Apparent Order Parameters for Flexible Chains

When molecules are not so simple as rigid rods or discs, one may introduce apparent partial order parameters different for different molecular moieties. This is especially evident for lyotropic liquid crystals [21], such as, for instance, the lamellar phase formed by surfactants in water, see Fig. 3.22b. A good example is a water solution of potassium laurate. A flexible hydrocarbon chain K-CH2-CH2-CD2-CH2-. can be deuterated with a position of deuterium label varied along the chain, as shown by in Fig. 3.22a. Then, by the NMR technique sensitive only to deuterium nuclei, the apparent order parameter of the corresponding chain link can be determined. As shown in Fig. 3.23, it decreases with increasing the distance from the potassium atom due to flexibility of the hydrocarbon chain. Thus, we can say that the hydrocarbon tail is solid at the left end and liquid at the right one [22]. 

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Liquid crystals and molecular structure nematics and cholesterics. In Luckhurst, G.R., Gray, G.W. (eds.) The Molecular Physics of Liquid Crystals, pp. 1-29. Academic, London (1979). Chapter 1 

Hollinghurst, J., Goodby, J.W. Chiral and achiral calamitic liquid crystals for display applications. In Codings, P., Patel, J. (eds.) Handbook of Liquid Crystal Research, pp. 17-71. Oxford University Press, New York (1997) 

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