Raoul Zana

Dimeric and Oligomeric Surfactants. Behavior at Interfaces and in Aqueous Solution : a review

Dimeric and oligomeric surfactants are novel surfactants that are presently attracting considerable interest in the academic and industrial communities working on surfactants. This paper first presents a number of chemical structures that have been reported for ionic, amphoteric and nonionic dimeric and oligomeric surfactants. The following aspects of these surfactants are then successively reviewed the state of dimeric and oligomeric surfactants in aqueous solutions at concentration below the critical micellization concentration (cmc); their behavior at the air/solution and solid/solution interfaces; their solubility in water, cmc and thermodynamics of micellization; the properties of the aqueous micelles of dimeric and oligomeric surfactants (ionization degree, size, shape, micropolarity and microviscosity, solution microstructure, solution rheology, micelle dynamics, micellar solubilization, interaction between dimeric surfactants and water-soluble polymers); the mixed micellization of dimeric surfactants with various conventional surfactants; the phase behavior of dimeric surfactants and the applications of these novel surfactants.

Effect of alcohol on the properties of micellar systems: I. Critical micellization concentration, micelle molecular weight and ionization degree, and solubility of alcohols in micellar solutions

Additions of alcohols of medium chain length (butanol to hexanol) to micellar solutions result in a decrease of critical micelle concentration and micelle molecular weight, and an increase of the micelle ionization degree. Moreover, the micelle molecular weight (or surfactant aggregation number) at a given alcohol concentration increases with the surfactant concentration and may reach values larger than in the absence of alcohol. Striking differences have been found in the changes of molecular weight of TTAB micelles in H/sub 2/O-pentanol mixtures in the presence of 0.1 M KBr and in the absence of salt. These various results have been explained by considering the effect of the micelle solubilized alcohol on the micelle surface charge density and on the dielectric constant of the palisade layer. 48 references.

Branched Threadlike Micelles in an Aqueous Solution of a Trimeric Surfactant

Very long threadlike micelles observed in aqueous solutions of some surfactants have attracted much attention because of the peculiar rheological properties of these systems. Molecular dynamics simulations have suggested that branched threadlike micelles should exist in concentrated solutions of dimeric surfactants. Here experimental evidence, obtained from transmission electron microscopy at cryogenic temperature, is presented of branched threadlike micelles in aqueous solutions of a triquaternary ammonium (trimeric) surfactant made up of three amphiphilic moieties connected at the level of the head-groups by two propanediyl spacers.

Gemini (dimeric) surfactants

Recent years have seen significant advances in the field of gemini (dimeric) surfactants. First, the effects of the length and nature of the spacer group on the behavior of gemini surfactants at the air/solution interface, on the shape of their micelles, and on the solution rheology and microstructure have been characterized. Second, dimeric surfactant containing systems have been theoretically approached. The particular behavior of such systems has been explained in part and interesting predictions made. Last, studies of the phase behavior of dimeric surfactants and of their mixed micellization with conventional surfactants have been initiated. These surfactants appear to hold promise for the future.

Simulating the Self-Assembly of Gemini (Dimeric) Surfactants

The morphologies and dynamics of aggregates formed by surfactant molecules are known to influence strongly performance properties spanning biology, household cleaning, and soil cleanup. Molecular dynamics simulations were used to investigate the morphology and dynamics of a class of surfactants, the gemini or dimeric surfactants, that are of potential importance in several industrial applications. Simulation results show that these surfactants form structures and have dynamic properties that are drastically different from those of single-chain surfactants. At the same weight fraction, single-chain surfactants form spherical micelles whereas gemini surfactants, whose two head groups are coupled by a short hydrophobic spacer, form thread-like micelles. Simulations at different surfactant concentrations indicate the formation of various structures, suggesting an alternative explanation for the unexpected viscosity behavior of gemini surfactants.

Recent advances in the formation mechanisms of organized mesoporous materials

Since the discovery of the organized mesoporous solids by Mobil Oil Co. scientists, numerous patents and papers dealing with the synthesis, mechanisms of formation, properties and applications of these exciting solids have been published. A better understanding in the mechanisms of formation has been achieved through the use of in situ techniques of investigation. It appears that the mechanism depends much on the experimental conditions of synthesis. Even if the interaction between the inorganic precursor and the organic template is the key factor in the control of the formation of these materials, none of the proposed mechanisms provides an exclusive and definitive answer.

Light scattering investigations of the behavior of semidilute aqueous micellar solutions of cetyltrimethylammonium bromide: Analogy with semidilute polymer solutions

Micellar solutions of cetyltrimethylammonium bromide (CTAB) in H2O-0.1 M KBr and H2O-0.25 M KBr have been investigated up to high concentrations, in the semidilute range, by means of elastic and quasielastic light scattering, with particular emphasis on the effect of the scattering wave vector on both the intensity of scattered light and collective translational diffusion coefficient. All the results could be intepreted in terms of theories used to describe the behavior of solutions of long flexible polymer chains in the semidilute range, i.e., when the polymer coils overlap forming a network. The concentration dependences of the scattered intensity and collective diffusion coefficient extrapolated to zero wave vector were found to follow the power laws derived for semidilute polymer solutions in good solvent. These results give a strong support to a model of long flexible entangled micelles in aqueous CTAB solutions in the presence of 0.1 or 0.25 M KBr.

Aggregation behavior of mixed fluorocarbon and hydrocarbon surfactants in aqueous solutions

The aggregation behavior of lithium perfluorooctanesulfonate (LiFOS), of mixtures of LiFOS with lithium dodecyl sulfate (LiDS) and with octa- and hexaoxyethylene glycol dodecyl ether (C12E8 and C12E6), and of C12E6LiDS in aqueous solutions has been investigated by means of pyrene fluorescence probing. For the pure LiFOS, the micelle aggregation number N as obtained from the analysis of the fluorescence decay of micelle-solubilized pyrene in the presence of a micelle-solubilized quencher was found to increase considerably with the surfactant concentration. In these micelles, pyrene is located very close to, or at, the micelle surface. The measurements of the pyrene fluorescence lifetime τ0 and of the ratio I1I3 of the intensities of the first and third bands of the pyrene monomer fluorescence spectrum appear to indicate that only one type of mixed micelle exists in the mixed systems LiDSLiFOS, C12E6LiFOS, and C12E8LiFOS. The micelle aggregation numbers for these three systems have been determined as has that for the C12E6LiDS system. They decrease as the mole fraction of LiFOS in the first three systems is increased. The evidence for probe intermicellar migration in the C12E6-containing mixed systems has been obtained. This migration is inhibited by the incorporation of LiFOS or LiDS in C12E6 micelles.

Alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants (dimeric surfactants). Part 6. CMC of the ethanediyl-1,2-bis (dimethylalkylammonium bromide) series

Abstract Recently, Dam et al. (Colloids and Surfaces A 118 (1996) 41) reported that dynamic surface tension did not permit them to observe the CMC of two dimeric surfactants, one of them being ethanediyl-1,2-bis(dimethyltetradecylammonium bromide) (14-2-14). We report that the CMC of this surfactant and of its longer chain homologue 16-2-16 show as a sharp break in the plots of the pyrene fluorescence intensity ratio I 1 I 3 and of the conductance versus 14-2-14 concentration. The CMC had previously been detected for the shorter homologues 12-2-12 and 8-3-8. The plot of log CMC versus carbon number is very close to linear, indicating very little premicellar association for the 16-2-16 surfactant, contrary to other series of dimeric surfactants with different spacers.

Network properties of semidilute aqueous KBr solutions of cetyltrimethylammonium bromide

Abstract Elastic and quasi-elastic light scattering and rheological (shear viscosity, viscoelastic relaxation time) measurements have been performed on cetyltrimethylammonium bromide (CTAB) aqueous solutions, in the presence of 0.1 or 0.25 M KBr, at surfactant concentrations where the micelles are very elongated, and between 20 and 60°C. The results provide additional evidence for the previously noted analogy of behavior between concentrated solutions of very elongated micelles and solutions of polymer chains in the semidilute range where the chains are entangled. The results confirm that the micelles keep growing when the surfactant concentration exceeds the cross-over concentration where the micellar domains overlap. The power laws governing the rheological behavior of semidilute polymer solutions all apply to the micellar systems investigated when the micelles are sufficiently elongated. This appears to be the case for CTAB solutions at concentrations above 0.3 M , in the presence of 0.1 M KBr or more, and temperatures below about 35°C.