Acoustic attenuation spectroscopy

On-line particle sizing by ultrasonic (acoustic attenuation) spectroscopy was developed for use during batch crystallization processes.14 Crystallization of the alpha polymorph of (l) -glutamic acid from aqueous solution was monitored by continuously pumping the crystallizing solution through an on-line ultrasonic spectrometer. The method enabled measurement of the crystal size distribution and solid concentration throughout the... 

Acoustic attenuation spectroscopy measurements can be made without the need for sample dilution and can be used in the particle size range of 10 nm to 100 pm. As sound travels through a slurry or colloid, it is attenuated. The level of attenuation is related to the particle size distribution as discussed in Refs. 20 and 21. Acoustic attenuation measurements can be made on high[Pg.624]

Acoustic attenuation spectroscopy (ultrasonic) AAS Acoustic wave interaction 0.025->100... 

Different from acoustic attenuation spectroscopy, in electroacoustic spectral analysis, sound waves are generated by an applied high frequency electric field across a colloidal suspension and subsequently detected. This is called the electrokinetic sonic amplitude effect (ESA) [38]. These sound waves arise because the alternating electric field pushes the suspended particle forwards and backwards. By measuring the magnitude and phase angle of the sound waves at multiple frequencies (typically from 1-10 MHz), the particle dynamic mobility, Pd, can be determined, provided the concentration and the density of the... 

Acoustic spectroscopy measures the speed and attenuation of sound waves interacting with a colloidal suspension. When a sound wave in the range of 1 to 100 MHz interacts with a colloidal suspension, the measured acoustic attenuation and... 

Acoustic Methods Ultrasonic attenuation spectroscopy is a method well suited to measuring the PSD of colloids, dispersions, slurries, and emulsions (Fig. 21-15). The basic concept is to measure the frequency-dependent attenuation or velocity of the ultrasound as it passes through the sample. The attenuation includes... 

Ultrasonic experiments using laser induced phonon spectroscopy have been performed in a nematic liquid single crystal elastomer [48]. The experiments reveal a dispersion step for the speed of sound and a strong anisotropy for the acoustic attenuation constant in the investigated frequency range (100 MHz -1 GHz). These results are consistent with a description of LCEs using macroscopic dynamics [54-56] and reflect a coupling between elastic effects and the nematic order parameter as analyzed in detail previously [48]. 

The contribution of electrokinetic losses to the total sound attenuation is almost always negligibly small (9) and will be neglected. This opens an opportunity to separate acoustic spectroscopy from electroacoustic spectroscopy because acoustic attenuation spectra are independent of the electric properties of the dispersed system. 

P. Mougin, D. Wilkinson, K.J. Roberts, R. Tweedie, Characterization of particle size and its distribution during the crystallization of organic fine chemical products as measured in situ using ultrasonic attenuation spectroscopy. J. Acoust. Soc. Am. 109(1), 274-282 (2001). doi 10. 1121/1.1331113... 

The attenuation of ultrasound (acoustic spectroscopy) or high frequency electrical current (dielectric spectroscopy) as it passes through a suspension is different for weU-dispersed individual particles than for floes of those particles because the floes adsorb energy by breakup and reformation as pressure or electrical waves josde them. The degree of attenuation varies with frequency in a manner related to floe breakup and reformation rate constants, which depend on the strength of the interparticle attraction, size, and density (inertia) of the particles, and viscosity of the Hquid. 

Tsai, C. S. and Lee, C. C. (1987). Nondestructive imaging and characterization of electronic materials and devices using scanning acoustic microscopy. In Pattern recognition and acoustical imaging (ed. L. A. Ferrari). SPIE 768,260-6. [ 110,202] Tsukahara, Y. and Ohira, K. (1989). Attenuation measurements in polymer films and coatings by ultrasonic spectroscopy. Ultrasonics Int. 89, 924-9. [204]... 

The ring-opening metathesis polymerization of dicyclopentadiene was monitored by ultrasonic spectroscopy.16 The thermoset poly(dicyclopentadiene) is formed by ringopening and cross-linking in a reaction injection molding system. A reaction cell with a plastic window was constructed for use with pulse echo ultrasonic spectroscopy. Realtime measurements of density, longitudinal velocity, acoustic modulus and attenuation were monitored. Reaction kinetics were successfully determined and monitored using this technique. 

FTIR reflectance and transmission spectroscopy is used for analysis of thin films. Nevertheless, due to the high absorptivities of mid-IR bands, the film thickness must be limited (up to 100 pm, depending on the specific bands chosen) in order to perform an accurate qualitative analysis. Other IR methods, such as attenuated total reflectance (ATR) and photoacoustic methods provide IR spectra of thick material, because they penetrate a very thin layer at the surface of a sample. However, is important to point out that the effective pathlength for the ATR and the photo-acoustic methods depends on the refractive index and thermal diffusivity, respectively. Therefore, the use of these techniques for the quantitative analysis of non-homo-geneous materials can be difficult. 

The attenuation and velocity of acoustic energy in polymers are very different from those in other materials due to their unique viscoelastic properties. The use of ultrasonic techniques, such as acoustic spectroscopy, for the characterization of polymers has been demonstrated [47,48]. For AW devices, the propagation of an acoustic wave in a substrate causes an oscillating displacement of particles on the substrate surface. For a medium in intimate contact with the substrate, the horizontal component of this motion produces a shearing force. In such cases, there can be sufficient interaction between the acoustic wave and the adjacent medium to perturb the properties of the wave. For polymeric materials, attenuation and velocity of the acoustic wave will be affected by changes in the viscoelastic behavior of the polymer. 

Part II of the book deals with lesser known aspects of US for the analytical chemists such as its use as an energy source for detection purposes. Thus, ultrasound-based detection techniques viz. US spectrometry in its various modes including ultrasound attenuation, ultrasonic velocity, resonant ultrasound, laser-generated, ultrasound reflection and acoustic wave impedance spectroscopies) are dealt with in Chapter 9. Finally, Chapter 10 is devoted to seleoted applioations of US spectrometry — mostly non-analytical applications from whioh, however, analytical chemists can derive new, interesting analytical uses for ultrasound-based deteotion techniques. 

While the operating principles are relatively simple, the analysis of the attenuation data to obtain particle size distributions does involve a degree of complexity in fitting experimental results to theoretical models based on various acoustic loss mechanisms. The advent of high-speed computers and the refinement of these theoretical models has made the inherent complexity of this analysis of little consequence. In comparison, many other particle sizing techniques such as photoncorrelation spectroscopy also rely on similar levels of complexity in analyzing experimental results. 

Only the first four loss mechanisms (viscous, thermal, scattering, and intrinsic) make a significant contribution to the overall attenuation spectra in most cases. Structural losses are significant only in structured systems that require a quite different theoretical framework. These four meeha-nisms form the basis for acoustic spectroscopy. 

In the field of emulsions characterization, it is well known that dilution may create perturbation on the surface properties of the droplets and on interactions between the droplets. To give an example, matter transfers resulting from osmotic shocks may occm causing polydispersity changes as has been shown when such events are required (5,6). In fact, very few techniques avoid dilution, namely, dielectric or hert-zian spectroscopy (7-9), rheology (2), conductimetry (6,7), and more recent ones based on acoustical methods (10), focussed beam reflectance (11,12), or microwave attenuation (13). All these techniques are complementary and new techniques are always wel come. 

In a similar manner to light, other types of radiation, e.g., electromagnetic waves in the X-ray domain, high-frequency electric fields, or acoustic waves, offer ways to monitor changes in composition and structure of suspensions. For instance, dielectric spectroscopy was used to investigate the moisture uptake and stability of cosmetic creams (Sutananta et al. 1996 Tamburic et al. 1996), and acoustic parameters (resonance frequency, attenuation, sound speed) were shown to correlate with sol-gel transition in suspensions of coUoidal silica (Senouci et al. 2001), as well as with the phase transition of renneted milk (Bakkali et al. 2001). 

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