Microfluidics as a tool has evolved and lead to miniaturization of devices and appli-
cation in point-of-care diagnostics. Portability of devices, lesser consumption of bio-
samples and reagents, faster performance of biochemical assays and the ability to per-
form multiple processes in a device widely known as lab-on-a-chip has brought unique

attraction to the field of microfluidics. Among various liquid driving mechanisms, cap-
illary powered devices which are self-driven gained popularity, as it is devoid of compli-
cated setup and relatively easy to use. However, the manipulation of liquids in capillary

circuits is a challenging task. Passive control of the fluid systems is realized by imple-
menting different fluid control elements such as trigger valves, stop valves, actuators

and capillary pumps which have contributed toward the expansion of the applications
of the capillary driven point-of-care devices. Alternately, deformable membranes are
used with the microchannels to manipulate the capillary flow, which is broadly studied

in the field of elastocapillarity. Elastocapillarity refers to the study of the effects of de-
formation of flexible structures or soft substrates under the action of capillary forces.

The interaction of thin deformable membrane with liquid droplets can be manipulated
to act as a sensor and actuator in microchannels.
The work presented in the thesis is organised into three sections. First, bio-inspired
(from hummingbird’s tongue) liquid transport via elastocapillary interaction of a thin
polydimethylsiloxane (PDMS) membrane with liquid meniscus was studied. Two cases
are considered, a thin rectangular membrane forming a wedge with a rigid substrate
(soft wedge) and a flat thin rectangular membrane undergoes large deformation when
it interacts with liquid meniscus. The membrane deformation leads to the formation of
a confinement which in turn results in elastocapillary flow along the membrane length.

A simple theoretical model based on Euler Bernoulli law was used to predict the mem-brane deformation profiles which compare well with that obtained from experiments.
In the wedge case, the membrane surface and liquid are selected such that Concus-Finn
criterion is not satisfied to contrast the present case of elastocapillary flow from the
typical corner flow reported in literature. The meniscus location versus time studies

indicated that the flow exhibit the typical Washburn regime, except with a sudden in-
crease in velocity at the end of the membrane length. Effects of membrane thickness

and width, liquids and substrates were studied to determine the expression for the mod-
ified Washburn constant in both wedge and flat membranes. It was found that gravity

plays a role for Bond number K > 0.94 and for K = 1.9 , the effect of inclination angle
on the flow was studied. The elastocapillary flow with thin membranes could open up
opportunity for a new area namely “membrane microfluidics” or “lab on a membrane”
for diagnostics and other applications.
Subsequently, an elastocapillary flow driven lab on a membrane device based on
differential wetting and sedimentation effect for the separation of plasma from whole
blood was investigated. Interaction between a thin PDMS membrane (thickness ∼35 μm)
bonded to the edge of a PDMS substrate and a sample blood drop (of volume ∼70 μl)
gives rise to deformation of the soft membrane due to the capillary forces providing a

conduit and consequent elastocapillary flow of blood. The surface of the PDMS mem-
brane is hydrophilic up to a certain length along the flow direction to support the elas-
tocapillary flow and hydrophobic thereafter to impede the flow. In the hydrophobic

region, owing to a much smaller sedimentation time scale (∼100 s) as compared to the
capillary flow time scale (∼1000 s), sedimentation of blood cells occurs thus facilitating

separation of plasma from the blood cells in the hydrophobic region. The role of dif-
ferential wetting and sedimentation effects on the blood plasma separation was studied.

The effects of membrane width and thickness, length of the hydrophilic region, erythro-
cyte sedimentation rate (ESR) on the separation of plasma were investigated. Using a

membrane of width 3 mm, thickness 35 μm, total length 25 mm and hydrophilic length
of 4 mm and 70 μl of whole blood with ESR varying in the range 4 mm h−1

to 40 mm

h
−1

, the volume of plasma was in the range of 7.5 μl to 20 μl, respectively, which corre-
sponds to a plasma recovery of 22%–49%, respectively. Purity of the plasma from the

proposed device was compared with that obtained from centrifugation which showed a
good match. The device was integrated with a commercially available detection strip to detect the level of glucose present in the plasma from blood samples of healthy and dia-
betic patients which were in qualitative agreement with that obtained from conventional

tests.
Finally, the dynamical behavior of a thin and flat rectangular polymeric membrane,

fixed at both ends in contact with a volatile liquid solvent droplet is studied. Depend-
ing on the solvent, liquid volume and membrane thickness, three different regimes –

no buckling, buckling, and snapping are observed. The study revealed that dynamic
behavior depends on the dimensionless solubility parameter of the solvent and the ratio
of the sum of swelling-induced force and capillary force to the elastic restoring force,

i.e. force ratio. Using correlations obtained from simple scaling, the model can esti-
mate the maximum force ratio in terms of known quantities and consequently predict

the operating regime and maximum deflection. The study will find significance in the
design and analysis of systems involving flexible microbeams.