Suspension of nanoparticles in SU-8: Processing and characterization of nanocomposite polymers

Composite materials consisting of polymers and nanoparticles can provide additional functionality to existing formulations. Diamondoids, single-wall carbon nanotubes (SWNT), and gold nanospheres were physically incorporated into the negative photoresist SU-8 to investigate their effects on residual stresses and introduce piezoresistivity. The mixtures were spin cast onto silicon or aluminum-coated silicon wafers, lithographically patterned and released from the substrate. The residual stresses, elastic moduli, and viscosity effects of the nanocomposites were measured and compared with those of control samples of SU-8. Electrical properties of SU-8/SWNT nanocomposites were also investigated. The effective elastic modulus of SU-8/diamantane samples remained approximately 1.5–1.6 GPa until the diamantane content exceeded 7 wt%. The viscosity of SU-8/diamantane nanocomposite samples of all tested weight percents decreased compared with control SU-8 at high shear rates (>20 Hz), though high weight percent solutions (>5%) had increased low-frequency viscosity. The effective elastic modulus of the SU-8/SWNT nanocomposites decreased with small wt% additions of SWNT. Additionally, SU-8/SWNT nanocomposites showed increased resistivity with increased strain, suggesting a gauge factor for the 1 wt% SU-8/SWNT nanocomposite of approximately 2–4.