Passive and Non-mechanical Pumping in Microfluidic Devices

Last couple of decades have witnessed massive upsurge in efforts of transporting and manipulating solutes and moieties in microfluidic devices, motivated by their wide applications in disciplines ranging from astrophysics to nanomedicine. Pressure-driven transport scales as the square of the channel height, and therefore demands massive pumping power for microchannels making it unusable in several microfluidic applications. Accordingly, there have been a plethora of endeavors to devise novel non-mechanical fluid driving techniques in microchannels, e.g., transport by applying electrostatic, magnetic, or acoustic forces. However, these mechanisms, often necessitate special fluid properties, as well as cumbersome fabrication requirements. Hence, there has been a tremendous drive to develop passive pumping mechanisms, that successfully exploit the inherent geometric and physical characteristics of the microchannel and the fluid, yet are free from the above constraints.

In this thesis, several aspects of one of the foremost microfluidic passive pumping mechanisms, namely capillary-driven transport, has been analyzed. Firstly, the effect of a transient velocity profile on a classical capillary filling problem has been investigated. All the existing analyses invariably consider a fully-developed velocity profile—accordingly, the proposed model could reveal several yet unaddressed non-trivial mechanisms inherent in a capillary filling problem, intrinsic to the consideration of a more generalized situation of a developing velocity profile.

Secondly, an appropriate analytical model has been developed to describe the pressure-field at the entrance of the capillary. This pressure-field improves on the existing expressions in the sense that it is applicable to capillaries of all possible aspect ratios, and manifest its influence by predicting a capillary filling length that is different from that hypothesized by the existing models.

Thirdly, important correlations interrelating the wetting and other physical properties of popular biomicrofluidic solvents such as BSA (Bovine Serum Albumin) solution or microbead suspension have been derived from thoroughly performed experimental studies. These correlations are next employed to study the capillary dynamics of these two liquid as a functions of its physical properties.

Finally, effects of additional body forces, such as gravity or electrostatics, in affecting a capillary transport have been investigated.