Viscous fingering at ultralow interfacial tension

Abstract

We experimentally study the viscous fingering instability in a fluid-fluid phase separated colloid-polymer mixture by means of laser scanning confocal microscopy and microfluidics. We focus on three aspects of the instability. (i) The interface between the two demixed phases has an ultralow surface tension, such that we can address the role of thermal interface fluctuations. (ii) We image the interface in three dimensions allowing us to study the interplay between interface curvature and flow. (iii) The displacing fluid wets all walls completely, in contrast to traditional viscous fingering experiments, in which the displaced fluid wets the walls. We also perform lattice Boltzmann simulations, which help to interpret the experimental observations.

Optical trapping of interfaces at ultra-low interfacial tension

“…The experimental dynamic proles are well described by eqn (5) as is evident from the solid lines in Fig. 2(b).…”

“…[3][4][5][6] In atomic and molecular systems, the amplitude of interface uctuations is typically in the (sub)nanometer range, making the relevant interface dynamics experimentally very hard to access. 1,2 Importantly, at these length scales molecular uctuations and interface dynamics strongly inuence the transport and the response of the uids.…”

Off-equilibrium surface tension in miscible fluids

“…Most of the previous works have focused on the interface between phase-separated colloidal fluids at thermodynamical equilibrium [52][53][54][55] ; however, colloidal suspensions are also excellent candidates for investigating off-equilibrium surface tension, since diffusion is comparatively slow in colloids or polymers, The first experimental investigation of the EIT in complex fluids miscible in all proportion has been performed by Zoltowski et al 13 , who studied drops of dodecyl-acrylate (DA) in mixtures of DA and poly(dodecyl acrylate) (PDA, molecular weight 25 kD), using a spinning drop tensiometer. Most of the previous works have focused on the interface between phase-separated colloidal fluids at thermodynamical equilibrium [52][53][54][55] ; however, colloidal suspensions are also excellent candidates for investigating off-equilibrium surface tension, since diffusion is comparatively slow in colloids or polymers, The first experimental investigation of the EIT in complex fluids miscible in all proportion has been performed by Zoltowski et al 13 , who studied drops of dodecyl-acrylate (DA) in mixtures of DA and poly(dodecyl acrylate) (PDA, molecular weight 25 kD), using a spinning drop tensiometer.…”

Fingering versus stability in the limit of zero interfacial tension

“…Such unstable interfaces are important in applications, significantly for sugar refining, oil recovery, hydrology and carbon sequestration [2][3][4][5][6] and much recent work has focused on how to control the instabilities [7][8][9][10] . Viscous fingering plays a central role in our understanding of pattern formation in part because it is amenable to both theory and experiment 1,6,[11][12][13][14] . Of particular importance is the limit where the characteristic finger width, set by the mostunstable wavelength, l c , approaches zero.…”