Figures—continued Photographs, Structures

Schematically, the structure of the a-gel state is given in Figure 9.2, which can be deduced from the photographs (Figures 9.7 and 9.8) in the reference of Heertje et al. (1998). The structure consists of a continuous phase of bilayers, which are stacked parallel to one another in regions with a speeifie domain size, and of droplets being embedded in this continuous phase. The droplets consist of bilayers that are stacked concentrically, like the layers in an onion, and are separated by water layers. For obvious reasons these droplets are sometimes denoted by the term onions.

A complicated many-layer structure of foam cells is formed when gas bubbles are sparged into solutions of surfactants. According to [429], each bubble has a two-sided envelope which is a layer of the solvent containing hydrophilic polar parts of surfactant molecules (see Figure 7.2). Nonpolar hydrophobic parts of molecules on the inner surface of the envelope are oriented toward the bubble, and on the outer surface, outward the envelope. Between two cells, each of which is a capsule with envelope, there is a lamella, that is, an interlayer of a complicated structure. In the middle of the lamella, there is a liquid layer that is a continuous phase. On each of two surfaces of this layer, there is a monolayer of the surfactant. The hydrophobic parts ( tails ) of surfactants molecules in each monolayer and the tails of the envelope form two direct plate micellae [413], which separate the envelope and the continuous liquid film at the center. Thus, gas bubbles in foam are separated at least by five distinct layers. The multilayer structure of a foam lamella is well seen in photographs (e.g., see [429], p. 54). This fact is also confirmed by the ladder-type shape of the disjoining pressure... 

Figure 14 shows photographs of uncured (a, b) and cured (c, d) 25/75 PAI-l/LCP sanq)les, respectively. The 25/75 PAI-l/LCP blend shows fiber formation in the uncured sanq)le (Figure 14) in both the skin (a) and core (b). Distinct phases are absent ch indicates better dispersion. The core also shows finer fibers than the skin. The fiber structures are destroyed on heat treatment (Figure 14c, d). The core section shows phase separation with LCP being the continuous and PAI-1 the discrete phase. The cured samples also show voids due to the release of volatiles. No agglomeration of the PAI-1 phase seems to have occurred in this case. 

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