Dynamics of micelles of the triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in aqueous solution.

A number of results reported on the kinetics of exchange of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, between micelles and the intermicellar aqueous solution are reviewed and analyzed to extract the rate constants k(+) for the entry of a copolymer into a micelle and k(-) for the exit of a copolymer from a micelle. Contrary to what is generally observed for conventional surfactants, the rate constant for the entry of a copolymer into a micelle is slower to much slower than for a diffusion-controlled process and decreases as the degree of polymerization of the PO block, n(PO), increases. The effect of the degree of polymerization of the EO block, n(EO), on the two rate constants is significant only for low values of n(EO).

Effect of the nature of the counterion on the properties of anionic surfactants. 5. Self-association behavior and micellar properties of ammonium dodecyl sulfate.

Micelles formed in water from ammonium dodecyl sulfate (AmDS) are characterized using time-resolved fluorescence quenching (TRFQ), electron paramagnetic resonance (EPR), conductivity, Krafft temperature, and density measurements. TRFQ was used to measure the aggregation number, N, and the quenching rate constant of pyrene by dodecylpyridinium chloride, k(Q). N depends only on the concentration (C(aq)) of ammonium ions in the aqueous phase whether these counterions are derived from the surfactant alone or from the surfactant plus added ammonium chloride as follows: N = N0(C(aq)/cmc0)(gamma), where N0 is the aggregation number at the critical micelle concentration in the absence of added salt, cmc0, and is equal to 77, 70, and 61 at 16, 25, and 35 degrees C, respectively.

Effect of the nature of the counterion on the properties of anionic surfactants. 4. Characterizing micelles of tetraalkylammonium dodecyl sulfate as reaction media.

Micelles formed in water from tetramethyl-, tetraethyl-, tetrapropyl- and tetrabutylammonium dodecyl sulfate (TMADS, TEADS, TPADS, and TBADS, respectively) are characterized as reaction media. All of the results are identical in the presence or absence of added salt, provided micelles of the same aggregation number, N, are compared. The microviscosity (eta) deduced from the rotational motion of the nitroxide group of a spin probe increases modestly as a function of N in TMADS and TEADS, decreases slightly in TPADS, and decreases slightly before increasing in TBADS.

A reinterpretation of the hydration of micelles of dodecyltrimethylammonium bromide and chloride in aqueous solution.

The hydration of dodecyltrimethylammonium (DTAB) micelles is reinterpreted in light of the results of the companion paper (immediately preceding this paper) that showed that the location of the spin probe 16-doxylstearic acid methyl ester (16DSE) changes as a function of the aggregation number, N, of anionic micelles, i.e, that it does not conform to the zero-order model (ZOM). The ZOM requires that the NO(*) moiety diffuse throughout the Stern layer of the micelle and nowhere else.

Partial phase behavior and micellar properties of tetrabutylammonium salts of fatty acids: unusual solubility in water and formation of unexpectedly small micelles.

The tetrabutylammonium (TBA) salts of fatty acids, from dodecanoic acid (C12) to octacosanoic acid (C28), have been prepared by direct neutralization of the fatty acid by TBA hydroxide. Unexpectedly, all of these surfactants have been found to be soluble in water under the form of micelles at a sufficiently high temperature. For instance, the solubility of TBA octacosanoate in water is of about 7 wt % at 46 degrees C.

Adsorbed layer structure of cationic gemini and corresponding monomeric surfactants on mica.

We report a comprehensive study of the adsorbed layer morphologies of cationic gemini surfactants of the type dodecanediyl-alpha,omega-bis(dimethylalkylammonium bromide) and their corresponding monomers, dimethyldodecylalkylammonium bromide, on mica using atomic force microscopy soft-contact imaging. As in the bulk, aggregate curvature of the adsorbed geminis is found to increase with increasing spacer length, but the adsorbed aggregate curvature also increases in the presence of CsCl and CsBr. The monomeric surfactants exhibit an unexpected transition from globular adsorbed aggregates to a bilayer when the alkyl side chain reaches butyl, and this transition is also sensitive to added electrolyte.

Tetrabutylammonium alkyl carboxylate surfactants in aqueous solution: self-association behavior, solution nanostructure, and comparison with tetrabutylammonium alkyl sulfate surfactants.

A series of long and ultralong chain tetrabutylammonium alkyl carboxylate (TBACm, TBA = tetrabutylammonium ion; Cm = carboxylate ion C(m-1)H(2)(m-1)CO(2)(-) of total carbon number m) surfactants have been obtained by direct neutralization of the fatty acids with m = 12, 14, 18, 22, and 24 by tetrabutylammonium hydroxide. Time-resolved fluorescence quenching has been used to determine the micelle aggregation number (N) of the surfactants with m = 12, 14, and 18 in the temperature range 10-50 degrees C and of the surfactants with m = 22 and 24 in the temperature range 25-60 degrees C. In all instances the values of N were well below those that can be calculated for the maximum spherical micelle formed by surfactants with the same alkyl chain as the investigated surfactants on the basis of the oil drop model for the micelle core.

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants: II. Krafft temperature and melting temperature.

The melting temperature T(M) of two series of dimeric (gemini) surfactants, the alkanediyl-alpha,omega-bis(dodecyl and hexadecyl dimethylammonium bromide), referred to as 12-s-12 and 16-s-16, respectively (s = carbon number of the alkanediyl spacer), and the Krafft temperature T(K) of 1 wt% aqueous solutions of these surfactants have been measured. The melting temperature of the solid surfactant increases with the carbon number m of the alkyl chain. For each surfactant series, T(M) goes through a maximum at s close to 5, irrespective of the value of m.

Dimeric (gemini) surfactants: effect of the spacer group on the association behavior in aqueous solution.

Dimeric (gemini) surfactants are made up of two amphiphilic moieties connected at the level of, or very close to, the head groups by a spacer group of varying nature: hydrophilic or hydrophobic, rigid or flexible. These surfactants represent a new class of surfactants that is finding its way into surfactant-based formulations. The nature of the spacer group (length, flexibility, chemical structure) has been shown to be of the utmost importance in determining the solution properties of aqueous dimeric surfactants.

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants 10. Behavior in aqueous solution at concentrations below the critical micellization concentration: an electrical conductivity study.

Ion pairing and premicellar association have been often invoked to explain results obtained in studies of aqueous solutions of ionic dimeric surfactants (gemini surfactants), mainly by means of surface tension and electrical conductivity, at concentrations below the critical micellization concentration (cmc). The present work was undertaken in an attempt to find out under which conditions these effects come into play. For this purpose the electrical conductivity of solutions of many dimeric surfactants of the type spacer-alpha,omega-bis(alkyldimethylammonium bromide) have been measured.

Microstructures in the aqueous solutions of a hybrid anionic fluorocarbon/hydrocarbon surfactant.

The aqueous solutions of the anionic hybrid fluorocarbon/hydrocarbon surfactant sodium 1-oxo-1[4-(tridecafluorohexyl)phenyl]-2-hexanesulfate (FC6HC4) shows peculiar rheological behavior. At 25 degrees C the viscosity vs concentration curve goes successively through a maximum and a minimum, while the viscosity vs temperature curve of the 10 wt% aqueous FC6HC4 solution goes through a marked maximum at 36 degrees C [Tobita et al., Langmuir 13 (1997) 5054].

Fluorescence probing investigation of the mechanism of formation of MSU-type mesoporous silica prepared in fluoride medium.

The mechanism of formation of a MSU-type siliceous material from tetraethyl orthosilicate (TEOS) in the presence of the nonionic surfactant tergitol T-15-S-12, sulfuric acid, and sodium fluoride has been investigated using mainly fluorescence probing techniques and, to a lesser extent, dynamic light scattering (DLS) and 29Si NMR spectroscopy. The tergitol micelles present in the systems obtained by progressively generating the reaction mixture giving rise to the mesostructured material by adding to an appropriate tergitol solution sulfuric acid, TEOS, and NaF were characterized by fluorescence probing (micelle aggregation number, micropolarity, and microviscosity) and also by dynamic light scattering (apparent micelle diameter). 29Si NMR experiments were also performed on selected systems after hydrolysis of the TEOS.

Direct visualization of mesh structures at solid/solution interfaces by atomic force microscopy.

The formation of adsorbed surfactant layers consisting of a mesh or network of branched cylindrical aggregates on muscovite mica by several surfactant systems is described. The curvature of the adsorbed aggregates is varied by a variety of mechanisms that all generate morphologies between adsorbed cylinders and bilayers, and the resulting lateral structure is imaged by "soft contact" atomic force microscopy. We compare the direct images and Fourier transforms of the adsorbed layer structures, and relate them to those formed in bulk solution.

Cloud point of aqueous solutions of tetrabutylammonium dodecyl sulfate is a function of the concentration of counterions in the aqueous phase.

The cloud point of the surfactant tetrabutylammonium dodecyl sulfate is shown to be a function of the tetrabutylammonium counterion concentration in the aqueous phase whether the counterions are provided by the surfactant or both the surfactant and added tetrabutylammonium bromide. The micellized surfactant dissociates 17% of its counterions to aqueous phase.

Rings-on-a-string chain structure in DNA.

Using fluorescence microscopy (FM), which permits the observation of single molecules, we found that a pearling structure is generated on a single long DNA molecule upon the addition of a gemini (dimeric) surfactant. This pearling structure was further investigated by performing atomic force microscopy measurements on the same DNA molecules as observed by FM. These observations revealed that the pearling structure is composed of many rings that are interconnected by elongated coil parts along a single DNA molecule, i.

Effect of the nature of the counterion on the interaction between cesium and tetraalkylammonium dodecylsulfates and poly(ethylene oxide) or poly(vinylpyrolidone).

The interaction between poly(ethylene oxide) or poly(vinylpyrrolidone) and cesium and tetraalkylammonium (tetramethyl to tetrabutyl ammonium) dodecylsulfate has been investigated by means of electrical conductivity measurements to determine the critical aggregation concentration (cac) of the surfactants in the presence of polymer. The cac values were compared to the values of the critical micellization concentration (cmc) of the surfactants in the absence of polymer. The value of the cac/cmc ratio increased with the radius of the counterion in the sequence: Na(+) View Article and Find Full Text PDF

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.