Surfactant Micelles Research Articles

Interface Adsorption versus Bulk Micellization of Surfactants: Insights from Molecular Simulations.

Surfactants play essential roles in many commonplace applications and industrial processes. Although significant progress has been made over the past decades with regard to model-based predictions of the behavior of surfactants, important challenges have remained. Notably, the characteristic time scales of surfactant exchange among micelles, interfaces, and the bulk solution typically exceed the time scales currently accessible with atomistic molecular dynamics (MD) simulations. Here, we circumvent this problem by introducing a framework that combines the general thermodynamic principles of self-assembly and interfacial adsorption with atomistic MD simulations. This approach provides a full thermodynamic description based on equal chemical potentials and connects the surfactant bulk concentration, the experimental control parameter, with the surfactant surface density, the suitable control parameter in MD simulations. Self-consistency is demonstrated for the nonionic surfactant C12EO6 (hexaethylene glycol monododecyl ether) at an alkane/water interface, for which the adsorption and pressure isotherms are computed. The agreement between the simulation results and experiments is semiquantitative. A detailed analysis reveals that the used atomistic model captures well the interactions between surfactants at the interface but less so their adsorption affinities to the interface and incorporation into micelles. Based on a comparison with other recent studies that pursued similar modeling challenges, we conclude that the current atomistic models systematically overestimate the surfactant affinities to aggregates, which calls for improved models in the future.

Phase behavior, micellization and rheology of erucic acid-based ionic liquid surfactant in deep eutectic solvents

Fatty acid-based ionic liquid surfactants have attracted significant attention due to their environmental friendliness, showing significant potential in some specific applications (e.g., personal & house care products). Deep eutectic solvents (DES) are a kind of new green and promising solvent. However, the self-assembly of ultra-long-chain fatty acid-based ionic liquid surfactants in DES has rarely been reported to date. In this paper, erucic choline (ErCho), as a representative of ultra-long-chain ionic liquid surfactants, was synthesized and characterized, and then its micellization behavior in three different DES (ChGly, ChEG, and ChPh, which were obtained by mixing glycerol, ethylene glycol, phenol, and choline chloride in a 2:1 M ratio) was investigated. ErCho can self-assemble into micelles in DES, as well as in water, but a relatively larger critical micelle concentration (cmc) was obtained in DES due to a small hydrophobic association. The hydrophobic association of ErCho in ChGly was the smallest, and the standard free energy of micellization per mole of monomer unit was the largest (-37.67 kJ·mol−1). However, at high shear rates, typical shear-thinning was observed in the ChGly solution of ErCho, showing pseudoplastic fluids behavior, which was not found in ChEG, ChPh, and H2O. This reflects the presence of large aggregates, and cryo-TEM observation confirmed the formation of wormlike micelles in the ChGly solution of ErCho with a small flow activation energy (∼43 kJ·mol−1). In addition, ErCho in ChGly solution can further evolve into a hexagonal phase, and then to lamellar crystalline phases upon increasing concentration.

Depletion-driven antiferromagnetic, paramagnetic, and ferromagnetic behavior in quasi-two-dimensional buckled colloidal solids.

We investigate quasi-two-dimensional buckled colloidal monolayers on a triangular lattice with tunable depletion interactions. Without depletion attraction, the experimental system provides a colloidal analog of the well-known geometrically frustrated Ising antiferromagnet [Y. Han et al., Nature 456, 898-903 (2008)]. In this contribution, we show that the added depletion attraction can influence both the magnitude and signof an Ising spin coupling constant. As a result, the nearest-neighbor Ising "spin" interactions can be made to vary from antiferromagnetic to para- and ferromagnetic. Using a simple theory, we compute an effective Ising nearest-neighbor coupling constant, and we show how competition between entropic effects permits for the modification of the coupling constant. We then experimentally demonstrate depletion-induced modification of the coupling constant, including its sign, and other behaviors. Depletion interactions are induced by rod-like surfactant micelles that change length with temperature and thus offer means for tuning the depletion attraction insitu. Buckled colloidal suspensions exhibit a crossover from an Ising antiferromagnetic to paramagnetic phase as a function of increasing depletion attraction. Additional dynamical experiments reveal structural arrest in various regimes of the coupling-constant, driven by different mechanisms. In total, this work introduces novel colloidal matter with "magnetic" features and complex dynamics rarely observed in traditional spin systems.

HylleraasMD: A Domain Decomposition-Based Hybrid Particle-Field Software for Multiscale Simulations of Soft Matter

We present HylleraasMD (HyMD), a comprehensive implementation of the recently proposed Hamiltonian formulation of hybrid particle-field molecular dynamics. The methodology is based on a tunable, grid-independent length-scale of coarse graining, obtained by filtering particle densities in reciprocal space. This enables systematic convergence of energies and forces by grid refinement, also eliminating nonphysical force aliasing. Separating the time integration of fast modes associated with internal molecular motion from slow modes associated with their density fields, we enable the first time-reversible, energy-conserving hybrid particle-field simulations. HyMD comprises the optional use of explicit electrostatics, which, in this formalism, corresponds to the long-range potential in particle-mesh Ewald. We demonstrate the ability of HyMD to perform simulations in the microcanonical and canonical ensembles with a series of test cases, comprising lipid bilayers and vesicles, surfactant micelles, and polypeptide chains, comparing our results to established literature. An on-the-fly increase of the characteristic coarse-grain length significantly speeds up dynamics, accelerating self-diffusion and leading to expedited aggregation. Exploiting this acceleration, we find that the time scales involved in the self-assembly of polymeric structures can lie in the tens to hundreds of picoseconds instead of the multimicrosecond regime observed with comparable coarse-grained models.

Two Spectrophotometric Methods Based on Diazotization Coupling Reaction for Determination of Genistein in Pure and Supplement

Genistein (GEN) is one of the predominant dietary isoflavones found in legumes such as soybeans. Genistein has been recommended as an osteoporosis treatment for postmenopausal women and elderly men, with the intention of reducing cardiovascular disease and hormone-dependent malignancies. Therefore, two sensitive and simple methods for quantifying it in the supplements preparation were developed.The first method (A) comprised employing the surfactant Triton X-114 to extract the result of the diazotization reaction with 4-Aminoacetophenone(4AMA) utilizing a cloud point extraction technique. The product was extracted using micelles of a non-ionic surfactant (TritonX-114) and then spectrophotometrically detected at a specified wavelength of 437nm. The linearity of the calibration curve was in the range of 0.25 -2.75 µg/mL of GEN(r = 0.9978) under optimal conditions. The average sample recovery was determined to be between 96 and 101 %. For 2 µg/mL of GEN, the relative standard deviation (RSD) was (0.27%). The second method (B) involved using the spectrophotometric-flow injection methodology for the same diazotization coupling reaction described above, and the orange colored dyewas measured at a wave length of 437 nm.Calibration curve were linear at different concentration range of GEN 10 to 100 µg/mL , relative standard deviation RSD% were 0.23 to 1.21. The proposed methods were applied to determine the presence of GEN in Supplements.

A novel enhanced defluorination of perfluorooctanoic acids by surfactant-assisted ultrasound coupling persulfate

A novel enhanced defluorination of perfluorooctanoic acids (PFOA) by surfactant-assisted ultrasound (US) coupling persulfate (PS) was proposed in this study. Instead of adding the surfactant into the PFOA solution directly, the promoted defluorination was obtained by adding the surfactant to the US bath outside of the PFOA reactor. In this situation, the effects of the critical micelle concentration (CMC), concentration and type of the surfactant, the US frequency and the pH of the US bath liquid on the PFOA defluorination were investigated. The results demonstrated that the PFOA defluorination at low-frequency levels (25 kHz-59 kHz) was facilitated by raising US frequency. Besides, the addition of three surfactants (Triton X-100, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)) all increased the PFOA defluorination by Triton X-100 > CTAB > SDS, which is opposed to their CMC (Triton X-100: 0.28 mM＜CTAB: 1.07 mM＜SDS: 7.69 mM). Rising the surfactant concentration would not enhance the defluorination, the best one was obtained at its CMC. Moreover, changing the pH of the US bath liquid by adding acid or alkaline solution inhibited the defluorination, which might be attributed to acid or base causing damage to the chemical properties or physical structure of surfactant (certified by the SEM tests). Additionally, the mechanism of enhanced PFOA defluorination was examined by electron paramagnetic resonance analysis, which proved that adding surfactant facilitated the generation of the radicals (·OH and SO4∙-), as well as the radicals’ amount increased over time during 60 min. Finally, the inhibited defluorination of adding surfactant directly to the PFOA solution was studied by the SEM analysis, the results demonstrated that adsorption and wrapping between surfactant micelles and PFOA reduced the contact between PFOA and radicals and affected the surfactant effect on the surface tension.

Dynamic Exchange of Amphiphilic Random Copolymers between Micelles in Water: Kinetics and Mechanism Analyzed by TR-SANS

Amphiphilic random copolymers bearing poly(ethylene glycol) (PEG) and alkyl groups as side chains are intermolecularly self-assembled into size-controlled multichain micelles in water. The random copolymer micelles are known to induce the exchange of their polymer chains, whereas the details of the kinetics and mechanism have not been elucidated yet. Herein, we investigated the exchange kinetics and mechanism of the random copolymer chains between their micelles by time-resolved small-angle neutron scattering (TR-SANS). For this purpose, random copolymers carrying PEG and deuterated butyl or dodecyl groups were designed for deuterated micelles. After mixing deuterated and non-deuterated micelle solutions, the resulting mixtures were monitored by TR-SANS at various concentrations and temperatures. The scattering intensity of the micelle mixtures decayed with time, indicating that deuterated copolymers were gradually mixed with non-deuterated copolymers via chain exchange between their micelles to form micelles consisting of both deuterated and non-deuterated copolymers. The kinetic analysis revealed that the exchange of their polymer chains involved two mechanisms: A unimer release and insertion pathway was dominant in diluted conditions, whereas the contribution of a micelle collision pathway increased with increasing total polymer concentration and temperature. The activation energy of the polymer exchange process was dependent on the hydrophobic alkyl groups and larger than that of a related surfactant micelle.

Polymer–Surfactant Complexes Impact the Stratification and Nanotopography of Micellar Foam Films

Freestanding films of soft matter drain via stratification due to confinement-induced structuring and layering of supramolecular structures such as micelles. Neutral polymers, added as rheology modifiers to cosmetics, foods, pharmaceuticals, and petrochemical formulations, often interact with monomers and micelles of surfactants, forming polymer-surfactant complexes. Despite many studies that explore interfacial and bulk rheological properties, the corresponding influence of polymer-surfactant complexes on foam drainage and lifetime is not well understood and motivates this study. Here, we report the discovery and evidence of drainage via stratification in foam films formed with polymer-surfactant (PEO-SDS) complexes. We show that the stratification trifecta of coexisting thick-thin regions, stepwise thinning, and nanoscopic topological features such as nanoridges and mesas can be observed using IDIOM (interferometry, digital imaging, and optical microscopy) protocols we developed for nanoscopic thickness mapping. We determine that for polymer concentrations below overlap concentration and surfactant concentrations beyond the excess micelle point, polymer-surfactant complexation impact the nanoscopic topography but not the step size, implying the amplitude of disjoining pressure changes, but periodicity remains unchanged.

When Ions Defy Electrostatics: The Case of Superchaotropic Nanoion Adsorption

Nanometer-sized anions, like polyoxometalates and borate clusters, bind to nonionic hydrated matter driven by the chaotropic effect, which arises from the favorable dehydration of the ions. Herein, we evaluate the adsorption and activity coefficient of the superchaotropic Keggin polyoxometalate SiW12O404- (SiW) on nonionic surfactant (C8E4) micelles by modeling small-angle X-ray and neutron-scattering spectra. Neither hard sphere nor electrostatic repulsion models reproduce the experimental activity coefficient of adsorbed SiW ions on the micelles. However, the activity and binding of SiW on the micelles is well-described by a Langmuir adsorption isotherm. These results imply that adsorbed SiW ions are non-interacting and "create" around themselves adsorption sites on the micelle. The temperature dependence of the adsorption constant showed that the SiW adsorption is enthalpically driven and entropically unfavorable, in line with the typical chaotropic thermochemical signature. The adsorption enthalpy can be split into an electrostatic term and a water-recovery term to evaluate and qualitatively predict the superchaotropicity of a nanoion.

Micelle formation and physico-chemical variables for the sodium dodecyl sulfate/cetylpyridinium chloride and their mixture in aqueous propranolol hydrochloride drug solvent: Conductivity and theoretical analysis

Herein, study of both single and mixed micelle development of an anionic surfactant sodium dodecyl sulfate (SDS) and a cationic surfactant cetylpyridinium chloride (CPC) in propranolol hydrochloride (PPH) drug medium has been performed using a conductometric technique at different temperatures and compositions. The critical micelle concentration (CMC) along with degree of ionization (g) were assessed from the specific conductivity (κ) versus [surfactant] plots. Within the concentration of surfactant studied, a single CMC was achieved in the situations of pure and mixed surfactant micellization. The CMC and g values have been noticed reliant on the employed drug concentrations, variations of mole fractions of the mixture of surfactants and experimental temperature. For the micellization of single SDS/ CPC surfactants in aq. PPH drug medium, PPH drug causes delayed micelle development which has been detected as the upsurge of CMC values of SDS/CPC in PPH drug media. For the association of SDS/ CPC surfactants in aq. PPH drug medium, the CMC values experienced a lessening with the growth of study temperature. At a fixed temperature, the experimental CMC values, of the SDS + CPC mixture, endure a decline through the upsurge of mole fractions of CPC (α1), attain a minimum value and the CMC values tend to enhance at and above α1= 16.2 × 10-5. The ideal critical micelle concentrations (CMCid) are detected always as higher values than experimental CMC up to the α1= 10.8 × 10-5. The -β values and |β| > |ln(CMC1/ CMC2)| for the present study reveal that the interaction among the amphiphiles under analysis is synergistic. The negative free energy (-ΔGmO) of micellization were obtained throughout the study. The enthalpy (ΔHmO) and entropy (ΔSmO) of micellization reveal the presence of hydrophobic interaction as the principal type of interaction among the studied constituents. The negative excess free energy (ΔGex) values inferred that stable mixed micelles are formed for the mixture of SDS + CPC in aq. PPH drug medium. The micellar mole fractions (both experimental and ideal values), activity coefficients of components in mixed micelles as well as enthalpy–entropy compensation parameters were also measured and illustrated. It is possible that the knowledge gained from the current analysis may be used to enhance pharmaceutical formulations, drug delivery carriers, along with drug act proficiency.

Antagonistic Toxic Effects of Surfactants Mixtures to Bacteria Pseudomonas putida and Marine Microalgae Phaeodactylum tricornutum.

Surfactants can be found in an ever-widening variety of products and applications, in which the combination of several types of surfactants is used to reinforce their properties, looking for synergistic effects between them. After use, they tend to be discarded into wastewater, ending up in aquatic bodies with concerning harmful and toxic effects. The aim of this study is the toxicological assessment of three anionic surfactants (ether carboxylic derivative, EC) and three amphoteric surfactants (amine-oxide-based, AO), individually and in binary mixtures of them (1:1 w/w), to bacteria Pseudomonas putida and marine microalgae Phaeodactylum tricornutum. Critical Micelle Concentration (CMC) was determined to demonstrate the capacity to reduce surface tension and the toxicity of the surfactants and mixtures. Zeta potential (ζ-potential) and micelle diameter (MD) were also determined to confirm the formation of mixed surfactant micelles. The Model of Toxic Units (MTUs) was used to quantify the interactions of surfactants in binary mixtures and to predict if the concentration addition or response addition principle can be assumed for each mixture. The results showed a higher sensitivity of microalgae P. tricornutum to the surfactants tested and their mixtures than bacteria P. putida. Antagonism toxic effects have been detected in the mixture of EC + AO and in one binary mixture of different AOs; this is to say, the mixtures showed lower toxicity than expected.

Microenvironment Engineering to Promote Selective Ammonia Electrosynthesis from Nitrate over a PdCu Hollow Catalyst.

The electrosynthesis of recyclable ammonia (NH3 ) from nitrate under ambient conditions is of great importance but still full of challenges for practical application. Herein, an efficient catalyst design strategy is developed that can engineer the surface microenvironment of a PdCu hollow (PdCu-H) catalyst to confine the intermediates and thus promote selective NH3 electrosynthesis from nitrate. The hollow nanoparticles are synthesized by in situ reduction and nucleation of PdCu nanocrystals along a self-assembled micelle of a well-designed surfactant. The PdCu-H catalyst shows a structure-dependent selectivity toward the NH3 product during the nitrate reduction reaction (NO3 - RR) electrocatalysis, enabling a high NH3 Faradaic efficiency of 87.3% and a remarkable NH3 yield rate of 0.551mmol h-1 mg-1 at -0.30V (vs reversible hydrogen electrode). Moreover, this PdCu-H catalyst delivers high electrochemical performance in the rechargeable zinc-NO3 - battery. These results provide a promising design strategy to tune catalytic selectivity for efficient electrosynthesis of renewable NH3 and feedstocks.

Influence of premixed chlorine salt on the pore characteristics of cement-based hardened grout containing a large amount of bentonite

Moderate content of premixed chlorine salt could improve the fluidity and strength of cement-based grouts containing a large amount of bentonite, while its effect on pore structure is still unclear. In this study, pore characteristics were systematically described by low-field NMR combined with low-pressure CO2 and N2 adsorption. Pores were classified into five types according to their size to clarify the effect of chloride content, curing time, and chloride type (NaCl or CaCl2) on various pore volumes. This was further analyzed by the introduction of unit volume variation (U). Results show that the volume of inter gel pore (2–10 nm) and middle capillary pore (50–1000 nm) increases with the increase of chloride content while that of fine (10–50 nm) and large (>1000 nm) capillary pore decreases. The inter gel pore volume and fine capillary pore volume depend on C–S–H content and surfactant micelles number, respectively. The volume of middle and large capillary pores is mainly affected by the hydration product content. For intra sheet pores (<2 nm), their volumes show an inverted “N” shape with the increase of NaCl content and a “U” shape for CaCl2, which is mainly related to the ettringite dissolution and nano-SiO2 dispersion. The chloride content and curing time also have a large reduction effect on the U of intra sheet pores, fine and large capillary pores. Furthermore, CaCl2 contributes more than NaCl to the development of pore structure, especially for inter gel pores and middle capillary pores.

Conjugated surfactant micelles: A non‐denaturing purification platform for concentrated human immunoglobulin G

AbstractAs downstream purification and separation technologies progress towards raising the concentration of therapeutic‐grade monoclonal antibodies (mAbs) in cell culture, downstream processing has begun to face increased difficulty in efficiently coping with such high immunoglobulin G (IgG) titers (≤25 mg mL−1). In the current study, we demonstrate the ability of a non‐chromatographic, ligand‐free procedure to recover almost quantitatively (84–99% yield, by densitometry) polyclonal, human IgG present at high concentrations (15–25 mg mL−1) in E. coli lysate. Instead of chromatographic media and columns, we use conjugated, mixed‐micelles comprising non‐ionic detergents, tyrosine monomers, and the amphiphilic [(bathophenanthroline)3:Fe2+] complex. Capture and extraction processes are performed at pH 6.5–7, thereby avoiding antibody exposure to acidic, potentially denaturing conditions. Recovered IgG is monomeric as determined by dynamic light scattering (DLS). Process upscaling from 0.1 to 5 mL requires only proportional increase in all reagents and does not affect overall yield or antibody purity.

Probing self-assembled micellar topologies via micro-scale diffusive dynamics of surfactants

HypothesisSurfactants spontaneously self-assemble in aqueous solutions and are critical in energy, biotechnology, and the environment. The self-assembled micelles may experience distinct topological transitions beyond a critical counter-ion concentration, yet the associated mechanical signatures are identical. By monitoring self-diffusion dynamics of individual surfactants in micelles via a non-invasive 1H NMR diffusometry, we may distinguish various topological transitions overcoming challenges associated with traditional microstructural probing techniques. ExperimentsThree micellar systems based on CTAB/5mS, OTAB/NaOA and CPCl/NaClO3 are considered at various counter-ion concentrations, and their rheological properties are assessed. A systematic 1H NMR diffusometry is conducted and the resulting signal attenuation is measured. FindingsWith no counter-ion, surfactants self-diffuse freely with a mean squared displacement Z2∼Tdiff in the micelles. As counter-ion concentration increases, self-diffusion becomes restricted with Z2∼Tdiffα, and α→0.5. Beyond the viscosity peak, for the OTAB/NaOA system that shows a linear-shorter linear micelle transition, Z2∼Tdiff0.5. Conversely, for the CTAB/5mS system that experiences a linear wormlike-vesicle transition above the viscosity peak, a free self-diffusion is recovered. The diffusion dynamics in CPCl/NaClO3 are similar to those of OTAB/NaOA. Hence, a similar topological transition is surmised. These results highlight the unique sensitivity of the 1H NMR diffusometry to micelles topological transitions.

Molecular simulations of adsorption of surfactant micelles on partially and fully covered iron surfaces

Surfactant – metal interactions are important in applications like corrosion inhibition and synthesis of metallic nanoparticles, wherein surfactants are often added above their critical micelle concentration. Under these conditions, surfactant micelles exist in dynamic equilibrium with free surfactant molecules. Due to their faster diffusion compared to the micelles, free surfactant molecules rapidly adsorb onto metal-water interfaces. Therefore, adsorbing surfactant micelles invariably encounter metal-water interfaces with some adsorbed surfactants. We have studied, via atomistic simulations, adsorption behavior of micelles of a quaternary ammonium-based surfactant at iron-water interfaces that are partially or fully covered with adsorbed surfactant molecules. We find that on a partially covered surface, a micelle prefers to adsorb on a bare metal patch. On a fully covered surface, the micelle adsorbs on top of already adsorbed molecules and attains a hemispherical morphology. The adsorption free energy decreases as the coverage of iron-water interface with surfactants increases.

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

Hollow mesoporous nanoparticles with controllable size (less than 100 nm) are desired as drug-delivery carriers. Herein, we report the synthesis of monodispersed hollow mesoporous organosilica (HMOS) and hollow mesoporous silica (HMS) nanoparticles using soft and hard templating methods. HMOS shells, with 1,2-bis(triethoxysilyl)ethane (BTEE) as the precursor and hexadecyltrimethylammonium bromide and sodium dodecyl sulfate (SDS) as the soft templates, were formed on monodispersed silica nanoparticles (SNPs), which were used as the hard templates. HMOS and HMS nanoparticles were obtained by removing the SNPs after three rounds of ammonia dialysis. The hollow size of HMOS can be tuned by changing the size of the SNPs. By using SNPs with a size of 36.5 nm, hollow spaces of approximately 20 nm connected the surface through narrow pores (<5 nm). Mesopores of approximately 12 nm were formed by the surfactant micelles. Additionally, the interparticle space in HMOS and HMS was approximately 12 nm. The shell thicknesses of HMOS and HMS could be tuned in the range of 5-9 nm by changing the BTEE amount. Moreover, the amount of surfactant used varied the porous structure. The HMOS with a thickness of 5 nm exhibited a Brunauer-Emmett-Teller (BET) surface area of 268 m2/g and a total pore volume of 1.14 cm3/g. Meanwhile, HMS demonstrated a BET surface area of 553 m2/g and a total pore volume of 1.82 cm3/g while maintaining a hollow structure. HMOS displayed a high loading capacity for ibuprofen (3009 mg/g), and its drug release system showed a sustained-release property. Therefore, the HMOS preparation using hard and soft templates proposed herein can control the hollow size and shell thickness for drug-delivery applications.

Amphiphilic Near‐Infrared Fluorescent Molecular Probes: Optical Properties in Solution and in Surfactant Micelle Microenvironment

AbstractIn this work, the optical properties of two novel near‐infrared fluorescent tricarbocyanines with amphiphilic nature, CyN and CyS, were studied in solution and in micelles of representative surfactants (anionic, cationic and non‐ionic) by means of spectroscopic techniques. Interestingly, the spectral properties of the new fluorophores depend on the nature of the heteroatom at the meso position. Dependence on the solvent polarity and the viscosity were also observed in both cases. Furthermore, changes on photophysical properties occurred upon encapsulation of the dyes. The incorporation of the dye from the aqueous solution to the surfactant supramolecular assembly produced a drastic change in the fluorescence emission from quenched state to fluorescence enhancement, rendering an OFF‐ON response to the exchange of environment. In addition, a significant protective effect against photobleaching was determined when the dyes were included in Pluronic® micelles (F127) resulting in a promising system to be used as a fluorescent nanosized container. The novel amphiphilic NIR fluorophores also interact as a Förster resonance energy transfer (FRET) pair and the process was studied within micelles loaded with both dyes.

Unsupervised Data-Driven Reconstruction of Molecular Motifs in Simple to Complex Dynamic Micelles.

The reshuffling mobility of molecular building blocks in self-assembled micelles is a key determinant of many their interesting properties, from emerging morphologies and surface compartmentalization, to dynamic reconfigurability and stimuli-responsiveness. However, the microscopic details of such complex structural dynamics are typically nontrivial to elucidate, especially in multicomponent assemblies. Here we show a machine-learning approach that allows us to reconstruct the structural and dynamic complexity of mono- and bicomponent surfactant micelles from high-dimensional data extracted from equilibrium molecular dynamics simulations. Unsupervised clustering of smooth overlap of atomic position (SOAP) data enables us to identify, in a set of multicomponent surfactant micelles, the dominant local molecular environments that emerge within them and to retrace their dynamics, in terms of exchange probabilities and transition pathways of the constituent building blocks. Tested on a variety of micelles differing in size and in the chemical nature of the constitutive self-assembling units, this approach effectively recognizes the molecular motifs populating them in an exquisitely agnostic and unsupervised way, and allows correlating them to their composition in terms of constitutive surfactant species.

Role of Dual Nature of Ionic Liquid in Solvation Dynamics and Rotational Diffusion in Mixed Micelles: A Time‐Resolved Fluorescence and Fluorescence Anisotropy Study

AbstractThe present work demonstrates the role of the dual nature of an ionic liquid, 1‐dodecyl‐3‐methylimidazolium bromide (C12mimBr), in the solvation dynamics and rotational diffusion of Coumarin 153 (C‐153) in the aqueous mixed micellar solutions of three cationic gemini surfactants, 12‐s‐12,2Br− (where s = 4, 6 and 8) using different spectroscopic and light scattering techniques. Ionic liquid within the micelles controls the weightages of solvation components. In pure micelles of a gemini surfactant, the fast and slow solvation components are major and minor, respectively, which vary based on the concentration of the ionic liquid. The effective solvation rate enhances with increasing concentration of C12mimBr. Dual nature of C12mimBr governs the size of mixed micelles. Thus the associated time constant for rotational motion also alters accordingly. In micelle, lateral diffusion coefficient (DL) value enhances with its increasing size due to mixed micelle's increased porosity. Gemini spacer chain length effect is also discussed.