Gemini Surfactant Micelles Research Articles

Distinct Solubilization Mechanisms of Medroxyprogesterone in Gemini Surfactant Micelles: A Comparative Study with Progesterone

The solubilization behavior of medroxyprogesterone (MP) within gemini surfactant micelles (14-6-14,2Br−) was investigated and compared with that of progesterone to uncover distinct solubilization mechanisms. We employed 1H-NMR and 2D ROESY spectroscopy to elucidate the spatial positioning of MP within the micelle, revealing that MP integrates more deeply into the micellar core. This behavior is linked to the unique structural features of MP, particularly its 17β-acetyl group, which promotes enhanced interactions with the hydrophobic regions of the micelle, while the 6α-methyl group interacts with the hydrophilic regions of the micelle. The 2D ROESY correlations specifically highlighted interactions between the hydrophobic chains of the surfactant and two protons of MP, H22 and H19. Complementary machine learning and electron density analyses supported these spectroscopic findings, underscoring the pivotal role of the molecular characteristics of MP in its solubilization behavior. These insights into the solubilization dynamics of MP not only advance our understanding of hydrophobic compound incorporation in gemini surfactant micelles but also indicate the potential of 14-6-14,2Br− micelles for diverse drug delivery applications.

Transformation of an Aqueous Micellar Phase to a Bilayer of Gemini Surfactants on Gold Nanoparticles: A Steady-State and Time-Resolved Fluorescence and Fluorescence Anisotropy Study by Tuning the Precise Locations of Probes

The present work reports the transformation of aqueous micelles of gemini surfactants (12-4-12,2Br– or 12-8-12,2Br–) to a bilayer of surfactants on the surface of gold nanoparticles (AuNPs) capped with citrate during their in situ synthesis. The synthesized AuNPs are characterized using surface plasmon resonance (SPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), scanning transmission electron microscopy (STEM), and high-resolution transmission electron microscopy (HR-TEM) techniques. The transformation of micelles to a surfactant bilayer with time is understood with the help of fluorescence measurements such as steady-state and time-resolved fluorescence and fluorescence anisotropy, probed by tuning the precise locations of two fluorophores, Coumarin-480 (C-480) and rhodamine 6G (Rh6G), present in the micelles. As the formation of AuNPs initiates, the dyes get relocated from micelles to a site near the NP surface, which results in fluorescence quenching and a decrease in lifetime due to the nanomaterial surface energy transfer (NSET) from the donor dye to the acceptor AuNPs. The results indicated that Rh6G lies close to the head groups of the surfactant in micelles. Fast segmental/tumbling motions of Rh6G in micelles/bilayers are primarily responsible for the decay of anisotropy to zero. Lateral diffusion is responsible for slow rotational relaxation. With the growth of rod/needle-shaped NPs, the average lifetime and rotational relaxation time increase with an increase in fluorescence intensity due to the transfer of dye molecules from the NP surface to the interior of the bilayer. A significant change in the weightage of the slow component of C-480 compared to that of Rh6G with the formation of the bilayer supports that the former dye is located deep inside the bilayer with an equal contribution to depolarization from both the rotational motions at equilibrium. The excitation wavelength-dependent rotational relaxation time of Rh6G in the bilayer supports the prolate ellipsoidal shape of AuNPs surrounded by the bilayer. This study can help understand the mechanism of drug loading in forming metal NP-based hybrid drug delivery systems in an aqueous micellar solution of gemini surfactants.

Determination of the Aggregation Number of Pyrene-Labeled Gemini Surfactant Micelles by Pyrene Fluorescence Quenching Measurements.

A cationic gemini surfactant referred to as Py-3-12 and composed of two alkylated diammonium bromide head groups, a propyl spacer, and dodecyl and 1-pyrenehexyl hydrophobic tails was synthesized. Its critical micellar concentration (CMC) was determined to equal 0.15 (±0.02) mM by surface tension and time-resolved fluorescence measurements. The state of the pyrene molecules, whether they were incorporated inside the Py-3-12 micelles or unassociated in the aqueous solution, was determined by applying the global model-free analysis (MFA) to the fluorescence decays acquired with Py-3-12 aqueous solutions. The unassociated Py-3-12 surfactants emitted as pyrene monomers and showed a long fluorescence lifetime. The excited pyrenyl groups located inside Py-3-12 micelles formed an excimer by a rapid encounter with a ground-state pyrene with an average rate constant equal to 0.69 (±0.06) ns-1. After having the photophysical properties of Py-3-12 in aqueous solution characterized, the number (Nagg) of surfactants per micelle was determined by conducting quenching experiments with dinitrotoluene (DNT). Although DNT is fairly hydrophobic, it was found to partition itself between the Py-3-12 micelles and the aqueous phase. Fluorescence quenching experiments performed on the pyrene monomer and excimer generated by the Py-3-12 aqueous solutions yielded the concentration ([Q]b) of DNT bound to the Py-3-12 micelles and the average number ⟨n⟩d of DNT quenching an excimer by diffusive encounters. A combination of steady-state and time-resolved fluorescence quenching experiments on the excimer yielded the number (⟨n⟩s) of DNT molecules that were bound to the micelles and quenched the excimer in a static manner. A plot of the sum ⟨n⟩d + ⟨n⟩s as a function of [Q]b yielded an Nagg value of 14.0 (±0.2) Py-3-12 units per micelle. This study represents the first example in the literature where Nagg is determined for a micelle, where each surfactant molecule is labeled with pyrene.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane.

The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br–/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (Wo) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given Wo are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.

Kinetic study of the metal-dipeptide complex with ninhydrin facilitated by gemini (m-s-m) surfactant micelles

The three Gemini (m-s-m; m (head group) = 16 and s (spacer) = 4, 5, 6) surfactants have been synthesized and their impact on reaction of zinc(II)-glycylleucine complex ([Zn(II)-Gly-Leu]+) and ninhydrin were studied at temperature (343 K) and pH (5.0) using spectroscopic method. Influence of several factors, viz., [Zn(II)-Gly-Leu]+, [ninhydrin], temperature and pH were also carried out on title reaction in geminis. Rates of reaction are the first-order path in concentration of [Zn(II)-Gly-Leu]+ complex and fractional order path in concentration of ninhydrin. The catalysis of gemini 16-s-16 surfactant micelles was investigated below and above their critical micelle concentration (cmc) value and detailed elaboration were provided in the text. In the present case, rate constants, kψ, increased on increasing geminis ([gemini] are below their cmc, region I) and stayed nearly constant (region II). The shape of (region I and II) surfactants ([gemini] = 0 to 400 × 10−5 mol dm−3) are similar to a cetyltrimethylammonium bromide, CTAB (single hydrophilic head group and hydrophobic part). Later, a sharp increment in rate was observed with higher [gemini] (region III, (Fig. 5). The study was catalyzed and accelerated quite enough by geminis (at concentrations below their cmc) compared to aqueous. An appropriate mechanism has been proposed for accounting for the distribution of reactants between aqueous and micellar pseudo phases. Resulting kinetic data were used to determine the binding constants of micelle-substrate (KB) and micelle-ninhydrin (KNin).

Study of the interaction between ninhydrin and chromium(III)-amino acid in an aqueous-micellar system: Influence of gemini surfactant micelles

Chromium(III)-amino acid ([Cr(III)-His]2+) and ninhydrin in an aqueous-micellar system were combined in acetate buffer at 353 K and analyzed by UV–vis spectroscopy. Dimeric geminis (16-s-16, s, spacer, = 4 to 6) were chosen as a surfactant and their influence on the reaction rate was determined. To show this behavior of gemini surfactants on rate constant (kψ), kψ was plotted against different surfactant concentrations. kψ increases with increasing [16-s-16] (at concentrations lesser than their cmc values, segment I) and levelling-off regions attain (concentration upto 400 × 10−5 mol dm−3, segment II). Later, [16-s-16] generates a third region of increasing kψ at higher [16-s-16] ([16-s-16] > 400 × 10−5 mol dm−3, segment III). The uncommon plot behavior of kψ vs. [16-s-16] was revealed, effectively, by utilizing a pseudo-phase model of micellar activity. Critical micellar concentration of pure gemini surfactants, as well as their mixed solution with reactants, was determined by conductometry. Based on the data, various thermodynamic parameters and binding constants were calculated under different experimental reaction conditions.

Influence of dimeric gemini surfactant micelles on the study of nickel-glycylleucine dipeptide and ninhydrin

Influence of dimeric gemini surfactant micelles on the study of nickel-glycylleucine dipeptide ([Ni(II)-Gly-Leu]+) and ninhydrin was carried out in the temperature ranging from 333 K to 353 K. An UV–vis spectrophotometer was employed to record the absorbance of product at definite time intervals. Rate of reaction was strongly catalyzed by the gemini surfactants. In the present reaction, the first-order dependence in metal-dipeptide complex and fractional-order dependence in ninhydrin were observed. For the measurements of critical micelle concentration (CMC), conductivity method was used. Rate constants (k ψ) increase and levelling-off regions are detected with [gemini] (just like conventional monocationic surfactant). Later, gemini produces a third region at higher [gemini] where, fast increment in k ψ is observed. The catalytic role of surfactants has been described below and above the CMC of gemini surfactants. From this study, binding constants of reactants and thermodynamic parameters have been evaluated. The kinetic results and observed catalysis could plausibly be rationalized by Menger and Portnoy’s pseudo-phase model of micellar catalysis.

Micelles of cleavable gemini surfactant induce fluorescence switching in novel probe: Industrial insight

In this communication we have observed that cleavable gemini surfactant micelles induce fluorescence switching in novel probe (bound to lysozyme) at lower concentrations (∼2.63 mM) compared to conventional surfactants, which are known to induce such phenomenon at above 30 mM. Fluorescence switching being important in sensing, binding, and probing the conformational states of proteins; therefore, in future this study could be significant to protein analytics and other relevant industrial domains.

Development of curcumin-loaded gemini surfactant nanoparticles: Synthesis, characterization and evaluation of anticancer activity against human breast cancer cell lines

BackgroundCurcumin, the polyphenolic constituent of turmeric, has been recognized as an effective anticancer agent in the treatment of breast cancer. However, the poor bioavailability of curcumin triggers finding of new approaches for elevating its therapeutic efficiency. PurposeWe aimed to use gemini surfactant nanocarriers for curcumin in order to overcome its limitations. Study designWe investigated the in vitro characterization of gemini surfactant–curcumin (Gemini–Cur) and examined its antiproliferative & apoptotic activities on breast cancer cell lines. MethodsGemini–Cur polymersomes were synthesized through nanoprecipitation method and characterized by dynamic light scattering (DLS), transmission and scanning electron microscopies, HPLC and X-ray diffraction (XRD). The anticancer effect of Gemini–Cur nanoparticles was studied on three different breast cancer cell lines including MCF-7, SkBr-3 and MDA-MB-231 through uptake kinetics, viability & cytotoxicity recordings and apoptotic assays. Furthermore, qRT-PCR was performed to evaluate the expression of apoptotic genes including p16INK4a, p14ARF, Bax and Bcl-2. ResultsAccording to physicochemical analysis, the average particle size, zeta potential value and drug entrapment efficiency for Gemini–Cur compound were recorded as 161 ± 6.2 nm, +5.32 mV and 89.13% ± 0.93, respectively. XRD analysis also confirmed the incorporation of curcumin in gemini surfactant micelles. Regarding the enhanced cellular uptake of sphere shaped Gemini–Cur, our data showed that this nano compound suppresses cancer cell proliferation via induction of apoptosis. Moreover, qRT-PCR analysis revealed that Gemini–Cur could effectively upregulate the expression of p16INK4a, p14ARF and Bax, while significantly decreasing the Bcl-2 expression in these breast cancer cells. ConclusionOur data demonstrates the great potential of gemini surfactants for efficient delivery of curcumin and subsequently, the improvement of its anticancer effect. Therefore, it is sagacious to support the idea that Gemini–Cur nano compound might have the potential to be considered as an anticancer agent.

Effect of Urea on Solvation Dynamics and Rotational Relaxation of Coumarin 480 in Aqueous Micelles of Cationic Gemini Surfactants with Different Spacer Groups.

The present work highlights the effect of urea on solvation dynamics and the rotational relaxation of Coumarin 480 (C-480) in the Stern layer of aqueous micelles of cationic gemini surfactants, 12-4(OH)n-12 (n = 0, 1, 2). UV–visible absorption, steady-state fluorescence and fluorescence anisotropy, time-resolved fluorescence and fluorescence anisotropy, and dynamic light scattering measurements have been carried out for this study. The formation of micelles becomes disfavored in the presence of urea at high concentration. Solvation dynamics is bimodal in nature with fast solvation as a major component. The average solvation time increases, reaches a maximum, and then decreases with increasing concentration of urea because the degree of counterion dissociation also follows the same order with the addition of urea in the micellar solution. With increased degree of counterion dissociation, the extent of clustering of water molecules is increased, resulting in slower solvation process. The −OH group present in the spacer group of gemini surfactant controls the rate of solvation by shielding the water molecules from the probe molecules forming hydrogen bond. The microviscosity of micelles is decreased with increasing concentration of urea, as a result of which the rotational relaxation process becomes faster. In the presence of the −OH group in the spacer group, the microviscosity of micelles is enhanced, resulting in longer rotational relaxation time. Rotational relaxation process is bimodal in nature with the major contribution from the fast component to the fluorescence depolarization. Slow rotational relaxation is mainly due to the lateral diffusion of C-480 molecules along the surface of the micelle. The tumbling motion of the micelle as a whole is much slower than the lateral diffusion of C-480. Wobbling motion of C-480 becomes faster with increasing concentration of urea as a result of decreased microviscosity of micelles. The alignment of C-480 molecules in micelles might change with changing microviscosity.

Synthesis and Characterization of Dicationic Gemini Surfactant Micelles and their Effect on the Rate of Ninhydrin–Copper-Peptide Complex Reaction

Abstract Herein, we have synthesized and characterized dicationic Gemini surfactants. The effect of their micelles on the rate constant of ninhydrin with [Cu(II)-Gly-Gly]+ complex reaction was investigated under pseudo-first-order-conditions. Experiments were carried out by means of spectrophotometry. First- and fractional-order dependencies on [Cu(II)-Gly-Gly]+ and ninhydrin, respectively, were found. The results indicated that the efficiency of micellar catalysis by Gemini surfactants was significantly higher as compared to single-chained surfactant cetyltrimethylammonium bromide, CTAB. The Gemini surfactant produces a catalytic effect and leveling-off regions (just like CTAB) on the reaction rate. Later, Gemini with higher concentrations gives a third region of increasing k ψ. The effect of surfactants was rationalized by hydrophobic and electrostatic interactions. The observed kinetic effects are explained by applying the Menger-Portnoy model.

Highly stable and reduction responsive micelles from a novel polymeric surfactant with a repeating disulfide-based gemini structure for efficient drug delivery

The synthesis of a novel polymeric surfactant with a repeating disulfide-based gemini structure (poly(gemini surfactant)) and its micellar properties for GSH-dependent intracellular drug delivery are described. A linear polyethylene glycol (PEG) was end-functionalized with N-stearoylcysteine and the cysteine thiol groups of the telechelic surfactant were oxidized intermolecularly in the micellar state to produce poly(gemini surfactant). Compared with the telechelic surfactant, poly(gemini surfactant) possessed a lower critical micelle concentration and higher solubilization capacity for doxorubicin (DOX). Moreover, the poly(gemini surfactant) micelles revealed excellent colloidal stability against excess sodium dodecyl sulfate (SDS) as a micelle-destabilizing agent. Cytotoxicity experiments showed that poly(gemini surfactant) composed of PEG, cysteine, and stearic acid was virtually non-cytotoxic up to 100 mg L−1. In the presence of glutathione (GSH), poly(gemini surfactant) was degraded back into the telechelic surfactant, leading to the release of encapsulated DOX to induce cytotoxicity against cancer cells.

Effect of Hydrophobicity of Tails and Hydrophilicity of Spacer Group of Cationic Gemini Surfactants on Solvation Dynamics and Rotational Relaxation of Coumarin 480 in Aqueous Micelles.

Solvation dynamics and rotational relaxation of coumarin 480 in aqueous micelles of cationic gemini surfactants with diethyl ether (EE) spacer group (m–EE–m) and tails with varying tail lengths (m = 12, 14, and 16) have been studied. Studies have been carried out by measuring UV–visible absorption, steady-state fluorescence and fluorescence anisotropy, time-resolved fluorescence and fluorescence anisotropy, 1H NMR spectroscopy, and dynamic light scattering. Effects of hydrocarbon tail length and hydrophilicity of spacer group on solvation dynamics and rotational relaxation processes at inner side of the Stern layer of micelles have been studied. With increasing hydrophobicity of tails of surfactants, water molecules in the Stern layer become progressively more rigid, resulting in a decrease in the rate of solvation process with slow solvation as a major component. With increasing hydrophilicity of the spacer group of gemini surfactant, the extent of free water molecules is decreased, thereby making the duration of the solvation process longer. Solvation times in the micelles of gemini surfactants with hydrophilic spacer are almost 4 times longer compared to those in the micelles of their conventional counterpart. Rotational relaxation time increases with increasing tail length of surfactant as a result of increasing microviscosity of micelles with fast relaxation as a major component. With increasing hydrophilicity of the spacer group, the anisotropy decay becomes slower due to the formation of more compact micelles. Rotational relaxation in gemini micelles is also slower compared to that in their conventional counterpart. The anisotropy decay is found to be biexponential with lateral diffusion of the probe along the surface of the micelle as a slow component. Rotational motion of micelle as a whole is a very slow process, and the motion becomes further slower with increasing size of the micelle. The time constants for wobbling motion and lateral diffusion of the probe become longer with increasing microviscosity of micelles.

Gemini Surfactants with Polymethylene Spacer: Supramolecular Structures at Solid Surface and Aggregation in Aqueous Solution

AbstractAggregation of α,ω‐bisammonium cationic gemini surfactants with a variable polymethylene spacer and two dodecyl chains has been studied on a solid surface and in aqueous solution. Scanning electron microscopy and dynamic light scattering with the time‐resolved fluorescence quenching technique were used for the experiments on the solid surface and in aqueous solution, respectively. As the results from the scanning electron microscopy indicate, the morphology of supramolecular structures of gemini surfactants at the solid surface depends on the spacer length. In aqueous solution, gemini surfactants with spacers consisting of 4, 6, 8, 10, and 12 CH2 groups form spherical micelles with diameters between 2 and 3.5 nm. Micelles of gemini surfactant with a short ethylene spacer show an increase in size up to 13 nm at the maximum concentration investigated. The aggregation number of micelles determined by time resolved fluorescence quenching was found to be in the range 14–25 for the spacer lengths from 6 to 12 CH2 groups with only a moderate increase with surfactant concentration. For micelles of gemini surfactants with the short ethylene spacer, the increase of the aggregation number up to 50 at the maximum concentration was observed. The findings support micellar growth of gemini surfactants with short ethylene spacer.

Bile salt assisted morphological changes of cationic gemini surfactant (12-4-12) micelles

pH and concentration dependent growth of gemini surfactant (12-4-12) micelles in the presence of bile salts.

Interactions in the mixed micelles of monomeric and gemini surfactants: Influence of some co-solvents as a function of temperature

Mixed micellar behavior of a series of m-2-m cationic gemini surfactants (where m=10, 12 and 14) with monomeric surfactants (dodecyltrimethylammonium bromide, tetradecyltrimethyl-ammonium bromide and cetyltrimethylammonium bromide) has been studied in aqueous and in aqueous n-propanol, n-butanol, tertiary butanol, propylene glycol and glycerol solutions using conductivity, surface tension, viscosity and dynamic light scattering techniques at 298.15, 308.15 and 318.15K, respectively. In mixtures of 10–2–10 with monomeric surfactants, the synergistic interactions increase with the chain length of monomeric surfactants whereas the mixtures with 12–2–12 and 14–2–14 exhibit the opposite trends. However, the synergistic interactions decrease with the increase in temperature of all the mixtures. The thermodynamic and surface parameters have been evaluated and the influence of the variations in hydrophobic chain length of the surfactants and the type of the co-solvent on these parameters has been discussed. The hydrodynamic diameter increases with the chain length of the surfactants.

Gemini surfactants affect the structure, stability, and activity of ribonuclease Sa.

Gemini surfactants have important advantages, e.g., low micromolar CMCs and slow millisecond monomer ↔ micelle kinetics, for membrane mimetics and for delivering nucleic acids for gene therapy or RNA silencing. However, as a prerequisite, it is important to characterize interactions occurring between Gemini surfactants and proteins. Here NMR and CD spectroscopies are employed to investigate the interactions of cationic Gemini surfactants with RNase Sa, a negatively charged ribonuclease. We find that RNase Sa binds Gemini surfactant monomers and micelles at pH values above 4 to form aggregates. Below pH 4, where the protein is positively charged, these aggregates dissolve and interactions are undetectable. Thermal denaturation experiments show that surfactant lowers RNase Sa's conformational stability, suggesting that surfactant binds the protein's denatured state preferentially. Finally, Gemini surfactants were found to bind RNA, leading to the formation of large complexes. Interestingly, Gemini surfactant binding did not prevent RNase Sa from cleaving RNA.

Interaction between dipeptide (glycyl-phenylalanine) and ninhydrin: Role of CTAB and gemini (16-s-16, s = 4, 5, 6) surfactant micelles

The kinetics of interaction of dipeptide glycylphenylalanine (Gly-Phe) with ninhydrin have been studied by following the reaction spectrophotometrically at 70°C and a particular pH 5.0 in the absence and presence of conventional cetyltrimethylammonium bromide (CTAB) and gemini (alkanediyl-α,ω-bis(dimethylhexadecylammonium bromide)) surfactants. The rate shows first- and fractional-order dependence on [Gly-Phe] and [ninhydrin], respectively. The surfactants were found to catalyse the reaction. Furthermore, whereas the typical rate constant (kΨ) increase and leveling-off regions are observed with geminis, just like as seen with conventional surfactants, the former produced a third region of increasing kΨ at higher concentrations. A kinetic rate law consistent with experimental results has been derived on the basis of the proposed mechanism.

Thiol-responsive micelles based on nonionic gemini surfactants with a cystine disulfide spacer

Thiol-responsive micelles consisting of novel nonionic gemini surfactants with a cystine disulfide spacer are reported. The gemini surfactants, (C18-Cys-mPEG)2 and ((C18)2-Lys-Cys-mPEG)2, were synthesized from polyethylene glycol, cysteine, and stearic acid, and their structures were confirmed by 1H NMR and gel permeation chromatography. (C18-Cys-mPEG)2 and ((C18)2-Lys-Cys-mPEG)2 formed micelles with average diameters of 13 and 22 nm above the critical micelle concentration of 6.5 and 4.7 µg mL−1, respectively. The micelles of ((C18)2-Lys-Cys-mPEG)2 containing more stearoyl groups showed encapsulated more hydrophobic indomethacin (IMC) with higher entrapment efficiencies than those of (C18-Cys-mPEG)2. The gemini surfactant micelles exhibited an accelerated release of encapsulated IMC with the concentration of the reducing agent, glutathione (GSH), whereas they were unaffected by the presence of reduced GSH (GSSG). The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)−2-(4-sulfophenyl)−2H-tetrazolium studies revealed the noncytotoxic nature of the gemini surfactant micelles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 582–589

Study on Mixed Micelles of Cationic Gemini Surfactants Having Hydroxyl Groups in the Spacers with Conventional Cationic Surfactants: Effects of Spacer Group and Hydrocarbon Tail Length

Gemini surfactants, being more surface-active than their conventional counterparts, have potential applications in various industries. The properties of mixed surfactant systems are far better than those of neat surfactants in many cases, and as a result, mixed surfactants are used in many industrial applications. In the present work, the micellar properties of binary mixtures of the monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB) with the cationic gemini surfactants 1,3-bis(dodecyl-N,N-dimethylammonium bromide)-2-propanol and 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol were studied in aqueous solution at 303.15 K by means of conductivity, steady-state fluorescence, and fluorescence anisotropy techniques. The presence of a small amount of gemini surfactant was found to improve the physicochemical properties of the conventional surfactant. For example, the cmc value of DTAB was reduced to one-sixth of its original value in the presence of 0.1 mole fraction of a gemini surfactant. The spacer group of the gemini surfactant and the hydrocarbon chain of the monomeric surfactant play a significant role in the interactions between the surfactants in mixed micelles. These interactions are greatest when there are similarities in the structures of their hydrocarbon chains; however, the micellization process is favored by increasing hydrophobicity of the monomeric surfactant. The microenvironments of mixed micelles were studied using fluorescence techniques.