Cationic ester-containing gemini surfactants: Adsorption at tailor-made surfaces monitored by SPR and QCM

Adsorption of a series of ester-containing cationic surfactants at a surface containing 90% methyl groups and 10% carboxyl groups was studied by two surface analysis techniques, surface plasmon resonance (SPR) and quartz crystal microbalance (QCM). Such a surface, which is at the same time hydrophobic and negatively charged, is of interest as a model for many polymeric surfaces. Two different types of ester gemini surfactants and their monomeric counterparts were included together with nonester containing surfactants of similar structure. The results show that the gemini surfactants give the same adsorbed amount at the surface as the monomeric surfactants when compared at the same bulk concentration normalized to the critical micelle concentration (cmc) in bulk. Since the cmc of the geminis is around 20 times lower than the cmc of the corresponding monomeric surfactants, the gemini surfactants are much more effective in covering the surface. The two techniques gave similar relative values but the QCM values were always higher than those from SPR, which is due to the former method taking also adsorbed water into account. The adsorption, as measured by both methods, was found to follow closely the Langmuir adsorption model

Cationic Ester-Containing Gemini Surfactants: Physical-Chemical Properties

Three ester-containing cationic gemini surfactants, two with decanoyl chains and either a three-carbon or a six-carbon spacer unit and one with dodecanoyl chains and a three-carbon spacer, were synthesized and evaluated. A corresponding monomeric cationic ester surfactant was used for comparison. This type of amphiphile, a so-called esterquat, is known to undergo rapid hydrolysis above the critical micelle concentration because of micellar catalysis. The esterquat geminis of this work were found to be much more susceptible to hydrolysis than the esterquat monomer. This difference is believed to be caused by anchimeric assistance by the second cationic headgroup in the gemini amphiphiles. However, there is no correlation between the rate of chemical hydrolysis and the rate of biodegradation. The monomeric esterquat, which is the most stable in the chemical hydrolysis experiments, was the only surfactant that passed the test for “readily biodegradable”. We also observed a considerable difference in the hydrolysis rate within the small series of gemini surfactants. The amphiphile with two decanoyl chains and a three-carbon spacer, N,N′-bis(2-(decanoyloxy)ethyl)-N,N,N′,N′-tetramethyl-1,3-propanediammonium dibromide, had the fastest rate of hydrolysis. This surfactant also exhibited a considerably lower degree of micelle ionization than the other surfactants, which is believed to be due to the closer proximity of the charged groups on the micelle surface. A small distance between headgroups will give more pronounced neighboring group participation, accounting for the increased rate of hydrolysis. An interesting property of the surfactant that is the most susceptible to hydrolysis is that it gives rise to an extremly stable foam. We propose that the foam stability is a result of the partial hydrolysis of the surfactant generating sodium decanoate, an anionic surfactant, that forms a mixed film with the starting cationic gemini surfactant. It is known that mixed monolayers in which there is a strong attractive interaction between surfactant headgroups can lead to stable foams

Solubilization of two organic dyes by anionic, cationic and nonionic surfactants

In this study, the solubilization of two organic dyes, Sudan I (1-phenylazo-2-naphtol) and Quinizarin (1,4-dihydroxyanthraquinone), was studied in the presence of different types of surfactants (nonionic, anionic, cationic, and nonionic block copolymers) using UV-vis spectroscopy. The effects of temperature, pH and electrolyte on dye solubilization were investigated for single surfactants and for binary surfactant mixtures. The results showed that the solubilization of both dyes in the surfactant micelles increased with the temperature and with addition of salt and that there was no synergy when a mixture of surfactants was used. A straight chain alkyl tail seemed to be better than an alkylaryl tail, as judged from the comparison of solubilization power for the pairs sodium dodecyl sulphate (SDS)/sodium dodecyl benzene sulphonate (SDBS) and penta(ethylene glycol)monoundecyl ether (C11E5)/nona(ethylene glycol)monononylphenyl ether (NPE9). While the solubilization of both dyes in the presence of SOS and C11E5 remained almost the same within the pH interval 3-12, the solubilization of the dyes was much higher above pH 8.2 in the presence of the cationic surfactant dodecyltrimethylammonium bromide. This was attributed to an attractive interaction between the ionized form of the dye and the positively charged head group of the micellized surfactant

Solubilization of two organic dyes by cationic ester-containing gemini surfactants

Solubilization of two different types of organic dyes, Quinizarin with an anthraquinone structure and Sudan I with an azo structure, has been studied in aqueous solutions of a series of cationic gemini surfactants and of a conventional monomeric cationic surfactant, dodecyltrimethylammonium bromide (DTAB). Surfactant concentrations both above and below the critical micelle concentration were used. The concentration of solubilized dye at equilibrium was determined from the absorbance of the solution at lambda(max) with the aid of a calibration curve. The solubilization power of the gemini surfactants was higher than that of DTAB and increased with increasing alkyl chain length. An increase in length of the spacer unit resulted in increased solubilization power while a hydroxyl group in the spacer did not have much effect. Ester bonds in the alkyl chains reduced the solubilization power with respect to both dyes. A comparison between the absorbance spectra of the dyes in micellar solution with spectra in a range of solvents of different polarity indicated that the dye is situated in a relatively polar environment. One may therefore assume that the dye is located just below the head group region of the micelle. Attractive it-cation interactions may play a role for orienting the dye to the outer region of the micelle

Comparison of a Cationic Gemini Surfactant and the Corresponding Monomeric Surfactant for Corrosion Protection of Mild Steel in Hydrochloric Acid

A cationic gemini surfactant, N,N'-didodecyl-N,N,N',N'-tetramethyl-1,4-butanediammonium dibromide (12-4-12) and the corresponding monomeric surfactant dodecyltrimethylammonium bromide were compared with respect to corrosion inhibition efficiency in 1 M hydrochloric acid solution. Polarization and electrochemical impedance spectroscopy were used to evaluate corrosion inhibition. The 12-4-12 surfactant showed an extremely high corrosion inhibition efficiency at very low concentration. Surface tension measurements performed under the strongly acidic conditions revealed that the gemini surfactant is remarkably electrolyte tolerant, which is beneficial for adsorption at the steel surface

Effect of aging time on corrosion inhibition of cationic surfactant on mild steel in sulfamic acid cleaning solution

The stability of the 1 M sulfamic acid solutions containing a gemini cationic surfactant (12-4-12) or its monomeric counterpart (DTAB) during 23 days of storage were studied by electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and surface tension measurements. The EIS studies indicated that in comparison to DTAB solution, 12-4-12 solution considerably retained the corrosion inhibition during the storage period. The surface tension of DTAB solution was increased around 10 mN/m during storage while the surface tension of 12-4-12 solution was almost unchanged. The higher stability of 12-4-12 acidic solution than that of DTAB was also depicted by XRD results

Self-assembled nano structures of cationic ester-containing gemini surfactants: The surfactant structure and salt effects

The aggregation behavior of ester-containing cationic gemini surfactants, dodecyl esterquat and dodecyl betainate geminis was investigated using tensiometry, conductometry, viscometry, dynamic light scattering (DLS), transmission electron microscopy (TEM) and optical microscopy techniques in the absence and presence of NaBr electrolyte. The effect of chemical structure (i.e. the presence of ester bond in alkyl chain and the spacer length) on physicochemical properties and morphology of the surfactants was studied. The results showed that the ester-containing gemini surfactants formed spherical aggregates at dilute concentration (1.1 %wt). At higher concentration (∼3.7 %wt) the morphology is different depending on the position of ester bond in alkyl chain and the spacer length. Dodecyl betainate gemini with short spacer (s = 2) formed gel as a result of the formation of worm-like micelles in the aqueous solution. Dodecyl betainate gemini (s = 3) formed large vesicles enclosing smaller ones and dodecyl esterquat gemini (s = 3) formed both short cylindrical and spherical micelles. The salt addition induced the growth of micelles and in the case of dodecyl betainate (s = 2) gemini changed the morphology from worm-like micelles to lamellar phase

Micelle growth of cationic gemini surfactants studied by NMR and by time-resoved fluorescence quenching

The micelle growth of a series of five cationic gemini surfactants has been investigated by time-resolved fluorescence quenching (TRFQ) and by two NMR techniques, line width analysis and diffusometry. The surfactant series was designed such that the effect of a number of variables could be assessed: length of the spacer unit, presence of ester bonds in the tails close to the head groups, and presence of a hydroxyl group in the spacer. For the gemini with long spacer, the micelles remained relatively small in size upon an increase of the concentration. The gemini surfactants with short spacer, on the other hand, showed a considerable micellar growth as the concentration was raised. It is of particular interest that the relatively simple line width analysis of one dimensional H-1 NMR spectra gave qualitatively the same results as the more sophisticated TRFQ and NMR diffusometry techniques

An Ouzo Emulsion of Toluene in Water Characterized by NMR Diffusometry and Static Multiple Light Scattering

An Ouzo emulsion is an emulsion that is formed spontaneously by adding water to a system comprising a hydrophobic substance (like anethole in the Ouzo beverage), a water-miscible solvent and (optionally) water. Formation of such an emulsion does not require the use of surfactants, dispersing agents, or mechanical agitation. In this work, Ouzo emulsions were prepared from the ternary mixture toluene-ethanol-water and the emulsion stability was studied by a combination of two techniques: static multiple light scattering and NMR diffusometry. A bimodal distribution of the droplets was found. The light scattering technique revealed the presence of large drops, several micrometer in size. NMR measurements confirmed the large drops but also showed the additional presence of droplets of the order of 100 nm in diameter. The distribution of toluene between the three environments (i) large drops, (ii) small droplets, and (iii) the continuous ethanol-water phase could also be assessed. It was found that addition of an anionic surfactant to the system yielded an improved dispersed system, i.e., more toluene was present as small droplets and less toluene was dissolved in the ethanol-water phase; however the presence of the amphiphile reduced the emulsion stability. (C) 2016 Elsevier B.V. All rights reserved

Mesoscopically Ordered Bone-Mimetic Nanocomposites

A sustainable approach that highly mimics bone-material deposition is reported to produce mechanically stable, degradable composites with nanostructures resembling that of natural bone. Molecular self-assembly combining intermolecular crosslinking leads to resilient matrices possessing long-range ordered aqueous domains, inside which moderately aligned poorly crystalline apatite is converted from the transient amorphous calcium phosphate phase