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Eingeladener Vortrag
- nein (80)
On the thermal behaviour and thermo-oxidative stability of liquid crystalline triphenylene compounds
(1999)
Columnar discotic materials are considered for applications in the area of photoconductivity and light-emitting diodes. A major requirement is their stability at elevated temperatures and in the presence of oxygen. The thermal and thermo-oxidative behaviour of discotic triphenylene derivatives was investigated by us using various methods, in particular by chemiluminescence (CL), UV-vis absorption spectroscopy and in situ thermogravimetry-mass spectroscopy (TG-MS). Various degradation processes are described for increasing temperature, and their influences on functional properties are discussed.
Polarized fluorescence and orientational order parameters of a liquid-crystalline conjugated polymer
(1999)
We report a study of the orientational order of aligned thin films of the liquid crystalline conjugated polymer poly(9,9-dioctylfluorene). Steady state polarized fluorescence measurements were used to determine the orientational order parameter <P2> and <P4>. The influence of intermolecular and intramolecular excitation energy transfer on the degree of polarization is discussed. The role of film morphology is also examined by comparison of the results for glassy and crystalline films.
The thermo-oxidative degradation of a polymeric optical cable is investigated by chemiluminescence, The results are reliable and reproducible. Two distinct processes are reported marked by a peak and a plateau behavior versus the time, respectively. Both processes are ruled by thermally activated processes. Beside the dependencies of temperature and time, the influence of absorbed water is discussed. Chemiluminescence is proposed as a promising candidate for a suitable testing method assessing the thermo-oxidative stability of plastic optical fibers and cables. it requires not more than a simple one-day testing procedure and has the advantage that it can be carried out even within the lo cv temperature ranges of the cables' intended use.
Conjugated polymers based on 1,4-phenylenevinylene units are very promising materials for applications as light-emitting diodes. A major requirement is their stability at elevated temperatures of operation. The thermo-oxidative behaviour of a soluble poly(1,4-phenylenevinylene) derivative, poly[2,5-bis(2-ethylhexyloxy)-1,4-phenylene vinylene], was investigated by using chemiluminescence and UVVis absorption spectroscopy. Extremely sensitive chemiluminescence is successfully applied since even minor chemical changes could lead to a considerable loss of photo- and electro-optical properties. Various degradation processes are described as a function of time and temperature and their influences on functional properties are discussed. The investigated material does not show sufficient thermo-oxidative stability within the temperature range of intended use in contact with air. For industrial application, direct contact with oxygen during processing and operation has to be avoided.
A liquid crystalline mainchain conjugated polymer for polarized electroluminescence applications
(1997)