Shape Of Micelles Research Articles

Surface adsorption and solution aggregation of a novel lauroyl-l-carnitine surfactant

Hypothesisl-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated l-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits. ExperimentsThis work evaluated the surface adsorption of lauroyl-l-carnitine (C12LC) and its aggregation behavior. The size and shape of the aggregates of C12LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C12LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations. FindingsAt pH 7, the limiting area per molecule (ACMC) of the zwitterionic C12LC adsorbed layer at the air/water interface was found to be 46 Å2 from surface tension and neutron reflection, smaller than the values of C12PC, C12E5, DTAB, C12C4betaine and C12C8betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å2, indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C12LC. As the concentration increased, area per molecule reached a plateau of 37–39 Å2, indicating the dissolution of the more surface-active lauric acid into the micelles of C12LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core–shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C12LC potentially attractive as a solubilizing agent.

Compatibility of aqueous film-forming foams (AFFF) with sea water

This contribution combines the observations from fire experiments with modelling of ionisation of fluorosurfactants to explain the compatibility of AFFF with sea water. We report detailed chemical structures of fluorosurfactants introduced into the firefighting foam market since the development of the so-called light water by the US Naval Research Laboratory (NRL) in late 1960s and study their ionisation constants (i.e., pKa). The analyses of recent formulations of foam concentrates indicate that, almost all of them include four species of high purity C6 fluorotelomer and non-fluorotelomer surfactants, which have their roots in fluorosurfactant chemistries developed by 3M, Ciba-Geigy and Elf Atochem (and its predecessors). The earliest fluorosurfactants emerged as derivatives of perfluorocarbon acyl and sulfonyl fluorides, from a series of discoveries made by the 3M Company. We review the foaming and filming technologies developed by 3M, derived from the products of electrochemical fluorination (ECF), comprising acidic, propane-sultone, acrylic and amine-oxide concentrates, with potassium perfluorooctane sulfonate (K-PFOS) filmers used together with the sultone and acrylic foamers. To the best of our knowledge, these chemistries have not been documented in one reference in the open literature, and some of the chemicals used have not yet been identified in the environment. While we do not cover the development of fluorotelomer chemistries in the same detail, we discuss the fluorotelomer surfactants that have proven themselves to be successful in compatibility with sea water and compare their structure with those of the ECF-derived chemicals. We discovered that, the chemical compatibility with sea water is related to the formation of the specific ionised species that combine with divalent alkaline-earth metal cations to form ionic assemblies in the premix (solution made by mixing foam concentrates with water). These species arise at high pH values that are characteristic of sea water. We also reveal that, changes in the ionisation state of amine-oxide and tertiary-amine head groups, as pH varies between that of fresh and sea-water premix, may impact the performance of fluorosurfactants. The physical compatibility of fluorosurfactants with sea water manifests itself by shielding of the ionised head groups by metal cations decreasing the surface tension and modifying the size, shape and diffusion of micelles. For foam concentrates that satisfy the necessary condition of chemically compatible with sea water, the physical effect usually improves the foam quality and the fire-suppression performance of AFFF. We analyse in detail the patent literature and the early NRL reports to gain an intimate understanding of the first formulations introduced by the 3M Company. Although PFOS has been banned internationally, Chinese manufacturers produce PFOS-type concentrates for the domestic market, in addition to fluorotelomer surfactants destined for export. We provide detailed formulations of all types of concentrates that employed the ECF-based fluorosurfactant technologies, including hydrocarbon surfactants, solvents, corrosion inhibitors and buffers and link the chemical composition of the concentrates with the firefighting performance of the foams. We outline the correlations between the ionisation states of fluorosurfactants and their fundamental properties, such as surface packing and interfacial tension and comment that very little is known about these critical structure-activity relationships. Finally, we stress the need to reboot the progress in the field and give directions for future research.

Small-angle X-ray scattering as an effective tool to understand the structure and rigidity of the reverse micelles with the variation of surfactant

This study is aimed to utilize the small-angle X-ray scattering technique for getting new insights on the effect of the structure of surfactants on the shape, size, thickness of the diffusion layer, and rigidity of the reverse micelles, formed within a water-in-oil microemulsion. For this study, two important features of the structure of the surfactant i.e. hydrophobic alkyl chain length and the nature of the hydrophilic head group (cationic, anionic, and non-ionic) are taken into consideration. The primary information regarding the shape, diffusion length, and internal structure of reverse micelles was evaluated using the model-free approach. It was found that the reverse micelles formed in the case of cationic and anionic surfactants were spherical whereas cylindrical-shaped reverse micelles were formed with non-ionic surfactants. After critically analyzing the inferences from the model-free approach, an appropriate model for fitting the SAXS data was selected. For cationic and anionic surfactant-based microemulsions, the spherical shell model was chosen while the cylindrical shell model was used for microemulsions formed using non-ionic surfactants. We believe that this study will give a systematic approach to analyze the SAXS data and further add to our understanding of the relation between the surfactant and the structure of the reverse micelles.

Investigating the influence of block copolymer micelle length on cellular uptake and penetration in a multicellular tumor spheroid model.

The efficient penetration of drug nanocarriers into tumors is an important prerequisite for therapeutic and diagnostic success. The physicochemical properties of nanocarriers, including size, shape and surface chemistry have been shown to influence their transport in biological systems. Recent studies have shown that elongated nanoparticles (NPs) can exhibit advantageous properties in comparison to spherical NPs, but these experiments have involved a variety of different materials, many of which are characterized by a broad size distribution. Here we describe a series of rigid rod-like micelles of uniform width, with narrow length distributions, and common surface chemistry, and examine their cell uptake and penetration into multicellular tumor spheroids (MCTSs) formed from two human breast cancer cell lines (MDA-MB-436 and MDB-MB-231). These micelles were prepared from a polyferrocenylsilane (PFS) diblock copolymer (BCP) with a corona block consisting of a statistical polymer of aminopropyl methacrylamide and oligo(ethyleneglycol methacrylate) (PFS27-b-PAPMA3-stat-POEGMA48). The rigid rod micelles, with a common width (12 nm) and lengths ranging from 80 to 2000 nm, were prepared by seeded growth crystallization-driven self-assembly in ethanol and then transferred to water. To consider whether changing the shape of these micelles affects its uptake and penetration behavior, analogous spherical micelles were prepared by direct nanoprecipitation into water. Both micelle shape and length were found to influence cellular uptake and penetration into 500 μm MCTSs. Laser confocal fluorescence microscopy was used to examine penetration of these micelles into three-dimensional MCTS up to 90 μm depth. Micelles with an elongated shape and short length (80 nm) demonstrated the deepest penetration into the MCTSs formed by MDA-MB-436 cells. Micelles with lengths of 200 nm also showed substantial penetration into these MCTS, but the extent and depth of tumor penetration of the rod-like micelles decreased with increasing aspect ratio. MCTS of MDA-MB-231 cells had a less dense, more open structure than those formed by MDA-MB-436 cells. Here more extensive penetration was observed, particularly for the longer micelle samples.

Laser diagnostics of reverse microemulsions: Influence of the size and shape of reverse micelles on the Raman spectrum on the example of water/AOT/cyclohexane system

In this study, the influence of the size and shape of reverse micelles in water/AOT-Na/cyclohexane microemulsions on the spectral characteristics of vibrational spectra was studied using Raman laser spectroscopy and method of dynamic light scattering. The sensitivity of the spectral bands of stretching vibrations of OH groups of water molecules and SO3 groups of AOT anions to the processes of self-organization of surfactants in microemulsions was established and explained. It is proposed to use this sensitivity of the OH and SO spectral bands of the Raman spectrum of microemulsions to create a method of determining the size of reverse micelles using Raman spectra. For this purpose, calibration curves of the spectral characteristics of these bands on the size of the reverse micelles were obtained. It was shown that the developed method can provide the best accuracy of determining the size of spherical reverse micelles 4.4%. The proposed method of laser diagnostics of microemulsions can also be applied to microemulsions with another composition.

Solubilization of polycyclic aromatic hydrocarbons (PAHs) in PEO-PPO-PEO type linear and star block copolymers

Pluronics® and Tetronics® are used in industry for solubilizing various kinds of hydrophobic compounds since decades. In present study, moderately hydrophobic linear and star block copolymer viz. Pluronic® P104 and Tetronic® T1304 are employed for the solubilization of four polycyclic aromatic hydrocarbons (PAHs) viz. naphthalene (Np), anthracene (An), phenanthrene (Ph) and pyrene (Py). The aggregation behaviour of these block copolymers in an aqueous media has been investigated by cloud point (CP), viscometry, dynamic light scattering (DLS), and small angle neutron scattering (SANS) techniques. The aqueous solubilities of these PAHs are quite poor, hence their extractions from contaminated areas are difficult. Cloud point of block copolymers linearly decreases as a function of PAHs concentration and strongly depends on the structure of PAHs. The aqueous solutions of both block copolymers are Newtonian fluid. The solubilization of PAHs in these copolymeric micelles leads to increase in the viscosity of solution suggesting the growth of micelles. The effect of concentration and temperature on the size and shapes of micelles were evaluated from DLS and SANS studies. The study provides an alternative method for the remediation of PAHs using inexpensive commercially available block copolymers.

Micellization through complexation of oppositely charged diblock copolymers: Effects of composition, polymer architecture, salt of different valency, and thermoresponsive block

AbstractThe structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number Np of PCMs is a universal function of the ratio γ± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that Np of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm‐like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights.

Surface functionalization of poly(vinylidene fluoride) membrane by radiation‐induced emulsion polymerization of hydroxyethyl acrylates in an aqueous medium

AbstractDecades ago, surface modification of poly(vinylidene fluoride) (PVDF) membrane became an essential subject. The change is mainly to enhance the hydrophilicity properties of the membrane in order to increase the adsorption capacity, thus making as a novel adsorbent. This study aims to used radiation‐induced polymerization and compares the final properties of PVDF grafted hydroxyethyl acrylates (HEA) prepare by two different approaches. The PVDF‐grafted‐HEA has achieved either direct polymerization or emulsion polymerization. Tween‐20 has been used as a surfactant in emulsion polymerization. The final PVDF‐grafted poly‐HEA was analyzed using several different instruments to observe the changes in terms of morphological structure, topography properties, thermal stability, mechanical strength, and hydrophilicity. Significant differences were seen in morphology and contact angles properties. By emulsion polymerization, poly‐HEA grafted in the shape of micelles compare to by direct polymerization shown a thin homogenous layer. Thus, the surface roughness of PVDF by emulsion is higher lead to higher contact angles. Even though both approaches demonstrate significant changes in the physicochemical properties of the PVDF membrane, it is revealed that radiation‐induced direct polymerization approaches could achieve a hydrophilic PVDF‐grafted HEA.

Model for the Simulation of the CnEm Nonionic Surfactant Family Derived from Recent Experimental Results.

Using a comprehensive set of recently published experimental results for training and validation, we have developed computational models appropriate for simulations of aqueous solutions of poly(ethylene oxide) alkyl ethers, an important class of micelle-forming nonionic surfactants, usually denoted CnEm. These models are suitable for use in simulations that employ a moderate amount of coarse graining and especially for dissipative particle dynamics (DPD), which we adopt in this work. The experimental data used for training and validation were reported earlier and produced in our laboratory using dynamic light scattering (DLS) measurements performed on 12 members of the CnEm compound family yielding micelle size distribution functions and mass-weighted mean aggregation numbers at each of several surfactant concentrations. The range of compounds and quality of the experimental results were designed to support the development of computational models. An essential feature of this work is that all simulation results were analyzed in a way that is consistent with the experimental data. Proper account is taken of the fact that a broad distribution of micelle sizes exists, so mass-weighted averages (rather than number-weighted averages) over this distribution are required for the proper comparison of simulation and experimental results. The resulting DPD force field reproduces several important trends seen in the experimental critical micelle concentrations and mass-averaged mean aggregation numbers with respect to surfactant characteristics and concentration. We feel it can be used to investigate a number of open questions regarding micelle sizes and shapes and their dependence on surfactant concentration for this important class of nonionic surfactants.

Synthesis of an ionic sugar-amino acid based surfactant in aqueous media

Micellar catalysis has been used to synthesis a sugar-amino acid based cationic surfactant (N,N,N-trimethyl-2-oxo-2-(((2R,3S,4S,5R)-3,4,5-trihydroxy-6-(tetradecyloxy)tetrahydro-2H-pyran-2-yl)methoxy)ethan-1-aminium iodide) with renewable raw materials in aqueous media. The micellar catalysis method was compared with the method that uses dimethylformamide (DMF) as solvent. The results confirm the superiority of micellar catalysis method in terms of efficiency, energy consumption and environmental issues. Common physicochemical properties of surfactants like critical micelle concentration (CMC), the minimum surface area per molecule (Amin) and Krafft temperature were determined to evaluate the behavior of synthesized surfactant properties at the air-water interface. Computational chemistry method (DFT (B3LYP/6-311g(d)) was conducted to calculate the dimensional properties of the surfactant to determine the shape, size and aggregation number of micelles at their CMC by an approach that uses Connolly solvent accessible area as the effective area of surfactant head groups. Dynamic light scattering method (DLS) was used to determine the size of micelles. The results of DLS tests show good agreement with the calculation method. Finally, the biodegradability of synthesized natural based cationic surfactant was studied by close bottle standard test to investigate the biodegradation of synthesized surfactant.

Ketal core cross-linked micelles for pH-triggered release of doxorubicin

A ketal core cross-linked (CCL) micelle system of block copolymers of poly(oligo(ethylene glycol) methyl ether methacrylate)-b-poly(styrene-alt-maleic anhydride)-b-poly(styrene) (POEGMA-b-PSMA-b-PS) was prepared by the combination of the reversible addition-fragmentation chain transfer (RAFT) polymerization and amidation process. Doxorubincin (DOX), a model anticancer drug, was loaded into block copolymer micelles with POEGMA segment as hydrophilic corona and PSMA-b-PS block as hydrophobic core. Then core cross-linking was carried out by amidation reaction between maleic anhydride moiety and difunctional amino cross-linker bearing an acid cleavable bond (ketal). The ketal CCL micelles illustrated good stability under physiological condition but disassociated rapidly under acidic pH conditions. TEM images presented spherical shape of CCL micelles with average hydrodynamic diameter at around 45 nm. The DOX release experiments demonstrated a rapid DOX release at pH 5.0 compared to pH 7.4.

Morphology Modulation of Ionic Surfactant Micelles in Ternary Deep Eutectic Solvents.

Deep eutectic solvents (DES) are potentially greener solvents obtained through the complexation of simple precursors which, among other applications, have been investigated in recent years for their ability to support the self-assembly of amphiphilic molecules. It is crucial to understand the factors which influence surfactant solubility and self-assembly with respect to the interaction of the surfactant molecule with the DES components. In this work, small-angle neutron scattering (SANS) has been used to investigate the micellization of cationic (CnTAB) and anionic (SDS) surfactants in a ternary DES comprising choline chloride, urea, and glycerol, where the hydrogen bond donors are mixed in varying molar ratios. The results show that in each case either globular or rodlike micelles are formed with the degree of elongation being directly dependent on the composition of the DES. It is hypothesized that this composition dependence arises largely from the poor solubility of the counterions in the DES, especially at low glycerol content, leading to a tighter binding of the counterion to the micelle surface and giving rise to micelles with a high aspect ratio. This potential for accurate control over micelle morphology presents unique opportunities for rheology control or to develop templated syntheses of porous materials in DES, utilizing the solvent composition to tailor micelle shape and size, and hence the pore structure of the resulting material.

Oil solubilization in sodium dodecylbenzenesulfonate micelles: New insights into surfactant enhanced oil recovery

HypothesisThe current mechanism of surfactant enhanced oil recovery (EOR) mainly relies on forming middle-phase microemulsions to get ultra-low oil-water interfacial tension. However, residual oil can also be recovered using low concentration surfactant solutions without microemulsion formation, and the interaction between the surfactant solution and crude oil at very early contact has not been studied yet. We hypothesize micelle solubilization of oil as an alternative EOR mechanism. ExperimentsSodium dodecylbenzenesulfonate (SDBS), anisole and 1-hexene were used as a model surfactant and model polar and nonpolar compounds in crude oil, respectively. The interaction between SDBS micelles and these two additives was investigated with dynamic light scattering, UV–Vis spectroscopy, 1H NMR spectroscopy, cryogenic transmission electron microscopy, confocal microscope and small angle neutron scattering. FindingsSDBS micelles become larger upon increasing additive concentration to transfer into swollen micelles. 1-Hexene is localized in the micelle core, and retains the spherical micelle shape, while anisole resides in the palisade layer and weakens the electrostatic repulsions among surfactant headgroups, inducing a sphere–rod transition. No emulsion droplets were observed for 0.2 wt% SDBS solution until 1.5 wt% anisole or 1-hexene was introduced. These findings help understanding the role surfactant micelles in EOR and propose a new mechanism for surfactant EOR processes.

Impact of wormlike micelles on nano and macroscopic structure of TEMPO-oxidized cellulose nanofibril hydrogels.

In this work, we investigated the effect of adding surfactant mixtures on the rheological properties of TEMPO-oxidized cellulose nanofibril (OCNF) saline dispersions. Three surfactant mixtures were studied: cocamidopropyl betaine (CAPB)/sodium dodecyl sulfate (SDS), which forms wormlike micelles (WLMs); cocamidopropylamine oxide (CAPOx)/SDS, which forms long rods; and CAPB/sodium lauroyl sarcosinate (SLS), which forms spherical micelles. The presence of micelles in these surfactant mixtures, independent of their morphology, leads to an increase of tan δ, making the gels less solid-like, therefore acting as a plasticizer. WLMs were able to suppress strain stiffening normally observed in OCNF gels at large strains. OCNF/WLM gels have lower G' values than OCNF gels while the other micellar morphologies have a reduced impact on G'. The presence of unconnected micelles leads to increased dissipative deformation in OCNF gels without affecting the connectivity of the fibrils, while the presence of entangled micelles interferes with the OCNF network.

Micellar structure and transformations in sodium alkylbenzenesulfonate (NaLAS) aqueous solutions: effects of concentration, temperature, and salt.

We investigate the shape, dimensions, and transformation pathways of micelles of linear sodium alkylbenzenesulfonate (NaLAS), a common anionic surfactant, in aqueous solution. Employing Small Angle Neutron Scattering (SANS) and surface tensiometry, we quantify the effects of surfactant concentration (0.6-15 wt%), temperature (5-40 °C) and added salt (≤0.35 M Na2SO4). Spherical micelles form at low NaLAS (≤2.6 wt%) concentration in water, and become elongated with increasing concentration and decreasing temperature. Addition of salt reduces the critical micelle concentration (CMC) and thus promotes the formation of micelles. At fixed NaLAS concentration, salt addition causes spherical micelles to grow into cylindrical micelles, and then multilamellar vesicles (MLVs), which we examine by SANS and cryo-TEM. Above a threshold salt concentration, the MLVs reach diameters of 100 s of nm to few μm, eventually causing precipitation. While the salt concentrations associated with the micelle-to-cylinder transformation increase only slightly with temperature, those required for the cylinder-to-MLV transformation exhibit a pronounced, linear temperature dependence, which we examine in detail. Our study establishes a solution structure map for this model anionic surfactant in water, quantifying the combined roles of concentration, temperature and salt, at practically relevant conditions.

The Biosurfactant β-Aescin: A Review on the Physico-Chemical Properties and Its Interaction with Lipid Model Membranes and Langmuir Monolayers.

This review discusses recent progress in physicochemical understanding of the action of the saponin -aescin (also called -escin), the biologically active component in the seeds of the horse chestnut tree Aesculus hippocastanum. -Aescin is used in pharmacological and cosmetic applications showing strong surface activity. In this review, we outline the most important findings describing the behavior of -aescin in solution (e.g., critical micelle concentration () and micelle shape) and special physicochemical properties of adsorbed -aescin monolayers at the air–water and oil–water interface. Such monolayers were found to posses very special viscoelastic properties. The presentation of the experimental findings is complemented by discussing recent molecular dynamics simulations. These simulations do not only quantify the predominant interactions in adsorbed monolayers but also highlight the different behavior of neutral and ionized -aescin molecules. The review concludes on the interaction of -aescin with phospholipid model membranes in the form of bilayers and Langmuir monolayers. The interaction of -aescin with lipid bilayers was found to strongly depend on its . At concentrations below the , membrane parameters are modified whereas above the , complete solubilization of the bilayers occurs, depending on lipid phase state and concentration. In the presence of gel-phase phospholipids, discoidal bicelles form; these are tunable in size by composition. The phase behavior of -aescin with lipid membranes can also be modified by addition of other molecules such as cholesterol or drug molecules. The lipid phase state also determines the penetration rate of -aescin molecules into lipid monolayers. The strongest interaction was always found in the presence of gel-phase phospholipid molecules.

Reverse poly(ε-caprolactone)-g-dextran graft copolymers. Nano-carriers for intracellular uptake of anticancer drugs

A new fully biodegradable “reverse” oligosaccharide-based amphiphilic graft copolymer structure with a hydrophobic backbone and hydrophilic side chains, poly(ε-caprolactone)-g-dextran (PCL-g-Dex) was synthetized. For this purpose, “clickable” propargylated PCL (PCL-yne) and azido-dextran (Dex-N3) were prepared to further synthesize PCL-g-Dex copolymer by a Huisgen’s cycloaddition. This “reverse” copolymer architecture self-assembled in biodegradable nano-carriers, in the shape of dynamic polymeric micelles, and were loaded with doxorubicin (Dox) anti-cancer drug. Dox-loaded micelles showed different drug releases depending on the pH. Cytotoxicity tests showed that Dox-loaded micelles can selectively kill colon cancer cells (HCT-116) while they have no cytotoxic effect towards healthy cells (CCD-45SK). Fluorescent micelles based on FITC-labelled PCL-g-Dex copolymer were used for fluorescence imaging and flow cytometry assays. These experiments proved the effective and specific internalization of micelles by cancer cells, whereas healthy cells showed a very poor uptake. These results show that PCL-g-Dex micelles may be a promising Dox nano-carrier in cancer chemotherapy.

Enhanced micellization of Gemini surfactants using diphenhydramine hydrochloride as an organic counterion

Micellization of the Gemini surfactant sodium dilauramidoglutamide lysine (SDGL) in the presence of an antihistamine drug, diphenhydramine hydrochloride (DPC) was investigated. The anionic surfactant sodium dodecyl sulfate (SDS) was used for comparison. DPC significantly decreased the critical micelle concentration (cmc) of both SDGL and SDS in aqueous media and increasing the DPC concentration decreased the pyrene excimer/monomer polarity ratio in SDGL micelles but increased it in SDS micelles, suggesting that SDGL and SDS micelles have different shapes. The counterion binding and binding constant values reveal that SDGL micelles interact more strongly with DPC than SDS micelles. Thus, DPC, as an organic counterion, can enhance surfactant micellization. The evaluation of the solubility of a poorly water-soluble drug (clotrimazole) in SDGL and SDS micelles containing DPC revealed that the drug was more soluble in SDS micelles than SDGL micelles, indicating that the cmc and the shape and size of micelles are essential factors for controlling drug solubilization.

Surface‐enhanced Raman scattering as a tool to study cationic surfactants exhibiting low critical micelle concentration

AbstractThe collection of surface‐enhanced Raman scattering (SERS) by silver nanocolloids was used to identify the critical micelle concentration (CMC) of three cationic surfactants in 0.5‐M NaCl solutions: hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and benzalkonium chloride. Despite structural similarity between the three test surfactans, differences of the shape and size of the respective micelles affected the corresponding SERS signals. The CMC values determined by this method agreed with the respective values measured by conventional methods, including fluorescence probing and electrical conductivity measurements. The potential for the application of SERS technique for low CMC determination without surface modification of silver nanoparticles by a Raman‐active molecule was also demonstrated.

On the Thermodynamics of Micellizationof Oppositely Charged Surfactants in the Presence of Organic Additives in the Aqueous Medium

Abstract To investigate the effect of additives urea and thiourea, on the micellization behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), detailed conductance measurements were carried out in aqueous media at different temperatures. The critical micelle concentration (CMC), determined from the discontinuity in the plots of molar conductance versus square root of concentration, indicated an inhibitory effect of urea and thiourea on micelle forming ability of the surfactants SDS and CTAB in the range of composition studied. The demicellizing effect of urea has been found to be more pronounced in SDS than CTAB. These observations are further augmented by the evaluation of thermodynamic parameters of micellization. A negative change in enthalpy of micellization ( Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ ) indicates a strong interaction between water and the additives and a positive change observed in entropy of micellization ( Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ ) manifest, that the micellization is an entropy-driven process. Further Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ and Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ change in mutually compensating manner, so that Δ G m ∘ < 0 $\Delta{\text{G}}_{\text{m}}^{\circ} < 0$ is not significantly affected. Finally, the counterion binding values (β) obtained for SDS and CTAB remain practically constant from 0.6 to 0.8 between 25 °C and 45 °C indicate that the size and shape of micelle remain essentially constant. Moreover, the increase in Δ G II ∘ $\Delta{\text{G}}_{{\text{II}}}^{\circ}$ values, which represent the effect of co-solvent or additive on micellization, substantiates the above observations. Many early works has investigated the micellization behavior of surfactants using a fixed additive composition. However, in this study, variable aqueous compositions of urea (0.30–1.78 wt%) and thiourea (0.24–1.41 wt%) have been considered.