Threadlike micelles

Zheng Y, Lin Z, Zakin JL, Talmon Y, Davis HT, Scriven LE (2000) Cryo-TEM imaging the flow induced transition from vesicles to threadlike micelles. J Phys Chem B 104(22) 5263-5271... 

An interesting sonochemical synthesis of elongated copper nanoparticles (approx. 50 X 500 nm) has been described [164]. The principle of the method is the use of an organised medium of aqueous cetyltrimethylammonium p-toluenesulphonate as the supporting fluid for sonication. The resulting nanoparticles are produced from the sonication of copper hydrazine carboxylate in the interconnected threadlike micelles which act as a template. The nanoparticles are coated with a layer of the surfactant. In the absence of the detergent the particles were spherical (ca. 50 nm). 

The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM.[72] A continuous transformation from spherical micelles, into threadlike micelles, which become longer and stiffer, followed by the formation of bundles with dimensions similar to those found in the final material, was observed. The direct imaging... 

The amount, flexibility, and strength of the threadlike micelles determine the temperature range, critical wall-shear stress, and maximum DR ability of surfactant solutions. 

Danino D, Talmon Y, Levy H, Beinert G and Zana R 1995 Branched threadlike micelles in an aqueous solution of a trimeric surfactant Science 269 1420-1... 

It was suggested [284] that the perforated lamellar phase may form via the growth of branched and multiconnected threadlike micelles. Interconnection of threadlike micelles reduces the overall curvature of the monolayer making up the micelles and thereby reflects a preference for microstructures of decreasing curvature [119]. The suggested morphological sequence for the system cetylpyridinium chloride-hexanol-brine is spheres, small disks, long capped cylinders, branched cylinders, perforated bilayers, smooth bilayers, loose network of connected bilayers (foamlike structure), and multiphasic domain [284]. 

Another type of micelle formation has also attracted the attention of researchers, a brief mention of which will be made below. Gravsholt [93], in an early work, reported viscoelasticity in highly diluted aqueous solutions of some cationic surfactants, namely, certain derivatives of the base structure of cetyltrimethylammonium bromide (CTAB), CTA-X (where X=salicylate, m-chlorobenzoate, p-chlorobenzoate). He came to the conclusion that the viscoelastic behavior indicates a micellar shape other than spheres and rods. Later it has been shown [e.g. 94] by fluorescence anisotropy using fluorescent probe molecules that CTAB and sodium p-toluenesulfonate, NapTS (with suitably weak fluorescence) in aqueous solution could produce long, threadlike micelles with network structure in which the cross-points had finite lifetime. Sodium salicylate was another useful additive for synthesis, but the intensity of its fluorescence was found unsuitable for examining the behavior of the probes. 

In M, Aguerre-Chariol O, Zana R (1999b) Dynamics of branched threadlike micelles. Phys Rev lett 83 2278-2281... 

Interestingly, in addition to spherical reverse micelles, even very long, threadlike micelles with a water-rich core have been documented [63], indicating that a comparatively rigid zone of tightly packed hydrocarbon chains is present next to the polar head groups, granting mechanical stability as discussed previously in Section II.D. 

A similar mechanism can be concluded for the assumption of a network of connected or fused threadlike micelles. The cross-links between these micelles can be regarded as disc-like micelles from which the rods extend. In this case, the transient intermediate species in the various bond interchange mechanisms are assumed to be stable. In this situation, all the end-caps could be connected and the resulting network could be in the saturated or unsaturated state. The cross-link points could then slide along the thread-like micelles, and this process represents a one-dimensional diffusion with a concentration-independent diffusion coefficient. A knot can disappear, if two network points meet on their random diffusion paths. If the structural relaxation time is determined by this random movement, a similar equation, i.e. x 1/c, can be derived. 

Figure 1.6 Electron micrographs of 0.74 wt% (top) and 1 wt% (bottom) solutions of the dimeric (gemini) surfactant dimethylene-1,2-bis(dodecyldimethylamonium bromide) showing giant threadlike micelles (top), elongated micelles with a branching point (bottom, arrow) and a ringlike micelle (bottom, arrowhead). Reproduced from reference 39 with permission of the American Chemical Society.

The principle of the dielectric absorption relaxation technique is very similar to that of the ultrasonic relaxation. The coupling between electrical waves and the chemical equilibrium occurs through the change of dipole moment associated with the chemical reaction. The drawback of this method lies in its extreme sensitivity to all rotational motions occurring in the system and which all give rise to relaxation signals. The chemical contributions are then more difficult to extract and analyze. Nevertheless, the dielectric relaxation has been recently used for the study of the kinetics of processes occurring in systems of threadlike micelles. - ... 

Shear has been reported to induce the transformation of vesicles present in the cetyltrimethylammonium-3-hydrox-ynaphthalene-2-carboxylate/water system in threadlike micelles. The transformation was finished after a time shorter than 20 min, and this time decreased as the applied shear rate was increased. A similar transformation was investigated by Zheng et al. for the CTAC/sodium 3-methylsali-... 

The micellar structures formed by LiFOS and TEAFOS (tetraethylammo-nium perfluorooctanesulfonate) have been examined by measuring NMR chemical shifts and self-diffusion coefficients of both TEA and FOS [38,39]. The micellar self-diffusion coefficient in the TEAFOS system is about an magnitude lower than that of the LiFOS system. The slower self-diffusion in the TEAFOS system is related to a strong binding of TEA ions onto the micellar surface and a transformation from spherical to threadlike micelles, induced by TEA" counterions. 

The rheological behavior of TEAFOS threadlike micelles was investigated by Watanabe et al. [60]. The threads are, like polymer chains, oriented under strain and exhibit viscoelastic stresses. However, unlike polymer chains, the threadlike micellar aggregates dissociate and reform reversibly. In the linear viscoelastic regime, the threads form a transient network and exhibit a single-mode terminal relaxation. 

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