In the present study, gravity assisted capillary transport of microbead suspension is investigated theoretically.
An additional gravitational head from the reservoir which is placed at the top of the capillary is considered as
pressure force at the inlet of capillary. The pressure field distribution at the inlet of capillary is deduced to
calculate this inlet pressure force. The non-dimensional governing equation is derived by taking into account
the surface, viscous and gravity forces which act on the fluid front. Presence of microbeads delays the capillary
transport. It is observed from the numerical solution of the governing equation that, not only the aspect ratio of
the capillary but the aspect ratio of reservoir also plays a vital role in the flow front transport in the capillary.
Although higher fluid level in the reservoir has added advantage towards higher gravitational head, the resistance
from reservoir makes the progress of the flow front movement slow at the beginning of the transport. The physical
properties of the fluid also play an important role in deciding the progression fluid flow front.
The present study reports an investigation of capillary transport with a suspension of microbeads and biomolecules.
Series of experiments are performed to deduce the concentration based surface tension and contact angle expression
for microbead and biomolecule suspension. It is observed that, the microbead suspension restricts the
spreading of the fluid front. Hence a decrease in the surface tension and an increase in the contact angle is
observed as the concentration of suspension is increased. Different expressions for contact angle and surface
tension depending on the range of the microbead concentrations are deduced. Theoretical model to predict the
capillary transport in rectangular microchannel considering the change in physical and surface properties of the
fluid is developed. The capillary transport in a microfabricated silicon microchannel is observed for fluid with
and without microbead. Theoretical and experimental observations match quite well, whereas the quantitative
difference in case of transport with microbead suspension is observed. Thus, the effect of suspension on the fluid
properties can not be neglected in a capillary transport.
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