Degradation phenomena crystal structure

The phenomenon of electroluminescence in organic soUds has been known since the 1960 s at that time. Pope et al. [1] and Helfrich and Schneider [2] discovered and investigated the electroluminescence of anthracene crystals between two electrodes, an anode and a cathode. The thickness of the highly-purified anthracene crystal platelets was large in these first experiments 10-20 /wm or 1-5 mm. The two electrodes on the surfaces of the crystal platelets were silver paste or liquid, highly concentrated solutions of NaCl. The necessary external voltages varied between 50 and 2000 V. Later, Williams and Schadt [3] were the first to construct a display , likewise from anthracene crystals, but with solid, laterally-structured electrodes, and they encapsulated it to prevent its degradation in the air. 

This phenomenon is attributed to the melting point of the material - a correlation already demonstrated by Tokiwa and co-workers for different aliphatic polyesters [79]. In aliphatic-aromatic copolyesters, the melting behaviour is mainly determined by the length of the aromatic sequences in the polymer chains, which depends both on the composition and structure [86, 87]. For many aliphatic polyesters, a correlation of the degradability with the melting point was observed [2]. Marten [86] interpreted it as a decrease in the mobility of the polyester chains at lower temperatures in this situation the polymer chains are highly fixed in the polymer crystals and cannot adjust easily into the active sites of the extracellular enzymes. A random insertion of some aromatic monomers in aliphatic polymer chains disturbs the formation of crystals. 

The faster internal degradation is a general phenomenon [69-76]. However, in the case of crystallizable polyesters, no hollow structures have been obtained because of the crystallization of degradation products [72-76]. 

---