In this work, we investigate the piezoresistive response of epoxy-graphite composites. A resistive thick-film Wheatstone bridge is deposited by screen-printing onto an alumina beam, a weight is then applied on the tip of the beam and the resulting electrical signal response is recorded, allowing the calculation of the gauge factor. The characterization was made at room temperature, 60°C and 100°C for different matrixes (epoxies with different glass transition temperatures, Tg) and particles sizes (4 µm and 15 µm). The creep of the signal in time and temperature was also observed. The present work shows also the tremendous effect of Tg on piezoresistive behavior: the high Tg epoxy demonstrating better stability in time and temperature than the other one.
We investigate in this work the formulation of composite resistive pastes based on epoxy resins and graphite for micro-heater manufacturing via thick-film technology. These resistive pastes are designed for screenprinting onto a printed circuit board (PCB) substrate; further coating with expandable polydimethylsiloxane (PDMS), a composite based on an elastomeric matrix and expandable microspheres, results in one-shot thermal actuators allowing pumping and sealing in disposable microfluidic lab-on-a-chip devices. The resistive paste must therefore have controlled rheology and resistivity, and exhibit good temperature stability in order to allow high heating power densities. This paper details the formulation and characterisation of suitable epoxy-graphite resistive composites, and the control of their properties through solvents.
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