Kinetics of the self-assembly of gemini surfactants (original) (raw)
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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.
Structure of cationic surfactant micelles from molecular simulations of self-assembly
2010
Molecular dynamics simulations of self-assembly of n-decyltrimethylammonium bromide surfactants were performed using an atomistic model, and a detailed analysis of the spontaneously formed micellar aggregates was carried out. This allowed for a detailed study of the structure of cationic surfactant micelles free from any a priori assumptions regarding their size and shape. Atomic radial distribution functions, radial density profiles and bivariate water orientation distributions were computed. Together, they show the presence of a dry micelle core, with a hydrophobic environment similar to a liquid alkane, a well-defined head-group layer at the interface, and an outer layer of strongly bound bromide counterions. Water molecules penetrate the micelle as far as the innermost head site, adopting a sequence of orientations that is akin to that observed at planar interfaces with vapor or immiscible organic solvents. Water molecules at the exterior of the micelle are highly polarized by the electrical double-layer formed by cationic head-groups and bromide anions, orienting themselves with their dipole vector pointing towards the micelle core.
Universal Behaviour of the Structure and Dynamics of Micelles Formed from Cationic Surfactants
Zeitschrift für Physikalische Chemie, 2014
A systematic study of the aggregation behavior of alkyl trimethyl ammonium bromide surfactants as a function of concentration, temperature and alkyl chain length is presented based on small angle neutron scattering as well as Raman scattering. The variation of structural parameters of the micelles, their dissociation and the conformation of surfactant molecules within the micelles are quantitatively determined. All surfactant systems exhibit a universal behavior if described on a renormalized temperature scale. This finding is associated with the proximity of phase transitions into gel and solid phases.
Journal of Chemical & Engineering Data, 2011
A series of symmetrical cationic gemini surfactants of the type N,N 0-didodecyl-N,N,N 0 ,N 0-tetramethylalkane-R, ω-diammonium dibromide "12-s-12" (s = 2, 4, 6, 8, 10, and 12) are synthesized, and their micellization study in aqueous solution is systematically reported. Specific conductivity as a function of surfactant concentration was measured, and critical micelle concentration (CMC), degree of counterion dissociation (R) of the micelle, and thermodynamic parameters, namely, Gibbs energy (ΔG m), enthalpy (ΔH m), and entropy (ΔS m), of micellization were evaluated using this data at various temperatures. Surface tension studies at 298.15 K provided similar CMCs as given by conductometry along with information on the efficiency/ effectiveness and the area occupied per molecule. Small-angle neutron scattering (SANS) inferred the presence of few morphological geometries ranging from spherical to rodlike micelles. Results are explained in terms of the hydrophobicity of spacer chain length along with the electrostatic repulsion between the cationic centers of gemini surfactant molecules.
Gemini surfactants with short linkers: thermodynamics of Micelle formation
Journal of thermal analysis and calorimetry, 2024
We have been investigating the physical properties of simple Gemini surfactant with short linker chains using conductivity, dynamic light scattering (DLS) and isothermal titration calorimetry (ITC). The surfactants used here have the general formula (CH 3 (CH 2) 11)(CH 3) 2-N +-(CH 2) n-N + (CH 3 (CH 2) 11)(CH 3) 2 ·Br 2 , where n = 2, 3 or 4 and, as such, are designated as 12-2-12, 12-3-12 and 12-4-12. The ultimate goal of this work was to determine the enthalpy of demicellization using ITC. To determine the proper experimental conditions, it was necessary to first determine the critical micelle concentration (cmc) using conductivity and the size of the formed micelles using DLS for each surfactant. The results indicate a number of linear relationships between the number of carbons in the linker and certain physical properties such as cmc and ΔG mic as determined by conductivity studies. As expected, demicellization is enthalpically unfavorable but entropically driven. Linear relationships are also observed between the number of linker carbons and some thermodynamic properties as determined by ITC.
Quantifying the micellar structure formed from hydrocarbon-fluorocarbon surfactants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016
Many technological formulations contain mixtures of surfactants, each contributing some distinct property. Characteristics of each surfactant are often modulated in the mixture, based on the interactions between the various components present. Here, the mixing of the hydrocarbon surfactant cetyltrimethyl ammonium bromide (C16TAB) and the fluorocarbon surfactant, Zonyl-FSN-100 with average chemical structure of C8F17C2H4 (OC2H4)9OH, is quantified, in particular, the size and shape of the micelles and their critical micelle concentration (CMC). The CMC data suggest there are specific interactions between the two components which are strongly antagonistic. Small-angle neutron scattering (SANS) has been used to quantify the size and shape of the micelle, and these data indicate that the single component FSN-100 forms disc-like micelles with a small aggregation number (~65) and the C16TAB forms globular, charged micelles with a larger aggregation number (135). The aggregation number of the mixed micelle formed by in the mixed case is substantially
Micellization of binary systems of a cationic gemini surfactant butanediyl-1,4-bis(dimethylcetylammonium bromide) (16-4-16) and cationic/nonionic hydrotropes (aniline-hydrochloride, 2-methylanilinehydrochloride, 4-methylanilinehydrochloride, hydroxybenzene, 1,3-benzenediol, benzene-1,2,3-triol) have been studied using a conductometric technique. The critical micelle concentrations (cmc) for different mixing mole fractions at different temperatures have been calculated. To explain and compare the results, theoretical models of Clint, Rubingh and Motomura have been used to obtain the ideal cmc, mixed micelle composition, interaction parameters (b m ), free energies of micellization, and activity coefficients. The mixtures show nonideal behavior and the interactions between the surfactants and the hydrotropes are synergistic in nature which is confirmed by high negative b m values and low values of the activity coefficients. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values.
Studies of mixed micelle formation between cationic gemini and cationic conventional surfactants
Journal of Colloid and Interface Science, 2008
Mixed micellization of dimeric cationic surfactants tetramethylene-1,4-bis(hexadecyldimethylammonium bromide)(16-4-16), hexamethylene-1,6-bis(hexadecyldimethylammonium bromide) (16-6-16) with monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC), and tetradecyltrimethylammonium bromide (TTAB) have been studied by conductivity and steady-state fluorescence quenching techniques. The behavior of mixed systems, their compositions, and activities of the components have been analyzed in the light of Rubingh's regular solution theory. The results indicate synergism in the binary mixtures. Ideal and experimental critical micelle concentrations (i.e., cmc * and cmc) show nonideality, which is confirmed by β values and activity coefficients. The micelle aggregation numbers (N agg), evaluated using steady-state fluorescence quenching at a total concentration of 2 mM for CTAB/16-4-16 or 16-6-16 and 5 mM for TTAB/16-4-16 or 16-6-16 systems, indicate that the contribution of conventional surfactants was always more than that of the geminis. The micropolarity, dielectric constant and binding constants (K sv) of mixed systems have also been evaluated from the ratios of respective peak intensities (I 1 /I 3 or I 0 /I 1).
Journal of Surfactants and Detergents, 2013
New dimeric surfactants [16-s-16, s: (CH 2 ) 4 ; CH 2 -COO-(CH 2 ) 2 -OCO-CH 2 ; CH 2 -COO-ISO-OCO-CH 2 (ISO = D-isorbide) and CH 2 -CONH-(CH 2 ) 2 -NHCO-CH 2 ] were synthesized and characterized (I-IV, respectively). The micellization behavior of dimeric surfactants with various spacers was studied by conductance/steady-state fluorescence quenching (SSFQ) measurement and compared with the conventional surfactant (cetyltrimethylammoniumbromide, CTAB). The critical micelle concentration (CMC) values of several surfactants were found to be nearly the same by both techniques. Conductance measurements were used exclusively to obtain CMC and degree of dissociation (a) values at various temperatures, while SSFQ measurements were used to obtain a few CMC values (for comparison) and an aggregation number (N agg ). A decrease in CMC and N agg values and an increase in a were observed for dimeric surfactants when compared with CTAB. CMC decreases and then increases with a continuous increase in temperature (U-shaped behavior). The temperature of minimum CMC, T m , was distinctly different for CTAB and the dimeric surfactants. T m values were dependent on the nature of the spacer. The temperature dependence of CMC and a value was used to calculate the thermodynamic parameters of micelle formation for two classes of surfactant (conventional and dimeric). Enthalpyentropy compensation plots exhibited fair linearity except for IV. Compensation lines for spacers containing ester groups are parallel to one another. Micro-polarity and apparent dielectric constant (e a ) data suggest that the micellar environment felt by pyrene is similar to that of an alkanol with a 3-4 carbon chain. Scheme 1 Chemical structures of cetyl trimethyl ammonium bromide (CTAB) and dimeric surfactants (I-IV) J Surfact Deterg (2013) 16:739-749 741 J Surfact Deterg (2013) 16:739-749 749