Hoon Eui Jeonga,1, Jin-Kwan Leeb,1, Hong Nam Kima, Sang Heup Moonb,2 and Kahp Y. Suha,c,2
aSchool of Mechanical and Aerospace Engineering,
bSchool of Chemical and Biological Engineering, and
cInstitute of Advanced Machinery and Design, Seoul National University, Seoul 151-742, Korea
Edited by Robert Langer, Massachusetts Institute of Technology, Cambridge, MA, and approved February 13, 2009
1H.E.J. and J.-K.L. contributed equally to this work. (received for review January 13, 2009)
We present a simple yet robust method for fabricating angled, hierarchically patterned high-aspect-ratio polymer nanohairs to generate directionally sensitive dry adhesives. The slanted polymeric nanostructures were molded from an etched polySi substrate containing slanted nanoholes. An angled etching technique was developed to fabricate slanted nanoholes with flat tips by inserting an etch-stop layer of silicon dioxide. This unique etching method was equipped with a Faraday cage system to control the ion-incident angles in the conventional plasma etching system. The polymeric nanohairs were fabricated with tailored leaning angles, sizes, tip shapes, and hierarchical structures. As a result of controlled leaning angle and bulged flat top of the nanohairs, the replicated, slanted nanohairs showed excellent directional adhesion, exhibiting strong shear attachment (≈26 N/cm2 in maximum) in the angled direction and easy detachment (≈2.2 N/cm2) in the opposite direction, with a hysteresis value of ≈10. In addition to single scale nanohairs, monolithic, micro-nanoscale combined hierarchical hairs were also fabricated by using a 2-step UV-assisted molding technique. These hierarchical nanoscale patterns maintained their adhesive force even on a rough surface (roughness <20 μm) because of an increase in the contact area by the enhanced height of hierarchy, whereas simple nanohairs lost their adhesion strength. To demonstrate the potential applications of the adhesive patch, the dry adhesive was used to transport a large-area glass (47.5 × 37.5 cm2, second-generation TFT-LCD glass), which could replace the current electrostatic transport/holding system with further optimization.
Keywords: biomimetics, gecko, angled etching, slanted nanohair, hierarchical nanohair
2To whom correspondence may be addressed.
Author contributions: H.E.J., J.-K.L., S.H.M., and K.Y.S. designed research; H.E.J., J.-K.L., and H.N.K. performed research; H.E.J. and J.-K.L. analyzed data; and H.E.J., J.-K.L., S.H.M., and K.Y.S. wrote the paper.