Quartz crystal resonator liquid contact

Fig.l Schematic presentation of the quartz crystal resonator in contact with a liquid. The contacting medium is a thin film rigidly attached to the crystal surface from one side, at z = d. The opposite surface of the crystal (z = 0) is unconstrained, d is the thickness of the quartz crystal... 

Urbakh M, Daikhin L (1994) Roughness effect on the frequency of a quartz crystal resonator in contact with a liquid. Phys Rev B 49 4866-4870... 

Since the early work of Kanazawa [1] and Bruckenstein in 1985 [2], quartz crystal resonators have been used for more than 12 years in contact with liquids to assess changes in mass during electrochemical surface processes. Extensive use of the electrochemical quartz crystal microbalance (EQCM) has been done in the study of electrode processes with change of mass simultaneous to charge transfer. 

As the readers may see, quartz crystal resonator (QCR) sensors are out of the content of this chapter because their fundamentals are far from spectrometric aspects. These acoustic devices, especially applied in direct contact to an aqueous liquid, are commonly known as quartz crystal microbalance (QCM) [104] and used to convert a mass ora mass accumulation on the surface of the quartz crystal or, almost equivalent, the thickness or a thickness increase of a foreign layer on the crystal surface, into a frequency shift — a decrease in the ultrasonic frequency — then converted into an electrical signal. This unspecific response can be made selective, even specific, in the case of QCM immunosensors [105]. Despite non-gravimetric contributions have been attributed to the QCR response, such as the effect of single-film viscoelasticity [106], these contributions are also showed by a shift of the fixed US frequency applied to the resonator so, the spectrum of the system under study is never obtained and the methods developed with the help of these devices cannot be considered spectrometric. Recent studies on acoustic properties of living cells on the sub-second timescale have involved both a QCM and an impedance analyser thus susceptance and conductance spectra are obtained by the latter [107]. 

When a quartz crystal resonator operates in contact with a liquid, the shear motion of the surface generates motion in the liquid near the interface. The velocity field, v(r, a>), related to this motion in a semi-infinite Newtonian h-quid is described by the hnearized Navier-Stokes equation ... 

When a quartz crystal resonator operates in contact with a liquid, the shear motion of the surface generates motion in the liquid near the interface. The... 

Mason [46] first observed that the viscoelastic properties of a fluid in contact with quartz crystals can affect the resonant properties. However, Mason s work had been forgotten and for a long time there have not been studies of piezoelectric acoustic wave devices in contact with liquids until Nomura and Okuhara [15] found an empirical expression that described the changes in the quartz resonant frequency as a function of the liquid density, its viscosity and the conductivity in which the crystal was immersed. Shortly after the empirical observations of Nomura were described in terms of physical models by Kanazawa [1] and Bruckenstein [2] who derived the equation that describes the changes in resonant frequency of a loss-less quartz crystal in contact with an infinite, non conductive and perfectly Newtonian fluid ... 

More recently the treatment was extended to piezoelectric devices in contact with viscoelastic media (i.e., liquids and polymers). It was then realised that if the deposited mass was not rigidly coupled to the oscillating quartz crystal, separation of inertial mass and energy losses was not possible with the measurement of the resonant frequency alone. Quartz crystal impedance in the acoustic frequencies was introduced in order to study mass and viscoelastic changes and a full electrical characterization of the crystal behaviour near resonance was employed. 

Bruckenstein and Shay (93) conducted an in situ measurement of the resonant frequency of an oscillating quartz crystal having one electrode face in contact with an electrolytic solution. It was experimentally shown that the volume and the height of the liquid above the crystal has no significant effect on the resonant frequency, and the resonant frequency varies as the square root of the solution viscosity. In addition, changes in temperature caused significant frequency changes as a result of concomitant alternations in the viscosity and density of most liquids. 

The oscillation frequency of a quartz resonator in contact with liquid was also investigated by Kanazawa et al (94,95). The relationship which expresses the change in the oscillation frequency of the quartz crystal in terms of fluid and quartz parameters can be described by ... 

It is interesting to note that for both a snrface film rigidly attached to the resonator and a liquid in contact with the snrface of the quartz crystal, the shift of the resonant frequency can be written in the same form, as... 

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