Laser Fabrication of Polymer-Based Mechanical Sensors Through Simultaneous Curing and Graphitization

Abstract

Flexible, polymer-based wearable sensors have been extensively studied over the past 30 years. Conventional sensors usually consist of a conductive material deposited into or onto a polymer substrate. Laser direct writing (LDW), a more recent innovation, allows conductive graphitic carbon to be directly patterned onto the surface of a polymer sheet, eliminating the need for the addition of a separate conductor. However, there are still ways to further streamline the fabrication process, including the use of LDW to induce formation of the substrate and conductive material simultaneously. This thesis presents a route towards the functionalization of this technique through the laser irradiation of uncured, liquid-phase polydimethylsiloxane (PDMS), a thermosetting elastomer. Scanning a near-infrared, continuous wave laser in a grid pattern across the surface of PDMS produces a mesh of conductive, graphitic carbon lines within a matrix of cured, solid polymer. The resulting structure shows potential as a wearable sensor, with a resistance at rest of about 26.9 kΩ. Resistance increases with the application of external forces, and the sensor is able to detect changes in pressure and strain. As a possible avenue toward higher conductivity or graphene content, small concentrations of carbon black were added to uncured PDMS. No conductivity was observed for the resulting grid structures, possibly due to changes in material absorption.