Filters

2020 - 20223

More filters

2021 - 20223
Reset filters

Settings

Author: Hensel, René × Author: Wang, Yue × Type: Text × Publisher: Weinheim : Wiley-VCH ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Switchable Underwater Adhesion by Deformable Cupped Microstructures
    (Weinheim : Wiley-VCH, 2020) Wang, Yue; Kang, Victor; Federle, Walter; Arzt, Eduard; Hensel, René
    Switchable underwater adhesion can be useful for numerous applications, but is extremely challenging due to the presence of water at the contact interface. Here, deformable cupped microstructures (diameter typically 100 µm, rim thickness 5 µm) are reported that can switch between high (≈1 MPa) and low (<0.2 MPa) adhesion strength by adjusting the retraction velocity from 100 to 0.1 µm s–1. The velocity at which the switch occurs is determined by specific design parameters of the cupped microstructure, such as the cup width and angle. The results are compared with theoretical estimates of water penetration into the contact zone and expansion of the cup during retraction. This work paves the way for controlling wet adhesion on demand and may inspire further applications in smart adhesives.
  • Thumbnail Image
    Item
    Sliding Mechanism for Release of Superlight Objects from Micropatterned Adhesives
    (Weinheim : Wiley-VCH, 2022) Wang, Yue; Zhang, Xuan; Hensel, René; Arzt, Eduard
    Robotic handling and transfer printing of micrometer-sized superlight objects is a crucial technology in industrial fabrication. In contrast to the precise gripping with micropatterned adhesives, the reliable release of superlight objects with negligible weight is a great challenge. Slanted deformable polymer microstructures, with typical pillar cross-section 150 µm × 50 µm, are introduced with various tilt angles that enable a reduction of adhesion by a switching ratio of up to 500. The experiments demonstrate that the release from a smooth surface involves sliding of the contact during compression and subsequent peeling of the object during retraction. The handling of a 0.5 mg perfluorinated polymer micro-object with high accuracy in repeated pick-and-place cycles is demonstrated. Based on beam theory, the forces and moments acting at the tip of the microstructure are analyzed. As a result, an expression for the pull-off force is proposed as a function of the sliding distance and a guide to an optimized design for these release structures is provided.
  • Thumbnail Image
    Item
    Bioinspired Underwater Adhesion to Rough Substrates by Cavity Collapse of Cupped Microstructures
    (Weinheim : Wiley-VCH, 2021) Wang, Yue; Hensel, René
    Underwater or wet adhesion is highly desirable for numerous applications but is counteracted by the liquids in the contact which weaken intermolecular attraction. The problem is exacerbated in conjunction with surface roughness when liquids partially remain in grooves or dimples of the substrate. In the present study, a cupped microstructure with a cavity inspired by suction organs of aquatic animals is proposed. The microstructures (cup radius of 100 µm) are made from polyurethane using two-photon lithography followed by replica molding. Adhesion to rough substrates is emulated experimentally by a micropatterned model substrate with varying channel widths. Pull-off stresses are found to be about 200 kPa, i.e., twice atmospheric pressure. Evaluation of force–displacement curves together with in situ observations reveal the adhesion mechanism, which involves adaptation to surface roughness and an elastic force induced by the collapse of the cavity that holds sealed contact with the substrate during retraction. This new microarchitecture may pave the way for next generation microstructures applicable to real, rough surfaces under wet conditions.