Mesomorphic state
The mesomorphic state is a non-classical aggregate state that occurs with some substances, varying between the classic aggregate states solid and liquid .
Examples of substance groups with occurring mesomorphic states:
The transition from the solid to the liquid state takes place via mesophases . Liquid crystals form smectic and nematic phases between the solid and liquid state . First the long-range order in the crystal is given up, whereby a short-range order remains. In the opposite case, the short-range order is first dissolved in plastic crystals , whereby a long-range order is retained. Adamantane can be mentioned as an example , where the highly symmetrical ("spherical") molecules in the plastic state have corresponding degrees of freedom of rotation, but the space in the crystal lattice is retained.
Liquid crystalline mesophases often occur with rod-shaped (kalamitic liquid crystals) or disk-shaped (discotic liquid crystals) molecular shapes. Plastic crystalline phases are typical for spherical molecular shapes such as adamantane or cubane .
Plastic crystals and liquid crystals can be distinguished using X-ray diffraction . While plastic crystals result in defined Bragg reflections due to the still existing long-range order, liquid crystals show only broad reflections, similar to amorphous structures .
Individual evidence
- ↑ GJ Kabo, AV Blokhin, MB Charapennikau, AG Kabo, VM Sevruk: Thermodynamic properties of adamantan and the energy states of molecules in plastic crystals for some cage hydrocarbons. In: Thermochim. Acta . 345 (2000), pp. 125-133.
- ↑ FH Herbstein: Some applications of thermodynamics in crystal chemistry. In: J. Mol. Struct. 374: 111-128 (1996).