Quasi-Elastic Neutron Scattering Studies of the Slow Dynamics of Supercooled and Glassy Aspirin

Published

January 25, 2012

Author(s)

Yang Zhang, Madhu Sudan Tyagi, Sow-Hsin Chen

Abstract

Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass-former. Therefore,it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 K down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent β(Q) is independent of the wave vector transfer Q in the measured Q-range, and (ii) the structural relaxation time τ(Q) follows a power law dependence on Q. Consequently, the Q-independent structural relaxation time τ₀ can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of τ₀ can be fitted with the mode coupling power law, the Vogel-Fulcher-Tammann (VFT) equation and a universal equation for fragile glass forming liquids recently proposed by M. Tokuyama in the measured temperature range. The calculated dynamic response function χ_T(Q,t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows a direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement x₂ and non-Gaussian parameter α₂ extracted from the elastic scattering.

Citation

Journal of Physics Condensed Matter

Volume

24

Pub Type

Journals

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Keywords

glass forming liquids, neutron scattering, glass transition

Citation

Zhang, Y. , Tyagi, M. and Chen, S. (2012), Quasi-Elastic Neutron Scattering Studies of the Slow Dynamics of Supercooled and Glassy Aspirin, Journal of Physics Condensed Matter, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=908659 (Accessed December 15, 2024)