Inverted micelle method

Many approaches have been taken to prepare colloidal doped semiconductor nanocrystals. For example, hot-injection methods have been used to synthesize colloidal Mn2+-doped CdSe (47, 48), ZnSe (49), and PbSe (50) colloidal nanocrystals. Colloidal ZnO DMS-QDs doped with Co2+, Ni2+, and Mn2+ have been prepared by low-temperature hydrolysis and condensation (51-54). Sol-gel methods have been used to prepare colloidal doped TiC>2 (55-57) and Sn02 (58-62) nanocrystals. Inverted micelle methods have been used for preparation of a range of doped II-VI sulfide DMS-QDs at low temperatures (63-68). A high-temperature lyothermal single-source method was used to synthesize Co2+- and Eu3+-doped CdSe nanocrystals (69, 70). Autoclaving has occasionally been used to induce crystallization at lower temperatures than reached under atmospheric pressures while retaining colloidal properties, for... 

A deeper understanding of the chemistry from Fig. 8 is obtained by closer inspection of the final products. Figure 9(a) shows a set of absorption spectra (68) collected on Co2+ CdS QDs prepared by the same inverted micelle method and resuspended in Py. Over time, the Co2+ ligand-field absorption intensity... 

Fig. 2.26. TEM micrograph of BaCOs nanowires obtained by the inverted micelle method (reproduced with permission from [508])...

Crooks et al. reported the transfer of amine-functionalized poly(amidoamine) dendrimers into toluene containing dodecanoic acid [198], The method is based on the formation of ion pairs between the fatty acids and the terminal amine-groups. These dendrimer-fatty acid complexes resemble unimolecular inverted micelles and could be used as phase transfer vehicles for the transport of Methyl Orange, an anionic dye molecule, into an organic medium. 

In order to test further the applicability of 1-pyrene carboxaldehyde as a fluorescent probe, we applied Keh and Valeur s method (4) to determine average micellar sizes of sulfonate A and B micelles. This method is based on the assumption that the motion of a probe molecule is coupled to that of the micelle, and that the micellar hydrodynamic volumes are the same in two apolar solvents of different viscosities. For our purposes, time averaged anisotropies of these systems were measured in two n-alkanes hexane and nonane. The fluorescence lifetime of 1-pyrene carboxaldehyde with the two sulfonates in both these solvents was found to be approximately 5 ns. The micellar sizes (diameter) calculated for sulfonates A and B were 53 5A and 82 lOA, respectively. Since these micelles possesed solid polar cores, they were probably more tightly bound than typical inverted micelles such as those of aerosol OT. Hence, it was expected that the probe molecules would not perturb the micelles to an extent which would substantially affect the micellar sizes measured. 

An interesting approach recently applied to doped nanocrystals is the heterocrystalline core-shell method commonly applied to pure nanocrystals. In a series of papers (102, 103), Mn2+ CdS nanocrystals were synthesized in inverted micelles under conditions very similar to those described above and in Figs. 8, 9, and 13. The poor luminescent properties of the resulting Mn2+ CdS nanocrystals were attributed to nonradiative recombination at unpassivated CdS surface states. From the discussion in Section I and II.C, however, it is likely that a large fraction if not all of the Mn2+ ions resided on the surfaces of these as-prepared nanocrystals as observed for Co2+ (Fig. 9). This interpretation is supported by studies in other laboratories that showed large Mn2+ surface populations in Mn2+ CdS nanocrystals grown by the same inverted micelle approach (63). Nevertheless, growth of a ZnS shell around these Mn2+ CdS nanocrystals led to an approximately ninefold increase in Mn2+ 4T 1 > 6A i... 

Later, Yoshikawa and Matsubara [40] further studied a non-linear system and proposed a mechanism for the periodic behaviour that involved the formation of inverted micelles that suddenly moved to the oil phase after the concentration of adsorbed surfactants reached a critical value. They extended the experiment to a water/oil/water three-phase system in a U-shaped glass tube that gave spontaneous and stable oscillatory behaviour over a long period [41]. Since then, various characteristics of non-linear behaviour have been investigated and several mechaiusms for the non-linear behaviour have been proposed by many research groups including ours[2,5,10,42-48] however, the mechanism at a molecular level has not been clarified yet and no consensus has been achieved. The difficulty in the explanation seems to come from not only the complexity and diversity of the systems, but also limitations of the observation methods that enable us to monitor dynamic molecular behaviour at liquid/liquid interfaces with sufficient interfacial selectivity and time resolution. In this section, the TR-QELS method has been applied to the investigation of W/NB—sodium dodecyl sulfate (SDS) two-phase system [10]. 

Surfactants form inverted micelles in oil medium without the use of water. Dry powders of salts can, therefore, be dispersed in the surfactant solution and reduced with reducing agents such as LiBH4 and Na in oil. Extremely reactive and even pyrophoric reducing agents can be used since water is absent in the system. Wilcoxon and coworkers [420-422] have made use of this method to synthesize Au, Si, and Ge nanocrystals. Si and Ge nanocrystals were obtained by dispersion of the halides in an inverted micelle followed by reduction with LiAlH4 in THF. 

A two-component bilayer and isotropic NMR spectrum from a membrane (usually a natural membrane) has been interpreted in terms of a major bilayer structure encompassing a much smaller (<5%) population of inverted micelles. Although not the only explanation, the interpretation has many functionally attractive features (enhanced permeability, sites of membrane fusion, flip-flop regions, etc). Such isotropic spectral components are often produced by proteins interacting with the surface of lipid bilayers. The identity of the lipid type, in a mixed lipid membrane, which exists in this isotropic environment, can be determined using MAS NMR methods. 

Spectroelectrochemical methods have been used in recent years to study fast-photoinduced electron transfer at the liquid/liquid interface.- "- - Of particular importance is extending the idea of employing solvent (typically N,N-dimethylaniline or DMA) as an electron donor to the liquid/liquid interface.The advantage of this approach is that complications due to ion transfer across the interface and to diffusion are obviated. Several studies of ET between coumarin dyes and electron-donating solvents in micelles, reverse micelles, at the surface of proteins, and in nanocavities have demonstrated ultrafast electron transfer that is faster than solvation due to the close proximity of the redox pair. These experiments provided additional evidence for the existence of the Marcus-inverted region at liquid interfacial sy stems. ... 

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