Nanocasting of ABC Phases

Using the binary phase diagram of an amphiphihc block copolymer with water as a guidehne (an example is shown in Fig. 4), the structure of the final 

The nonionic ABC templates used for nanocasting commonly consist of a hydrophobic soft block (T below or around room temperature in order to warrant sufficient solubility at room temperature), such as poly(butadiene) [34], poly(ethylene-co-butylene) (Kraton Liquid) or relatively short poly(styrene) and a poly(ethylene oxide) block as the hydrophilic moiety [35]. 

Some phase diagrams of low-polydispersity amphiphilic block copolymers, exhibit areas of coexistence over a relatively wide range of composition (see Fig. 4) [32]. This is probably due to kinetic inertia or to the fact that at the borderline between two thermodynamically stable phases the energetic differences between two structures are marginal. Swelling these coexisting phases with a siliceous precursor affords a microphase-separated siliceous phase, which has the same structure as the binary mixture consisting of water and amphiphilic 

The applicability of nanocasting as an analytical tool has been demonstrated [38] by comparing the silica structures obtained from the lyotropic phase, which has been crosslinked using y-rays, in order to provide sufficient mechanical stability to allow thin-sectioning, with those of a silica nanocast obtained from a lyotropic phase of the same composition (Fig. 7). The similarity between the structures is striking. A reference sample was prepared by filHng the pore system of the crosslinked polymer gel with sihca and subsequent calcination. The pictures prove without doubt that the sol-gel process indeed does not have any structurally disrupting effect on the hquid crystalhne phase [38]. 

In contrast to precipitation procedures, nanocasting, particularly of amphiphilic block copolymer phases, ahows the fabrication of large objects (monoliths) that are macroscopically devoid of cracks and defects. Despite their mechanical robustness, the porosity of these monohths can be as high as 85%. 

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