Critical Micellar Concentration Values Research Articles

Histidine-based ionizable cationic surfactants: novel biodegradable agents for hydrophilic macromolecular drug delivery.

The aim of this study was to design surfactants based on histidine (His) for hydrophobic ion-pairing and evaluate their safety and efficacy. Lauryl, palmitoyl and oleyl alcohol, as well as 2-hexyl-1-decanol were converted into surfactants with histidine as head-group via esterification. The synthesized His-surfactants were characterized regarding pKa, critical micellar concentration (CMC), biodegradability, toxicity on Caco-2 cells, and ability to provide endosomal escape. Furthermore, the suitability of these agents to be employed as counterions in hydrophobic ion pairing was evaluated. Chemical structures were confirmed by 1H-NMR, FT-IR, and MS. The synthesized surfactants showed pKa values ranging from 4.9 to 6.0 and CMC values in the range of 0.3 to 7.0 mM. Their biodegradability was proven by enzymatic cleavage within 24h. Below the CMC, His-surfactants did not show cytotoxic effects on Caco-2 cells (cell viability > 80%). All His-surfactants showed the ability to provide endosomal escape in a pH-dependent manner in the range of 5.2 to 6.8. Complexes formed between His-surfactants and heparin or plasmid DNA (pDNA) via hydrophobic ion pairing showed at least 100-fold higher lipophilicity than the correspondent model drugs. According to these results, His-surfactants might be a promising safe tool for delivering hydrophilic macromolecular drugs and nucleic acids.

Iterative evaluation of micellar and thermodynamic properties of 12-2-12 in 1 % BSA aqueous solution in the presence of organic solvents and temperature

Abstract The interactions between a gemini surfactant 12-2-12 and bovine serum albumin (BSA) have been studied in aqueous and mixed aqueous media by conductance measurements using the iterative method at different temperatures ranging from 298.15 K to 313.15 K with step size 5. The critical micellar concentration (CMC) as well as the degree of ionization for the micelles (α) have been evaluated and their variation with solvent type and temperature has been discussed. The error for conductivity measurements was calculated and found to be much smaller than for surface tension measurements using the platinum ring method. The CMC values for the mixture of 12-2-12 and BSA in aqueous solvent solutions follow the sequence: DMF > AN > DMSO > water. These values were further confirmed by surface tension studies. From the thermodynamic parameters, hydrophobic interactions were found to be the driving force for micellization. The existence of enthalpy-entropy compensation was established from the linear plot of ΔH° m and ΔS° m .

Comparison of bubble parameters in natural and chemical surfactant solutions: a force analysis

The authors have investigated the potential of a plant-based natural surfactant in the modification of various bubble parameters. Bubble dynamics at the orifice were studied in natural surfactant solutions extracted from the plant Sapindus mukorossi at concentrations below and above its critical micellar concentration (CMC). The results were compared to the ones obtained with Sodium Dodecyl Sulfate solutions. The CMC values of Sapindus mukorossi and Sodium Dodecyl Sulfate are 7.5 × 10−3 g/cc and 2.39 × 10−3 g/cc, respectively. A photographic method was employed to observe bubble formation at the orifice. The results show that biosurfactants, like chemical surfactants, have a comparable effect on bubble density, size, and rise velocity. Experimentally determined bubble radius, volume, and radial velocity were used to calculate various forces contributing to the bubble dynamics. The buoyancy, pressure, and surface tension forces were significantly stronger in magnitude in comparison to the gas momentum, viscous drag, and added mass forces. Our findings suggest that the significance of various dynamic forces involved in bubble growth dynamics varies according to the bubble generation frequency regimes. We report for the first time the potential of Sapindus mukorossi in altering bubble properties and surface forces at the orifice and its usage in various bubble-related industrial applications.

Impact of Inulin on Self-Assembled Behavior of Anionic Surface Active Ionic Liquids: Conductometric, Spectroscopic and Antimicrobial Studies

The self-assembled behavior of greener anionic surface-active ionic liquids (SAILs), namely Tetrapropylammonium Dodecylsulfate (TPADS) and Tetrabutylammonium Dodecylsulfate (TBADS), in an aqueous solution of biocompatible saccharide inulin, has been extensively investigated using conductometric and fluorescence probe techniques at different temperatures. The critical micellar concentration (CMC) values have been determined by observing the breakage point in κ vs. [SAIL] plots. These values as obtained from fluorescence probe techniques have also been calculated. It has been found that the CMC values obtained through both conventional and spectroscopic techniques exhibited close agreement. Additionally, thermodynamic parameters of micellization, such as Gibbs free energy (ΔGmo), enthalpy (ΔHmo), and entropy (ΔSmo) were calculated using conductivity data as they play a crucial role in understanding the various interactions prevailing in the SAIL-inulin-water system. It was found that the micellization process for SAILs in the aqueous inulin solution occurs readily, as indicated by the Gibbs free energy of micellization. Furthermore, the antimicrobial properties of biocompatible SAILs in 0.2% w/w aqueous inulin solution were explored against bacterial strains, gram-positive i.e. B. cereus, S. aureus, and gram-negative namely P. aeruginosa. Molecular docking studies were also conducted to determine the binding energy and binding sites between TBADS and the proteins of the aforementioned bacteria. These investigations help to enhance the understanding of potential applications and interactions of SAILs in the presence of inulin.

Study of the interaction between polyphenol, quercetin and three micelles with different electric charges in acidic and aqueous media

The interactions between the polyphenol quercetin, Q, with three surfactant aggregates with different electric charges named micelles, were studied in aqueous solutions with pH values 4.7 and 7.0, to determine the following parameters: critical micellar concentration (CMC), micelle size and binding constant of the complex (Q-Micelle) proposing interaction sites for the formation of the complex. The surfactants used were: hexadecyltrimethyl ammonium bromide (cationic surfactant), CTAB, sodium dodecyl sulfate (anionic surfactant), SDS, and triton X-100 (non-ionic surfactant), TX100, used as Q fluorescence promoters to determine the CMC. The CMC values of the above surfactants at pH 4.7 were: 0.80 ± 0.10, 1.39 ± 0.07 and 0.59 ± 0.05 mM respectively, being lower than those reported in the water. With dynamic light scattering measurements, the hydrodynamic diameters of each micelle were calculated resulting in values of: 2.4 ± 0.5, 5.0 ± 1.1 and 8.4 ± 4.3 nm at pH 4.7 and: 2.1 ± 0.4, 4.9 ± 1.1 and 11.5 ± 4.1 nm at pH 7.0 respectively. In addition, the binding constants of the complex (Q-Micelle) with 1:1 stoichiometry were calculated from emission fluorescence data giving Log K values: 2.94 ± 0.02, 2.54 ± 0.02, and 3.63 ± 0.05 M-1 respectively. Finally, from the experimental data by UV–Vis spectrophotometry, the change in the behavior of the Q spectrum upon the addition of each of the surfactants to the system was analyzed, showing a decrease in absorbance when SDS and TX100 were added in an acidic medium, as a consequence of the photo-instability of the drug, suggesting that Q interacts with the outside of these micelles and is not fully incorporated inside them.

A proof of concept for the micellization of quercetin with anionic surfactants: Effect of counter ion

Strength of interaction of sodium/ammoniumdodecyl sulfates (SDS and ADS; CH3(CH2)10CH2SO4Na/CH3(CH2)10CH2OSO3NH4) with quercetin (QCT) through micellization is investigated. The strength and mode of interaction of QCT with SDS/ADS was analyzed using uv–visible, FTIR, and NMR spectral techniques. Characteristics of QCT/SDS and QCT/ADS micelles was determined by estimating the critical micellar concentration, particle size and zeta potential values. Thermodynamic parameters ΔG0m and ΔS0m suggest that the micellization of QCT/ADS occurs more spontaneously than QCT/SDS micellization. The small size of head group (-Na+) in SDS exhibits higher steric repulsion upon forming micelles with QCT, whereas the big size head group (-NH4+) in ADS exhibits strong micellization due to additional hydrogen bonding. The results suggests that ADS would be useful in developing QCT based skin formulations which could reduce the risk of surfactant penetration in skin. In this paper we have reported a second cmc of ADS as 0.6 mM which is probably for the first time.

Self-Aggregation, Antimicrobial Activity and Cytotoxicity of Ester-Bonded Gemini Quaternary Ammonium Salts: The Role of the Spacer.

Five ester-bonded gemini quaternary ammonium surfactants C12-En-C12 (n = 2, 4, 6), with a flexible spacer group, and C12-Bm-C12 (m = 1, 2), with rigid benzene spacers, were synthesized via a two-step reaction and analyzed. Furthermore, the effects of the spacer structure, spacer length and polymerization degree on the self-aggregation, antimicrobial activity and cytotoxicity of C12-En-C12 and C12-Bm-C12 and their corresponding monomer N-dodecyl-N,N,N-trimethyl ammonium chloride DTAC were investigated. The results showed that C12-En-C12 and C12-Bm-C12 had markedly lower critical micellar concentration (CMC) values and lower surface tension than DTAC. Moreover, the CMC values of C12-En-C12 and C12-Bm-C12 decreased with increasing spacer length. In the case of equivalent chain length, the rigidity and steric hindrance of phenylene and 1,4-benzenediyl resulted in larger CMC values for C12-Bm-C12 than for C12-En-C12. The antibacterial ability of C12-En-C12 and C12-Bm-C12 was assessed using Escherichia coli (E. coli) and Staphylococcus albus (S. aureus) based on minimum inhibitory concentrations (MICs). Furthermore, C12-En-C12 and C12-Bm-C12 exhibited higher antimicrobial activity than DTAC and had stronger function toward S. aureus than E. coli. The antimicrobial activity was enhanced by increasing the spacer chain length and decreased with the increased rigidity of the spacers. The cytotoxic effects of C12-En-C12 and C12-Bm-C12 in cultured Hela cells were evaluated by the standard CCK8 method based on half-maximal inhibitory concentration (IC50). The cytotoxicity of C12-En-C12 and C12-Bm-C12 was significantly lower than alkanediyl-α,ω-bis(dimethyldodecylammonium) bromide surfactants and DTAC. The spacer structure and the spacer length could induce significant cytotoxic effects on Hela cells. These findings indicate that the five ester-bonded GQASs have stronger antibacterial activity and lower toxicity profile, and thus can be used in the pharmaceutical industry.

Biossurfactant production by isolated bacteria from petroleum industry’s effluent targeting bioremediation

In this study, bacterial strains from the Bacillus genus were isolated from residual effluents from treatment unit of a Petroleum Factory to produce a biosurfactant, aiming the bioremediation of oil-contaminated soils. Five strains were selected to perform fermentation tests. Results showed that the strain LUB P1 presented a lipopeptide with excellent properties, which reduced the surface tension to rates below 30 mN/m. The bacteria were genetically identified as a species belonging to the Bacillus subtilis. Characterization of the biosurfactant confirmed that the main component is surfactin, with a critical micellar concentration (CMC) value of 15 mg.L−1 and high stability to temperature, salinity, and pH variations. In addition, showed low toxicity compared to synthetic surfactants. Bioremediation tests indicated motor oil removal efficiency of over 80% on the temperature of 60 °C in its CMC, presenting excellent properties for the application in bioremediation.

Ciprofloxacin-Loaded Mixed Polymeric Micelles as Antibiofilm Agents.

In this work, mixed polymeric micelles (MPMs) based on a cationic poly(2-(dimethylamino)ethyl methacrylate)-b-poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA29-b-PCL70-b-PDMAEMA29) and a non-ionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO99-b-PPO67-b-PEO99) triblock copolymers, blended at different molar ratios, were developed. The key physicochemical parameters of MPMs, including size, size distribution, and critical micellar concentration (CMC), were evaluated. The resulting MPMs are nanoscopic with a hydrodynamic diameter of around 35 nm, and the ζ-potential and CMC values strongly depend on the MPM's composition. Ciprofloxacin (CF) was solubilized by the micelles via hydrophobic interaction with the micellar core and electrostatic interaction between the polycationic blocks, and the drug localized it, to some extent, in the micellar corona. The effect of a polymer-to-drug mass ratio on the drug-loading content (DLC) and encapsulation efficiency (EE) of MPMs was assessed. MPMs prepared at a polymer-to-drug mass ratio of 10:1 exhibited very high EE and a prolonged release profile. All micellar systems demonstrated their capability to detach pre-formed Gram-positive and Gram-negative bacterial biofilms and significantly reduced their biomass. The metabolic activity of the biofilm was strongly suppressed by the CF-loaded MPMs indicating the successful drug delivery and release. The cytotoxicity of empty and CF-loaded MPMs was evaluated. The test reveals composition-dependent cell viability without cell destruction or morphological signs of cell death.

Design and simulation of a caprylic acid enzymatically modified phosphatidylcholine micelle using a coarse-grained molecular dynamics simulations approach

Computationally simulated micelle models provide useful structural information on the molecular and biological sciences. One strategy to study the self-aggregation process of surfactant molecules that make up a micelle is through molecular dynamics (MD) simulations. In this study, a theoretical approach with a coarse-grained MD simulation (CG-MD) was employed to evaluate the critical micellar concentration (CMC), the micellization process, building a tridimensional (3D) model system of a micelle using data from the experimentally enzymatically modified phospholipids (PL) by phospholipase A1 (PA1). This required enzymatic interesterification of soybean phosphatidylcholine (PC) with caprylic acid, along with purification and characterization by chromatographic techniques to measure the esterified fatty acids and the corresponding PL composition. The number of molecules used in the CG-MD simulation system was determined from the experimental CMC data which was 0.025%. The molecular composition of the system is: 1 C 18:2, 2 C 8:0/8:0, 3 C 8:0/18:3n-9, 4 C 8:0/18:0, 5 C8:0/18:2n-6, 6 C8:0/18:1n-9, and 7 C 8:0/16:0. According to our theoretical results, the micelle model is structurally stable with an average Rg of 3.64 ± 0.10 Å, and might have an elliptical form with a radius of 24.6 Å. Regarding CMC value there was a relationship between the experimental data of the modified PLs and the theoretical analysis by GC-MD, which suggest that the enzymatic modification of PLs does not affect their self-aggregation properties. Finally, the micellar system obtained in the current research can be used as a simple and useful model to design optimal biocompatible nanoemulsions as possible vehicles for bioactive small molecules.Communicated by Ramaswamy H. Sarma

Surface and thermodynamics properties of commercial fatty-alcohol ethoxylate surfactants

The present study provides the surface and thermodynamic properties data of commercial fatty-alcohol ethoxylate surfactants (FAEs) at different temperatures (25–60 °C). These compounds are a mixture of fatty-alcohol ethoxylate oligomers with different degree of ethoxylation (2.6–11) and length of the alkyl chain (C10-C18). In this work, we analyzed determinate the water content by the Karl-Fisher method and measured the surface tension using the Wilhelmy plate method. In addition, we studied the effect of their structural parameters (degree of ethoxylation and length of alkyl chain) and the temperature on the changes of the thermodynamic functions (Gibbs free energy, enthalpy, and entropy) for the processes of adsorption and micellization. It was found an exponential decrease of the critical micellar concentration (CMC) in molar scale with the length alkyl chain of the fatty-alcohol ethoxylate surfactants, and the CMC values and thermodynamic parameters agree with those values found in literature for pure compounds. Moreover, the micellization entropy increases with the degree of ethoxylation of the surfactant.

Engineering the rheology and IFT behavior of mixed formulations of anionic and non-ionic surfactants with added silica nanoparticles

Tertiary enhanced oil recovery (EOR) is one of the feasible exploitable fossils fuel to meet global energy consumption. The conventional EOR chemical approach has many disadvantages over the nano-EOR due to many unforeseen issues and loss of chemicals in the porous medium, affecting the techno-economic of the projects. The nano-EOR approach can augment and modify the rock-fluid interaction and mobility. It is a promising approach at the nanoscale to provide a unique platform to revolutionize the EOR process for ultimate oil gain. The other critical parameters, such as IFT, wettability, capillary pressure, and rheology, can also influence the rock-fluid interaction at the interface. The author has focussed mainly on the impact of IFT, surface tension, and rheology of nano silica-surfactant formulation (Alkyl benzene sulfonate-triton-x-100) in the presence of 3 wt% brine, synthetic formation water (SFW) and paraffin oil. The critical micellar concentration (CMC) value of the above composition was estimated at around 50 mg/lt. The IFT has been observed around 12.21mN/m against 3 wt% brine-surfactant composition at room temperature and 8.25mN/m at higher temperatures (∼60 °C). In the case of SFW, the IFT of 14.95mN/m at room temperature and 8.55mN/m at a higher temperature. The studies have also been conducted with nano silica-surfactant-3 wt% brine composition and found the IFT of 2.85mN/m at room temperature and 1.20mN/m at higher temperatures (∼60 °C). Whereas in the case of nano silica-surfactant-SFW formulation, it was found 4. 24mN/m at room temperature and<2.0mN/m at a higher temperature. The declining trends of IFT of the above systems will modify the rock-fluid interface properties and enhance mobility under in-situ conditions. The rheological studies also confirmed that 0.10 wt% of nano silica-surfactant with base fluid composition is an optimum and desired concentration for achieving favorable rheology and better techno-economics of nano-EOR applications.

Quercetin displacement caused by sodium dodecyl sulphate on inclusion complex quercetin-beta cyclodextrin in an acid environment

The global formation constants of two inclusion complexes formed from quercetin (QH5) and beta-cyclodextrin (βCD) in ClO4- 0.1 M pH 4.7 were calculated with the support of Stability Quotients from Absorbance Data (SQUAD), in addition, the effect of sodium dodecyl sulphate (SDS) on these complexes was studied. The molar ratios of the inclusion complexes formed QH5-βCD were 1:1 and 1:2 with log β values of 2.06 ± 0.22 and 3.69 ± 0.13 M−1 respectively. With measurements of surface tension and fluorescence, the critical micellar concentration (CMC) value of the SDS was calculated in the absence and presence of βCD resulting in an increase with the concentration of βCD, as a consequence of the formation of an inclusion complex βCD-SDS with log K of 3.589 ± 0.059 M−1. From the fluorescence results, the breakdown of the complex Q-βCD is inferred due to the interaction with the SDS causing its inclusion in the βCD cavity and displacement of the QH5. Finally, with the UV–vis spectrophotometric data it is shown that the formation of a ternary complex does not take place, as stated in some studies.

Critical micelle concentration of SDS through DPD simulations using COSMO-RS–based interaction parameters, the thermal effects

In order to obtain the critical micellar concentration (CMC) for sodium dodecyl sulfate (SDS) in water at 288.15, 293.15, 298.15, 303.15 and 308.15 K, two approaches were employed: the first, consisting of experimental Isothermal Calorimetric Titration (ITC) and the second by using Dissipative Particle Dynamics (DPD) simulations. To determine the experimental CMC the calorimetric signal was treated with the software D/STAIN, obtaining values between 8.24 and 9.22 mM, which are in good agreement with other experimental determinations. Also the SDS micellization enthalpies found agree with previous experimental reports. The pairwise aij DPD interaction parameters, needed to run the simulations, were obtained from quantum chemistry calculations under the application of the COSMO-RS solvation scheme jointly with the Flory-Huggins theory. A series of systems with variable concentration of SDS in water were simulated for each temperature. Then, the analysis of the percentage of aggregation of SDS molecules at each temperature, enable to visualized the theoretical aggregation isotherms. By delimiting an experimental CMC window, the DPD aggregation isotherms were used to identify the concentration where either the monomeric or micellar states domain. Intersection of linear fits, in the monomeric and in the micellar regime produced theoretical CMCs values from 8.1 to 8.9 mM. These results compare favorably with the experimental determinations at each temperature.

Study on the Effects of Biologically Active Amino Acids on the Micellization of Anionic Surfactant Sodium Dodecyl Sulfate (SDS) at Different Temperatures

The micellar properties of the anionic surfactant, sodium dodecyl sulfate (SDS) are modified by the biologically active amino acids. Amino acids (AAs) have experienced a variety of interactions and are proposed to influence SDS micelles due to their nominated hydrophobic interactions. The present study determines the critical micellar concentration (CMC) of SDS in aqueous solutions as well as in amino aqueous solutions. Three amino acids (glutamic acid, histidine, and tryptophan) are considered here. The conductometric measurements were carried out using a wide range of SDS concentrations at different temperatures. Surface tension experiments have also been applied to estimate many surface parameters including surface excess concentration (Γmax), surface occupied area per surfactant molecule (Amin), surface tension at CMC (γcmc), surface pressure at CMC (Πcmc) and Gibbs free energy of adsorption (∆Gads°), enthalpy ∆Hm° and the critical packing parameter (CPP). Interestingly, CMC values of SDS in water and in aqueous amino acids estimated by the surface tension method are comparable with the corresponding values obtained by the conductance method. The thermodynamic parameters of SDS micellization were also evaluated in both presence and absence of AAs. The additives of AAs work to reduce the CMC values, as well as the SDS thermodynamic parameters. This reduction is highly dependent on the hydrophobicity of the AA side chain. Negative values of ∆Gm°, ∆Hm° elucidate that micellization of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. The outcomes here might be utilized for pharmaceutical applications to stabilize proteins and inhibit protein aggregation.

A Novel Study on the Self-Assembly Behavior of Poly(lactic-co-glycolic acid) Polymer Probed by Curcumin Fluorescence.

Understanding the self-assembly behavior of block copolymers is of great importance due to their usefulness in a wide range of applications. In this work, the physical properties of poly(lactic-co-glycolic acid) (PLGA polymer) are studied for the first time in solution using the fluorescence technique and curcumin as a molecular probe. First, curcumin at a concentration of 2 μM was added to different concentrations of PLGA, and the fluorescence of curcumin was tracked. It was found that the critical micellar concentration (CMC) was equal to 0.31 g/L and the critical micellar temperature (CMT) was obtained to be 25 °C. Furthermore, an insight on the effect of NaCl salt on the CMC value of PLGA is assessed through curcumin probing. A decrease in the CMC has been observed with the increase in the concentration of NaCl, which could be due to the salting out effect. Moreover, in order to understand the aggregation behavior of PLGA in different solutions, CMC experiments were investigated using chloroform as a solvent. Results showed that the solvent does not affect the CMC value of the polymer; however, it only affects the shape of the obtained micelle forming a reversed micelle. Finally, fluorescence quenching of curcumin with hydrophobic cetyl-pyridinium bromide (CPB) and hydrophilic KI quenchers was established, where it was proved that curcumin is located near the hydrophobic pocket of the Stern layer of the PLGA micelle.

Micellar properties of cetyltrimethylammonium bromide in an acetonitrile–water mixture: Conductometric and fluorescence studies

The effect of acetonitrile (ACN) on the micellization of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), in aqueous solutions at different temperatures was studied. The critical micellar concentration (CMC) as well as the degree of counter ion dissociation (a) of CTAB in aqueous ACN mixtures (10-20 % v/v) at various temperatures (291.2-298.2 K) were determined by electrical conductivity measurements, while steady-state fluorescence measurements were used to determine several CMCs (for comparison) and a micellar aggregation number (Nagg) as well. At a fixed temperature, both an increase in CMC and a decrease in Nagg were observed for an increase in ACN in the solvent mixture. With a temperature increase, CMC values increased for 10 % (v/v) ACN, while for both 15 % and 20 % (v/v) ACN, CMC values were a minimum at T = 295.2 K with a temperature increase. In addition, some aspects related to the Krafft temperature behavior of CTAB in the examined micellar systems are discussed.

Hybrid Fluorocarbon-Hydrocarbon Surfactants: Synthesis and Colloidal Characterization.

Four double-tailed hybrid fluorocarbon-hydrocarbon (F-H) surfactants with a poly(ethylene glycol) (PEG) polar headgroup were synthesized. The hydrophobic scaffold consists of an amino acid core, onto which were grafted both fluorocarbon and hydrocarbon chains of different lengths. The PEG polar head was connected to the hydrophobic scaffold through a copper(I)-mediated click reaction. The four derivatives exhibit aqueous solubility >100 g/L and self-assemble into micellar aggregates with micromolar critical micellar concentration (CMC) values, as demonstrated by isothermal titration calorimetry (ITC), surface tension (ST) measurements, and steady-state fluorescence spectroscopy. The CMC value decreased by a factor of ∼6 for each additional pair of CH2 groups, whereas a decrease by a factor of ∼2.5 was observed when the size of the PEG polar head was reduced from 2000 to 750 g/mol. Dynamic light scattering (DLS) showed unimodal micelle populations with hydrodynamic diameters of 10-15 nm, in agreement with results obtained from size-exclusion chromatography (SEC). The aggregation number increased with the hydrocarbon chain length but decreased with increasing PEG chain lengths. The combination in one molecular design of both low CMC and high water solubility makes these new surfactants promising systems for novel drug-delivery systems.

Interfacial behavior and micellization of binary surfactant mixtures in the concentrated sodium aluminate solution

Methods to eliminate the negative effects of organics on alumina production have been required for many decades. Similar to sodium laurate (SL) and sodium stearate (SS), compounds such as sodium oxalate (SO), sodium benzoate (SB), and sodium citrate (SC) also exist as surfactants in concentrated sodium aluminate solutions. Herein, elevating the temperature reduced the maximum surface excess (Γmax) and saturated adsorption layer thickness (δ) but increased the cross-sectional headgroup area (Amin) of the surfactant molecules. The order of critical micellar concentration (CMC) was: SO > SC > SB > SL > SS, while the micellar size followed the sequence: SS > SL > SC > SB > SO. Addition of SO (or SC) increased the CMC of SB, SL, SS, and SC (or SO). However, SO and SC were observed to play different roles in the interfacial properties of the organics. Addition of SO increased the Γmax values of SC, SL, and SS, and decreased the Amin values. In contrast, adding SC reduced Γmax and δ values of SB, SO, and SS, and raised Amin values. SO could be readily incorporated into micelles relative to SC, possibly leading to formation of the small micelles in SB. Additionally, increasing the temperature reduced the molar fraction of SO (or SC) in the mixed micelles of the binary surfactant mixtures, and SC could assemble at the air/solution interface and be incorporated into mixed micelles at increasing temperatures. Finally, the CMC values calculated using a non-ideal model agreed well with those determined from experiments.

Effect of dicationic ionic liquids on cloud points of tergitol surfactant and the formation of aqueous micellar two-phase systems

A cloud point evaluation was performed for the nonionic surfactant Tergitol 15-S-7 in aqueous solutions of McIlvaine buffer (pH 7.0). Cloud point temperatures of the selected nonionic surfactant were studied in relation to the effect that the addition of dicationic ionic liquids (ILs) had on the systems. The dicationic ILs with different alkyl spacer lengths were derived from 1, n-bis(3-methylimidazolium-1-yl)alkane bromide ([BisAlk(MIM)2][2Br]) — in which Alk = But, Hex, Oct, and Dec. The dicationic ILs with longer alkyl spacer chains (Alk ≥ 6) led to an increase in the Tergitol’s cloud point values, due to their ability to fold their structures in solution, which increase the interactions of ILs with tergitol in the mixed micelles. This increase was even more pronounced when the concentration of the dicationic ILs was increased. Furthermore, the addition of dicationic ILs increased the micelles size; however, the hydrodynamic diameter of mixed micelles did not depend on the length of the ILs’ alkyl spacer chains. The Tergitol/IL systems with lower critical micellar concentration values will result in higher cloud point values, due to the greater colloidal dispersion stability.