The improved resistance of PDMS to pressure-induced deformation and chemical solvent swelling for microfluidic devices

We present a fabrication technique that increases the resistance of PDMS to deformation under pressure driven flow and chemical solvents swelling without the use of any foreign materials. This is achieved by enhancing the material properties of PDMS by coupling two previously isolated processes. First, the weight ratio of the prepolymer to the curing agent was increased from 10:1 to 5:1, with the latter showing 20% less deformation under pressurized conditions. Second, the cured PDMS was thermally aged at 200 °C for a few hours, resulting in 140% less deformation for the thermally aged chip under the same pressure conditions. The combined processes benefit from a nonlinear coupling effect on improvement and show 860% less deformation under pressure driven flow in the enhanced PDMS chip compared to that in the standard 10:1 PDMS chip. The deformation of the standard and the enhanced PDMS micro-channels under pressure driven flow is quantified using fluorescence microscopy. The compatibility of PDMS with nonpolar solvents was also explored by quantifying material swelling due to toluene absorption using brightfield imaging of the microchannel. The enhanced PDMS showed less than 10% swelling against toluene compared to 55% in the standard PDMS. The enhanced PDMS is also less permeable to the small hydrophobic molecule rhodamine B (RhB), as quantified by epi-fluorescence microscopy of the absorbed dye. The improved surface and material properties of the thermally treated PDMS are certainly beneficial in microfluidic applications that use this common soft lithography material. The exponential growth of soft lithography microfabrication techniques for Lab-on-a-Chip and micro-Total Analysis System applications makes polydimethylsiloxane (PDMS) the most common material for microfluidic devices due to its easy, rapid, and low cost fabrication, biocompatibility, and transparent properties [1–5]. The range of applications for PDMS-based devices requires broad geometrical shapes from simple straight channels to complicated geometries including high or low aspect ratio channels [6–8]. In addition, PDMS allows fabrication of feature sizes from the macroscale to the microscale, and even to the nanometer scale, providing further flexibility in geometry control [9–11]. Despite these advantages, the intrinsic properties of PDMS hinder this material in various microfluidic applications [12]. First, the typical Young's modulus of 10:1 PDMS remains less than 1.35 MPa [13], making PDMS structures highly compliant and flexible [14,15]. The high compliancy becomes especially problematic in channels with extreme aspect ratios under pressure-driven flow [16–18]. Gervais et al. [19] experimentally investigated the deformation of low aspect ratio …