scholarly journals Ratio of dynamic moduli and estimation of relaxation times

2002 ◽  
Vol 46 (4) ◽  
pp. 777 ◽  
Author(s):  
Jianhua Huang ◽  
Donald G. Baird
Keyword(s):  
Relaxation Times ◽  
Dynamic Moduli

Reinforcement Mechanisms in Carbon Black and Silica Loaded Rubber Melts at Low Stresses

1996 ◽  
Vol 69 (2) ◽  
pp. 253-265 ◽  
Author(s):  
H. Eggers ◽  
P. Schummer
Keyword(s):  
Relaxation Times ◽  
Polymer Structure ◽  
Rubber Matrix ◽  
Dynamic Moduli ◽  
Effectiveness Factors ◽  
Constant Height ◽  
Linear Viscoelastic ◽  
Hydrodynamic Effects ◽  
Very High ◽  
Thomas Equation

Abstract For a range of different fillers, silicas and carbon blacks, added to a rubber melt at various concentrations, dynamic moduli in the linear viscoelastic limit have been determined. It is shown that reinforcement is due to hydrodynamic effects and the formation of a secondary particulate structure within the rubber matrix. Both mechanisms can be distinguished experimentally by a frequency sweep. Hydrodynamic reinforcement depends on the filler volume to which immobilized polymer must be added. Its concentration dependence is well described by the semiempirical exponential Thomas Equation. Nominal and effective filler loadings are related by concentration-independent effectiveness factors which can be modelled for all types of fillers considering an immobilized layer of constant height around an agglomerated cluster of filler particles. This provides an explanation for the well-known dependence of reinforcement ability on surface area at small stresses. The chemical and microscopic structure of the filler surface appears to be less important with respect to immobilization ability in the linear viscoelasic regime. The secondary structure formed by the particles is found to be tied together by the elastomer. Its modulus correlates with the filler's immobilization ability and shows little dependence on the filler nature. Due to formation of a filler-polymer structure with individual relaxation times, a strict separability of hydrodynamic and interparticular-reinforcement mechanisms at very high loadings no longer applies.

An emerging technology: Nuclear magnetic resonance microscopy

1988 ◽  
Vol 46 ◽  
pp. 1000-1001
Author(s):  
M.J. Hennessy ◽  
E. Kwok
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Basic Research ◽  
Local Environment ◽  
Magnetic Resonance Images ◽  
Nmr Microscopy ◽  
Mri Scans ◽  
Temperature Relaxation ◽  
Nuclear Magnetic

Much progress in nuclear magnetic resonance microscope has been made in the last few years as a result of improved instrumentation and techniques being made available through basic research in magnetic resonance imaging (MRI) technologies for medicine. Nuclear magnetic resonance (NMR) was first observed in the hydrogen nucleus in water by Bloch, Purcell and Pound over 40 years ago. Today, in medicine, virtually all commercial MRI scans are made of water bound in tissue. This is also true for NMR microscopy, which has focussed mainly on biological applications. The reason water is the favored molecule for NMR is because water is,the most abundant molecule in biology. It is also the most NMR sensitive having the largest nuclear magnetic moment and having reasonable room temperature relaxation times (from 10 ms to 3 sec). The contrast seen in magnetic resonance images is due mostly to distribution of water relaxation times in sample which are extremely sensitive to the local environment.

On relaxation times

1999 ◽  
Vol 169 (10) ◽  
pp. 1163
Author(s):  
V.L. Vaks ◽  
V.V. Mityugov
Keyword(s):  
Relaxation Times

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

Relaxation times of normal breast tissues

1994 ◽  
Vol 35 (3) ◽  
pp. 258-261 ◽  
Author(s):  
Kirsti Dean ◽  
M. -L. Majurin ◽  
M. Komu
Keyword(s):  
Relaxation Times ◽  
Normal Breast ◽  
Breast Tissues

Some Aspects of Discrete Relaxation Time Spectra as Obtained from Dynamic Moduli Data

1995 ◽  
Vol 60 (11) ◽  
pp. 1815-1829 ◽  
Author(s):  
Jaromír Jakeš
Keyword(s):  
Relaxation Time ◽  
Least Squares ◽  
Discrete Spectrum ◽  
Integral Transform ◽  
Time Spectrum ◽  
Relaxation Time Spectrum ◽  
Dynamic Moduli ◽  
Best Fitting ◽  
Discrete Spectra ◽  
Well Posed

The problem of finding a relaxation time spectrum best fitting dynamic moduli data in the least-squares sense is shown to be well-posed and to yield a discrete spectrum, provided the data cannot be fitted exactly, i.e., without any deviation of data and calculated values. Properties of the resulting spectrum are discussed. Examples of discrete spectra obtained from simulated literature data and experimental literature data on polymers are given. The problem of smoothing discrete spectra when continuous ones are expected is discussed. A detailed study of an integral transform inversion under the non-negativity constraint is given in Appendix.

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