Abstract
Polymethylmethacrylate (PMMA) microfluidic devices have been fabricated using a hot embossing technique to incorporate micro-pillar features on the bottom wall of the device which when combined with either a plasma treatment or the coating of a diamond-like carbon (DLC) film presents a range of surface modification profiles. Experimental results presented in detail the surface modifications in the form of distinct changes in the static water contact angle across a range from 44.3 to 81.2 when compared to pristine PMMA surfaces. Additionally, capillary flow of water (dyed to aid visualization) through the microfluidic devices was recorded and analyzed to provide comparison data between filling time of a microfluidic chamber and surface modification characteristics, including the effects of surface energy and surface roughness on the microfluidic flow. We have experimentally demonstrated that fluid flow and thus filling time for the microfluidic device was significantly faster for the device with surface modifications that resulted in a lower static contact angle, and also that the incorporation of micro-pillars into a fluidic device increases the filling time when compared to comparative devices.
Highlights
In recent years, microfluidics has become an indispensable component of microelectromechanical systems (MEMS) technology [1,2,3], with polymer devices establishing a greater role in the development of disposable microfluidic systems [4]
Passive capillary flow is an important consideration for disposable polymeric microfluidic devices [2,10,11,12], where flow can be modified by adjusting the surface wettability or by incorporating surface roughness features on
Recent reports have shown that the surface wettability for polymer devices can be varied by plasma treatment [13,14,15,16] and the coating of diamond-like carbon (DLC) film [17,18] on the microchannel surfaces with numerous simulations describing the effects of surface roughness on microfluidic flow [2,19,20,21,22]
Summary
Microfluidics has become an indispensable component of microelectromechanical systems (MEMS) technology [1,2,3], with polymer devices establishing a greater role in the development of disposable microfluidic systems [4]. Surface modifications on the PMMA microchannel surfaces We utilized four different methods to modify the pristine PMMA surfaces following heat and pressure treatment by hot embossing, but prior to thermal bonding, to modify the surface properties and wettability of the devices. After the plasma treatment on the PMMA surface, the sample was stored in air for 48 h and the static water contact angle was measured as 58.1. The treatment time was 5 min for the gas mixture of Ar (5 sccm) and N2 (10 sccm) and the working pressure during deposition was maintained at 3.0 × 10-3 Torr. The meniscus movements were measured along the center line of the chamber
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