Self-Assembly Properties of Cationic Gemini Surfactants with Biodegradable Groups in the Spacer (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.
Aggregation Properties of Cationic Gemini Surfactants in Aqueous Solution
2002
New cationic gemini surfactants bearing two hydrogen methanesulphonate groups and two longchain alkyl groups (octyl, dodecyl or hexadecyl) were prepared in good yields by the reaction of N,N'-bis-alkyl,N,N'-bis(3-aminopropyl)ethylenediamine with methanesulphonic acid. All of these gemini salts showed good water solubility. Their aggregation ability in water has been determined by steady-state fluorescence spectroscopy. Furthermore, the micellar properties for the concentration near above the cmc have been characterized by the aggregation number, N agg. The presence of the dimeric segments in the surfactant molecule is found to be in charge of their unusual physicochemical behavior. They are very efficient at adsorbing at the free surface and at forming micelles in water. Accordingly, both the micelle-forming property, and the ability to lower the surface tension increased with the increase in the length of the hydrophobic chain. The studied surfactants were found to form stable and reproducible n-tetradecane emulsions, for which the multimodal size distribution, effective diameter and zeta potential in the system: n-tetradecane/water/surfactant IVa-c have been determined.
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.
Kinetics of the self-assembly of gemini surfactants
Journal of Surfactants and Detergents, 2004
A stopped-flow technique combined with pulsed-field-gradient spin-echo nuclear magnetic resonance (NMR) measurements was used to study the kinetics of exchange, size, and shapes in micellar systems of cationic surfactant dimers of the alkanediyl-α-ω-bis(dodecyldimethylammonium bromide) type, with alkanediyl being 1,2-ethylene, 1,3-propylene, and 1,4-butylene. By measuring the slow relaxation time for micelles, τ 2 , the micelle lifetime as a function of spacer length was obtained and was further confirmed by micelle exchange measurements by NMR diffusometry. The micelle lifetimes for the gemini surfactants were found to be in orders of magnitude longer than for the corresponding conventional surfactants. All three cationic surfactant dimers showed an increase in micelle size in one direction, i.e., became prolates, as the concentration was increased. The growth of the micelles was most pronounced for the gemini surfactants with the shortest linker unit, i.e., ethylene.
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.
Journal of Photochemistry and Photobiology A-chemistry, 2011
The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2 -12,2Br − with hydroxyl substituted spacer group have been studied. The changes in photophysical properties of a single probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) showing dipolar nature in its twisted intramolecular charge transfer (TICT) excited state have been exploited rather than using multiple probes to describe various properties of micellar aggregates. Formation of a number of premicellar aggregates has been demonstrated in addition to the description of the micropolarity and the microviscosity of environment using steady-state fluorescence spectroscopy and fluorescence anisotropy of DMASBT. Conductometric measurements have been carried out to determine degree of micellar ionization (˛) and to verify critical micelle concentration (CMC) values estimated by fluorescence method. Hydroxyl substituted spacer group induces the formation of premicellar aggregates. The micropolarity of environment around probe molecules increases on going from premicellar to micellar aggregates. The growth of micellar aggregates has been demonstrated by a continuous increase in the microviscosity of environment. The micropolarity of micellar environment of 12-4(OH) 2 -12 is found to be less than that of 12-3(OH)-12. The microviscosity of premicellar and micellar aggregates of 12-4(OH) 2 -12 are higher than that of 12-3(OH)-12. CMC increases, whereas ˛ decreases with increasing spacer chain length as well as number of hydroxyl substitution of a spacer group.
Colloids and Surfaces A: Physicochem. Eng. Aspects, 2019
Novel cationic gemini surfactants - pentanediyl-1,5-bis[mono(2-hydroxypropyl) alkylammonium] dibromide and pentanediyl-1,5-bis[di(2-hydroxypropyl) alkylammonium] dibromide {in the abbreviation form - CnC5Cn[iso-Pr(OH)] and CnC5Cn[iso-Pr(OH)]2; alkyl - CnH2n+1 with n = 8, 9, 12 and 16} were synthesized. Surface tension, electroconductivity and dynamic light scattering methods were applied to study aggregation properties of these surfactants in aqueous medium. By tensiometric method it was established that, at two studied concentrations in water, the synthesized gemini surfactants form aggregates. This occurs well below the critical micelle concentrations (CMC) of these surfactants. The influence of the length of the surfactants alkyl chain and the number of the 2-hydroxypropyl fragments in the head group on the surface activity parameters and binding degree of the counterion has been studied. By dynamic light scattering method, the impact of the number of the 2-hydroxypropyl groups in the gemini surfactants with C12–chain on the micelles sizes at the concentrations higher than CMC has been investigated. It was revealed that the synthesized surfactants possess an antimicrobial property.
Gemini surfactants: A distinct class of self-assembling molecules
2002
Gemini surfactant is the family of surfactant molecules possessing more than one hydrophobic tail and hydrophilic head group. These surfactants usually have better surface-active properties than corresponding conventional surfactants of equal chain length. Geminis are used as promising surfactants in industrial detergency and have shown efficiency in skin care, antibacterial property, metal-encapped porphyrazine and vesicle formation, construction of highporosity materials, etc. This review deals with synthesis, structure, critical micellar concentration, surface active properties and uses of geminis.
Journal of Photochemistry and Photobiology A: Chemistry, 2011
The micellar aggregation behavior and micropolarity characteristics of a series of N,N-bisalkyl-N,N-bis[(3-d-aldonylamido)propyl]ethylenediamines referred to as gemini bis(C n X) surfactants (where C n = n-butyl, n-octyl, n-decyl and n-dodecyl; X = gluconyl and lactobionyl, denoted as GA and LA, respectively) has been investigated by steady-state fluorescence, SSF (by emission spectra of pyrene) and time-resolved fluorescence quenching, TRFQ (using pyrene as the fluorescence probe and cetylpyridinium ion as the fluorescence quencher). Remarkably low magnitude cmc values were found for the studied aldonamide-type gemini surfactants, in a range from 4.5 × 10 −6 M (bis(C 12 GA)) to 2.3 × 10 −3 M (bis(C 4 LA)). The variation of cmc for bis(C n LA) (n = 4, 8, 10 and 12) follows a linear semi-logarithmic pattern. The obtained I 1 /I 3,c > cmc ratios from 1.41 to 1.5 indicate a considerable high polarity sensed by pyrene in micelles of bis(C n X), dependent upon both the kind of aldonyl entity, and the length of hydrophobic tail. According to TRFQ, all studied systems display micellar growth (demonstrated by values of an average aggregation number of surfactant chains per micelle) with increasing surfactant concentration typically from 100 up to 1000 times more than the cmc. The aggregation numbers, N agg (N tail) and the "polydispersity index", /N ω (less than ∼0.3), show that micelles of bis(C n LA)'s of up to ca. 500cmc, are nearly spherical and almost monodisperse. Their spheroidal micelle growth and enhanced micellar polydispersity is observed as the surfactant concentration increases. Such a behavior was found to be strictly related to geometric aspects of a given surfactant dimeric structure.