The mechanical properties of SU-8 at microscale were measured under both micropillar compression and nanoindentation on a film on a substrate. To the best of our knowledge, this paper reports the first set of results for microcompression of SU-8 micropillars for measurement of mechanical properties using viscoelastic analysis. The effects of loading rate and micropillar size are examined. It was determined that the SU-8 exhibits viscoelastic properties at room temperature, the time-average Young's modulus increases in general with the loading rate. The average Young's modulus determined by compression of a micropillar was 4.1 GPa at a strain rate near 10 −3 s −1 . For nanoindentation on a SU-8 film supported by a silicon substrate, the default output from the nanoindenter for the Young's modulus was approximately 6.0 GPa with the consideration of elastic-plastic behavior of the SU-8. When the viscoelastic effects were considered, the time-average Young's modulus at a given strain rate was determined to be near 3.6 GPa, which agrees with the reported values in the literature obtained from tension and bending, and also correlates reasonably well with data from microcompression. This work indicates that viscoelastic analysis is necessary to extract the valid mechanical properties at nano/microscales for SU-8.
We report a vertically-aligned carbon nanotube (CNT) forest on polydimethylsiloxane (PDMS) sheet as a novel widely stretchable and bendable anti-wetting super-lyophobic surface for naturally oxidized gallium-based liquid metals. The vertically-aligned CNT has inherent chemical inertness and a hierarchical texture combining micro/nanoscale roughness; these two characters render the developed sheet as a super-lyophobic substrate against gallium-based liquid metals. The vertically-aligned CNT forest was first grown on Si substrate and then transferred onto a PDMS sheet by imprinting. It was found that the transferred CNT on the PDMS sheet maintained its vertically-aligned nature as well as hierarchical micro/nano surface morphology. It was found that the static contact angles of the gallium-based liquid metal droplet on the CNT on Si and on the CNT on PDMS were both greater than 155° and the contact angle hysteresis on the CNT on Si was 4° and that on the transferred CNT on PDMS was 19°. These measurement results showed that the surface retains a super-lyophobic property before and after the CNT transfer onto PDMS. We tested the CNT on PDMS sheet for its mechanical flexibility using stretching (50% and 100%) and bending (curvature of 0.1 and 0.4 mm−1). We carried out a bouncing test and a rolling test on the stretched/bent CNT on the PDMS sheet and the results confirmed that the flexible sheet maintains anti-wetting characteristics under bending or stretching conditions.
We report real-time dynamically reconfigurable photomask by manipulating gallium-based liquid metal in microfluidic channel. As a demonstration of reconfigurable photomask, a polydimethylsiloxane (PDMS) based 7-segments microfluidic channel was designed and fabricated. With on-demand injection and withdrawal of gallium-based liquid metal in each segment channel, single digit numbers ('0' to '9') were dynamically reconfigured. For i-line and 400 nm wavelength UV lights, PDMS showed > 93% of light transmittance while PDMS + Galinstan ® showed < 1 % of the light transmittance. In order to investigate achievable minimum feature size, various sizes of line shape, a horse shoe shape and Texas state map shape were demonstrated. The minimum feature size reliably and reproducibly created was 10 µm with the current approach.
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