Dresden 2006 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 27: POSTER Polymer Physics and Materials
CPP 27.46: Poster
Donnerstag, 30. März 2006, 17:00–19:00, P2
Relaxation behavior, physical aging and crystallization kinetics — •T.R. Gopalakrishnan and M. Beiner — FB Physik, Universität Halle, D-06099 Halle/Saale, Germany
Recently the properties of amorphous pharmaceuticals attracted a lot of attention. We have studied the relaxation and crystallization behavior of amorphous acetaminophen produced by rapid quenching. DSC heating curves for this sample show a pronounced glass transition at Tg=23oC before spherulites are formed during the cold crystallization process at temperatures around Tc=85oC. Weak exothermal contributions in the range 110-130oC indicate a solid-to-solid transition to another polymorphic state which finally melts at Tm ≈158oC. In order to get more detailed information about the relaxation behavior of amorphous acetaminophen we have investigated the dynamic glass transition (α) between Tg and Tc by dielectric spectroscopy. A weak secondary relaxation (β) has been found in є" isotherms measured at temperatures below Tg. The crystallization kinetics will be described based on isothermal crystallization experiments by dielectric spectroscopy at temperatures between 30oC and 55oC. We observed that isothermal crystallization affects mainly the α relaxation strength Δ є while shape and position of the α peak in є" isotherms are nearly unaffected. This shows that the situation can be approximated by a two phase model. The dielectric results are consistent with data from calorimetric measurements detecting the change of the strength of the thermal glass transition Δ cp after different periods of isothermal crystallization at Tc. Characteristic crystallization times τc obtained by both methods are nearly identical.