Electrolyte effect on mixed micelle and interfacial properties of binary mixtures of cationic and nonionic surfactants

Ionic liquid-biosurfactant blends as effective dispersants for oil spills: Effect of carbon chain length and degree of saturation

The well-known toxicity of conventional chemical oil spill dispersants demands the development of alternative and environmentally friendly dispersant formulations. Therefore, in the present study we have developed a pair of less toxic and green dispersants by combining lactonic sophorolipid (LS) biosurfactant individually with choline myristate and choline oleate ionic liquid surfactants. The aggregation behavior of resulted surfactant blends and their dispersion effectiveness was investigated using the baffled flask test. The introduction of long hydrophobic alkyl chain with unsaturation (attached to choline cation) provided synergistic interactions between the binary surfactant mixtures. The maximum dispersion effectiveness was found to be 78.23% for 80:20 (w/w) lactonic sophorolipid-choline myristate blends, and 81.15% for 70:30 (w/w) lactonic sophorolipid-choline oleate blends at the dispersant-to-oil ratio of 1:25 (v/v). The high dispersion effectiveness of lactonic sophorolipid-choline oleate between two developed blends is attributed to the stronger synergistic interactions between surfactants and slower desorption rate of blend from oil-water interface. The distribution of dispersed oil droplets at several DOR were evaluated and it was observed that oil droplets become smaller with increasing DOR. In addition, the acute toxicity analysis of developed formulations against zebra fish (Danio rerio) confirmed their non-toxic behavior with LC₅₀ values higher than 400 ppm after 96 h. Overall, the proposed new blends/formulations could effectively substitute the toxic and unsafe chemical dispersants.

Impact of Adsorption Layer Properties on Drainage Behavior of Microscopic Foam Films: The Case of Cationic/Nonionic Surfactant Mixtures

Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology measurements are conducted by profile analysis tensiometry. The interfacial data are juxtaposed to drainage kinetics and stability results for microscopic foam films, investigated by microinterferometric thin liquid film instrumentation. The obtained results give experimental evidence of synergistic interactions in the studied solutions, as compared to the corresponding single surfactant systems. Specific runs of dynamic and equilibrium surface tension curves are registered against the total surfactant quantity; the surface dilatational elasticities for the mixtures are systematically higher. A clear correlation is established between adsorption layer performance and foam film characteristics. The maxima of the film lifetimes are well outlined, and the respective values are shifted towards lower overall concentrations. The reported results substantiate the key role of the adsorption layers, and the surface dilatational properties in particular, for foam film drainage kinetics and stability. The well-expressed synergy observed in adsorption layer and foam film properties suggests the substantial benefits of using mixed surfactant systems in the design and fine-tuning of foam systems for innovative applications.

Antagonistic mixing in micelles of amphiphilic polyoxometalates and hexaethylene glycol monododecyl ether

HYPOTHESIS

Polyoxometalates (POMs) are metal oxygen clusters with a range of interesting magnetic and catalytic properties. POMs with attached hydrocarbon chains show amphiphilic behaviour so we hypothesised that mixtures of a nonionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, and which would differ in size and shape from micelles formed by the individual surfactants. Due to the high charge and large size of the POM, we suggested that these would be nonideal mixtures due to the complex interactions between the two types of surfactants. The nonideality and the micellar composition may be quantified using regular solution theory. With supplementary information provided by small-angle neutron scattering (SANS), an understanding of this unusual binary surfactant system can be established.

EXPERIMENTS

A systematic study was performed on mixed surfactant systems containing polyoxometalate-headed amphiphiles (K₁₀[P₂W₁₇O₆₁OSi₂(C_nH_2n+1)₂], abbreviated as P₂W₁₇-2C_n, where n = 12, 14 or 16) and hexaethylene glycol monododecyl ether (C₁₂EO₆). Critical micelle concentrations (CMCs) of these mixtures were measured and used to calculate the interaction parameters based on regular solution theory, enabling prediction of micellar composition. Predictions were compared to micelle structures obtained from SANS. A phase diagram was also established.

FINDINGS

The CMCs of these mixtures suggest unusual unfavourable interactions between the two species, despite formation of mixed micelles. Micellar compositions obtained from SANS concurred with those calculated using the averaged interaction parameters for P₂W₁₇-2C_n/C₁₂EO₆ (n = 12 and 14). We attribute the unfavourable interactions to a combination of different phenomena: counterion-mediated interactions between P₂W₁₇ units and the unfolding of the ethylene oxide headgroups of the nonionic surfactant, yet micelles still form in these systems due to the hydrophobic interactions between surfactant tails.

Takes Two to Tango: Choreography of the Coadsorption of CTAB and Hexanol at the Oil-Water Interface

Mixed surfactant systems at the oil-water interface play a vital role in applications ranging widely from drug delivery to oil-spill remediation. Synergistic mixtures are superior emulsifiers and more effective at modifying surface tension than either component alone. Mixtures of surfactants with dissimilar polar head groups are of particular interest because of the additional degree of control they offer. The interplay of hydrophobic and electrostatic effects in these systems is not well understood, in part because of the difficulty in examining their behavior at the buried oil-water interface where they reside. Here, surface-specific vibrational sum frequency spectroscopy is utilized in combination with surface tensiometry and computational methods to probe the cooperative molecular interactions between a cationic surfactant cetyltrimethylammonium bromide (CTAB) and a nonionic alcohol (1-hexanol) that induce the two initially reluctant surfactants to coadsorb synergistically at the interface. A careful deuteration study of CTAB reveals that hexanol cooperates with CTAB such that both molecules preferentially orient at the interface for sufficiently large enough concentrations of hexanol. This work's methodology is unique and serves as a guide for future explorations of macroscopic properties in these complex systems. Results from this work also provide valuable insights into how interfacial ordering impacts surface tensiometry measurements for nonionic surfactants.

Review on Beneficiation Techniques and Reagents Used for Phosphate Ores

Phosphate ore is an important raw material for manufacturing fertilizers and phosphorous chemical products. While most of the phosphate resources cannot be directly treated as feed stock due to the low grade of P2O5 and high content of impurities. In order to obtain a qualified phosphate concentrate, the beneficiation of the low-grade phosphate ore is, hence, of great necessity. Many beneficiation techniques can be employed to upgrade the P2O5 grade of phosphate ores based on their characteristics in chemical composition and texture. The flotation process is most widely applied to balance the P2O5 recovery ratio and cost. In this review, the dominant techniques for the beneficiation of phosphate ores are introduced. Moreover, the factors that affect the flotation of phosphate ore, including the properties of mineralogy, flotation reagents (depressants and collectors) and flotation medium, were systematically analyzed.

Phase separation of mixed micelles and synthesis of hierarchical porous materials

The mixed micelle template approach is one of the most promising synthesis methods for hierarchical porous materials. Although considerable research efforts have been made to explore the formation mechanism, explicit theoretical guidance for appropriately choosing templates is still not available. We found that the phase separation occurring in the mixed micelles would be the key point for the synthesis of hierarchical porous materials. Herein, the pseudophase separation theory for the critical micelle concentration (cmc) combined with the Flory-Huggins theory for the chain molecular mixture were employed to investigate the properties of mixed surfactant aqueous solutions. The cmc values of mixed surfactant solutions were experimentally determined to calculate the Flory-Huggins interaction parameter between two surfactants, χ. When χ is larger than the critical value, χc, the phase separation would occur within the micellar phase, resulting in two types of mixed micelles with different surfactant compositions, and hence different sizes, which could be used as the dual-template to induce bimodal pores with different pore sizes. Therefore, the Flory-Huggins theory could be a theoretical basis to judge whether the mixed surfactants were the suitable templates for inducing hierarchical porous materials. We chose cetyltrimethylammonium bromide (CTAB) and n-octylamine (OA) as a testing system. The phase separation behavior of the mixed solutions as well as the successful synthesis of hierarchical porous materials by this dual-template indicated the feasibility of preparing hierarchical porous materials based on the concept of phase separation of the mixed micelles.

Mixed Micellization and Surface Properties of Ionic Liquids/Triton X-100 Mixture System in Aqueous Media

Two binary systems of nonionic surfactant Triton X-100 and imidazolium ionic liquid surfactants with different carbon chain: C12mimBr (1-dodecyl-3-methylimidazolium bromide) and C14mimBr (1-tetradecyl-3-methylimidazoliumbromide) have been studied in this paper. The micellization and surface properties of the binary systems were determined by surface tension and conductivity methods, respectively. The critical micelle concentration (CMC), the maximum surface excess (Γmax), minimum area per molecule (Amin) and surface pressure at the CMC (ΠCMC) of single and mixed systems were obtained. Rubingh's theory was used to calculate the composition of the mixtures, and the molecular interaction parameter β. Negative value of β indicates synergism in mixed micelle formation. The order of absolute value of β and average β: C12mimBr/Triton X-100 > C14mimBr/Triton X-100. The values of ΔG0 m and ΔG0 ads have also been calculated, and both of them were found to be negative in all pure and mixed surfactants, indicating the spontaneity of micellization and adsorption of the surfactants.

Effect of Temperature on the Supramolecular Behavior of Antidepressant Drug Amitriptyline Hydrochloride in the Presence of Nonionic Surfactants (Tweens and Brijs) as Pharmaceutical Excipients

The aggregational and adsorption behavior of an important antidepressant amphiphilic drug amitriptyline hydrochloride have been studied in the presence of nonionic surfactants at different temperatures by tensiometry. By using regular solution theory and other thermodynamic models, different physicochemical properties such as critical micellar concentration, micellar composition, interfacial adsorption, energetic parameters (free energy, enthalpy, entropy) of micellization are evaluated. The data clearly depict that there is strong interaction between the amitriptyline hydrochloride and nonionic surfactants. Steric factor appears to play an important role during interaction when surfactant molecular structure varies in size of the head group and chain length of the hydrophobic part. The temperature has been observed to be vital in controlling the dehydration and thermal solubility which, in turn, makes environment conducive for aggregational behavior of the drug-surfactant mixtures in aqueous solution.

The metastable states of foam films containing electrically charged micelles or particles: experiment and quantitative interpretation

The stepwise thinning (stratification) of liquid films containing electrically charged colloidal particles (in our case - surfactant micelles) is investigated. Most of the results are applicable also to films from nanoparticle suspensions. The aim is to achieve agreement between theory and experiment, and to better understand the physical reasons for this phenomenon. To test different theoretical approaches, we obtained experimental data for free foam films from micellar solutions of three ionic surfactants. The theoretical problem is reduced to the interpretation of the experimental concentration dependencies of the step height and of the final film thickness. The surface charges of films and micelles are calculated by means of the charge-regulation model, with a counterion-binding (Stern) constant determined from the fit of surface tension isotherms. The applicability of three models was tested: the Poisson-Boltzmann (PB) model; the jellium-approximation (JA), and the cell model (CM). The best agreement theory/experiment was obtained with the JA model without using any adjustable parameters. Two theoretical approaches are considered. First, in the energy approach the step height is identified with the effective diameter of the charged micelles, which represents an integral of the electrostatic-repulsion energy calculated by the JA model. Second, in the osmotic approach the step height is equal to the inverse cubic root of micelle number density in the bulk of solution. Both approaches are in good agreement with the experiment if the suspension of charged particles (micelles) represents a jellium, i.e. if the particle concentration is uniform despite the field of the electric double layers. The results lead to a convenient method for determining the aggregation number of ionic surfactant micelles from the experimental heights of the steps.