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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Crystallization, Nucleation and Self Assembly II

CPP 9.4: Vortrag

Montag, 31. März 2014, 16:00–16:15, ZEU 260

Relaxation of the complex heat capacity of eicosane in the metastable rotator phase. — •Carlo Di Giambattista, Jörg Baller, and Roland Sanctuary — Laboratory for the Physics of Advanced Materials, University of Luxembourg

Some normal alkanes show stable and/or meta-stable polymorphisms. Understanding the process behind the formation of these structures for n-alkanes (n≥20) could yield a better understanding of the crystallisation of polymers [1]. Upon cooling from the melt eicosane (C₂₀H₄₂) exhibits a transition to a metastable orthorhombic phase (rotator I) [2]. Upon further cooling there is a second transition to a stable triclinic structure. In this work, we investigate the metastable phase with Temperature Modulate Differential Calorimetry(TMDSC). We use stochastic temperature perturbations (TOPEM-Mettler Toledo). This allows us to get a frequency dependant complex heat capacity c_p^*(ω). In the metastable rotator phase the heat capacity of eicosane becomes time dependant. In the frequency domain itś complex heat capacity can be described by a temperature dependant Debye relaxator. There are two distinct temperature regions, one in which the relaxation time diverges on approaching the melting temperature and another region with an almost constant relaxation time at lower temperatures.

[1] Ungar, G. and N. Masic (1985). J. Phys. Chem. 89(6): 1036-1042.

[2] Sirota, E. B., H. E. King, et al. (1993). J. of Chem. Phys. 98(7): 5809-5824.