Excess thermal noise and low-frequency oscillations during capillary flow of aqueous solutions of poly(ethylene oxide)

Abstract

Abstract:The excess thermal noise generated in polymer solutions through narrow capillaries is studied in detail for aqueous solutions of poly(ethylene oxide), (m w ~ 4" 106), of varying concentration. With increasing flow rate, the excess noise level increases, the noise spectrum assuming a 1/f~-form with e ~ 1.5. Within a critical flow range, distinct peaks appear in the spectrum, their frequencies being multiples of a fundamental frequency. The latter frequency ()Co) is found to increase with the flow rate; this variation, as well as that brought about by varying concentration and capillary dimensions, can be accommodated in a single curve correlating f0 with the shear rate at the capillary wall. No such correlation was found for the total noise level. The value off0 appeared to be determined by transversal oscillations of the liquid stream entering the capillary. Addition of small amounts of silica pamcies (Aerosil) led to the disappearance of the peaks in the spectrum.

Electrical fluctuations and entry flow instabilities during capillary flow of aqueous poly (ethylene oxide) solutions

“…The flow noise data reproduced in the earlier papers [23][24][25] were obtained with platinum electrodes. Using other electrodes materials, such as gold, did not affect the results.…”

“…In contrast to the U 2-figures the spectra are based on linear voltages related to the square root of frequency in the fashion preseribed by the Nyqvist formula [25]. The spectral width of the frequency analysis equipment (FFT) was 0.05 Hz.…”

“…The flow cell containing the capillary, and the electronic equipment for the measurement of voltage fluctuations between two electrodes placed on both sides of the capillary have been described in [23][24][25].…”

“…The noise data are presented as U} / u~ with u~ denoting the mean square value of the noise during flow, Üt2 the corresponding thermal noise value at rest. U 2 was calculated using the Nyqvist formula [25] from the corresRg_nding resistance, temperature and band-width values. The U 2 figures were obtained by integration oveLa bandwidth of ca.…”

“…In a series of papers [23][24][25], the present authors have reported on electrical fluctuations generated without any external voltage during capillary flow of aqueous solutions of PEO, PAM and some other systems, including non-aqueous solutions. The fluctuations (noise) were characterized by a 1/f ~ type frequency spectrum with a plateau at its low frequency end.…”