Sonic absorption

Sonic absorption has been less systematically studied than sonic speed. Yet it is of considerable practical importance. Vibration damping in machinery, automobiles and aircraft constitutes an important task for both the reduction of noise and the prevention of fatigue failure of the materials. 

As to the absorption values in the literature (see Table 14.1) some tentative conclusions may be drawn  

This rule is valid for linear, non-cross-linked polymers. 

7 Linear loss modulus versus temperature for a PMA/PEMA 55/45 IPN.The background correction for E is also shown. From Chang et al. (1988). Courtesy John Wiley 8t Sons, Inc. 

The highest sonic damping is obtained in transition zones. The glass transition can be used for this purpose if cross-linked polymers are applied, with a rubbery solid state until far above Tg. Very interesting work in this field was done by Sperling and his coworkers (1987,1988) who studied the damping behaviour of homopolymers, statistical copolymers and interpenetrating networks (IPNs) of polyacrylics, polyvinyls and polystyrenes. 

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Sonic absorption on the other hand is - for linear polymers - a typical constitutive property, dependent of temperature and frequency, for which no additivity techniques are available. For cross-linked polymers the integrated loss modulus-temperature function (the "loss area") in the glass-rubber transition zone shows additive properties. 

Calf thymus (CT) DNA was first fragmented by sonication, then purified by a standard procedure. Agarose gel electrophoresis for the sonicated CT DNA revealed a distribution in molecular weight ranging from 30 kDa to 260 kDa which is equivalent in base pairs (bp) from 40 to 400 (1 bp = 660 Da). The DNA fragments were reacted with HEDS in the presence of l-cyclohexyl-3-(2-morpholinoethyl) carbodi-imide metho-p-toluenesulfonate (CMC/jTs). Finally, the reaction mixture was gel-filtered and the macro-molecular fractions, when displayed the characteristic absorption of 260 nm of the nucleic bases, were collected. 

Several precautions were taken to ensure the immobilization chemistry. First, the sulfhydryl groups containing the macromolecular fraction was spectrophotometrically determined according to the literature [15]. We found that every set of 150 base pairs contained approximately one disulfide group. Since the DNA fragment used has hundreds of base pairs, each DNA strand seems to have one disulfide as its terminal group. Next, we made IR spectral measurements in a reflection-absorption (RA) mode [14b]. A freshly evaporated gold substrate was immersed into the DNA solution for 24 h at 5°C. The substrate was carefully rinsed with deionized water, dried under vacuum and was immediately used for the measurements. An Au substrate treated with unmodified, native sonicated CT DNA solution was also prepared as the control measurement. The / -polar-ized radiation was introduced on the sample at 85° off the surface normal and data were collected at a spectral resolution of 4 cm with 2025 scans. 

Fig. 6.4 Change in the absorption spectra of aqueous solutions containing ImMof H2PtCl6 and 8 mM of SDS as a function of sonication time [38]...

Sathish Kumar et al. [45] prepared bimetallic Au-Ru nanoparticles by the simultaneous reduction of both Au3+ and Ru3+ ions by ultrasound irradiation at three different molar ratios (Au3+ Ru3+ 1 1, 1 3 and 1 5) in 4 h in the presence of PEG. A significant change in the absorption as a function of sonication time was observed for Au-Ru bimetallic particles (Fig. 6.10), which indicated the... 

Absorption spectra of CdS colloid indicate the formation of quantum sized CdS particles. The particle size increased upon sonication, indicated by the red shift in the onset of absorption. The particle size was highly dependent on the mercaptan used, because of the absorption of the mercaptan on the particle acting as a capping agent and the rate of H2S produced. Study of mercaptan systems revealed that there was also a thermal process responsible for CdS formation. 25% of the total CdS produced sonochemically was formed via a thermal mechanism presumably in the hot shell around the compressed bubble. CdS colloid could be dissolved quite readily by sonicating solutions under air saturated conditions [89] by the following reaction,... 

The attenuation of sonic energy by absorption is an exponential function of the pathlength, x, and the absorbance, a ... 

For the direct determination of OAs in beverages—for example, wine, beer, fruit juices, and soft drinks—the HPLC methods are very suitable. Sample treatment is usually limited to filtration (removal of solid particles) and sonication (removal of gases, mainly C02, from saturated drinks). The detection limit for individual OA compounds can be enhanced by monitoring at their absorption maximum. For BA this is 228 nm, for SA 259 nm, and for EsHBA 255 nm. But practical measurements are usually done, by compromise, at a wavelength of 235 nm (1,2). 

When PCP solution (Id4 M) under continuous air bubbling is subjected to ultrasound effects, the characteristic absorption bands decrease and the treatment leads to a complex mixture of products. Carbon-chlorine bonds are rapidly cleaved, and after a 150-min sonication time, 90% of the chlorine is recovered in the solution as chloride ions. PCP transformation in aerated solution occurs together with nitrite and nitrate formation. Carbon dioxide is a product of PCP degradation, and it has long been recognized as an inhibitor for sonochemical reactions. 

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