Bicontinuous network/structure

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. 

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%. 

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)...

Fig. 12 Schematic of gel microstructure through the yielding transition. Bottom fractal clusters of droplets (yellow) with diameter D. Middle bicontinuous network structure consisting of droplet-lean (blue) and droplet-rich (yellow) domains on the length scale of 10-100 D. Top macroscopic structure at a length scale of 100-1000 D, reprinted from Kim et al. [23], copyright 2014, Society of Rheology...

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]. 

In principle the bicontinuous 3-dimensional network structure of MCM-48 would act as a good catalytic support.[7] However, its lower hydrothermal and thermal stability has led to much less application of MCM-48 in catalysis. Recently, a family of mesoporous molecular sieves (denoted as MSU-G) with vesicle-like hierarchical structure, worm-like mesoporous structure and bicontinuous nano-porous silica had been synthesized.[8-10] It was proposed that highly accessible mesoporous materials could be obtained through different synthetic procedure and composition. 

First, the lyotropic phase is used as a template for the preparation of a bicontinuous silica structure, from which the polymer is removed by calcination or extraction. In the second step the porous inorganic structure is filled with monomer and crosslinker which is polymerized to form a bicontinuous organic polymer network from which the silica template is removed by treatment with hydrofluoric acid. An example for the preparation of hierarchical structures is the synthesis of bicontinuous pore structures by using two templates simultaneously [115]. In this case a liquid crystalline lyotropic phase of an amphiphilic block copolymer is used as a template together with suspended latex particles. The sol-gel process with subsequent calcination leads to a bicontinuous open pore structure with pores of 300 nm and 3 nm. 

Figure 5.2.4 shows a network surface structure of a VA/AA-based emulsion with 6.6 wt% soiids. The repeat unit in the network structure is between 5 and 10 jtm. The formation of the network or bicontinuous surfactant structure is well established in relatively high molecular weight ethylene oxide/propylene oxide segmented block copolymer nonionic surfactants, and it has been ascribed to the formation of liquid crystalline macromolecular assemblies. Upon dilution, the emulsion showed 5-10 ttm spherical domains that could form aggregates up to about 60p.m in size (Fig. 4.4.5). In Fig. 5.2.5, bubble surfaces are shown with the network surfactant structure, even in the diluted emulsion. Apparently, the surfactant macromolecules tend to concentrate on bubble surfaces and form a more viscous and probably elastic polymer surface layer. 

Figure 4.25 Normal structures and the lamellar phase (a) normal micellar cubic structure (Ii), (b) normal hexagonal structure (Hj), (c) lamellar phase (L ), (d) normal bicontinuous cubic structure (Vi). Here a portion of the gyroid structure is sketched. The amphiphilic molecules form a bilayer film separating two continuous labyrinths of water. The amphiphilic film is a network with threefold node points, which defines the gyroid phase...

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