Materials Science

Complex Discs

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Science  10 May 2002:
Vol. 296, Issue 5570, pp. 983
DOI: 10.1126/science.296.5570.983b

Molecules that exhibit liquid crystalline phases are known as mesogenic and possess an inherent rigidity that encourages their packing into semi-ordered arrays. The extent of ordering can be controlled by changing external variables such as temperature and pressure, whereas small changes in the molecular structure will vary the number and nature of liquid crystalline phases that are observed. For example, by coupling a mesogen to a polymer backbone, the number of liquid crystalline phases and the temperature range over which they are observed can increase because the polymer backbone suppresses crystallization. Rod-shaped molecules are the more common architecture, but disc-shaped molecules are receiving increased attention because of their potential for display technologies and as one-dimensional charge carriers.

Kouwer et al. have expanded the family of discotics by creating a molecule with a single functional tail and five methoxy substituents. On its own or coupled to a polymer backbone, the mesogen showed only one liquid crystalline phase. However, mixing the mesogen with a number of charge acceptor molecules increased the number and complexity of liquid crystalline phases that formed. Surprisingly, examination of the phases by x-ray diffraction and polarized optical microscopy often gave conflicting results as to the type of liquid crystalline phase present, suggesting that caution is needed when studying these more complex liquid crystalline materials.—MSL

Macromolecules 10.1021/ma0118567 (2002).


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