An interplay between spacer nature and alkyl chain length on aqueous micellar properties of cationic Gemini surfactants: A multi-technique approach (original) (raw)
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Journal of Molecular Liquids
Series of quaternary ammonium-based gemini surfactants with long alkyl chains (C12 and C18) containing different spacers and substituents attached to the polar head group have been synthesized and their aggregation properties in aqueous solution examined. The effect of the hydrophobic chain, the nature and structure of the spacer group and the polarity of the head group on the aggregation behavior of such dimeric surfactants has been investigated. The critical micelle concentration (cmc) values of gemini surfactants in aqueous solution were determined by conductivity, steady state fluorescence and potentiometric measurements. The size of aggregates formed by investigated amphiphiles above the cmc in aqueous solution was examined by dynamic light scattering. Gemini surfactants show cmc values significantly lower than those of comparable single chain surfactants. The tendency of trimeric surfactants with a rigid spacer to form aggregates is higher than that of the corresponding dimeric surfactants. As occurs for monomeric ionic surfactants, the cmc of gemini surfactants decreases with the elongation of the hydrophobic chain. However, the effect of lengthening the alkyl chain on the cmc depends on the structure of the spacer. C12 gemini surfactants with a rigid hydrophobic spacer exhibit cmc higher than those containing a flexible hydrophobic spacer. For gemini surfactants with C18 alkyl chains this effect is even more pronounced and leads to differences in cmc values greater than one order of magnitude. The structure of the spacer, flexible or rigid chain, has been found to be a critical parameter on the self-assembly of long chain gemini surfactants. Spherical micelles are spontaneously formed above the cmc for C12 gemini surfactants, whereas trimeric and C18 gemini surfactants seems to form vesicle-like aggregates when self-aggregation occurs.
Industrial & Engineering Chemistry Research, 2013
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,Ndimethylammonium 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.
Microcalorimetric studies of cationic gemini surfactant with a hydrophilic spacer group
Thermochimica Acta, 2005
The aim of this work is to investigate the micellization thermodynamics for gemini surfactants with a hydrophilic spacer group, i.e. Br − n-C 12 H 25 N + Me 2 CH 2 (CH 2 OCH 2) x CH 2 N + Me 2 n-C 12 H 25 Br − , referred to as 12-EO x-12, where x = 1, 3, 6, 7. These oligooxaalkanediyl-␣,bis(dimethyldodecylammonium bromide) dimeric surfactants were synthesized by a two step reaction. Their physicochemical properties in aqueous solutions have been studied by microcalorimetry at 298 K, electrical conductivity and surface tension measurements. The critical micellar concentration (cmc) and the head-group area (a 0) per molecule at the air-water interface increase with increasing number of oxide ethylene moieties in the spacer and, consequently, with the enhanced hydrophilic character of the molecule. The calorimetric studies of the self-assembly process confirm this trend, since the exothermic values of the differential enthalpy of micellization (mic H •) decrease as the ethylene oxide moieties are lengthened. Moreover, the values of the free energy and entropy of micellization indicate an entropy driven phenomenon for all surfactants. These results are compared with those obtained for gemini cationic surfactants with a hydrophobic spacer and the differences observed are discussed in terms of the hydrophilic head-group conformation in the micelle.
Surface activity and micellar properties of anionic gemini surfactants and their analogues
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004
The properties of didodecyldiphenylether disulfonate gemini-type surfactants have been studied and compared to mono-alkylated and monosulfonated analogous surfactants. Dynamic and equilibrium surface tension measurements indicate that the gemini surfactants have a higher surface activity compared to that of the monoalkyl analogues. The gemini-type surfactants have much larger surface area per molecule, opposite effect of carbon number on CMC and considerable swelling of the micelles upon increasing surfactant concentration. Determination of aggregation numbers by fluorescence measurements reveals that the longer chain gemini surfactants form micelles having less than 10 molecules per micelle.
Interaction Between Cationic Gemini and Monomeric Surfactants: Micellar and Surface Properties
Attraction effects in the mixed micelle of gemini (C 16 -12-C 16 , 2Br − and monomeric surfactants i.e., cetyltrimethylammonium bromide (CTAB), cetyltriphenylphosphonium bromide (CTPB) and cetyltributylphosphonium bromide (CTBuPB) mixtures in aqueous solution were investigated by conductivity and surface tension measurements. The attractive interaction of surfactants in the mixed micelle leading to non-ideality has been theoretically treated by Clint's and Rubingh's model in the light of regular solution theory. The experimental critical micelle concentration (cmc) values were lower than predicted from ideal mixture theory. The negative values of interaction parameters ( m and for mixed micelle formation indicate the attractive interaction for all the systems. The Motomura's theory was used to determine the composition of each compound in mixed micelles (X ideal . The excess free energy of the mixed systems was also calculated and the obtained negative values for all the mixed systems studied gave an indication that the mixed micelles are thermodynamically more stable relative to the individual component.
Gemini Surfactants with Acetylenic Spacers
Langmuir, 2000
A total of 24 dicationic geminis surfactants were synthesized, having a 2-butynyl spacer and chain lengths varying from 8 to 18 carbons. Geminis with more flexible butyl spacers were also synthesized for comparison purposes. Tensiometry gave critical micelle concentration (cmc) values, surface activity, and Gibbs areas. Film studies on the C18 geminis gave liftoff and collapse areas. The acetylenic geminis behave normally with the log cmc values decreasing linearly with chain length for all the dibromide salts. Anomalous behavior occurred, however, with the C18 gemini having a butyl spacer. It was found that cmc data correlate with spacer area, a relationship ascribed to packing constraints on curved surfaces and, possibly, to steric inhibition of ion binding. The effects are accentuated with the C18 surfactants. Geminis with heterocyclic headgroups were examined.
Canadian Journal of Chemistry, 2018
The micellar and morphological properties of symmetric, cationic gemini surfactants have been well studied in the literature as a function of nature and type of the spacer group and the length and type of hydrophobic chain. In this paper, we have examined the effects of tail asymmetry on the properties of a series of cationic surfactants, the N-alkyl-1-N′-alkyl-2-N,N,N′,N′-tetramethyldiammonium dibromide. A novel synthetic method is used to prepare a series of these surfactants and the consequences of asymmetry on micellar properties are presented. This new method has been shown to be more efficient, with higher yields of the asymmetric surfactants than the yields of the accepted literature method. The critical micelle concentration values and the micelle sizes of the asymmetric gemini surfactants, 12-4-12, 12-4-10, 12-4-8, and 12-4-6 gemini surfactants, were obtained from conductivity and dynamic light scattering. With increasing chain asymmetry, the size of the micelle increased d...
Effect of the spacer length on the association and adsorption behavior of dissymmetric gemini surfactants, 2004
A series of dissymmetric gemini surfactants with the general formula [C 12 H 25 (CH 3) 2 N(CH 2) s N(CH 3) 2 C 14 H 29 ]Br 2 designed as 12-s-14, where s = 2, 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12-s-14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length.
Journal of Colloid and Interface Science, 2005
The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization (β ave), minimum area per molecule of surfactant at the air-water interface (A min), surface excess concentration (Γ max), and Gibb's free energy of micellization (G mic) of the surfactants were determined from conductance and surface tension data. The aggregation numbers (N), dimensions of micelles (b/a), effective fractional charge per monomer (α), and hydration of micelles (h E) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, β ave , and G mic and an increase in N and b/a. This is well supported by the observed increase in hydration (h E) of micelles with increase in aggregation number (N) and dimension (b/a) of micelle.