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 (approximately 26 N/cm(2) in maximum) in the angled direction and easy detachment (approximately 2.2 N/cm(2)) in the opposite direction, with a hysteresis value of approximately 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 microm) 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 x 37.5 cm(2), second-generation TFT-LCD glass), which could replace the current electrostatic transport/holding system with further optimization.
Jeong HE, Lee J-K, Kim HN, Moon SH, Suh KY (2009) A nontransferring dry adhesive with hierarchical polymer nanohairs. Proceedings of the National Academy of Sciences 106: 5639–5644. Available: http://dx.doi.org/10.1073/pnas.0900323106.
We thank Dr. Khademhosseini for his enthusiastic discussion and comments. This work was supported by the Korea Science and Engineering Foundation through Nano R&D Program Grant 2007-02605, the Micro Thermal System Research Center of Seoul National University, National Research Laboratory Program Grant M10104000095-01J0000-04210, and the Center for Ultramicrochemical Process Systems. This work was also supported in part by King Abdullah University of Science and Technology Program KUK-F1-037-02 and a Korea Research Foundation Grant funded by the Korean Government Ministry of Education and Human Resource Development Grant KRF-J03000.