Bicontinuous networks

Another phase which has attracted recent interest is the gyroid phase, a bicontinuous ordered phase with cubic symmetry (space group Ia3d, cf. Fig. 2 (d) [10]). It consists of two interwoven but unconnected bicontinuous networks. The amphiphile sheets have a mean curvature which is close to constant and intermediate between that of the usually neighboring lamellar and hexagonal phases. The gyroid phase was first identified in lipid/ water mixtures [11], and has been found in many related systems since then, among other, in copolymer blends [12]. 

Explicit forms for the stress tensors d1 are deduced from the microscopic expressions for the component stress tensors and from the scheme of the total stress devision between the components [164]. Within this model almost all essential features of the viscoelastic phase separation observable experimentally can be reproduced [165] (see Fig. 20) existence of a frozen period after the quench nucleation of the less viscous phase in a droplet pattern the volume shrinking of the more viscous phase transient formation of the bicontinuous network structure phase inversion in the final stage. 

Microemulsions with different structures, like micelles, reverse micelles or bicontinuous networks, can be used for several inorganic, organic [72] or catalytic reactions which require a large contact area between oil and water. Besides enzyme catalysis, this can be the formation of nanoparticles [54, 73, 74], hydro-formylation reactions [75] or polymerisations [76-78]. 

If the surfactant concentration in a macroemulsion is greatly increased, or if the monomer concentration is greatly reduced, a microemulsion results. Microemulsions are thermodynamically stable systems in which all of the monomer resides within the micelles. At high surfactant concentration, the micelles may form a bicontinuous network, rather than discrete micelles. Polymerization (with water- or oil-soluble initiator) of the monomer within a microemulsion is referred to as microemulsion polymerization. The particles produced in this way are extremely small, ranging from 10 to 100 nm. 

Indeed, by analogy with the behaviours of soap films, catastrophic changes of the TFS topology can occur as the mutual arrangement of the templating ions is changed continuously. (For example, the TFS can jump from a bicontinuous network to disconnected sheets.) This effect may well be... 

Obviously, the performance of organic cells having bicontinuous network structures with quantum efficiencies of about 50% and power conversion efficiencies of about 5% remains far inferior to that of silicon cells, but is highly improved as compared to that of flat-junction organic cells, which have both quantum efficiencies and power conversion efficiencies of less than 0.1%. 

The breakup of the two percolating bicontinuous networks of oil and water regions (with an amphiphile film that is dominated by saddle-shaped configurations) into disconnected droplets near the critical endpoint can be seen very clearly in a sequence of typical configurations for different temperatures mo, as shown in Fig. 4. Note that K) 0 does not necessarily imply the predominance of cylindrical configurations. 

The conclusions from the cryo-TEM characterization, which have been validated for all the investigated systems, suggest that microstructures vary systematically with the oil/water ratio and, in particular, at comparable oil and water contents, both oil- and water-rich domains are mutually interwoven in an apparently bicontinuous network. 

The lack of the bipolar transport in binary blends of polymers for most of the compositions shows that controlling the thin-film morphology is challenging. Therefore, the key issue is to realize an interpenetrating and bicontinuous networks of binary polymer blends in order to establish ambipolar charge transport. 

To provide evidence for the presence of good interpenetrating bicontinuous network, the surface morphology of the blend was investigated by AFM. Figure 16.19... 

Fig. 5.2.4 Optical micrograph of a surface of a VA/AA-based emulsion (6.6 vrt% sohds) at 400X magnification, showing a bicontinuous network structure with 5-10 (jim open cells (With permission from Caneba and Axland, 2002)...

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