Finite reservoir effect on capillary flow of microbead suspension in rectangular microchannels

• Published in: Journal of colloid and interface science Vol. 351; no. 2; pp. 561 - 569
• Main Authors: Waghmare, Prashant R., Mitra, Sushanta K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.11.2010; Elsevier
• Subjects: Biomolecules; Capillarity; Capillary flow of microbead suspension; Channels; Chemistry; Exact sciences and technology; General and physical chemistry; Mathematical analysis; Microchannels; Microfluidic Analytical Techniques - instrumentation; Microfluidic Analytical Techniques - methods; Microfluidics; Microorganisms; Models, Chemical; Particle Size; Reservoir effects in capillary flow; Reservoirs; Surface Properties; Suspensions - chemistry; Transport; Reservoir effects in capillary flow; Capillary flow of microbead suspension; Microfluidics; Microchannels; Correlation; Volume fraction; Force; Device; Fluid; Equation; Reservoir; Suspension; Physical properties; Operating conditions; Resistance; Capillarity; Transport; Gravity
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2010.08.039

Theoretical study on the capillary transport of microbead suspension in microchannels with finite reservoir effect is presented. The presence of microbead in the working fluid changes the capillarity and the magnitude of the capillarity depends on the volume fraction of the microbeads. In reservoir with higher fluid level the flow front progresses very slowly at the beginning of the transport but surpasses the penetration depth corresponding to the lower fluid level reservoir with time. The gravitational head along with the capillarity can be an useful tool for transporting fluid in microchannels for LOC applications. [Display omitted] ► Dimensions of a finite size reservoir affects the capillary transport. ► It depends on the aspect ratios of the rectangular microchannel and the inlet reservoir. ► At the beginning of the fluid transport, capillarity always dominates the gravity. ► Capillarity has a dependence on microbead concentration. The present study reports a theoretical investigation of capillary transport of microbead suspension in microfluidic channels with finite size reservoirs at the inlet. The reservoir–microchannel combination is often the case in Lab-on-a-Chip (LOC) where biomolecules are transported using capillary force. To demonstrate such finite reservoir effect, the reservoir is placed vertically above the microchannel. Under such condition, the pressure field expression at the rectangular microchannel inlet is deduced. Appropriate correlations for effective physical properties are used to account for the presence of microbeads in the working fluid, mimicking biomolecules in actual LOC. The non-dimensional governing equation for capillary flow with finite size reservoir is derived based on the balance among the surface, viscous and gravity forces acting on the fluid front. The numerical solution of governing equation is obtained to investigate the impact of several operating parameters on the flow front progression. It is observed that the aspect ratio of the microchannel and reservoir play vital roles in deciding the behavior and magnitude of flow front progression in the microfluidic channels. Capillarity and gravity force dominant regions during the progression is observed. The microchannel width and reservoir width decide the interplay between gravity and capillarity. Although higher fluid level in the reservoir has an added advantage for more gravitational head, the resistance from the reservoir makes the flow front progress slowly at the beginning of the capillary transport. It is also found that microbead volume fraction in the working fluid plays an important role in delaying the capillary transport under various operating conditions. Hence, it can be concluded that the use of reservoir at the inlet of microfluidic channels has an impact on the overall capillary transport of biomolecules in LOC devices.