Adhesion and fingering in the lifting Hele-Shaw cell: Role of the substrate

Abstract

The lifting Hele-Shaw cell (LHSC) is used to study adhesion as well as viscous fingering. In the present paper we report a series of observations of development of the interface for different viscous fluids, both Newtonian and non-Newtonian, in a LHSC operated at a constant lifting force. Glass and perspex are used as the plates in two different sets of experiments. The objectives are 1) to measure the time required to separate the plates as a function of the lifting force and 2) to note the force above which viscous fingering appears. We find that for the Newtonian fluids, the plate separation time follows a universal power law with the lifting force, irrespective of fluid and substrate. The non-Newtonian fluids too, with proper scaling obey the same power law. The appearance of fingering, however, depends on the properties of the fluid as well as the substrate. We suggest a modified form of the capillary number which controls the onset of fingering; this new quantity, termed the "fingering parameter" involves the dielectric constants of the substrate and fluid in addition to the viscosity and surface tension.

Capillary-pressure driven adhesion of rigid-planar surfaces

“…The fingering patterns seen in the unstable experiments, just before complete detachment, have been observed and studied in similar systems [13,[22][23][24][25]. Two examples ( Fig.…”

“…Pr dr, as this leads to a fingering instability [21,13,[22][23][24][25] where the shape of the interface is no longer cylindrical. Therefore, it is useful to also consider the relationship between the fluid volume, gap spacing, and an arbitrary areâ…”

“…The de-wetting aspects that occur in an unstable configuration of the proposed problem is complicated, because of the sometimes simultaneous presence of a capillary [19,17,20] and a fingering instability [21,13,[22][23][24][25]. The discussion in this paragraph is limited to capillary instabilities since it results in rupture of the liquid bridge and yields detachment while fingering may influence the dynamics of the de-wetting process.…”

Computer simulation of viscous fingering in a lifting Hele-Shaw cell with grooved plates

“…Viscous fingering in the lifting Hele-Shaw cell (LHSC) is now a widely studied problem [1][2][3][4], because of its academic interest and also due to its application in practical problems such as adhesion [5,6].…”

“…The more viscous fluid, sandwiched between the two plates, forms fingering patterns at the interface, under proper conditions [1,4,5]. Different interesting modifications of the HS cell are reviewed in [10].…”