473 research outputs found
What can we learn by squeezing a liquid
Relaxation times for different temperatures, T, and specific volumes, V,
collapse to a master curve versus TV^g, with g a material constant. The
isochoric fragility, m_V, is also a material constant, inversely correlated
with g. From these we obtain a 3-parameter function, which fits accurately
relaxation times of several glass-formers over the supercooled regime, without
any divergence below Tg. Although the 3 parameters depend on the material, only
g significant varies; thus, by normalizing material-specific quantities related
to g, a universal power law for the dynamics is obtained.Comment: 12 pages, 4 figure
Thermodynamic Scaling of the Viscosity of Van Der Waals, H-Bonded, and Ionic Liquids
Viscosities and their temperature, T, and volume, V, dependences are reported
for 7 molecular liquids and polymers. In combination with literature viscosity
data for 5 other liquids, we show that the superpositioning of relaxation times
for various glass-forming materials when expressed as a function of TV^g, where
the exponent g is a material constant, can be extended to the viscosity. The
latter is usually measured to higher temperatures than the corresponding
relaxation times, demonstrating the validity of the thermodynamic scaling
throughout the supercooled and higher T regimes. The value of g for a given
liquid principally reflects the magnitude of the intermolecular forces (e.g.,
steepness of the repulsive potential); thus, we find decreasing g in going from
van der Waals fluids to ionic liquids. For strongly H-bonded materials, such as
low molecular weight polypropylene glycol and water, the superpositioning
fails, due to the non-trivial change of chemical structure (degree of
H-bonding) with thermodynamic conditions.Comment: 16 pages 7 figure
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