Absorption ultrasonic system

Ultrasonic absorption is used in the investigation of fast reactions in solution. If a system is at equilibrium and the equilibrium is disturbed in a very short time (of the order of 10"seconds) then it takes a finite time for the system to recover its equilibrium condition. This is called a relaxation process. When a system in solution is caused to relax using ultrasonics, the relaxation lime of the equilibrium can be related to the attenuation of the sound wave. Relaxation times of 10" to 10 seconds have been measured using this method and the rates of formation of many mono-, di-and tripositive metal complexes with a range of anions have been determined. 

Ultrasonic absorption is a so-called stationary method in which a periodic forcing function is used. The forcing function in this case is a sound wave of known frequency. Such a wave propagating through a medium creates a periodically varying pressure difference. (It may also produce a periodic temperature difference.) Now suppose that the system contains a chemical equilibrium that can respond to pressure differences [as a consequence of Eq. (4-28)]. If the sound wave frequency is much lower than I/t, the characteristic frequency of the chemical relaxation (t is the... 

The several experimental methods allow a wide range of relaxation times to be studied. T-Jump is capable of measurements over the time range 1 to 10 s P-jump, 10 to 5 X 10" s electric field jump, 10 to 10 s and ultrasonic absorption, 10 to 10 " s. The detection method in the jump techniques depends upon the systems being studied, with spectrophotometry, fluorimetry, and conductimetry being widely used. 

In ultrasonic relaxation measurements perturbation of an equilibrium is achieved by passing a sound wave through a solution, resulting in periodic variations in pressure and temperature.40,41 If a system in chemical equilibrium has a non-zero value of AH° or AV° then it can be cyclically perturbed by the sound wave. The system cannot react to a sound wave with a frequency that is faster than the rates of equilibration of the system, and in this case only classical sound absorption due to frictional effects occurs. When the rate for the host-guest equilibration is faster than the frequency of the sound wave the system re-equilibrates during the cyclic variation of the sound wave with the net result of an absorption of energy from the sound wave to supply heat to the reaction (Fig. 4). 

The sound absorption coefficient, a, is increased when the dynamics of the chemical system are of the same order of magnitude as the frequency of the sound wave,41 and experimentally this quantity is measured as a function of frequency of the ultrasonic sound wave (Fig. 4). When the frequency of the sound wave is of the same order as the frequency for the relaxation process, effects due to relaxation of the equilibrium give rise to characteristic changes in the quantity a//2, where a is the sound absorption coefficient measured at frequency /40 The variation of a with frequency, /, has an inflection point at the relaxation frequency of the system, fr, which is related to 1/t, where r is the relaxation time (1/t = 27i/r).40,41 The expression relating the quantity... 

The separation of the two stages is easier to discern when the rates of the two processes are so different, but it can also be seen in the ultrasonic spectra of metal-sulfate systems (Sec. 3.4.4). Ultrasonic absorption peaks can be attributed to formation of outer-sphere complexes (at higher frequency, shorter t) and collapse of outer-sphere to inner-sphere complexes (at lower frequency). In addition to uv spectral and ultrasonic detection, polarimetry and nmr methods have also been used to monitor and measure the strength of the interaction. There are difficulties in assessing the value of ATq, the outer-sphere formation constant. The assemblage that registers as an ion pair by conductivity measurements may show a blank spectroscopically. The value of Aq at T" K may be estimated using theoretically deduced expres-... 

Gordon Atkinson I think there is, at least in principle, a way to examine a system for distribution of very similar paths. This is by relaxation technique, particularly ultrasonic absorption. A distribution of similar, though not identical paths, implies a distribution of relaxation times centered at a certain frequency. But there is a subtle experimental problem involved in distinguishing between a single relaxation time and a rather closely spaced distribution of relaxation times. 

In collaboration with the laboratory of virology of the Institute of Molecular and Cellular Biology of Strasbourg, our laboratory studied the ultrasonic absorption of the BMV (Brom mosaic virus) capside and of the dissociated system. The capside is made of 180 proteins it can easily be dissociated into 90 dimers. 

One of our aims in using ultrasonics was to study the kinetics of the association-dissociation process. Kinetic effects would produce a maximum of absorption when the pH is changed at constant frequency. No information about the kinetics has been obtained so far. However, the difference of absorption in capsides and in the dissociated system turned out to be of interest, because of the unexpected increase of absorption by capsides. 

Pressure jump and electric field jump methods have also been used, as have methods depending upon periodic changes in some property. For example, absorption of ultrasonic sound causes a periodic change in the pressure of the system. 

There have been very few studies on the kinetics of micellization in block copolymer solutions. Micellization in aqueous surfactant systems close to equilibrium occurs on a time-scale far below one second. Experimental results obtained by fast reaction techniques, such as temperature jumps or pressure jumps or steady-state methods such as ultrasonic absorption, NMR and ESR, show that at least... 

Tn the critical region of mixtures of two or more components some physical properties such as light scattering, ultrasonic absorption, heat capacity, and viscosity show anomalous behavior. At the critical concentration of a binary system the sound absorption (13, 26), dissymmetry ratio of scattered light (2, 4-7, II, 12, 23), temperature coefficient of the viscosity (8,14,15,18), and the heat capacity (15) show a maximum at the critical temperature, whereas the diffusion coefficient (27, 28) tends to a minimum. Starting from the fluctuation theory and the basic considerations of Omstein and Zemike (25), Debye (3) made the assumption that near the critical point, the work which is necessary to establish a composition fluctuation depends not only on the average square of the amplitude but also on the average square of the local... 

In the case of labile complexes, an equilibrium between inner and outer sphere complexes may exist, as has been concluded by Eigen and Tamm (36) from measurements of ultrasonic absorption. They have studied sulphate complexes of Be2+, Mg2+ and the divalent ions of the first series of transition elements from Mn2+ on. In all those cases, the outer sphere complexes have been found to predominate, the inner sphere complexes being only 10—20% of the total. The values of AH reported for these systems (22, 23, 35) would certainly suggest a higher proportion of inner sphere complexes, being closer to the values of AH found for complexes which are more or less firmly established as inner sphere than to those found for complexes established as outer sphere. This question merits further investigation. 

Existing studies on the US-assisted hydrolysis of carbohydrates have failed to clarify the behaviour of chemical systems upon US irradiation [87]. Thus, Dubois et al. used a US bath at a frequency of 35 kHz — further details were not reported — as, in their opinion, a probe increases the temperature of the irradiated system significantly. They found very acid conditions (12 M sulphuric acid) to cause total degradation of carbohydrates — the sonicated solution did not exhibit any absorption at 485 nm after the addition of phenol for the development of the Dubois method [88]. They concluded that promoting hydrolysis in an acid medium — it is unclear whether they assayed different acid concentrations — is not feasible and performed the ultrasonicated hydrolysis step in pure water for 3 h, after which they added the acid to develop the derivatizing reaction. Further research on this topic is clearly required in order to clarify such an uncommon behaviour. 

Best fit parameters of the ultrasonic data to eq 2 for systems containing propanol, butanol and pentanol have been previously published [2,3]. Subsequently, studies were extended to include ultrasonic absorption measurements of ternary systems of DTAB-BE-water. Values of... 

The interesting behaviour observed for aggregate systems of surfactant and BE requires a broader investigation. Systematic thermodynamic and ultrasonic absorption studies of systems where the number of EO units in the alcohol is increased are currently in progress. The information obtained should be of benefit in extending the commercial application of these surfactant-cosurfactant systems. 

Ultrasonic absorption measurements were carried out over the frequency range from 0 2 to 65 MHz. Three different techniques were used depending on the frequency ranges from 0 3 to 1.7 MHz, we used the plano-concave resonator method coupled with the optical detection techniques, from 2 to 7 MHz range we used the cylindrical resonator method and from 15 MHz to 65 MHz we used the pulse method. The details of the experimental system are described elsewhere. ... 

Previous investigations of helix-coil transition kinetics, which used a variety of fast relaxation methods (electric field jump, ultrasonic absorption, dielectric relaxation and temperature jump), encountered many difficulties (12). The systems studied were long homopolymers (>200 residues) that often had hydrolyzable side chains. Controversial results have been reported, depending on the experimental technique employed, because unwanted side chain reactions or molecular reorientation were often difficult to distinguish from the helix-coil conformational change. However, as observed here, a maximum in the relaxation times was detected for these experiments ranging from 15 ps to 20 ns and was attributed to the helix-coil transition. 

The MgS04 System An interesting example is given by the interpretation obtained from ultrasonic absorption measurements on 2-2 electrolyte systems. Eigen and Tamm (1962) proposed a three-step process, for example. 

The ultrasonic absorption in relation to the transitions and critical phenomena in microemulsions has been studied by Lang et al. (72). The ultrasonic absorption is very sensitive to the concentration fluctuations which occur near the critical temperature or composition in binary liquids. Similar absorption maxima were also expected as the composition of the systems was varied in the vicinity of composition where water-in-oil microemulsions convert into the oil-in-water microemulsions. However, the most puzzling feature of these data is probably the very continuous change of the relaxation parameters with composition even in the range where W/0 microemulsions turn into 0/W microemulsions. 

Ultrasonic absorption and viscosity measurements are reported on Figures 4 and 5 for the ATP and ATB systems. The viscosity and ultrasonic absorption variations for the hard-sphere-like microemulsion ATP versus 4> are progressive while for ATB microemulsion, viscosity and ultrasonic absorption data show a large anomaly around [Pg.80]

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