Bio-inspired liquid transport via elastocapillary interaction of a thin membrane with a liquid meniscus

Abstract

We report bio-inspired (from a hummingbird's tongue) liquid transport via elastocapillary interaction of a thin membrane with a liquid meniscus. A soft wedge-thin rectangular membrane forming a wedge with a rigid substrate and a flat thin rectangular membrane undergo large deformation while interacting with liquid menisci. The membrane deformation leads to the formation of confinement which in turn results in elastocapillary flow along the membrane length. A simple theoretical model based on the Euler Bernoulli law is used to predict the membrane deformation profiles, which compare well with that obtained from experiments. In the wedge case, the membrane surface and liquid are selected such that the Concus-Finn criterion is not satisfied to contrast the present case of elastocapillary flow from the typical corner flow reported in the literature. The meniscus location versus time studies indicated that the flow exhibits the typical Washburn regime with , except for a sudden increase in velocity at the end of the membrane length. The effects of membrane thickness and width, liquids and substrates were studied to determine the expression for the modified Washburn constant W in both the wedge and flat membranes. It was found that gravity plays a role for Bo > 0.94 and for Bo = 1.9, the effect of inclination angle on the flow was studied. The elastocapillary flow with thin membranes could open up an opportunity for a new area, namely "membrane microfluidics" or "lab on a membrane", for diagnostics and other applications.

Elastocapillary flow driven lab-on-a-membrane device based on differential wetting and sedimentation effect for blood plasma separation

“…A thin PDMS membrane of thickness t, width w and length L m is bonded to the edge of a thick PDMS substrate to form a soft wedge. When a drop of sample blood is dispensed at one of the ends (inlet) of the soft wedge (figure 1(a)), the membrane tends to wrap around the blood drop due to capillary effects [50] and thus gets deformed to form a conduit (shown in figure 1(b)). Since the initial portion of the membrane is hydrophilic, the sample blood advances through the conduit due to the driving Laplace pressure.…”

“…Elastocapillary flow in flexible micro and nano channels have also been studied that showed improved performance as compared to that though rigid capillaries [44][45][46][47][48]. Recently, transport of liquid using flexible membranes have been demonstrated [49,50]. We reported elastocapillary flow at a soft-wedge comprising a rigid and a soft polydimethylsiloxane (PDMS) membrane as well as on a flat rectangular membrane [50].…”

“…Recently, transport of liquid using flexible membranes have been demonstrated [49,50]. We reported elastocapillary flow at a soft-wedge comprising a rigid and a soft polydimethylsiloxane (PDMS) membrane as well as on a flat rectangular membrane [50]. Biochemical assays can be performed by exploiting the elastocapillary flow on membranes which could lead to the development of the concept of 'Lab on a Membrane' [51].…”

Buckling and snapping of a thin polymeric membrane exposed to a solvent drop

“…The dynamic snapping of elastic beams and shells was considered to study the stability, deformation modes and snap-through dynamics of an elastic arch with clamped boundaries and subjected to concentrated load [27]. At small length scales, capillary force is much stronger and can lead to the wrapping of a liquid droplet in a planar sheet, the coalescence of slender structures, and drive elastocapillary flows along membranes and deformable microchannels [28][29][30][31][32][33][34][35][36]. A millimetre-sized water drop can trigger elastocapillary snap-through instability of a thin and pre-buckled polymer strip [20].…”

“…where ΔL is the elongation of the membrane of initial length L. Surface tension of liquids can deform freestanding thin elastic structures and buckled beams, which is attributed to elasto-capillarity [30][31][32][33][34][35][36][37]. In addition to F sw the vertical component of the surface tension will also tend to deform the membrane outward.…”