Molecular size, hydrophobic groups

Lyotropic liquid crystal phases are formed by amphiphihc molecules (surfactants, block copolymers) in solution, driven by repulsive forces between hydrophobic and hydrophihc parts. In a polar solvent, the hydrophihc parts associate with the solvent, whereas the hydrophobic parts interact to form the interiors of micelles (as in low-molecular smfactants). Micelles can be spherical, rod-like or discotic in shape. The contour of the micelle is determined by the relative sizes of the hydrophihc and hydrophobic groups. MiceUe shapes are influenced by solvent, concentration and temperatme. 

Figure 2.1.1 Typical surface modification of a solid by amphiphiles (left) or bolaam-phiphiles (right), lypical wetting angles of a water droplet on apolar (center) and polar (left) surfaces are shown. Hydrophobic hydrocarbon surfaces on the tongue produce a good mouthfeel and favor the development of aroma. Hydrophilic end groups may be used for the selective adsorption or desorption of aqueous solutes on the surface of solids. Gaps of molecular size may act as enzymelike reaction centers (right see Figs. 9.6.9 and 9.6.10).

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