Relaxation ultrasonic properties

The presence of hydrogen bonding in water is shown by its anomalous thermophysical properties and has been confirmed by more recent methods of investigating its structure such as NMR, neutron scattering, dielectric relaxation, ultrasonic absorption,... 

The density of eHDA is 1.13 g/cm3, which is about 4% less than the density of uHDA [200], The different degree of structural relaxation should be evident when studying the thermal stability at 1 bar. The well-relaxed state is expected to be thermally more stable, and this expectation is confirmed experimentally At 1 bar, eHDA is stable up to 135 K, whereas uHDA is stable merely up to 115 K [190, 194, 196], Earlier, Johari [201] had noticed that HDA produced from LDA ( eHDA ) shows ultrasonic properties that differ from HDA produced from ice Ih ( uHDA ). 

Schwan was one of the founders of biomedical engineering as a new discipline. Before World War II, in the laboratory of Rajewski at the Frankfurter Institut fiir Biophysik, he had started with some of the most important topics of the field on low-frequency blood and blood serum conductivity, counting of blood cells, selective heating and body tissue properties in the ultra-high-frequency range, electromagnetic hazards and safety standards for microwaves, tissue relaxation, and electrode polarization. He also worked with the acoustic and ultrasonic properties of tissue. In 1950, he revealed for the first time the frequency dependence of muscle... 

This report has been written in order to demonstrate the nature of spin-state transitions and to review the studies of dynamical properties of spin transition compounds, both in solution and in the solid state. Spin-state transitions are usually rapid and thus relaxation methods for the microsecond and nanosecond range have been applied. The first application of relaxation techniques to the spin equilibrium of an iron(II) complex involved Raman laser temperature-jump measurements in 1973 [28]. The more accurate ultrasonic relaxation method was first applied in 1978 [29]. These studies dealt exclusively with the spin-state dynamics in solution and were recently reviewed by Beattie [30]. A recent addition to the study of spin-state transitions both in solution and the... 

In a solution where a nonzero volume change between the electronic isomers, HS and LS, is encountered, the position of the spin equilibrium will depend on pressure. The volume change, usually denoted here AF°, may be obtained from the study of the pressure dependence of equilibrium properties such as the magnetic susceptibility or the electronic spectrum. In favorable cases, A F° values may be derived from the amplitude of sound absorption observed in ultrasonic relaxation measurements of a spin equilibrium as will be shown in the... 

Studies on the dynamics of complexation for guests with cyclodextrins have been carried out using ultrasonic relaxation,40 151 168 temperature jump experiments,57 169 183 stopped-flow,170,178,184 197 flash photolysis,57 198 202 NMR,203 205 fluorescence correlation spectroscopy,65 phosphorescence measurements,56,206 and fluorescence methods.45,207 In contrast to the studies with DNA described above, there are only a few examples in which different techniques were employed to study the binding dynamics of the same guest with CDs. This probably reflects that the choice of technique was based on the properties of the guests. The examples below are grouped either by a type of guest or under the description of a technique. 

Three groups of phenomena affect the frequency-dependence of ultrasonic wave propagation classical processes, relaxation, and scattering, of which scattering is likely to dominate in foodstuffs due to their particulate nature. The two classical thermal processes are radiation and conduction of heat away from regions of the material, which are locally compressed due to the passage of a wave they can lead to attenuation but the effect is negligible in liquid materials (Herzfield and Litovitz, 1959 Bhatia, 1967). The third classical process is due to shear and bulk viscosity effects. Attenuation in water approximates to a dependence on the square of the frequency and because of this it is common to express the attenuation in more complex liquids as a()/o or a(f)jf2 in order to detect, or differentiate from, water-like properties. 

The study of molecular interactions in liquid mixtures is of considerable importance in the elucidation of the structural properties of molecules. Interactions between molecules influence the structural arrangement and shape of molecules. Dielectric relaxation of polar molecules in non-polar solvents using microwave absorption has been widely employed to study molecular structures and molecular interactions in liquid mixtures [81]. Ever since Lagemann and Dunbar developed a US velocity approach for the qualitative determination of the degree of association in liquids [82], a number of scientists have used ultrasonic waves of low amplitude to investigate the nature of molecular interactions and the physico-chemical behaviour of pure liquids and binary, ternary and quaternary liquid mixtures, and found complex formation to occur if the observed values of excess parameters (e.g. excess adiabatic compressibility, intermolecular free length or volume) are negative. These parameters can be calculated from those for ultrasonic velocity (c) and density (p). Thus,... 

The experimental techniques used to obtain the properties necessary to derive the kinetic constants of interest from the ultrasonic relaxation times have been previously described in detail [2,3]. Briefly, the degree of micelle ionization (P) and the binding constant (Ka) of an alcohol to mixed micelles were obtained from specific conductivity measurements as a function of surfactant concentration at various fixed alcohol compositions. The binding constant was determined from the slopes of the curves above the cmc, as proposed by Abu-Hamdiyyah et al... 

A special feature of amorphous materials is the anomalous behaviour of several properties at very low temperatures, such as in the low temperature specific heats. Most of these anomalies are attributed to the presence of two-level states (TLS) separated by small barriers, which gives rise to tunneling excitations. These excitations are characterized by wide distribution of relaxation times and energies. Several ultrasonic and low temperature specific heat measurements have been performed to characterize the TLS but their physical nature such as their structures, etc. is far from having been understood. These are the ADWP states discussed earlier in Chapter 7 in some detail. 

Chief among the interfacial properties of aqueous systems that suggest the occurrence of thermal anomalies are the following index of refraction, density, activation energy for ionic conductance, rates of surface reactions, surface tension, surface potentials, membrane potentials, heats of immersion, zeta potentials, rate of nucleation, viscous flow, ion activities, proton spin lattice relaxation times, optical rotation, ultrasonic velocity and absorption, sedimentation rates, coagulation rates, and dielectric properties. 

Another approach to determining the viscoelastic properties of dense microemulsions at high frequencies is to conduct ultrasonic absorption experiments. In such experiments it has been found that the percolation process is correlated to a shift of the ultrasonic dynamics from a single relaxation time to a distribution of relaxation times [121]. Other experiments showed an increase in the hypersonic velocity for samples at and beyond the percolation threshold. The complex longitudinal modulus deduced from such experiments is also correlated with the occurrence of the percolation phenomenon, which suggests that the velocity dispersion is clearly correlated with structural transformations [122]. 

I. Equilibrium Physical Properties, II. Dielectric and Ultrasonic Relaxation Studies," Polymer, 28... 

The optoacoustic properties of plasmon-resonant gold nanoparticles originate from photoinduced cavitation effects. This process can be summarized as follows (i) thermalization of conduction electrons on the subpicosecond timescale/ (ii) electron-phonon relaxation on the picosecond timescale and thermalization of the phonon lattice, with a subsequent rise in temperature by hundreds to thousands of degrees (iii) transient microbubble expansion upon reaching the kinetic spinodal of the superheated medium, initiated on the nanosecond timescale (iv) microbubble collapse, resulting in shockwaves and other forms of acoustic emission. The expansion and collapse of a cavitation bubble takes place on a microsecond timescale, and are easily detected by ultrasonic transducers. 

The theoretical treatment of the model of Aniansson and Wall is not directly applicable to the time constants obtained in ultrasonic experiments, but this gap has been bridged.The amplitude is predicted to be zero at the c.m.c. then increases with concentration to a broad maximum and thence slowly decreases, as observed for sodium dodecyl sulphate. An analysis of amplitudes in P-jump kinetics implies the possibility of a third relaxation process due to a change in electrolyte properties. This counterion binding equilibrium may have been observed in ultrasonic studies of sodium decyl sulphate. Attempts by the former authors to modify the Aniansson and Wall theory... 

The interpration of the ultrasonic relaxation spectrum in terms of the multistep mechanism is complicated but gives detailed kinetic information. It requires, however, a basic knowledge of the equilibrium distribution. In practice the ultrasonic technique is often used to the investigate ion of systems for which the equilibrium properties cannot be measured by other experimental means and hence the detailed equilibrium description is not known. In those situations it is still possible to obtain some information about the rates involved by using the two state consideration (13). It must be stated, that the rate constants obtained by this procedure are sort of mean values that may differ somewhat from the individual true rate constants. 

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