Micellar films

Fig. 9 Schematic representation of three approaches to generate nanoporous and meso-porous materials with block copolymers, a Block copolymer micelle templating for mesoporous inorganic materials. Block copolymer micelles form a hexagonal array. Silicate species then occupy the spaces between the cylinders. The final removal of micelle template leaves hollow cylinders, b Block copolymer matrix for nanoporous materials. Block copolymers form hexagonal cylinder phase in bulk or thin film state. Subsequent crosslinking fixes the matrix hollow channels are generated by removing the minor phase, c Rod-coil block copolymer for microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes. (Adapted from [33])...

Figure 32. (a) Schematic representation of hierarchical self-organization of 30 into ordered microporous structure, (b) Fluorescence photomicrograph of solution-cast micellar film of 30 with m = 10 and n = 300. (Reprinted with permission from ref 109. Copyright 1999 American Association for the Advancement of Science). 

Factors such as micellar concentration, micelle size, chain lengths, film area, electrolyte concentration, temperature, presence of solubilized oil on the micellar film structuring, and thus foam stability are highlighted. 

Figure 1. TEM micrographs of regular mono micellar films (a) loaded with (a) LiAuCU, and (b) where the aurate ions were converted to a single Au cluster per micelle prior to film casting. The scheme illustrates that in both cases a single gold particle remains at the place of the micelle.

The approach described here represents a remarkably simple procedure for the preparation of nanometer sized dots in a rather regular pattern. Without further effort we have prepared ordered films of 3x3cm. In principle there is no limitation in size. Besides the diblock copolymers which we employed, also other amphiphilic diblock copolymers form reverse micelles in a non-polar solvent and can be used to bind a large variety of metal compounds like H2PtClg, Pd(Ac)2, TiCU, FeCls, etc.. Chemical transformation of the inorganic compound can be performed before deposition of the micellar film or upon removal/oxidation of the film. While noble metals are deposited in the elementary state, less noble compounds can only be deposited in their oxidic form, i.e., Ti02, Fe203, InO. ... 

Figure 4. SFM micrographs (1x1 pm ) of (a) a PS-b-P2VP film and (b) a PS(1700)-b- P[2VP(HAuCl4)o.4(450)] film cast from a micellar solution. A, B, and C mark structural variations as described in the text. The T M micrograph (c) shows the same micellar film as in (b). (d) The scheme depicts the structural difference of the film from PS-b-P2VP and PS(1700)-b-P[2VP(HAuCl4)o.4(450)] respectively.

Loveland and Elving observed four capacity peaks on the differential capacitance curves obtained by the oscillographic method. The two outer peaks were considered to be due to the complete desorption of alcohol molecules from the electrode surface, while the two inner ones were explained in terms of the removal of a second layer of adsorbed molecules which, at small electrode charges, form a micellar film [3]. 

Gupta arrived at the conclusion about the formation of condensed micellar films when studying the adsorption of methyl orange on mercury by the tensammetric method. Capacitance peaks associated with the formation and destruction of micellar films are observed in the C-E curves of alkyl sulphate anions with a carbon chain of sufficient length (12 or more carbon atoms) as well as those of sodium laurate and caprylate [3],... 

Figure 3 shows typical TEM pictures of such gold colloid containing block copolymer films which were obtained after reduction of PS-b-PEO/LiAuCU complexes in toluene either by BHs/methanol or by N2H4(aq). It was generally observed that reduction with BHs/methanol led to bimodal products containing very small (1.5 nm) and larger (ca. 15 nm) particles in each micelle core (Figure 3A). In contrast, reduction with hydrazine hydrate led to particles with sizes mostly between 6 and 15 nm (Figure 3B). Size and location of the particles was, however, not directly related to a micellar film structure.

Electrostatic LbL self-assembly was also applied to the preparation of photoactive nanostructured micellar films on quartz or silicon plates from amphiphilic poly(sodium styrenesulfonate-itot-2-vinylnaphthalene) and the cationic polyelectrolytes poly(diallyldimethylammonium chloride) or poly(allylamine hydrochloride) [144]. Similar to the examples described before, AFM studies evidenced the preservation of the micellar structure in the films. Such materials might be interesting for (bio)sensing applications, light emitting and photochromic devices, or energy conversion systems. 

Figure 3.2. Electron diffraction at 120 kV from a cast micellar film with 3.5-nm spacing at left, unfiltered at right, filtered to include only zero-loss electrons. (From Du Chesne [31], (1999) Wiley-VCH used by permission.)...

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