Optical observation of high-frequency drop oscillations by a spectrum compression technique applied to the capillary pressure tensiometry.
Image acquisition and subsampling of periodic high-frequency drop oscillations is presented as an advantageous metrological procedure in capillary pressure tensiometry (CPT). The observation of a finite sequence of single tone or of multiharmonic cycles, subsampled in an expanded time-scale interval, allows the characteristics of the real oscillations to be well-reconstructed in a frequency-compressed spectrum, where each component is translated toward lower frequencies. The introduced technique is applied to nanoliter-sized water drops, oscillating in a hydrocarbon matrix up to 150 Hz frequency, by using a standard PAL CCD camera provided with an electronic shutter. Application examples show the important role of this technique in data analysis and interpretation of typical high-frequency oscillating drop/bubble experiments. In particular, this technique is effective to check the onset of critical hydrodynamic effects and allows for the determination of the intrinsic elasticity of the liquid/cell system as a function of frequency by comparison of the liquid volume, as displaced by a piezo-actuator, and the actually observed drop volume-amplitude oscillation. The knowledge of this quantity is fundamental for the calculation of the dilational viscoelasticity from the acquired pressure data in the CPT.
University of Florence, Department of Organic Chemistry, Via della Lastruccia, 13, I-50019 Sesto Fiorentino, Firenze, Italy. loglio@unifi.it
Giuseppe
G
Loglio
Piero
P
Pandolfini
Reinhard
R
Miller
Francesca
F
Ravera