The capillary flow in SU8 based microfluidic devices fabricated in SF-100 by lithographic technique has been recorded and analysed in this report. Leakage free microfluidic flow is achieved by indirect bonding between polymethyl methacrylate (PMMA) coated glass lid surface and SU8 channel substrate during hard baking. The working liquids are dyed ethylene glycol, dyed ethanol, dyed isopropyl alcohol (IPA) and dyed liquid mixture (water and IPA). The capillary flow of dyed ethylene glycol is found to be slower in each device due to higher viscosity and lower surface wettability as compared to other working liquids. Square SU8 micropillar arrays (80 μm and 120 μm of side lengths) are fabricated on the glass bottom wall surface of SU8 based microchannel. The capillary flow of any particular working liquid is observed to be faster through the square micropillars of smaller side length due to their lower surface area to volume ratio in the device. Also, the capillary flow of polar liquids is found to be faster on the microchannel surface of higher polar component of surface free energy. The above results are highly significant to control the speed of capillary flow in lab-on-a-chip systems. © 2012 Elsevier Ltd.

Susanta Sinha Roy

Physics

(SoNS) School of Natural Sciences

Mukhopadhyay S.

Banerjee J.P.

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Shiv Nadar University

International Journal of Adhesion and Adhesives

In this research paper, in total 212 individual leakage-free Polymethylmethacrylate (PMMA) microfluidic devices are fabricated by maskless lithography, hot embossing lithography and direct bonding technique. The effect of channel aspect ratio on dyed water flow is investigated using these microfluidic devices. Experimental studies show that the dyed water flow is faster on the surface of higher wettability. The effect of capillary pressure on dyed water flow is studied in the fabricated PMMA microfluidic devices. According to the experimental observations, the centrifugal force has prominent effect on the dyed water flow. Also, the effect of bend angle is investigated on the surface-driven capillary flow of water. The polystyrene microparticles have been separated in the microfluidic lab-on-a-chip systems using the investigated flow features. A 100\% separation efficiency is achieved in these lab-on-a-chip systems. These microfluidic lab-on-a-chip systems can be used to separate blood cells from human whole blood for further clinical tests. These experimental studies are important in bioengineering applications. The effect of bend angle as channel geometry to control the surface-driven capillary flow is investigated as a novel approach to control the separation time in microfluidic lab-on-a-chip systems. Also, the effect of surface wettability as surface property to control the surface-driven capillary flow is investigated as a novel approach to control the separation time in microfluidic lab-on-a-chip systems. © 2017 World Scientific Publishing Company.

Surface Review and Letters

Effects of surface properties on fluid engineering generated by the surface-driven capillary flow of water in Microfluidic Lab-On-A-Chip systems for bioengineering applications

Journal of Micromechanics and Microengineering

Experimental study on capillary flow through polymer microchannel bends for microfluidic applications

The Journal of Physical Chemistry B

Solute-Free Interfacial Zones in Polar Liquids

Microfluidics and Nanofluidics

Micro-injection moulding of polymer microfluidic devices

Microfluidic channels with integrated pillars are fabricated on SU8 and PDMS substrates to understand the capillary flow. Microscope in conjunction with high-speed camera is used to capture the meniscus front movement through these channels for ethanol and isopropyl alcohol, respectively. In parallel, numerical simulations are conducted, using volume of fluid method, to predict the capillary flow through the microchannels with different pillar diameter to height ratio, ranging from 2.19 to 8.75 and pillar diameter to pitch ratio, ranging from 1.44 to 2.6. The pillar size (diameter, pitch and height) and the physical properties of the fluid (surface tension and viscosity) are found to have significant influence on the capillary phenomena in the microchannel. The meniscus displacement is non-uniform due to the presence of pillars and the non-uniformity in meniscus displacement is observed to increase with decrease in pitch to diameter ratio. The surface area to volume ratio is observed to play major roles in the velocity of the capillary meniscus of the devices. The filling speed is observed to change more dramatically under different pillar heights upto 120 μm and the change is slow with further increase in the pillar height. The details pertaining to the fluid distribution (meniscus front shapes) are obtained from the numerical results as well as from experiments. Numerical predictions for meniscus front shapes agree well with the experimental observations for both SU8 and PDMS microchannels. It is observed that the filling time obtained experimentally matches very well with the simulated filling time. The presence of pillars creates uniform meniscus front in the microchannel for both ethanol and isopropyl alcohol. Generalized plots in terms of dimensionless variables are also presented to predict the performance parameters for the design of these microfluidic devices. The flow is observed to have a very low Capillary number, which signifies the relative importance of surface tension to viscous effects in the present study. © Springer-Verlag 2008.

Experimental and numerical investigation of capillary flow in SU8 and PDMS microchannels with integrated pillars

We perform three-dimensional numerical and experimental study of the dynamic contact angle using volume of fluid (VOF) method applied to microfluidic channels with integrated pillars. Initially, we evaluated different dynamic contact angle models (hydrodynamic, molecular kinetic and empirical) for capillary filling of a two-dimensional microchannel using analytical formulation. Further, the models which require a minimum prescription of adjustable parameters are only used for the study of capillary filling of microchannels with integrated pillars using different working fluids such as DI water, ethanol and isopropyl alcohol. Different microchannel geometry with varying diameter/height/spacing were studied for circular pillars. Effect of square pillars and changing the overall number of pillars on the capillary phenomena were also simulated. Our study demonstrated that the dynamic contact angle models modifies the transient response of the meniscus displacement and also the observed trends are model specific for the various microchannel geometries and working fluids. However, the different models have minimal effect on the meniscus profile. Different inlet boundary conditions were applied to observe the effect of grid resolution selected for numerical study on the capillary filling time. A grid dependent dynamic contact angle model which incorporates effective slip in the model was also used to observe the grid convergence of the numerical results. The grid independence was shown to improve marginally by applying the grid dependent dynamic contact angle model. Further we did numerical experiments of capillary filling considering variable surface wettability on the top and bottom walls of the microchannel with alternate hydrophilic-hydrophobic patterns. The meniscus front pinning was noticed for a high wetting contrast between the patterns. Non uniform streamline patterns indicated mixing of the fluid when using patterned walls. Such a microfluidic device with variable surface properties with integrated pillars may be useful for carrying out biological operations that often require effective separation and mixing of the fluids. © 2009 Elsevier Inc. All rights reserved.