Direct Micelles Research Articles

A micellar-enhanced fluorescence photoinduced four-way calibration method for the determination of multiclass pesticides in lemon juice

In this work, a four-way multivariate calibration method for the simultaneous determination of four pesticides - carbendazim (CBZ), thiabendazole (TBZ), pirimiphos-methyl (PMM), and clothianidin (CLT) - in lemon juice is presented. Third-order data were acquired by registering the photoinduced fluorescence of the analytes as excitation-emission matrices at different times of UV-light irradiation, in the presence of organized media (direct micelles) as fluorescence enhancers. The optimal experimental conditions (pH 11.5 and 32 mmol L−1 hexadecyltrimethylammonium chloride surfactant) were determined through a central composite design using the response surface methodology. The analytes were individually calibrated, except for TBZ and CBZ due to the inner filter effect of TBZ on CBZ. Test samples containing all analytes and imidacloprid (as potential interference) were analysed. PARAFAC was utilized to evaluate both the trilinearity and quadrilinearity of the third-order data and four-way arrays, respectively. PMM was successfully determined with quadrilinear PARAFAC decomposition, whereas CLT, TBZ, and CBZ were satisfactorily modelled using U-PLS/RTL due to the loss of quadrilinearity caused by different phenomena. The profitable applicability of the analytical method in the CBZ, TBZ, PMM, and CLT determination in lemon juice samples was demonstrated, achieving limits of detection below the maximum residue levels reported by the European Commission, and mean recoveries at 90 ± 5%.

Dilution and packing of anionic liquid surfactant in presence of divalent and trivalent counter-ions

Alkyl ether carboxylates are part of a new class of ionic liquids based on the Concept of Melting Point Lowering due to Ethoxylation (COMPLET) and possess unique aggregation behaviour due to the simultaneous anionic and non-ionic nature of the surfactant anion. Previous publications on H[C8E8c] (Polyoxyethylene(8) octyl ether carboxylic acid) and its monovalent salts have shown a variety of phases in aqueous systems with a transition from small spherical micelles at high water contents towards a phase of interdigitated head groups at low water contents. In the present paper, we examine the shorter homologue H[C8E5c] (Polyoxyethylene(5) octyl ether carboxylic acid) and its di- and trivalent transition and rare earth metal salts using X-ray scattering methods in the small- and wide-angle range (SWAXS). These measurements confirm the presence of spherical micelles in diluted aqueous systems which aggregate and whose head groups interdigitate at higher concentrations of the isotropic, non-birefringent ionic liquid. Swelling experiments yield two-dimensional swelling of the microstructure, and combined with the scattering pattern, the data infer prolate spheroidal direct (o/w) micelles with interdigitated head groups, which align to form short linear chains. These chains are offset to form a localised hexagonal close-like packing of the micelles. Most interesting, within this packing, the metal cations are confined into channels between the micelles in linear chains with ion-ion distances of 0.4–1.1 nm. In particular, in the water-free ionic liquid, this confinement may be responsible for some of the unique properties of these systems. It is suggested that the confinement of the cations leads to strong ion-ion aggregation that could be at the origin of the very peculiar magnetic properties of these simple one-component liquids, which contrasts with classical ferrofluids, in which magnetic nanoparticles are dispersed in another liquid.

Tetraalkoxysilane-Assisted Self-Emulsification Templating for Controlled Mesostructured Silica Nanoparticles.

Although mesoporous silica nanoparticles (MSNs) have been intensively investigated, their mesostructure and formation mechanism are still a topic of debate. Here, we show that MSNS are generated at the interface of the biphasic water-surfactant-triethanolamine-tetraalkoxysilane (TAOS) quaternary system. The spontaneous microemulsification of the hydrophobic TAOS generates microdroplets and direct micelles that both determine the particle size and the pore size. We confirmed also that the dendritic morphology with conical pores is an intermediate species, which readily transforms into regular MSNs concomitantly with the collapse of the microemulsion due to the continuous consumption of TAOS. The prominent effect of the microemulsion on the mechanism growth as a primary template is thoroughly investigated and named here tetraalkoxysilane-assisted self-emulsification templating.

Diffusion of surfactant from a micellar solution to a bare interface. 1. Absorbing boundary

We analyze dynamic adsorption of surfactant from a micellar solution to a rapidly created surface that acts as an absorbing boundary for surfactant monomers (single molecules), along which the monomer concentration vanishes, with no direct micelle adsorption. This somewhat idealized situation is analyzed as a prototype for situations in which strong suppression of monomer concentration accelerates micelle dissociation, and will be used as a starting point for analysis of more realistic boundary conditions in subsequent work. We present scaling arguments and approximate models for particular time and parameter regimes and compare the resulting predictions to numerical simulations of the reaction–diffusion equations for a polydisperse system containing surfactant monomers and clusters of arbitrary aggregation number. The model considered here exhibits an initial period of rapid shrinkage and ultimate dissociation of micelles within a narrow region near the interface. This opens a micelle-free region near the interface after some time τe, the width of which increases as t1/2 at times t≫τe. In systems that exhibit disparate fast and slow bulk relaxation times τ1 and τ2 in response to small perturbations, τe is usually comparable to or greater than τ1 but much less than τ2. Such systems exhibit a wide intermediate time regime τe<t<τ2 in which the remaining micellar region reaches a state of partial local equilibrium, followed by a final stage t≫τ2 in which full local equilibrium is established.

Review on Microemulsions for Conformance Improvement Technology: Fundamentals, Design Considerations, and Perspectives

The area of conformance improvement technology (CIT) encompasses the application of a myriad range of conventional fluids, including polymers, gels, foams, polymer-enhanced gels and foams, bacteria, and emulsions. However, these routes show operational limitations in terms of chemical degradation, thermal degradation, formation damage, susceptibility to high salinity, and segregation within pore spaces. To mitigate these problems, it is necessary to employ conformance agents that can be effectively tuned for a wide variety of reservoir conditions. Microemulsions are a promising class of fluids that exhibit thermodynamic stability, robust structure, and tunable properties. The concept of this research is to inject the optimal (correct) dosage of surfactants, which form micelles with in situ hydrocarbons to form microemulsions. Microemulsions are characterized by direct and reverse micelles, which contribute to their intermolecular interactions responsible for fluid stability and propagation under dynamic shear conditions. Design and reservoir considerations must comprise of a number of factors, namely, salinity, pH, temperature, slug concentration, and fluid activation/placement. An optimal microemulsion can be identified by understanding the flow mechanisms while accounting for mobility control, rock permeability and heterogeneity, thief zone permeabilities, and the presence of anomalies. It has been established in this review that microemulsions help plug the high permeability pore throats via a combination of the “Jamin effect” and viscosity modification. By adoption of a proper workflow design, the reservoir may be tuned via the introduction of microemulsions to suit the needs of the industry. However, considerable research is still needed to validate the design aspects and application of microemulsions for conformance improvement.

Direct and Reverse Pluronic Micelles: Design and Characterization of Promising Drug Delivery Nanosystems.

Pluronics are a family of amphiphilic block copolymers broadly explored in the pharmaceutical field. Under certain conditions, Pluronics self-assemble in different structures including nanosized direct and reverse micelles. This review provides an overview about the main parameters affecting the micellization process of Pluronics, such as polymer length, fragments distribution within the chain, solvents, additives and loading of cargo. Furthermore, it offers a guide about the most common techniques used to characterize the structure and properties of the micelles. Finally, it presents up-to-date approaches to improve the stability and drug loading of Pluronic micelles. Special attention is paid to reverse Pluronics and reverse micelles, currently underexplored in the literature. Pluronic micelles present a bright future as drug delivery agents. A smart design and thorough characterization will improve the transfer to clinical applications.

The effect of the structural transition within a direct hexagonal (HI) mesophase on the internal lipid mobility

The current study analyzes the cause of the extreme change in dermal permeation resulting from a minute structural transformation within a temperature-sensitive direct hexagonal mesophase by a multiple-method approach. The evaluated mesophase is composed of Tween 80, propylene glycol, isopropyl myristate, benzyl alcohol, and water. 1 wt% ketoconazole (KCZ) was loaded in the concentrate as a model lipophilic drug. Evaluation of the mesophase at 25 °C indicated that the hexagonal mesophase region (33.0–42.5 wt% water along water dilution line N91) consists of two distinct structures. At water content below 39.0 wt%, the mesophase is structured as a bidiscontinuous hexagonal mesophase (BHM) consisting of occluded hydration centers and hexagonally oriented direct micelles. Above 39.5 wt% water, dilution of the BHM obstructs the hydration centers, transforming the mesophase to a water continuous hexagonal mesophase (CHM). FTIR evaluation indicated that the both the added water upon dilution and the water molecules released from the hydration centers bind to the surfactant's non-hydrated ethoxylates. Evaluation of the structural transition by PGSE-NMR and DSC indicated that the binding of water to the surfactant's heads immobilizes the inner core of the solubilized lipids. The reduction of the lipid core’s mobility prevents its crystallization at cryogenic temperatures. SAXS and rheological evaluations pointed out that both BHM and CHM are temperature-sensitive mesophases, which lose their range order and storage modulus at 32 °C. Obstruction of the hexagonal mesophase enhances KCZ's diffusion from both mesophases’ via cellulose acetate at 35 °C. Despite the similarity of both mesophases at elevated temperatures (35 °C), the lipidic inner core’s rotational correlation time for deformed CHM micelles remains substantially lower than from the deformed BHM. Franz cell evaluation indicated that the lipidic core mobility substantially influences KCZ's distribution upon dermal application, whereas from CHM KCZ's transdermal flux via a dermatome bovine graft at 35 °C, was 1.60 ± 0.28 µg/cm2 h, no flux was detected from BHM. On the other hand, KCZ's dermal accumulation from BHM, at 35 °C, was found to be more than double than that from CHM, indicating that the decrease in the lipidic inner core’s mobility of direct micelles prevents the accumulation of lipophilic compounds in the dermis, thereby enhancing their transdermal flux.

Cloud point, auto-coacervation, and nematic ordering of micelles formed by ethylene oxide containing carboxylate surfactants

HypothesisIn a recent paper, we determined the phase behavior of an aqueous solution of octyl ether octaethylene oxide carboxylic acid ([H+][C8E8c−], Akypo™ LF2) and with partial replacement of H+ by Na+ and Ca2+. It was found that even the neat surfactants are liquid at room temperature and that they form only direct micelles for any aqueous content and over large temperature ranges. The aim of the present work was to find an explanation for the clouding in these systems as well as for the coacervation observed at very low surfactant content. We expected that very similar phase diagrams would be found for a full replacement of H+ by the mentioned ions. ExperimentsWe established the respective phase diagrams of the above-mentioned salts in water and determined the structures of the occurring phases in detail with small-and wide-angle X-ray scattering, small-angle neutron scattering, dynamic light scattering, heat flux differential scanning calorimetry, as well as surface tension, ESI-MS, and NMR experiments. FindingsTo our surprise, we discovered a new type of nematic phase between an isotropic and a hexagonal phase. Based on the complete description of all occurring phases both in the acidic and the charged surfactant systems, we were able to design a coherent and unified picture of all these phases, including the auto-coacervation at low surfactant concentration, the non-conventional clouding at high temperatures, the unusual liquid crystalline phases in a small domain at high surfactant concentrations, and the Lβ phase at low temperatures and at very low water content. It turned out that all phenomena are a consequence of the subtle interplay between a) the packing constraint due to the very large head-group, b) the relatively small hydrocarbon chain and c) the tunable electrostatic interactions versus entropy.

Work of Formation of Direct and Inverse Micelle as a Functions of Aggregation Number

Work of Formation of Direct and Inverse Micelle as a Functions of Aggregation Number

Determination of ciprofloxacin drug with molecularly imprinted polymer/co- metal organic framework nanofiber on modified glassy carbon electrode (GCE)

In this paper, we report the Co-metal organic frameworks (MOFs) were successfully synthesized with the aid of 2,6-pyridinedicarboxylic acid ammonium as an organic ligand in polylactic acid (PLA) as a biodegradable and biocompatibility polymer substrate through the ultrasonic-assisted electrospinning method. Co-MOFs/PLA nanofiber used as a new nanocomposite for design and construction of nanosensor based on the polymer prepared of the 4-aminobenzoic acid electrolytic molecule for measuring ciprofloxacin (CIP) drug class. The molecularly imprinted polymer (MIP) and non-imprinted polymer (NIP) sensors were studied by differential pulse voltammetry (DPV) to study changes in oxidation peaks and reduction of potassium ferricyanide. The calibration curve for ciprofloxacin was in the range of 0.5–150 μM also the detection limit was 0.017 μM and the standard deviation for five consecutive measurements at 60 μM concentration was calculated1.7% respectively. For characterizing the synthesized Co-MOF/PLA nanofiber we used X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDAX), Transmission electron microscopy (TEM) and Dynamic light scattering (DLS). In this study, we present new nanosensors with Co-MOF/PLA nanofiber as a biodegradable and bioactive composite for the first time in modified carbon paste electrode using the ultrasound-assisted direct micelle (UADM) method as the determination of ciprofloxacin drug.

OPTIMIZING THE STRUCTURE OF AMPHIPHILIC INVERTIBLE POLYMERS (AIPs) MADE OF PEGs AND FATTY COMPOUND SEGMENTS TO OBTAIN A SINGLE CRITICAL MICELLE CONCENTRATION

Amphiphilic biopolyesters containing hydrophilic segments (PEGs) and hydrophobic blocks (silicon fatty from a castor oil derivative) showed the ability to self-assembly in inverted micelles. Due to their capability to form also direct micelles, these biopolyesters could be classified as amphiphilic invertible polymers AIPs. The micellar concentrations CMC and ICMC corresponding to the direct and inverted micelles respectively precisely correlated with PEG length. The methodology used in this investigation allowed to determine the PEG length needed to obtain the adequate structural biopolyester able to self-assembly in direct and inverted micelles from a unique concentration. Inverted micelle diameters, determined by DLS analysis, increased as the molecular polarity of the biopolyesters decreased. No individual inverted micellar were observed by TEM technique due to the concentration change during the sample preparation, however micellar macromolecular aggregations were revealed.

Sensitized photo-oxidation of gadusol species mediated by singlet oxygen

Gadusols are efficient nature UV sunscreens with antioxidant capacity. The kinetics of the quenching reactions of singlet oxygen O2(1∆g) by gadusol species was evaluated in aqueous solution as well as in the presence of direct charged micelles. Time-resolved phosphorescence detection of O2(1∆g) indicated that gadusolate, the main species under biological pH, is a more efficient quencher than the enol form with a rate constant of ca. 1.3 × 108 L mol−1 s−1. The deactivation proceeds via a collisional mechanism with clear dominance of chemical pathways, according to the rates of gadusol and oxygen consumptions, and typical photooxidation quantum yields of ca. 7%. The relative contributions of the chemical and physical quenching steps were not affected by the presence of anionic or cationic micelles emulating simple pseudo-biological environments. The products of the photo-oxidative quenching support a type II mechanism initiated by the addition of O2(1∆g) to the C-C double bond of gadusolate. These results point to the relevance of considering the role of sacrifice antioxidant along with the UV-screening function for gadusol, particularly in the context of potential biotechnological applications of this natural molecule.

Influence of the AOT Counterion Chemical Structure on the Generation of Organized Systems.

The impact of the imidazolium counterion structure on the organized systems formed by the surfactant 1,4-bis-2-ethylhexylsulfosuccinate, AOT, both in aqueous solutions and in nonpolar solvents is investigated. With this in mind, we investigated if the ionic liquid-like (IL-like) surfactant 1-ethyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, emim-AOT, forms direct micelles or vesicles in water. Dynamic light scattering, zeta potential, conductivity, fluorescence spectroscopy, and UV-visible spectroscopy measurements were performed to characterize the organized systems in aqueous solutions. We also studied the self-aggregation of emim-AOT, 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, bmim-AOT, and of 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, hmim-AOT, in nonpolar solvents. The results obtained showed that the IL-like surfactant emim-AOT forms direct micelles in water, as sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) does. However, emim-AOT aggregates are larger, have a lower surface charge, are more stable, and have a more polar and less fluid micellar interface than Na-AOT micelles. It was also observed that emim-AOT and hmim-AOT form reverse micelles in nonpolar solvents. The size of the imidazolium cations dramatically influences the size of the reverse micelles and their ability to solubilize water.

Study of Mandacaru (Cereus jamacaru DC), in natura and modified by microemulsion, as a biosorbent for diesel oil

Biosorbents have emerged as an alternative to remove organic contaminants because they are natural products with a high availability, low cost, biodegradability, and good sorption capacity. The Mandacaru (Cereus jamacaru DC) was investigated as sorbent of diesel, and compared with the Mandacaru modified with microemulsions. The sorbents were also submitted to a physycal-chemical characterization for FT-IR, TG/DTG, MEV and CHN-O. The granulometry range 500-150 µm of the Mandacaru particulate, this was the granulometry range chosen as the standard one, being used in the modification and sorption tests. The unclassified Mandacaru presented a medium sorption capacity of the diesel oil of 1.61 g g-1. Whereas the Mandacaru modified with a microemulsion comprised of direct micelles (oil/water) showed a remarkable increase in the sorption capacity of 80-111% (3,08 to 3,54 g g-1).

Application of SDS surfactant microemulsion for removal of filter cake of oil-based drilling fluid: influence of cosurfactant

After drilling oil wells using oil-based drilling fluid, there is the occurrence of a formation of a thin layer of solids adsorbed on the surface, called filter cake, which must be removed to obtain satisfactory well cementation. The present work developed microemulsion systems from sodium dodecyl sulfate, a biodegradable surfactant, with kerosene as oil phase, n-butanol as cosurfactant and distilled water, in order to evaluate its efficiency in removing the filter cake. The results showed that the microemulsion systems composed of inverse and bicontinuous micelles removed 100% of the filter cake regardless of the content of the constituents in the formulation, while the direct micelles only reached 100% with the formulation composed by 10% kerosene and cosurfactant/surfactant ratio = 4. It was observed that the cosurfactant/surfactant ratio is a determining variable for direct micelles to remove 100% of the filter cake and that they are compatible with cement, offering desirable thermal stability and improving the wettability of the rock in water.

Modification of the Mass Action Law for Reverse Micelles

Two modifications of the mass action law are considered as applied to defining the critical micelle concentration (CMC) via constant K of the law. The first, traditional, modification defines the CMC as $${{K}^{{1/(1 - n)}}},$$ where n is the aggregation number, and the second one—as $${{(Kn)}^{{1/(1 - n)}}}.$$ In both cases, the formulation of the mass action law is extremely simplified due to the exclusion of the constant, while all concentrations are expressed in the CMC units, which is slightly lower in the second case. The second modification of the law is more adequate at moderate and low aggregation numbers, which are characteristic of reverse micelles; therefore, these two modifications are conditionally attributed to the direct and reverse micelles. For both modifications, the concentrations of micelles and monomers are analyzed as depending on the total surfactant concentration in a micellar solution, while explicit analytical expressions are derived for the inverse dependences. An explicit relation has been found between the aforementioned concentrations and the micellization degree of solution . The dependence of the critical micellization degree (corresponding to CMC) on the aggregation number has been determined.

Self-assembly of glycerol monooleate with the antimicrobial peptide LL-37: a molecular dynamics study.

Over the past decade, the rapid increase in the incidence of antibiotic-resistant bacteria has promoted research towards alternative therapeutics such as antimicrobial peptides (AMPs), but their biodegradability limits their application. Encapsulation into nanocarriers based on the self-assembly of surfactant-like lipids is emerging as a promising strategy for the improvement of AMPs' stability and their protection against degradation when in biological media. An in-depth understanding of the interactions between the structure-forming lipids and AMPs is required for the design of nanocarriers. This in silico study, demonstrates the self-assembly of the amphiphilic lipid glycerol monooleate (GMO) with the antimicrobial peptide LL-37 into nanocarriers on the molecular scale. Molecular dynamics (MD) simulations show the formation of direct micelles, with either one or two interacting LL-37, and vesicles in this two-component system in agreement with experimental results from small-angle X-ray scattering studies. The hydrophobic contacts between LL-37 and GMOs in water appear responsible for the formation of these nanoparticles. The results also suggest that the enhanced antimicrobial efficiency of LL-37 in these nanocarriers that was previously observed experimentally can be explained by the availability of its side chains with charged amino acids, an increase of the electrostatic interaction and a decrease of the peptide's conformational entropy upon interacting with GMO. The results of this study contribute to the fundamental understanding of lipid–AMP interactions and may guide the comprehensive design of lipid-based self-assembled nanocarriers for antimicrobial peptides.

Systematic Study of NaF Nanoparticles in Micelles loaded on Polylactic Acid Nanoscaffolds: In Vitro Efficient Delivery

The overall aim of this work was developing and optimized NaF nanoparticles in micelles structures loaded on polylactic acid nanoscaffolds as biocompatible and biodegradable polymers for use in dental delivery. In this research, NaF nanoparticles were successfully synthesized in micelles structures and loaded on the biopolymers on as dental resins through direct micelle assisted electrospinning method. NaF nanoparticles as a heterogeneous structure were dispersed in biopolymers nanoscaffolds which makes it suitable in dental delivery. The synthesis parameters for preparation of NaF nanoparticles loaded on polylactic acid nanoscaffolds were evaluated by design of experiments and the process control was systematically studied using analysis of variance. Products were characterized with scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller and nitrogen adsorption isotherms. In vitro drug release of NaF nanoparticles loaded on polylactic acid nanoscaffolds was studied with Franz Cells and data release was investigated through UV–vis spectroscopy about λ = 486. The obtained results showed the released value of NaF nanoparticles from the formulation containing 0.5% PLA at λ = 486 nm about 84% after 240 min.

AOT direct and reverse micelles as a reaction media for anisotropic silver nanoparticles functionalized with folic acid as a photothermal agent on HeLa cells

Herein, we report the synthesis of silver nanoparticles (AgNPs) using direct micelles and reverse micelles of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) as reaction media. We evaluated the effect of these self-organized aggregates in the nucleation and growth mechanism of AgNPs. The results show the effect of water when it is a confined medium, where their properties are different from those of net water. These factors strongly influence the size, polydispersity and shape of nanoparticles. Moreover, the presence of ions from the reducing agents and the surfactant, it is a key factor in the anisotropy of the AgNPs obtained. For our knowledge, this is the first report in which the effect of the reaction media is evaluated by using direct and reverse micelles to synthesize silver nanoparticles. Additionally, AgNPs synthesized through the two systems were functionalized with folic acid and evaluated their cytotoxicity and photothermal properties. The results show that AgNPs synthesized through the two systems are potential photothermal agents, reaching to reduce up to 47% of the viability of the HeLa cells, using a laser of 808 nm.

Polyelectrolyte-colloid complex formation via polymerization: reaction kinetics in direct micelles, inverted micelles, and homogeneous solution studied by NMR and conductometry

Formation of polyelectrolyte-surfactant complexes (PESCs) in polymerization process of corresponding amphiphilic monomer is a promising way of pure stoichiometric PESC obtained in salt-free systems. Polymerization of micelle-forming monomer dodecylammonium 2-acrylamido-2-methylpropanesulfonate (DDA-AMPS) in different media was studied by means of 1H-NMR and conductance measurements. Kinetics of polymerization in direct micelles, inverted micelles, and homogeneous solution was considered in terms of classical solution polymerization and microemulsion polymerization. Reaction orders on monomer and initiator were measured in water and dioxane. The rate of polymerization is strongly dependent on monomer micelle existence, being considerably higher in micellar solution than in homogeneous one.