Temperature dependence of self-diffusion in compressed monohydric alcohols

Abstract

The p,T-dependence of the self-diffusion coefficient D for methanol, methan(2H)ol and ethanol has been studied between 150 and 450 K at pressures up to 250 MPa. The experiments were performed in strengthened high-pressure glass cells by the application of the nuclear magnetic resonance (NMR) spin-echo technique with pulsed magnetic-field gradients. Upon cooling, molecular mobility is strongly reduced, leading to a pronounced non-Arrhenius temperature dependence of D. Applying the rough hard-sphere model (Chandler) to our data, a dramatic decrease of the A-parameter with falling temperature is observed. This behavior indicates that attractive intermolecular interactions dominate translational mobility. The best description of the data is given by the empirical Vogel–Tammann–Fulcher (VTF) equation, with ideal glass transition temperatures T0, that are in excellent agreement with those obtained from calorimetric studies. The isotope effect for self-diffusion in methanol and methan(2H)ol increases from ∼5% at high temperatures to about 40% in the supercooled region. This drastic increase is assumed to originate from a difference in hydrogen bond strength of the isotopes, as has already been found for light and heavy water.

Short-Time Relaxational Dynamics of the “Strong” Glass-Former Methanol

“…The simulated methanol is too compressed, resulting in calculated values of compressibility, thermal expansion coefficient, and the translational diffusion coefficient D, which are all too small. The mobility of the simulated methanol is less than that experimentally found for real methanol 30 and decreases more rapidly with decreasing temperature. We refer to this hypothetical glass-former as (methanol) SK , distinguishing it from actual methanol.…”

Poly[1-(trimethylsilyl)-1-propyne] as a solvent resistance nanofiltration membrane material

“…The diffusion coefficient calculated is 1.27 × 10 −8 m 2 /s and higher by an order of magnitude than the value of ethanol selfdiffusion (1.1 × 10 −9 m 2 /s), which was estimated for a temperature of 25 • C [27]. This marked difference can be explained that assumption of the model, polymer is dense non-porous membrane, is not obviously applicable for PTMSP.…”

Glassy dynamics in supercooled-liquid and glassy ethanol: A molecular dynamics study

“…The calculated coefficients agree quite well with the experimental data and follow the Vögel-Tamman-Fulcher ͑VTF͒ law used by Karger et al to fit their NMR data. 37 Below 160 K, the data start to deviate from the VTF law, although the values of the self-diffusion coefficient are already so small that it is impractical to give a physical meaning to this fact and to their behavior below that temperature. The fact that this temperature matches that defined by the change in slope of the energy or the volume indicates that the thermodynamic and dynamic properties are being sampled in the same time scale.…”