174 research outputs found
Approximate square-root-time relaxation in glass-forming liquids
We present data for the dielectric relaxation of 43 glass-forming organic
liquids, showing that the primary (alpha) relaxation is often close to
square-root-time relaxation. The better an inverse power-law description of the
high-frequency loss applies, the more accurately is square-root-time relaxation
obeyed. These findings suggest that square-root-time relaxation is generic to
the alpha process, once a common view, but since long believed to be incorrect.
Only liquids with very large dielectric losses deviate from this picture by
having consistently narrower loss peaks. As a further challenge to the
prevailing opinion, we find that liquids with accurate square-root-time
relaxation cover a wide range of fragilities
A model for the generic alpha relaxation of viscous liquids
Dielectric measurements on molecular liquids just above the glass transition
indicate that alpha relaxation is characterized by a generic high-frequency
loss varying as , whereas deviations from this come from one or
more low-lying beta processes [Olsen et al, Phys. Rev. Lett. {\bf 86} (2001)
1271]. Assuming that long-wavelength fluctuations dominate the dynamics, a
model for the dielectric alpha relaxation based on the simplest coupling
between the density and dipole density fields is proposed here. The model,
which is solved in second order perturbation theory in the Gaussian
approximation, reproduces the generic features of alpha relaxation
Thermo-elastic multiple scattering in random dispersions of spherical scatterers
Copyright 2014 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. The following article appeared in the Journal of the Acoustical Society of America, 136 (6), 3008 and may be found at: http://scitation.aip.org/content/asa/journal/jasa/136/6/10.1121/1.4900566?aemail=authorUltrasonic monitoring of concentrated suspensions and emulsions is limited in concentration
range due to the inaccuracy of the multiple scattering models currently used to interpret
measurements. This paper presents the development of a model for the additional multiple
scattering caused by mode conversion to/from thermal waves. These effects are believed to cause
significant deviation from established models for emulsions at high concentration, or small
particle size, at low frequency. The relevant additional scattering coefficients (transition factors)
are developed, in numerical and analytical form, together with the modification to the effective
wavenumber. Calculations have been carried out for a bromohexadecane-in-water emulsion to
demonstrate the frequency-dependence of the scattering coefficients, and the effective speed and
attenuation
Time-temperature superposition in viscous liquids
Dielectric relaxation measurements on supercooled triphenyl phosphite show
that at low temperatures time-temperature superposition (TTS) is accurately
obeyed for the primary (alpha) relaxation process. Measurements on 6 other
molecular liquids close to the calorimetric glass transition indicate that TTS
is linked to an high-frequency decay of the alpha loss, while
the loss peak width is nonuniversal.Comment: 4 page
Acoustic scattering by a spherical obstacle: Modification to the analytical long-wavelength solution for the zero-order coefficient
This article was published in the Journal of the Acoustical Society of America and is also available at: http://dx.doi.org/10.1121/1.3543967Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low kca (typically kca < 0.01) and above at kca > 0.1, where kc is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A0. It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately
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