Supporting Information

Transcription

1 Supporting Information The adhesion circle: A new approach to better characterize directional gecko-inspired dry adhesives Yue Wang, Samuel Lehmann, Jinyou Shao and Dan Sameoto* Department of Mechanical Engineering, University of Alberta Donadeo Innovation Centre for Engineering, St. NW, Edmonton, AB, Canada, T6G 1H9 Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi an Jiaotong University, Xi an, Shaanxi , China * sameoto@ualberta.ca

2 S-1 Fabrication of Microfibers with Offset-Caps (1) A 4'' silicon wafer is coated with a bi-layer of chrome/gold. PMGI SF slow series 19 diluted 1:1 by weight in PMGI thinner was spun on the wafer at 500 rpm for 10s firstly and 1000 rpm for 40s, followed by 3min baking at 150 C in an oven. The resulting final PMGI thickness is approximately 1.5 µm. (2) A thin layer of HPR504 photoresist (Fujifilm) was spun on the PMGI at 3000 rpm for 30 s, baked for 1 min at 100 C and then exposed and developed to obtain the patterned HPR504 film. (3) The PMGI was exposed to 254 nm light using the HPR504 as a mask with a dose of ~0.5 J cm -2 to define the undercut size of the fibers. Following this, a photoresist AZ 4620 was spun on the PMGI at 500 rpm for 10s firstly and 1000 rpm for 40s, followed by 2min baking at 100 C in an oven. The resulting photoresist thickness was ~18 µm on average. (4) The wafer was then submerged in the deionized (DI) water to rehydrate for 20 min, and then was dried off in N 2 gas. Following this, the AZ 4620 was exposed aligned with the exposed PMGI micro-patterns to 30s of i-line UV light at a nominal power of ~40 mw cm 2. The alignment is necessary to achieve an offset cap. (5) The wafer was then developed in AZ 400 K developer for ~2min, and then MF-319 solution was used to develop the PMGI to define the final dimensions of caps. Next, the wafer was rinsed in DI water, followed by an N 2 dry. (6) Sylgard 184 was mixed at a ratio of 10:1 prepolymer to catalyst, and degassed for 20 min under vacuum. Afterward, it was poured on the photoresist, and was then degassed for 20min under vacuum. (7) Curing of PDMS was done for at least 12 h at 50 C, followed by demolding. After the PDMS was demolded, a post-cure bake at 200 C for 30 min was used to increase the strength of the PDMS before adhesion tests. S-1

3 S-2 Fabrication of Microfibers with defect-caps (1) SU (Microchem) was first spun on a cleaned PMMA substrate followed by soft baking at 90 C for 3 min in an oven, and the resulting thickness was approximately 2.8 µm. (2) The SU8 film was then exposed to a 450 mj cm 2 dose of I-line followed by baking at 90 C for 20 min in an oven and developing in the SU8 developer to get the patterned film. (3) Next, a photoresist HPR 504(Fujifilm) was spun on the SU8 and baked at 90 C for 3 min in an oven, following by the exposure to 25 mj cm 2 dose of I-line. To define the final shape of the defects, alignment exposure with the micro-patterned SU8 pillars was carried out. After exposure, a development of the HPR 504 photoresist was done to achieve patterned film. (4) Reactive ion etching (RIE) was used for 3 min to etch down a defect of approximately 800 nm in the SU-8 layer using the HPR 504 as the mask with the following settings: 100 sccm of O 2 and 5 sccm of CF 4, 150 W RF power and 125 mtorr chamber pressure. (5) The remaining HPR 504 was fully exposed by the I-line and then washed away by using the developer. (6) The substrate was then exposed to 126 J cm 2 of un-collimated 254 nm deep UV (DUV) using the SU-8 as the DUV mask. The acrylic substrate would be developed in SU8 developer because of the degradation of PMMA molecular by the DUV, and PMMA fibers with overhanging defect-su8 caps were achieved after developing. (7) TC-5030(BJB Enterprises) silicone rubber was mixed at a ratio of 10:1 prepolymer to catalyst and then casted on the acrylic template following by degassing. Curing of TC-5030 was done for at least 1h at 75 C in an oven. After it was demolded, a post-cure bake at 200 C for 30 min was used to increase the strength of the PDMS for the following process. (8) After getting the TC-5030 mold, there were two methods to achieve Sylgard 184 silicone rubber and Kraton G1657 SEBS elastomer. S-2

4 For the fabrication of Sylgard 184 fibers: 1. Sylgard 184 was mixed at a ratio of 10:1 prepolymer to catalyst, and degassed for 20 min under vacuum. Afterward, it was heated for 5min at 75 C to be partially cured and then poured on the TC-5030 silicone mold. The TC5030 mold was treated by using CF 4 -Plasma before to permit demolding of the Sylgard 184 silicone rubbers 2. Curing of Sylgard 184 was done for at least 12 h at 75 C, followed by demolding. After the Sylgard 184 was demolded, a post-cure bake at 200 C for 30 min was used to increase the strength of the PDMS before adhesion tests. For the fabrication of Kraton G1657 SEBS elastomer fibers: 1. The Kraton G1657 polymer was placed on a microscope glass slide on a hot plate at 215 C to get melted. Then the TC-5030 mold without surface treatment was placed on top of the melt and then a 100lb was loaded to squeeze the melt into the mold to form the fibers. 2. After unloading, the Kraton/silicone was then removed from the hotplate and waited to cool down at room temperature. The silicone master was then peeled off the Kraton, achieving the thermoplastic micro-fibers. S-3

5 S-3 Microscope Images of the Array of Fibers Figure S1 Microscope images of the array of fibers with offset-caps and defect-caps and some important geometry dimensions. S-4