Micellar Range Research Articles

Color-tunable fluorescent silica-based hybrid film of stacked structure based on a single amphiphilic AIEgen

The large-area and color-tunable fluorescent (FL) films have great potential applications in light-emitting devices and color displays. Yet, the challenge of realizing truly color-tunable emissions using a single fluorophore remains. Herein, we present a large-area, transparent and ultra-stable free-standing FL silica-based film (FSFSF) with color-tunable emissions prepared by using an amphiphilic aggregation-induced emission (AIE) luminogen (AIEgen) as both a structure-directing agent and a light-emitting source. The color-tunable FSFSFs have been facilely prepared at the gas–liquid (GL-FSFSF) and solid–liquid interfaces (SL-FSFSF) by simply stacking the AIEgen/SiO2 composite layers with different self-assembled structures using an approach combining self-assembly with sol-gel process. These films exhibited variable excitation-dependent emission colors, emitting bright blue and green fluorescences as well as dark red fluorescence from one single visual field under excitation with UV, blue, and green lights, respectively. The research found that the resulting GL-FSFSF had a sandwich-like structure with an alternate arrangement of cylindrical and spherical AIEgen micelles in the silica matrix, and exhibited unusual excitation-dependent multi-wavelength and morphology-dependent dual-center emission characteristics. It has been reported that the luminescence of many AIE compounds is morphology-dependent. Therefore, we speculate that the two emission centers of the film are related to the two self-assembled morphologies of amphiphilic AIEgen. Its bright blue and green fluorescence is attributed to the same emission intensity of the two luminescent centers. This study has demonstrated that morphology- and excitation-dependent color-tunable emissions based on one AIE fluorophore can be achieved by incorporating AIEgen aggregates with different self-assembled morphologies in the matrix. Such a simple strategy can be extended to construct other multicolor-tunable FL hybrid materials.

Goat milk powders enriched with grape pomace seed extract: Physical and techno-functional properties

This study aimed to evaluate the physical (particle size and ζ-potential) and techno-functional properties (emulsifying and foaming) of goat milk powders enriched with grape pomace seed extract (TME), as promising food ingredients in the formulation of functional food. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and Raman spectroscopies, along with advanced chemometric tools were employed as well as Scanning Electron Microscopy (SEM) for analyzing TME powders. All powders exhibited a unimodal particle size distribution and ζ-potential values more negative than −36 mV. ATR-FTIR and Raman spectroscopies combined with principal component analysis (PCA) demonstrated distinct separation among skimmed goat milk (M), thermally treated skimmed goat milk (TM), and TME powders in different spectral regions (amide I, II, III, and fingerprint region). This separation resulted from the applied thermal treatment, the presence of phenolic compounds and their complexes with goat milk proteins, and the formation of Maillard reaction products. SEM analysis confirmed the different morphology and shapes of M, TM and TME powders. The 0.1% solutions of M, TM and TME exhibited good emulsifying properties (emulsion activity index and emulsion stability index) but showed poor foaming properties, except for the M sample. Solution concentrations higher than 0.1% for all samples (0.5% and 1.0%) displayed poor techno-functional properties. In summary, a schematic representation of the arrangement of casein micelles in 0.1% M, TM and TME samples, on oil/water and air/water surfaces was provided. The production of TME powders represents an innovative strategy for waste recovery in the production of functional food ingredients with good emulsifying properties.

Variation of meso- and macroporous morphologies in resorcinol–formaldehyde (RF) gels tailored via a sol–gel process combined with soft-templating and phase separation

A wide-range control over multimodal pore systems in porous monoliths is a key technology for developing functional materials, as the favorable pore structures in different length scales are required to be tailored depending on their application fields. In the alkoxy-derived sol–gel systems of silica and organosilicates, the synthetic methodology of meso- and macroporous monoliths with tunable pore properties has been developed by combining the supramolecular self-assembly of a Pluronic surfactant and polymerization-induced phase-separation techniques. This strategy has been applied to the sol–gel process of phenolic resins, giving rise to the hierarchically porous polymer gels with ordered mesoporosity and the corresponding carbon monoliths after carbonization. However, the controllable size range has been limited so far. This study has explored the relationship between the starting composition and the bimodal pore properties in further detail aiming at a better control of pore properties in phenolic resins. The enlargement of mesopore size has been achieved, yet associated with broadening the mesopore size distribution and coarsening the macropore morphology, resulting in the particle aggregates. The systematical investigation also reveals that the addition of KCl can improve the micelle arrangement in macroframework and provide the narrower mesopore size distribution.

The rheological behavior of organic salt/Gemini surfactant mixed systems: Effect of isomerization of additives

The effect of isomerization of organic salts (2-hydroxybenzoic acid monosodium salt (o-ph-ONa), 3-hydroxybenzoic acid monosodium salt (m-ph-ONa), and 4-hydroxybenzoic acid monosodium salt (p-ph-ONa)) on the formation and properties of wormlike micelles in 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (abbreviated as 12-3(OH)-12) aqueous solutions were investigated using rheological methods, surface tension, and 1H–1H 2D NOESY NMR. The results indicate that the addition of organic salts can promote the formation of wormlike micelles. However, the effect of o-ph-ONa is the strongest and that of p-ph-ONa is the weakest. These are attributed to the occupying area of molecules. The hydroxyl and carboxylate groups in o-ph-ONa molecules are on the micelle interface and can interact with the hydroxyl group in the spacer of 12-3(OH)-12 by electrostatic interaction and/or hydrogen bonding associations, inducing a closer micelle arrangement than the other two kinds of salts so that the occupying area of molecules may be the smallest. The hydroxyl group in m-ph-ONa is located at the meta-position of carboxylate groups, which widens the gap of surfactant molecules and increases the occupying area of molecules. The whole p-ph-ONa molecule is located within the micelle interior and shows low viscosity owing to the high molecular occupying area.

Gelation and long-time relaxation of aqueous solutions of Pluronic F127

We have studied the gelation dynamics of solutions of Pluronic F127, a triblock copolymer, using oscillatory rheometry. As the solutions are slowly heated from 10 to 85°C, they undergo a transition from sol to gel around room temperature, followed by a gel-sol transition at a higher temperature. The sol-gel transition temperature decreases and the width in the temperature of the gel phase broadens with increasing concentration. The reverse transitions occur on cooling. Both transitions are hysteretic, and the temperature range over which the transitions occur is different on cooling than on heating. Near the phase transitions, the rheological relaxation time becomes very long, up to of order τs∼104s. Gelation in Pluronic solutions is due to the arrangement of micelles into an organized large-scale structure, and our results suggest that the rearrangement of micelles into or out of the gel structure is a slow process at temperatures within the phase transitions.

Insights Into Molecular Interaction of Antitumor Drug Mitoxantrone With Anionic Surfactant Sodium Dodecyl Sulfate at Different Temperatures

AbstractA study of the interaction of antitumor drug mitoxantrone with anionic surfactant sodium dodecyl sulfate (SDS) has been carried out by UV–Vis absorption spectroscopy at submicellar and micellar surfactant concentrations, pH 7.4 and 10, and over a temperature range of 293.15–323.15 K. The variation of the monomer drug absorbance as a function of SDS concentration indicates, at pH 7.4 and all investigated temperatures, two definite processes: process I in the submicellar range, attributed to the electrostatic interaction between mitoxantrone and SDS monomers; and process II in the micellar range, when the drug is incorporated into SDS micelles in monomer form. At pH 10, the results have indicated only the process II at micellar SDS concentrations. The monomer absorbance changes occurring as a result of the interactions between mitoxantrone and SDS were rationalized in terms of binding constant, micelle/water partition coefficient, and the corresponding thermodynamic parameters for binding and partitioning processes. Thermodynamic parameters indicate that at pH 7.4 both binding process of mitoxantrone to SDS and partition process of mitoxantrone between micellar and bulk aqueous phases are spontaneous and enthalpy controlled, while at pH 10 both processes are spontaneous and entropy controlled.

Toluidine blue-sodium lauryl ether sulfate complexes: Influence of ethylene oxide length

Sodium Lauryl Ether Sulfates (SLES) are an increasingly important and versatile type of surfactants. The complexation between ortho-Toluidine blue (TBO) and a homologous series of SLES, including Sodium Lauryl Sulfate (SDS) without Ethylene Oxide (EO), has been investigated using visible spectrophotometry. Upon increasing the molar surfactant-dye-ratio (S/D), three TBO organization regimes can be identified from the absorption spectra: (i) Ion-pair formation, (ii) Pre-micellar aggregation and (iii) Micellar aggregation. The limited solubility of SDS-TBO ion pairs, leading to precipitation of ion-pair clusters, causes a decrease of the TBO monomeric peak height when S/D is increased. The better solvability of TBO-SLES ion-pairs causes the onset of precipitation to occur at higher S/D when the EO-block length increases. In an intermediate S/D range, metachromasy is observed as a result of dye-stacking onto the SDS arranged in a pre-micellar state at surfactant concentrations well below the critical micelle concentration (CMC). For SDS, the S/D range showing pre-micelles depends on TBO concentration but seems independent of variation of ionic strength (phosphate buffer, pH = 7.0, Cbuffer = 0.1–10 mM), whereas the metachromatic peak height increases with decreasing ionic strength. The pre-micellar region for all SLES-TBO is located at the same S/D range but the maximum metachromatic peak height follows the trend: EO2 > EO4 > SDS > EO12 ≈ EO30. The onset of the micellar range, in which TBO is again present in monomeric form, is shown to coincide with the CMC. These findings could proof helpful in either formulation or analysis of SLES. Likewise, understanding the dyes' interactions may facilitate formulation of dyeing solutions for optimal performance, or alternatively, as part of the textile plant effluent treatment to remove, and possibly recycle, dyes.

Study of host–guest interaction between ß-cyclodextrin and alkyltrimethylammonium bromides in water

Cyclodextrins were found to play important roles in self-assembly systems of surfactants. The interactions between host molecule s-cyclodextrin (CD) and model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C12TAB), tetradecyl-(C14TAB) and hexadecyl-(C16TAB) are studied by means of conductivity measurements at 313.2 K. The data obtained indicate that inclusion complexes (CD:S+) had formed, and apparent critical micelle concentration (CMC*) is equivalent to the combined concentrations of surfactant monomers complexed with the CD and that of a free dissolved monomer in equilibrium with the micellized surfactant without CD. Inclusion complexes were characterized by an equilibrium binding constant K 11, which value increases as the length of alkyl chains, and consequently the hydrophobicity, increases. From mathematical model the concentrations of the uncomplexed cyclodextrin, uncomplexed surfactant ion, and inclusion complex in the submicellar, as well as in the micellar range were calculated. The competition between the micellization and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed cyclodextrin in equilibrium with the micelles is independent on cyclodextrin concentration for a particular ternary system and is 31, 37, and 34 % for C12TAB/water/s-CD, C14TAB/water/s-CD and C16TAB/water/s-CD, respectively. By using standard Gibbs free energy for micellization and surfactant complexation by CD, we can explain the observed behavior.

Small-angle X-ray scattering in sodium dodecyl sulfate solutions and micelle clustering

The small-angle X-ray scattering (SAXS) in micellar sodium dodecyl sulfate solutions has been studied in the range of overall concentrations c from 8 mM (CMC1) to 300 mM and the absolute values of scattering vector q from 0.07 to 3.0 nm–1. The total intensity of isotropic scattering has been revealed to increase with solution concentration. At c > 27 mM, the SAXS spectra have been found to exhibit an interference peak, which testifies a correlation in the arrangement of micelles in the bulk solution. This peak corresponds to the magnitude of q close to 1.55 nm–1. Using the position of this maximum, average distance r 0 between the centers of micelles has been determined, which is equal to 4.1 nm and remains almost unchanged upon an increase in the overall concentration of sodium dodecyl sulfate. The observed regularities have been explained in terms of the DLVO theory taking into account the electrostatic and molecular intermicellar interaction.

The effect of functional groups on the sphere-to-wormlike micellar transition in quaternary ammonium surfactant solutions

Abstract To investigate the effects of functional groups on the formation of wormlike micelles, a cationic surfactant, N-tetradecyl-N-(2-hydroxyethyl)dimethylammonium bromide (DM), was synthesized in this work. The viscoelastic behaviors of DM aqueous solution mixed with sodium salicylate (NaSal), sodium benzoate (NaBen) and sodium laurate (NaLau), respectively, have been studied with rheological measurements. Cryogenic transmission electron microscopy (cryo-TEM) and 1 H NMR technology have been employed to investigate the morphology and arrangement of wormlike micelles. The results show that the effects of NaSal and NaLau on wormlike micellar growth are significantly higher than that of NaBen. Superficially, such a great difference in the rheology properties arises from the effect of hydroxyl group in NaSal because this is the sole difference between the NaSal and NaBen. By comparing with NaBen in DM solution, the long hydrocarbon chain of NaLau induces greater hydrophobic interactions between Lau − anions and DM surfactants than aromatic phenyl group of NaBen, and hydrophobic interactions play an important role in the growth of micelles.

Structure and dynamics of concentrated micellar solutions of sodium dodecyl sulfate

In micellar solutions of sodium dodecyl sulfate, as the concentration of surfactants increases, the spheroid shape of the micelles changes from almost spherical to ellipsoidal with increasing ratio of half-axes ratio, and further the transition to cylindrical micelles occurs. The micelles in an aqueous solution can directly contact (compact aggregates) or be separated from one another by layers of intermicellar medium (periodical colloid structures). In the latter case, the thickness of the layer can significantly exceed the micelle size, and then no mutual correlation in micelle arrangement is observed. According to the data of small-angle X-ray scattering, the relationship between the surfactant concentration and formation of “quasi-crystalline” micellar structure is nonlinear, which can be due to both micelle aggregation processes and nonuniformity of their structure. The possible influence of ordered micellar structures on the diffusion mobility of micelles is shown.

Spatial arrangement of casein micelles and whey protein aggregate in acid gels: Insight on mechanisms

Skim milk used for the yoghurt manufacture contains 2 main colloidal particles, the native micellar casein (NMC) and the heat-induced whey protein aggregates (WPA). The aim of this study was to understand how these 2 colloids organize in space to form binary acid gels. While acid milk gels were considered homogeneous for scales typically above ∼10 μm, shorter length scales were examined to investigate the early stages of particle aggregation. The NMC and WPA were dispersed in milk permeate at different protein concentrations, separately or in an 80/20 w/w mixture (MIX). Acidification was performed at 35 °C with glucono-δ-lactone to achieve a final pH at ∼4.5 in 6 h. Acid gelation was studied by rheology, while the microstructure of the gels at pH 4.5 was studied by confocal scanning laser microscopy and transmission electron microscopy (TEM). Using Shih et al.'s (1990) model on the rheological data, it seemed that aggregation in the NMC and MIX mixtures was driven by the casein micelles and therefore differed from that of the WPA suspension. The different organizations were confirmed using image analysis of confocal or TEM images. The differences in gel formation were discussed in terms of the different interactive properties of the surface of these 2 colloids, together with their different internal structure.

Spiral and Mesoporous Block Polymer Nanofibers Generated in Confined Nanochannels

Spiral-like or various porous polymer nanofibers have great applications in biosensor, bioengineering, and template-fabrication of functional inorganic materials. However, the fabrication of polymer nanostructures with controllable porous or spiral morphology in one process is a big challenge. Here we first demonstrated a general and easy method to generate spiral or porous block copolymer (BCP) nanofibers by using geometric confinement of nanochannels to disturb the self-assembly of BCP while nonsolvent is induced into BCP solution. Continuous spiral polymer nanofibers and polymer nanofibers with hierarchical porous nanostructures can be easily generated within channels of anodic aluminum oxide (AAO) membranes by tuning the composition and concentration of BCP. This study first reports the influence of cylinder confinement to the arrangement of BCP micelles. These spiral and porous BCP nanostructures are not only good templates to generate functional inorganic nanostructures, but also promising candidates to create biosensors or to load catalyst because their enlarged surface area enables high guest concentrations.

Interaction of Cationic CTAB Surfactant with Curcumin, an Anticarcinogenic Drug: Spectroscopic Investigation

Abstract Curcumin, the most active polyphenolic constituent of turmeric cucuminoids obtained from rhizome Curcuma longa, holds a high place in ayurvedic medicine but its role in conventional disease management is also established. Unfortunately, the compound has poor aqueous solubility, which results in poor bioavailability following high doses by oral administration. In order to enhance its effectiveness and improve bioavailability, surfactant assemblies as the colloidal drug carriers with desired properties have been largely utilized. The interaction of curcumin with cetyltrimethylammonium bromide (CTAB) surfactant has been investigated by absorption spectroscopy as a function of surfactant concentration in pre-micellar and micellar range at acidic pH of 6.4. The pre-micellar and micellar region of pure CTAB surfactant at acidic pH of 6.4 is examined through tensiometry and conductometry techniques. Spectral data shows that in presence of curcumin at lower CCTAB, the change in absorbance and peak form initially was assigned to attraction of positive head group of CTAB towards the β-diketone group of drug. In micellar region including CMC, the type of interaction corresponds to the attachment of C16 chains of CTAB to nonpolar aryl groups of drug and simultaneously displacement of polar head group from β-diketone group of the drug. Finally at post micellar CCTAB, the encapsulation of the curcumin into micelles, predominantly in intact monomeric form is observed with the sharp peak at λmax = 423 nm.

Thermodynamics of Micellization of Triton X-100 in Aqueous Glycine: Tensiometric and Ultrasonic Studies

Abstract Surface tension and compressibility behavior of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(oxyethylene glycol) (Triton X-100, TX-100) in aqueous mixture of glycine (Gly) have been studied at 298.15, 303.15, 308.15, and 313.15 K below and above the micellar composition range. Critical micelle concentration, cmc, of the surfactant TX-100 was obtained by surface tension, γ, density, ρ, and ultrasonic velocity, u, measurements at different temperatures. From the surface tension data, the surface excess concentration, Γ max σ , minimum area per molecule, A min , Gibbs free energy, ΔG mic 0, enthalpy, ΔH mic 0, and entropy, ΔS mic 0 of micelle formation have been evaluated. Apparent molar adiabatic compressibility, κ ϕ , was calculated from density and ultrasonic velocity data. The values of κ ϕ and apparent molar adiabatic compressibility at infinite dilution, κ ϕ 0, in the pre-micellar region and apparent molar compressibility upon micellization, Δκ ϕ m , were obtained. The observed cmc of TX-100 in aqueous glycine is found to be smaller than its value in pure water. A comparison of Γ max σ in aqueous glycine with that in pure water suggests higher adsorption of TX-100 molecules at the air–liquid interface in the former solvent than in the latter one. This was attributed to the highly hydrophilic nature of glycine molecules, causing dehydration of the surfactant molecules, thereby, facilitating the adsorption of TX-100 molecules at the air–liquid interface in the presence of glycine than in its absence. The calculated values of the Gordon parameter, G parameter, suggest that aqueous glycine acts as a good solvent for the micellization of TX-100 amphiphiles. Negative values of ΔG mic 0 and ΔH mic 0 indicate that the process of micellization of the surfactant is spontaneous and exothermic. Moreover, higher values of − TΔS mic 0 than those of ΔH mic 0 truly endorse the view that micellization of TX-100 in aqueous glycine is primarily governed by the entropy gain due to the transfer of hydrophobic groups of the surfactant from the solvent environment to the interior of the micelle. The trends in the behavior of the compressibility parameters also endorse the micellization of TX-100 in aqueous glycine.

Membrane Perturbation by Carbon Nanotube Insertion: Pathways to Internalization

Carbon nanotubes (CNTs) can penetrate the membranes of cells, offering prospects for nanomedicine but problems for nanotoxicity. Molecular simulations are used to provide a systematic analysis of the interactions of single-walled and multi-walled CNTs of different radii with a model lipid bilayer membrane. The simulations allow characterization of the mechanism of spontaneous exothermic insertion of CNTs into lipid bilayer membranes. The size and type of CNT determine the nature and extent of the local perturbation of the bilayer. Single-walled CNTs are shown to insert via a two-step mechanism with initial transient formation of a water filled pore followed by full insertion of the CNT into the bilayer. The latter stage is associated with formation of a persistent inverted micelle arrangement of lipid molecules trapped inside the CNT. This suggests a possible vehicle for nano-encapsulation of drugs, enabling their entry into and subsequent release within cells following endocytosis of CNT-containing membranes.

Foam films in the presence of functionalized gold nanoparticles

Dry aqueous foams made of anionic surfactant (SDS) and spherical gold nanoparticles are studied by small angle X-ray scattering and by optical techniques. To obtain stable foams, the surfactant concentration is well above the critical micelle concentration. The specular reflectivity signal obtained on a very thin film (thickness 20nm) shows that functionalized nanoparticles (17nm typical size) are trapped within the film in the form of a single monolayer. In order to isolate the film behavior, investigations are made on a single film confined in a tube. The film thinning according to the ratio of functionalized nanoparticle and SDS micelles (1:1, 1:10, 1:100) is mainly governed by the structural arrangement of SDS micelles. In thick films, nanoparticles tend to form aggregates that disappear during drainage. In particular self-organization of nanoparticles (with different surface charge) inside the film is not detected.

Coupled spectral and electrochemical evaluation of the anticancer drug mitoxantrone–sodium dodecyl sulfate interaction

In-vitro evaluation of the interaction of anticancer drug mitoxantrone with anionic surfactant sodium dodecyl sulfate (SDS), was performed in physiological conditions (phosphate buffer, pH 7.4) by spectral (UV–vis absorption) and electrochemical (cyclic and linear voltammetry) methods. The stoichiometry of interaction, the binding constants and diffusion coefficients of free and bound drug were determined. The partition coefficient of mitoxantrone between aqueous phase and SDS micelles was calculated, and the results indicated that it is strongly dependent on the drug concentration. Both absorption and cyclic voltammetry results have outlined two distinct processes depending on the surfactant concentration: process I in premicellar range, assigned to the interaction of the drug with the surfactant molecules, when electrostatic forces play an important role in the formation of the mitoxantrone-SDS complex with a defined stoichiometry; and process II in micellar range, when the surfactant micelles are formed and the drug is encapsulated in micelles in monomer form. The spectral results have indicated that the drug is most probably located in the micelle surface layer, both electrostatic and polar interactions playing important role in the binding of drug to SDS micelles. Possible application of this system as a micellar drug–carrier was also considered.

On the mechanism of SDS‐induced protein denaturation

To understand the mechanism of ionic detergent-induced protein denaturation, this study examines the action of sodium dodecyl sulfate on ferrocytochrome c conformation under neutral and strongly alkaline conditions. Equilibrium and stopped-flow kinetic results consistently suggest that tertiary structure unfolding in the submicellar and chain expansion in the micellar range of SDS concentrations are the two major and discrete events in the perturbation of protein structure. The nature of interaction between the detergent and the protein is predominantly hydrophobic in the submicellar and exclusively hydrophobic at micellar levels of SDS concentration. The observation that SDS also interacts with a highly denatured and negatively charged form of ferrocytochrome c suggests that the interaction is independent of structure, conformation, and ionization state of the protein. The expansion of the protein chain at micellar concentration of SDS is driven by coulombic repulsion between the protein-bound micelles, and the micelles and anionic amino acid side chains.

Complex Crystal Structures Formed by the Self-Assembly of Ditethered Nanospheres

We report the results from a computational study of the self-assembly of amphiphilic ditethered nanospheres using molecular simulation. As a function of the interaction strength and directionality of the tether-tether interactions, we predict the formation of four highly ordered phases not previously reported for nanoparticle systems. We find a double diamond structure comprised of a zinc blende (binary diamond) arrangement of spherical micelles with a complementary diamond network of nanoparticles (ZnS/D), a phase of alternating spherical micelles in a NaCl structure with a complementary simple cubic network of nanoparticles to form an overall crystal structure identical to that of AlCu2Mn (NaCl/SC), an alternating tetragonal ordered cylinder phase with a tetragonal mesh of nanoparticles described by the [8,8,4] Archimedean tiling (TC/T), and an alternating diamond phase in which both diamond networks are formed by the tethers (AD) within a nanoparticle matrix. We compare these structures with those observed in linear and star triblock copolymer systems.