Copolymers bubbles formation

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine cel] structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The physical properties of polyurethanes are derived from their molecular structure and determined by the choice of building blocks as well as the suprainolecular structures caused by atomic interaction between chains. The ability to crystallize, the flexibility of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, e.g., polyurethane foains, other factors such as density determine the final properties. 

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. 

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