Preparation, Micro‐Patterning and Electrical Characterization of Functionalized Carbon‐Nanotube Polydimethylsiloxane Nanocomposite Polymer

Summary : We present the preparation, improved micro‐patterning, and electrical property characterization of COOH‐ functionalized mutli‐walled carbon nanotube (MWCNT) and polydimethylsiloxane (PDMS) conductive nanocomposite polymers that can be employed for lab on a chip applications. The nanocomposites are prepared by mixing functionalized MWCNTs into an uncured PDMS matrix and employing high frequency ultrasonics (∼ 42‐50 kHz) using a horn tip probe. The prepared nanocomposites are micromolded using soft lithography techniques down to a feature size of 25 µm against a micropatterned SU‐8 polymer master. An array of peg like microstructures have been fabricated with a radii of 25 µm and height of 100 µm, that are embedded on a non‐conductive PDMS substrate using novel and improved fabrication techniques. The percolation threshold of the prepared nanocomposite is achieved at 1.5 weight percentage (wt.%) of COOH‐ functionalized MWCNT in the PDMS matrix. Resistivity levels at 2 wt.% of functionalized MWCNTs are 62 Ω‐cm or better, which is an improvement over our previously reported nanocomposite resistivity value of 100 Ω‐cm at 2 wt.% of nonfunctionalized MWCNT's in a PDMS matrix. The nanocomposites also have fairly uniform dispersion and no agglomeration of COOH‐ functionalized MWCNT as shown by SEM analysis. Furthermore, the nanocomposites show a negative temperature coefficient of resistivity (NTCR), making them ideal candidates for micropatternable temperature microsensors for lab on a chip systems.