wormlike micelles composed of sodium oleate (NaOA) with potassium chloride (KCl) and two-dimensional lamellar nano-molybdenum disulfide (nano-MoS2). The morphology of nano-MoS2 was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cryogenic transmission electron microscopy (Cryo-TEM) revealed the formation of wormlike micelles. Then, rheological tests show that the viscosity and viscoelasticity of the system can be enhanced with a certain concentration of nano-MoS2. In addition, environmental scanning electron microscopy (ESEM) demonstrated the adsorption and combination of nano-MoS2 with wormlike micelles can form a tighter three-dimensional network structure. Finally, the strengthening effect of nano-MoS2 on worm-like micelles was confirmed by rheological parameters. The interaction between nano-MoS2 and wormlike micelles was elucidated and the mechanism of nano-MoS2 reinforcing wormlike micelles was proposed. Through this research, we hope to broaden the range of applications of two-dimensional nanomaterials.

PH-switchable wormlike micelles with high viscoelasticity formed by pseudo-oligomeric surfactants

A pH-switchable wormlike micellar system with high viscoelasticity was prepared by mixing N-(3-(dimethylamino) propyl) stearamide (SAM) and phthalic acid (PA) at the molar ratio of 2:1. By simple in situ neutralization reaction, SAM and PA could dynamically combine to fabricate a pseudo-oligomeric surfactant without additional inorganic salts. Through the results of surface activity, rheology and Small-angle X-ray scattering (SAXS), it was found that the pseudo-oligomeric surfactant was readily to form viscoelastic wormlike micelles and showed remarkable thickening ability. The maximum zero shear viscosity (η0) was up to 9.4 × 103 Pa·s, which was higher than most of wormlike micelles formed by the conventional covalently linked oligomeric counterparts. The viscoelastic fluid formed by the pseudo-oligomeric surfactant was highly sensitive to pH, whose viscosity could be decreased to 0.001 Pa·s instantly by adding a small amount of acid or alkali.

Preparation and mechanism of pH and temperature stimulus-responsive wormlike micelles

A quaternary ammonium salt surfactant with tertiary amine groups (C16MIMBr) was prepared by the reaction of bromohexadecane with N, N, N, N-tetra methylpropane diamine, and the structure of the product was demonstrated by 1H NMR. A viscoelastic wormlike micellar system was constructed with C16MIMBr as the main agent and potassium bromide as the counterion salt, and the ratio of surfactant to counterion was optimized. It was shown that the viscosity of the system was maximum when the molar ratio of the C16MIMBr-KBr system was 1:4, and the rheological test also indicated that the viscoelasticity was best at 1:4. The pH-stimulated responsiveness and temperature-stimulated responsiveness of the C16MIMBr-KBr system were investigated by rheology and cryo-transmission electron microscopy, and the response mechanism was investigated and analyzed. It is shown that when the system is acidic, the positive charges on both sides of the surfactant lead to strong electrostatic repulsions within and between the surfactant molecules, resulting in a cone-like structure of the surfactant molecules and the formation of spherical micelles with very low viscosity. When the system is deprotonated under alkaline conditions, only one end of the surfactant head group is positively charged, and the inter-and intra-molecular electrostatic repulsive forces are greatly weakened, resulting in the intertwined growth of micelles and the formation of wormlike micelles. The temperature response mechanism analysis of the C16MIMBr-KBr system shows that at low temperature, only a small amount of cation can cross-mix with micelles to form a curved vesicle structure due to the low solubility of the system, resulting in a low viscosity of the system. As the temperature rises to 60 °C, the water solubility of the system is enhanced, and it desorbs from the vesicles into the solution. According to the equation of critical accumulation parameter, the critical accumulation parameter of the system decreases and the transition from vesicles to wormlike micelles occurs, leading to an increase in system viscosity.

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.

Triple-responsive wormlike micelles based on cationic surfactant and sodium trans-o-methoxycinnamic acid

The ability to modulate the viscoelastic behavior of wormlike micellar systems with smart features is of great importance in both fundamental and applied science. In this paper, the novel triple stimuli-responsive (pH, temperature and light) wormlike micellar system is formed by mixing a cationic surfactant, 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R16HTAB) and sodium trans-o-methoxycinnamic acid (NaOMCA) in aqueous solutions. The rheological techniques, nuclear magnetic resonance (1H NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and cryogenic-transmission electron microscopy (cryo-TEM) were employed to demonstrate the multi-responsive behaviors of wormlike micellar systems. The rheological properties of wormlike micelles systems were studied under three trigger conditions (pH, temperatures, and UV irradiation), and the mechanism of multiple-responsiveness was discussed in detail by a combination of 1H NMR, FTIR and cryo-TEM. It was found that the viscoelastic behavior of a mixed system was reversible under different excitation conditions. We hope that the study of this triple response system can provide new theoretical foundation for future applications.

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 ∝ C9.6). This work further promotes new applications of forest resources.

Effect of the Strength of Attraction Between Nanoparticles on Wormlike Micelle- Nanoparticle System

The nanoparticle-Equilibrium polymer (or Wormlike micellar) system shows morphological changes from percolating network-like structures to non-percolating clusters with a change in the minimum approaching distance (EVP-excluded volume parameter) between nanoparticles and the matrix of equilibrium polymers. The shape anisotropy of nanoparticle clusters can be controlled by changing the polymer density. In this paper, the synergistic self-assembly of nanoparticles inside equilibrium polymeric matrix (or Wormlike micellar matrix) is investigated with respect to the change in the strength of attractive interaction between nanoparticles. A shift in the point of morphological transformation of the system to lower values of EVP as a result of a decrease in the strength of the attractive nanoparticle interaction is reported. We show that the absence of the attractive interaction between nanoparticles leads to the low packing of nanoparticle structures, but does not change the morphological behavior of the system. We also report the formation of the system spanning sheet-like arrangement of nanoparticles which are arranged in alternate layers of matrix polymers and nanoparticles.

Flow-induced concentration gradients in shear-banding of branched wormlike micellar solutions

HypothesisShear-banding of branched wormlike solutions is a topic of active investigation which has not been fully elucidated. Here, we surmise that flow-induced microstructuring in the shear banding regime is associated with spatial concentration gradients. ExperimentsThe experiments focus on the flow-induced behavior of a CTAB/NaSal wormlike micellar system. A unique approach based on a microfluidic-spitter geometry, combined with particle-image velocimetry and high-speed video microscopy, is used to separate the streams flowing out from the core and the near wall zones of the microchannel. FindingsHere, we present the first direct experimental evidence of the correlation between phase separation and shear banding. By increasing the pressure-drop across a microcapillary, the onset of a grainy texture close to the wall, showing a flow-induced demixing effect, is observed. We use a splitter to measure effluent streams from the center and the near-wall zones in terms of viscosity, conductance and dry mass. We observe that phase-separation induced by the flow correlates with chemical concentration gradients. This confirms our hypothesis that shear-induced local de-mixing of the system is strongly related to chemical concentration gradients.

The mechanism difference between CO2 and pH stimuli for a dual responsive wormlike micellar system.

To indicate the difference between pH and CO2 stimuli mechanisms, a dual responsive system is constructed with the aid of N-[3-(dimethylamino)propyl]docosanamide (NDPD) and sodium salicylate (NaSal), which is responsive to pH and CO2. The dual responsive system is characterized by rheometry, cryo-TEM and 1H NMR spectroscopy. After bubbling CO2 or adjusting the pH, the rheological properties indicate the formation of wormlike micelles. The cyro-TEM images also confirmed wormlike micelles. The effect of temperature is also clarified. By comparing the rheological properties of the wormlike micelles with pH and CO2 stimuli conditions, combined with cryo-TEM and 1H NMR results, the stimuli mechanisms of pH and CO2 to the dual responsive system are shown. Through this work, we expect to deepen our understanding of the responsiveness of a self-assembled system.

Can More Nanoparticles Induce Larger Viscosities of Nanoparticle-Enhanced Wormlike Micellar System (NEWMS)?

There have been many reports about the thickening ability of nanoparticles on the wormlike micelles in the recent years. Through the addition of nanoparticles, the viscosity of wormlike micelles can be increased. There still exists a doubt: can viscosity be increased further by adding more nanoparticles? To answer this issue, in this work, the effects of silica nanoparticles and temperature on the nanoparticles-enhanced wormlike micellar system (NEWMS) were studied. The typical wormlike micelles (wormlike micelles) are prepared by 50 mM cetyltrimethyl ammonium bromide (CTAB) and 60 mM sodium salicylate (NaSal). The rheological results show the increase of viscoelasticity in NEWMS by adding nanoparticles, with the increase of zero-shear viscosity and relaxation time. However, with the further increase of nanoparticles, an interesting phenomenon appears. The zero-shear viscosity and relaxation time reach the maximum and begin to decrease. The results show a slight increasing trend for the contour length of wormlike micelles by adding nanoparticles, while no obvious effect on the entanglement and mesh size. In addition, with the increase of temperature, remarkable reduction of contour length and relaxation time can be observed from the calculation. NEWMS constantly retain better viscoelasticity compared with conventional wormlike micelles without silica nanoparticles. According to the Arrhenius equation, the activation energy Ea shows the same increase trend of NEWMS. Finally, a mechanism is proposed to explain this interesting phenomenon.

Inertio-elastic instability in Taylor-Couette flow of a model wormlike micellar system

In this work, we use flow visualization and rheometry techniques to study the dynamics and evolution of secondary flows in a model wormlike micellar solution sheared between concentric cylinders, i.e., in a Taylor-Couette cell. The wormlike micellar solution studied in this work contains cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). This system can be shear banding and highly elastic, nonshear banding and moderately elastic, or nearly Newtonian as the temperature is varied over a narrow range. The effect of elasticity on transitions and instabilities is probed by changing the temperature over a wide range of elasticity (El ≪ 1, El ≈ 1, and El ≫ 1). Elasticity is defined as the ratio of the Weissenberg number to the Reynolds number. For shear banding wormlike micelle solutions where El ≫ 1, a primary transition from the base Couette flow to stationary vortices that are evenly spaced in the axial direction of the shear cell and are characterized by an asymptotic wave-length is observed. The dimensionless wave-length at the onset of this shear banding transition for CTAB/NaSal system turns out to be much larger than those reported for other shear banding wormlike micelle systems. For the same fluid at a temperature where it shear-thins but does not display shear banding, El ≈ 1, and for slow ramp speeds, the primary transition is to distinct structures that are not stationary but rather travel in the axial direction. At low elasticity (El ≪ 1), where the fluid behaves as a nearly Newtonian fluid, several transitions from purely azimuthal Couette flow to modified Taylor vortex flows and finally chaotic regimes are documented. The behavior in the shear-banding and nonshear-banding regimes are discussed and compared with results in related systems. The possibility of hysteresis in the flow transitions as well as the effects of co-rotation and counter-rotation of the cylinders on transitions and instabilities are also examined for a wide range of elasticity.

Investigation of Novel Triple-Responsive Wormlike Micelles.

Smart wormlike micelles with stimuli-tunable rheological properties may be useful in a variety of applications, such as in molecular devices and sensors. The formation of triplestimuli-responsive systems so far has been a challenging and important issue. In this work, a novel triplestimuli (photo-, pH-, and thermoresponsive) wormlike micelle is constructed with N-cetyl-N-methylmorpholinium bromide and trans-cinnamic acid (CA). The corresponding multiresponsive behaviors of wormlike micellar system were revealed using cryogenic transmission electron microscopy, a rheometer, and 1H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed by 1H NMR, chemical structure of a CA molecule can be altered by the multiple stimulation from an exotic environment. We expect it to be a good model for triple-responsive wormlike micelles, which is helpful to understand the mechanism of triple-responsiveness and widen their applications.

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

Responsive wormlike micelles are very useful in a number of applications, whereas it is still challenging to create dramatic viscosity changes in wormlike micellar systems. Here we developed a pH-responsive wormlike micellar system based on a noncovalent constructed surfactant, which is formed by the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and citric acid at the molar ratio of 3 : 1 (EACA). The phase behavior, aggregate microstructure and viscoelasticity of EACA solutions were investigated by macroscopic appearance observation, rheological and cryo-TEM measurements. It was found that the phase behavior of EACA solutions undergoes transition from transparent viscoelastic fluids to opalescent solutions and then phase separation with white floaters upon increasing the pH. Upon increasing the pH from 2.03 to 6.17, the viscosity of wormlike micelles in the transparent solutions continuously increased and reached ∼683 000 mPa s at pH 6.17. As the pH was adjusted to 7.31, the opalescent solution shows a water-like flowing behaviour and the η0 rapidly declines to ∼1 mPa s. Thus, dramatic viscosity changes of about 6 magnitudes can be triggered by varying the pH values without any deterioration of the EACA system. This drastic variation in rheological behavior is attributed to the pH dependent interaction between UC22AMPM and citric acid. Furthermore, the dependence on concentration and temperature of the rheological behavior of EACA solutions was also studied to assist in obtaining the desired pH-responsive viscosity changes.

Rheological properties and application of wormlike micelles formed by sodium oleate/benzyltrimethyl ammonium bromide

A pH-responsive anionic wormlike micellar (WLM) system formed by sodium oleate (NaOA) and benzyltrimethyl ammonium bromide were studied via rheological measurements and dynamic light scattering measurements. The anionic WLMs were used as templates to synthesize mesoporous silicas (MSs). The microstructures of the WLM system can be controlled by altering the pH. The transformation between NaOA and oleic acid changes the charges on the micelle surface and affects the viscoelasticity of the system. High NaOA concentration increases the activation energy (Ea) of the system, whereas a high pH value promotes the formation of spherical micelles and reduces the Ea of the solutions. By contrast, a low pH value increases the viscosity of the system given that the electrostatic repulsion between NaOA head-groups is weakened. However, if numerous NaOAs transform into insoluble oleic acids, the viscosity of the system will dramatically decrease. In addition, micelle length and NaOA concentration affect the microstructure of MSs.

Flow-induced structures observed in a viscoelastic reverse wormlike micellar system by magnetic resonance imaging and NMR velocimetry

Organogel formed by lecithin reverse wormlike micelles in the isotropic concentrated regime exhibits flow induced micro-heterogeneities detected by rheo-NMR and NMR-velocimetry.