The Deformation of Polydimethylsiloxane (PDMS) Microfluidic Channels Filled with Embedded Circular Obstacles under Certain Circumstances

Abstract

Experimental investigations were conducted to determine the influence of polydimethylsiloxane (PDMS) microfluidic channels containing aligned circular obstacles (with diameters of 172 µm and 132 µm) on the flow velocity and pressure drop under steady-state flow conditions. A significant PDMS bulging was observed when the fluid flow initially contacted the obstacles, but this phenomenon decreased in the 1 mm length of the microfluidic channels when the flow reached a steady-state. This implies that a microfluidic device operating with steady-state flows does not provide fully reliable information, even though less PDMS bulging is observed compared to quasi steady-state flow. Numerical analysis of PDMS bulging using ANSYS Workbench showed a relatively good agreement with the measured data. To verify the influence of PDMS bulging on the pressure drop and flow velocity, theoretical analyses were performed and the results were compared with the experimental results. The measured flow velocity and pressure drop data relatively matched well with the classical prediction under certain circumstances. However, discrepancies were generated and became worse as the microfluidic devices were operated under the following conditions: (1) restricted geometry of the microfluidic channels (i.e., shallow channel height, large diameter of obstacles and a short microchannel length); (2) operation in quasi-steady state flow; (3) increasing flow rates; and (4) decreasing amount of curing agent in the PDMS mixture. Therefore, in order to obtain reliable data a microfluidic device must be operated under appropriate conditions.

Keywords: ANSYS Workbench; PDMS bulging; embedded obstacles; flow velocity; pressure drop; steady-state flow.

Figure 1

Close-up image of the obstacles with no flow and high flow rate (4.0 µL/min).

Figure 2

(a) Analysis of PDMS bulging with several references (Red box: current study); (b) Comparison of pressure drop analysis in the PDMS microfluidic channels.

Figure 3

(a) Geometry and mesh in ANSYS Workbench for PDMS bulging (15 μm channel depth); (b) Comparison of numerical and experimental PDMS bulging (mixing ratio = 10:1).

Figure 4

Comparison of the PDMS bulging ratio as a function of flow rates (PDMS bulging of quasi-steady state flow to steady-state flow).

Figure 5

(a) Flow velocity analysis as a function of the flow rates in 15 µm microfluidic channels; and (b) Flow velocity analysis as a function of the flow rates in 100 µm microfluidic channels.

Figure 6

Comparison of the pressure drop/length analysis in 15 µm and 100 µm microfluidic channels.

Figure 7

(a) Schematic diagram of the experimental apparatus; (b) Actual image of the microfluidic devices.