Micelles In Solution Research Articles

Two-species model for nonlinear flow of wormlike micelle solutions. Part II: Experiment

Applications often expose wormlike micelle solutions to a very wide range of shear and temperature conditions. The two-species model presented in Part I [Salipante et al., J. Rheol. 68 (2024)] describes the nonlinear rheology over a wide range of shear rates. Here, we compare the model predictions to measurements using a combination of microcapillary and rotational rheology to measure the viscosity of surfactant solutions across seven decades of shear rate and five decades of viscosity. The effect of temperature is studied between 20 and 60 °C for different surfactant concentrations. Model parameters are determined from both small-amplitude shear measurements and fitting to the nonlinear data. Under shear stress, the model predicts due to hindered combination kinetics that the average micelle length decreases from several micrometers to a few hundred nanometers. At sufficiently high stress, the micelle shear rheology exhibits a transition from entangled wormlike behavior to a dilute rod rheology in agreement with the model. Transient stress-growth measurements exhibit a large overshoot, which is rather well predicted by the model with hindered combination rate. Microcapillary flow birefringence also is adequately predicted by the model, confirming the accuracy of its predicted micelle lengths and exhibiting a marked change in stress-optic response at the transition between entangled polymers and dilute rods. The relaxation of retardance after flow cessation follows model predictions that include micelle-micelle interactions, which are sensitive to the rotational diffusivity and length. These methods can be applied broadly to explore relationships between composition and performance.

Two-species model for nonlinear flow of wormlike micelle solutions. Part I: Model

We develop a rheological model to approximate the nonlinear rheology of wormlike micelles using two constitutive models to represent a structural transition at high shear rates. The model is intended to describe the behavior of semidilute wormlike micellar solutions over a wide range of shear rates whose parameters can be determined mainly from small-amplitude equilibrium measurements. Length evolution equations are incorporated into reactive Rolie-Poly entangled-polymer rheology and dilute reactive-rod rheology, with a kinetic exchange between the two models. Although the micelle length is remarkably reduced during flow, surprisingly, we propose that they are not shortened by stress-enhanced breakage, which remains thermally driven. Instead, we hypothesize that stretching energy introduces a linear potential that decreases the rate of recombination and reduces the mean micelle length. This stress-hindered recombination approach accurately describes transient stress-growth upon start-up shear flow, and it predicts a transition of shear viscosity and alignment response observed at high shear rates. The proposed mechanism applies only when self-recombination occurs frequently. The effect of varying the relative rate of self-recombination on the rheology of wormlike micelles at high shear rates is yet to be explored.

Stabilizing Effect of PS-b-PMMA Diblock Copolymers in PS/PMMA-Based THF-in-THF Emulsions.

We have investigated the common solvent-based emulsion composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) solutions in tetrahydrofuran in the presence of PS-b-PMMA diblock copolymers. The stabilization effect of the diblock was determined visually and by confocal laser scanning microscopy at various phase volume fractions, concentrations, and compositions of the copolymer. The behavior of PS-b-PMMA in each homopolymer solution was studied with static and dynamic light scattering. The copolymer formed micelles above a critical homopolymer concentration. Light scattering measurements showed that small amounts of the other homopolymer added to the micelle solution entered the micelles spontaneously, suggesting that the observed emulsion stability is caused by the diblock copolymer laminar layer formation covering the surface of the dispersed droplets.

Micelle-encapsulated IR783 for enhanced photothermal therapy in mouse breast cancer

BackgroundPhotothermal therapy, an emerging cancer treatment, selectively eliminates lesions using photothermal compounds that convert light into heat. IR783, a near-infrared fluorescent heptamethine cyanine dye, has been used to achieve selective hyperthermic effects in target tissues via near-infrared irradiation. To implement IR783 as a photothermal agent, IR783 biodistribution must be calibrated to achieve a constant and uniform concentration in target cells. Accordingly, we developed micelle-encapsulated IR783 (IR783 micelles) and evaluated their effectiveness as photothermal drugs. MethodsIn vitro, the photothermic effects of free IR783 and IR783 micelle solutions induced by near-infrared light irradiation were analyzed. Additionally, we investigated the mechanism of cell death mediated by photothermal therapy using free IR783 and IR783 micelles in mouse breast cancer (EMT6) cells. In vivo, the efficacy of photothermal therapy with both free IR783 and IR783 micelles was examined in EMT6-bearing mice. ResultsIn vitro, the temperature of free and micelle-encapsulated IR783 solutions increased after near-infrared irradiation. Near-infrared irradiation with free IR783 and IR783 micelles induced cytotoxicity in cancer cells by generating heat. In vivo, IR783 micelles elicited more preferential tumor tissue uptake and enhanced the antitumor effects of photothermal therapy at a lower light dose relative to free IR783. ConclusionsOverall, these results suggest that IR783 micelles could accumulate in mouse breast cancer tissues and exhibit enhanced antitumor effects when used as a photothermal therapy, with superior effects obtained at 2.1 W/cm2 (252 J/cm2) compared with that of free IR783.

Pegylated surfactants based on fatty acids: 12-hydroxystearic acid versus stearic acid

We describe the aqueous behavior of short Polyethylene glycol (PEG) chains of Mw 4 kDa that are either mono-functionalized or di-functionalized by 12-hydroxy stearic acid (HSA), and stearic acid (SA), respectively. The end capping of the chains by the fatty acids is achieved by Steglich esterification, after a step of protection of the 12-OH functional group in the case of HSA. Small Angle Neutron Scattering (SANS) shows that mono-functionalized chains with both SA or HSA sticky ends self-assemble in star micelles in aqueous solution, and interact through repulsive steric interactions. The di-functionalized telechelic chains self-assemble in flower micelles that interact through interactions that are attractive on average due to the formation of bridges by chains that share their both ends in two different micelles. Solutions of telechelic chains undergo a phase separation between a dilute solution of micelles and a dense hexagonal crystalline network of flower micelles above a given polymer concentration threshold. This threshold is lower for SA-PEG-SA than for HSA-PEG-HSA. We postulate that this difference of behavior arises from the formation of hydrogen bonds between the OH groups at the C12 of the alkyl chain in case of HSA that increase the stability of the hydrophobic core of the micelles.

Influence of the presence of ions on the dielectric properties of reverse micelle systems

AOT/isooctane/water reverse micelle solution was doped with ionic salts solutions: sodium chloride, potassium chloride, tetramethylammonium chloride, tetramethylammonium bromide, sodium butyrate and sodium benzoate. Each system was investigated for the influence of ionic additives on dielectric properties: electric permittivity, conductivity and nonlinear dielectric effect (NDE). Studies showed that addition of salts noticeably changes the dielectric parameters. Based on the salts used in this research, the most common effect is a decrease of electric permittivity, conductivity and NDE effect. However, addition of some ions can lead to their increase, which was proved in the case of sodium benzoate. The registered changes were explained based on the percolation effect and changes in rigidity of the micellar surfactant shell due to the incorporation of the dissolved ions into the micellar structure.

Effect of Electrostatic Interactions in Wormlike Micelles of Surfactants Based on Betaine and Charged Tertiary Amine with the Same Hydrophobic Groups

The viscoelastic properties and structure of solutions of mixed wormlike micelles based on a zwitterionic surfactant, oleylamidopropyldimethylcarboxybetaine (OAPB), and positively charged oleylamidopropyldimethylamine (OAPA) have been studied at different ratios between the components. At a small fraction of the cationic surfactant, OAPA, the solution exhibits viscoelastic properties characteristic of semidiluted solutions of entangled wormlike micelles, the presence of which has been confirmed by cryogenic electron microscopy data. It has been found that, as the molar fraction of the charged surfactant increases to 0.1, the viscosity and relaxation time of the solutions decrease by a factor of three, and the values of the storage modulus remain unchanged at short stress action times. The studied surfactants have a similar structure; therefore, when replacing zwitterionic OAPB molecules by positively charged OAPA molecules, the main factor of variations in the properties and structure is the enhancement of the electrostatic repulsion on the micelle surface. It has been shown that this factor leads to a decrease in the average length of micelles and an increase in their number, which have a weak effect on the rheological properties of the system as long as the length of the micelles is larger than the length of the subchains in the network. With an increase in the molar fraction of OAPA from 0.1 to 0.5, the viscosity and relaxation time drop drastically by several orders of magnitude and the viscoelastic response of the solution is lost; i.e., the network is destroyed. This transition from a semidilute solution to a dilute one is explained by a decrease in the length of the wormlike micelles and the formation of spherical ones. Cryogenic electron microscopy images have confirmed the formation of a mixture of long and short wormlike micelles with spherical micelles at an OAPA molar fraction of 0.5.

Ordered mesoporous nanofibers mimicking vascular bundles for lithium metal batteries.

Hierarchical self-assembly with long-range order above centimeters widely exists in nature. Mimicking similar structures to promote reaction kinetics of electrochemical energy devices is of immense interest, yet remains challenging. Here, we report a bottom-up self-assembly approach to constructing ordered mesoporous nanofibers with a structure resembling vascular bundles via electrospinning. The synthesis involves self-assembling polystyrene (PS) homopolymer, amphiphilic diblock copolymer, and precursors into supramolecular micelles. Elongational dynamics of viscoelastic micelle solution together with fast solvent evaporation during electrospinning cause simultaneous close packing and uniaxial stretching of micelles, consequently producing polymer nanofibers consisting of oriented micelles. The method is versatile for the fabrication of large-scale ordered mesoporous nanofibers with adjustable pore diameter and various compositions such as carbon, SiO2, TiO2 and WO3. The aligned longitudinal mesopores connected side-by-side by tiny pores offer highly exposed active sites and expedite electron/ion transport. The assembled electrodes deliver outstanding performance for lithium metal batteries.

Pulmonary Delivery of Anti-microRNA Oligonucleotide and Glycyrrhizic Acid Using Ternary Peptide Micelles for the Treatment of Acute Lung Injury

Acute lung injury (ALI) is a devastating inflammatory disease. In lungs with inflammation, microRNA155 (miR155) induces inflammatory cytokines by inhibiting the expression of suppressor of cytokine signaling-1 (SOCS1). In addition, glycyrrhizic acid (GA) has been suggested as an anti-inflammatory drug for ALI, since it is an efficient inhibitor of nuclear factor-κB. In this study, a combined delivery system of anti-miR155 oligonucleotides (AMO155) and GA was developed with R3V6 for the treatment of ALI. R3V6s formed comicelles with cholesterol-conjugated AMO155 (AMO155c) by charge and hydrophobic interactions. GA, an amphiphilic drug, was integrated to AMO155c-R3V6 micelles, producing AMO155c-R3V6-GA ternary micelles. The size of AMO155c-R3V6-GA was smaller than that of AMO155c-R3V6, suggesting that GA integration reduced the size of the micelles effectively. In addition, AMO155c-R3V6-GA had higher delivery efficiency than AMO155c-R3V6 micelles. In the comparison of AMO155-R3V6-GA and AMO155c-R3V6-GA, cholesterol moiety of AMO155c increased the stability and delivery efficiency of the ternary micelles. For in vivo evaluation, nebulized AMO155c-R3V6-GA micelle solution were administrated into the lungs of the ALI animal models intratracheally. AMO155c-R3V6-GA micelles had improved AMO155c delivery efficiency, compared with the AMO155c-polyethylenimine complex and AMO155c-R3V6 micelles in the lungs. As a result, SOCS1 expression was increased, and proinflammatory cytokines were reduced in the AMO155c-R3V6-GA micelle groups, compared with the other groups. In conclusion, AMO155c-R3V6-GA ternary micelles may be a useful delivery system for combined therapy of AMO155 and GA for the treatment of ALI.

Flow instabilities in circular Couette flow of wormlike micelle solutions with a reentrant flow curve

In this work, we numerically investigate flow instabilities of inertialess circular Couette flow of dilute wormlike micelle solutions. Using the reformulated reactive rod model (RRM-R) (Hommel and Graham, 2021), which treats micelles as rigid Brownian rods undergoing reversible scission and fusion in flow, we study the development and behavior of both vorticity banding and finger-like instabilities. In particular, we focus on solutions that exhibit reentrant constitutive curves, in which there exists some region where the shear stress, τ, has a multivalued relation to shear rate, γ̇. We find that the radial dependence of the shear stress in circular Couette flow allows for solutions in which parts of the domain lie in the region of the flow curve where ∂τ/∂γ̇>0, while others lie in the region where ∂τ/∂γ̇<0; this mixed behavior can lead to complex flow instabilities that manifest as finger-like structures of elongated and anisotropically-oriented micelles. In 3D simulations we find that the initial instability is 2D in origin, and 3D finger-like structures arise through the axial instability of 2D sheets. Finally, we show that the RRM-R can capture vorticity banding in narrow-gap circular Couette flow and that vorticity bands are linearly stable to perturbations.

The Formation Mechanism of Ordered Mesoporous Carbon with Network-Structure: A Novel Support Material for Pt-Based Catalysts in PEFC Cathodes

INTRODUCTIONTo achieve carbon neutrality in the upcoming sustainable society, it is crucial to utilize hydrogen as a fuel in the transportation sector. Fuel cell vehicles are expected to play an important role in the future hydrogen society, but there are still challenges to be overcome before their widespread adoption. For example, Pt/C-based catalysts used in PEFC cathodes have an issue with poisoning of the Pt due to direct contact with the ionomer, especially during low-load operation. Recently, a new approach using accessible-pore carbons has been proposed, where Pt is placed at an appropriate position within the nanopores of a carbon support to suppress ionomer poisoning of Pt [1]. In order to realize this concept, it is essential to design a mesoporous carbon support that possesses nanopores with appropriate size and proper ordering. We have developed an ordered mesoporous carbon with a hierarchical network structure (Net-OMC) consisting of small OMC particles of several tens of nm in size, which are connected to form a network structure with well-developed primary pores. The Net-OMC exhibited highly ordered nanopores on the surface of the OMC primary particles, with a pore size ca. 5 nm and an interpore distance of ca. 8 nm. Pt nanoparticles were loaded selectively within the Net-OMC nanopores by the selective Pt-deposition technique developed by our research group. Pt/Net-OMC catalyst exhibited higher mass activity and durability for the ORR in comparison with those for a commercial Pt/CB catalyst [2]. In this study, the formation mechanism of Net-OMC and the relationship between the catalytic properties of Pt/Net-OMC and its pore structure was investigated in detail.EXPERIMENTALNet-OMC powder was synthesized with resol-nonionic surfactant micelles as a carbon source and structure-directing agent. Resol-F127 (nonionic surfactant) micelles were synthesized by mixing phenol, formaldehyde, water and F127 with sodium hydroxide. After hydrothermal treatment of the mixture, the resulting solid was filtered and washed thoroughly and dried under vacuum. The obtained powder was carbonized at 700 ºC followed by annealing at 1000 ºC. Pt was deposited on the Net-OMC powder by selective deposition techniques. Cyclic voltammetry and linear sweep voltammetry were carried out in N2-saturated and O2-saturated 0.1 M HClO4 solution at 25 ºC using the conventional rotating disk electrode (RDE) technique. Potential step cycling measurements simulating load cycling between 0.6 V and 1.0 V vs. RHE were carried out according to the FCCJ protocol. Coating of the catalyst on a glassy carbon disk substrate was carried out by an electrospray (ES) coating technique developed by our group [3]. N2 adsorption measurements at liquid nitrogen temperature were carried out. The morphology of the Pt/ns-OMC was observed by scanning transmission electron microscopy (STEM).RESULTS AND DISCUSSIONSTEM images for the ordered mesoporous carbon particles with network structure (Net-OMC) with varying concentration during hydrothermal synthesis are shown in Figure 1. In Fig. 1(a), the network structure formed by connection of OMC primary nanoparticles with developed macropores is clearly observed. The OMC nanoparticles were tightly connected via a thick necking structure. From the high magnification image (Fig. 1(a), inset), highly ordered nanopores were observed on the surface of the OMC particles. The OMC primary particle size and the connecting neck diameter changed with the resol micelle concentration during the hydrothermal treatment. When the concentration of the micelle solution was decreased, both the primary particle size and necking length decreased. At a concentration of 1.8 mmol l-1, the formation of monodisperse particles with roughly the same size from the resol-F127 micelle particles was observed, as estimated by dynamic light scattering analysis. Thus, it is believed that the Net-OMC structure is formed through the self-assembly of micelle particles during the hydrothermal synthesis. The controllable network structure of Net-OMC is expected to provide a favorable porous structure of the catalyst layer for the MEA measurement even during high-load operation.

Mechanism of Synergistic Photoinactivation Utilizing Curcumin and Lauric Arginate Ethyl Ester against Escherichia coli and Listeria innocua.

This study investigated the mechanism of how lauric arginate ethyl ester (LAE) improves the photoinactivation of bacteria by curcumin after diluting the 100 µmol/L stock curcumin-LAE micelle solution to the concentration used during the treatment based on the curcumin concentration. The photoinactivation of bacteria was conducted by irradiating the 1 µmol/L curcumin-LAE solution containing cocktails of Escherichia coli and Listeria innocua strains (7 log CFU/mL) for 5 min with UV-A light (λ = 365 nm). The changes in solution turbidity, curcumin stability, and bacterial morphology, viability, and recovery were observed using SEM, TEM, and live/dead cell assays. The study found that LAE enhances the photoinactivation of bacteria by increasing the permeability of cell membranes which could promote the interaction of reactive oxygen species produced by photosensitized curcumin with the cell components. The combination of curcumin and LAE was demonstrated to be more effective in inhibiting bacterial recovery at pH 3.5 for E. coli, while LAE alone was more effective at pH 7.0 for L. innocua.

Interplay of wall slip and shear banding in wormlike micelle solutions

Interplay of wall slip and shear banding in wormlike micelle solutions

The effect of instrument inertia on the initiation of oscillatory flow in stress controlled rheometry

In a recent paper [Hassager, J. Rheol. 64, 545–550 (2020)], Hassager performed an analysis of the start up of stress-controlled oscillatory flow based on the general theory of linear viscoelasticity. The analysis provided a theoretical basis for exploring the establishment of a steady strain offset that is inherent to stress controlled oscillatory rheometric protocols. However, the analysis neglected the impact of instrument inertia on the establishment of the steady periodic response. The inclusion of the inertia term in the framework is important since it (i) gives rise to inertio-elastic ringing and (ii) introduces an additional phase shift in the periodic part of the response. Herein, we modify the expressions to include an appropriate inertial contribution and demonstrate that the presence of the additional terms can have a substantial impact on the time scale required to attain the steady state periodic response. The analysis is then applied to an aqueous solution of wormlike micelles.

Structural Changes during Polymerization of Acrylamide in Semidilute Solutions of Wormlike Surfactant Micelles

Structural Changes during Polymerization of Acrylamide in Semidilute Solutions of Wormlike Surfactant Micelles

Can wormlike micelle stiffness be estimated from zero‐shear viscosity? Experimental investigation with a model system and specific salt interactions

AbstractThe microstructure of wormlike micelles (WLM) directly affects the rheological properties of their solutions. Investigating the structure–property relationships of WLM has long been a popular topic for researchers who have developed theoretical and empirical models to describe their viscoelastic behavior. All these models rely on a collection of characteristic “length” parameters that are often difficult to estimate using relatively simple rheological tests. In particular, the micelle stiffness, as described by the persistence length, can be difficult to measure experimentally, while being very impactful on the bulk rheology of WLM solutions. Here, an array of inorganic salts (NaCl, LiCl, MgCl2, NaBr, NaI, and Na2SO4) have been used to induce wormlike micelle formation in an aqueous solution of the surfactant sodium lauryl ether sulfate. Ion dissociation/association with the surfactant head groups and the hydrogen bond network of the water alters the effective stiffness of the micelles, allowing for an estimation of the stiffness using three different methods: (1) small angle neutron scattering (SANS) measurements, (2) oscillatory rheological measurements, and (3) steady rheological measurements with a thermodynamic packing parameter model. Each of these methods are then compared and shown to be consistent with each other for the micelle solutions tested. The consistency of the results across all the measurements suggests that the approach used in this study, which estimates micelle parameters using steady shear rheology and a thermodynamic model, could provide a simpler and more accessible method for estimating micelle parameters in a wide range of surfactant systems.

Beyond the Conventional Paradigm of Radial (Normal) Stretching of Tethered Chains. Do Theories of Micellization in Solutions of Block Copolymers Need to Be Revised?

Beyond the Conventional Paradigm of Radial (Normal) Stretching of Tethered Chains. Do Theories of Micellization in Solutions of Block Copolymers Need to Be Revised?

Structural Changes during Polymerization of Acrylamide in Semidilute Solutions of Wormlike Surfactant Micelles

The structure and rheological properties of aqueous solutions of the anionic surfactant potassium oleate and the water-soluble monomer acrylamide before and after radical polymerization have been studied. In the absence of monomer and in the presence of a low-molecular-weight salt, potassium oleate forms a network of long entangled cylindrical (wormlike) micelles. The addition of the monomer does not lead to a change in their cylindrical shape and radius, but it promotes the transformation of branched micelles into linear ones. The structure of surfactant aggregates changes significantly after polymerization: according to neutron scattering data, it becomes bicontinuous and its local geometry becomes lamellar. The coexistence of such a structure with polyacrylamide macromolecules in a semidilute solution leads to a significant synergistic increase in viscosity and elastic modulus.

Stimuli-Responsive Systems Based on Polymer-like Wormlike Micelles of Ionic Surfactants and Their Modern Applications

Solutions based on polymer-like micelles of ionic surfactants attract the attention of scientists as stimuli-responsive systems that can transform from a low-viscosity Newtonian fluid to a viscoelastic solution having a viscosity of up to 10 kPa s and an elastic response. The shape of micelles and their length are determined by the balance of hydrophobic and electrostatic interactions; therefore, the use of various low molecular weight substances or functional nanoparticles as additives can significantly change the rheological properties of such solutions and impart new stimuli-responsive properties to them. This review presents the most commonly used methods for controlling the properties of multicomponent solutions of wormlike surfactant micelles, including nanocomposite systems. Modern areas of practical application of such systems and prospects for their development are described.

Synergistic effects of surfactant and polymer on the viscosity and oil displacement efficiency

For chemical flooding, choosing suitable surfactant and polymer mixture to optimize the viscosity and interfacial tension is an important procedure for preparing the combination flooding system. In this work, a systematic study was conducted on the properties of the surfactant/polymer mixed solution, involving viscoelasticity, oil/water interfacial tension and oil displacement efficiency. Zwitterionic-anionic surfactant mixture (HDPS-SDS) was chosen to show the effect of concentration and micelles type. Partially hydrolyzed polyacrylamide (HPAM) and hydrophobically associating polymer (HPOC) were selected to show the effect of polymer concentration and type. It has been found that for polymer solutions, adding HDPS-SDS reduces the oil/water interfacial tensions to the magnitude of 10−2 mN·m−1, but negative synergistic effect for spherical micelles and positive synergistic effect for wormlike micelles on viscosity are observed. For wormlike micelles solutions, adding HPAM or HPOC increases the viscosity. Moreover, the positive synergistic effect on viscosity by HPOC is far stronger than that of HPAM, and the viscosity of wormlike micelle solution can be reinforced by adding a small amount of HPOC. The synergistic effect on viscosity will also affect the oil displacement efficiency of the surfactant/polymer mixed system. For example, the enhanced oil displacement efficiency E of surfactant/polymer flooding unexpectedly reduces with adding spherical micelles formed by low concentration HDPS-SDS to 1500 mg L−1 HPOC solutions. Whereas the enhanced oil displacement efficiency E of wormlike micelles/polymer flooding reaches 28.8% with adding 800 mg L−1 HPOC to 5500 mg L−1 HDPS-SDS wormlike micelles solutions.