Fluorescence depolarisation monitoring of liquid flow before and after exiting a slit nozzle

Abstract

Steady-state fluorescence depolarisation was used to study the hydrodynamics of ethylene glycol flow inside a quartz slit nozzle for 24 mm (Re~200) and outside as a free thin jet, for 14 mm. The polarisation profiles (over 1000 points) allowed direct evaluation of the velocity gradient within the flowing liquid from this molecularlevel probe. Inside the nozzle two lateral boundary layers were observed. The velocity profile was flattened, which was attributed to strong chemical interactions with the walls of the cell. Within the jet, four polarisation profile maxima were observed for the first time, corresponding to two internal converging streams.

Observation of wall wettability under imposed flow by fluorescence depolarization: dependence on surface oxygen content and degree of polymer branching

“…Fluorescence depolarization of the same probe in MCFF, i.e., films flowing within thin microchannel flow cells (MFcells), allowed direct observation of the boundary layers and showed that the velocity profile is flattened due to strong chemical interactions with the walls [2]. The method has already proved its usefulness in the nondestructive detection of chemical alterations at internal walls of 10-µm-thick MFcells [12] and in the identification of inner wall coatings for crude oil ducts that are best to inhibit paraffin deposition [13].…”

“…Traditional fluid mechanics concepts such as laminar and turbulent regimes do not apply when the flow consists mainly of superimposed boundary layers [1,2]. Molecular hydrodynamics rules these processes due to chemical interactions between the microchannel walls and the flowing liquid molecules, the strength of which can be so high that they overcome gravity, among other effects [3,4].…”

Detection of chemical alterations at internal walls of microchannel flow cells by nondestructive fluorescence depolarization

“…Fluorescence depolarization kinetics was obtained with picosecond resolution within certain regions, indicating a strong anisotropy in θ and φ rotational diffusion dynamics [12]. Previous results have shown that for thin channels the flow consists mainly of superposed boundary layers where interfacial chemical interactions become predominant over bulk flow [13]. Recently, PLF-FI was used to evaluate relative dynamic Γ SL for monoethylene glycol flowing on either glass or tin dioxide and it was found that dynamic Γ SL was stronger for glass than for tin dioxide [5].…”

Construção e avaliação de célula de fluxo para estudo da tensão interfacial dinâmica da interface fluxo líquido - sólido por despolarização da fluorescência

“…Foi recentemente demonstrado que é sensível à tensão interfacial dinâmica ao monitorar fluxos líquidos em jatos laminares 6,7 , filmes finos 8-11 e em células de fluxo 12,13 .…”