The Experts below are selected from a list of 708 Experts worldwide ranked by ideXlab platform
Hoon Eui Jeong - One of the best experts on this subject based on the ideXlab platform.
-
Oxford Scholarship Online - Skin and Dry Adhesion
Oxford Scholarship Online, 2018Co-Authors: Changhyun Pang, Hoon Eui Jeong, Chanseok Lee, Kahp-yang SuhAbstract:Close observation of various attachment systems in animal skins has revealed various exquisite multi-scale architectures for essential functions such as locomotion, crawling, mating, and protection from predators. Some of these Adhesion systems of geckos and beetles have unique structural features (e.g. high-aspect ratio, tilted angle, and hierarchical nanostructure), resulting in mechanical interlocking mediated by van der Waals forces or liquid secretion (capillary force). In this chapter, we present an overview of recent advances in bio-inspired, artificial Dry adhesives, and biomimetics in the context of nanofabrication and material properties. In addition, relevant bio-inspired structural materials, devices (clean transportation device, interlocker, biomedical skin patch, and flexible strain-gauge sensor) and microrobots are briefly introduced, which would shed light on future smart, directional, and reversible Adhesion systems.
-
Precise tip shape transformation of nanopillars for enhanced Dry Adhesion strength
Soft Matter, 2012Co-Authors: Hoon Eui JeongAbstract:We present a simple, yet robust, technique for controlling the tip geometry of nanopillars by utilizing a two-step process of partial photopolymerization of UV-curable polyurethane acrylate (PUA) resin and subsequent tip shape modification. With this technique, head structures of nanopillars were precisely transformed from hemispherical to protruding, mushroom-like tips without any loss in structural integrity of the nanopillars. Nanoscopic and macroscopic Adhesion measurements for angled nanopillars with modified tips demonstrated that mushroom-like structures fabricated by our approach could greatly enhance Adhesion strengths as compared to unmodified, round head structures. Also, directional Adhesion characteristics of angled nanopillars were maintained regardless of tip shapes.
-
Bio-inspired slanted polymer nanohairs for anisotropic wetting and directional Dry Adhesion
Soft Matter, 2010Co-Authors: Moon Kyu Kwak, Hoon Eui Jeong, Hyunsik YoonAbstract:Slanted polymer nanohairs possess a number of attractive properties in terms of anisotropic wetting and directional Adhesion. This highlight provides an overview of the recent progress in the development of bio-inspired slanted polymer nanohairs and their applications towards anisotropic wetting and directional Dry Adhesion properties. With the advanced nano-fabrication techniques, it is possible to fabricate angled, directionally bent polymer nanohairs in a highly reproducible and geometry-controllable manner. The fabrication methods can be categorized into two streams: direct replica molding from a master with slanted structure or nanofabrication (photolithography or molding) with post treatment such as e-beam exposure, thermal annealing and mechanical compression. In this highlight, the fabrication methods for angled, high aspect ratio polymer nanohairs are briefly described along with their potential applications in anisotropic wetting and directional Adhesion. Particular emphasis is given to recent achievements and future directions in biomimetic functional surfaces.
-
Effect of leaning angle of gecko-inspired slanted polymer nanohairs on Dry Adhesion
Applied Physics Letters, 2010Co-Authors: Hoon Eui Jeong, Moon Kyu Kwak, Jin-kwan Lee, Sang Heup Moon, Kahp-yang SuhAbstract:We present analysis of Adhesion properties of angled polymer nanohairs with a wide range of leaning angles from 0° to 45° and ultraviolet (UV)-curable polyurethane acrylate (PUA) materials of two different elastic moduli (19.8 and 320 MPa). It is demonstrated that shear Adhesion and Adhesion hysteresis can be greatly enhanced by increasing the leaning angle of nanohairs both for soft and hard materials due to increased contact area and reduced structural stiffness.
René Hensel - One of the best experts on this subject based on the ideXlab platform.
-
A Design Strategy for Mushroom-Shaped Microfibrils with Optimized Dry Adhesion: Experiments and Finite Element Analyses
Journal of Applied Mechanics, 2020Co-Authors: Xuan Zhang, Yue Wang, René Hensel, Eduard ArztAbstract:Abstract Enhanced Dry Adhesion of micropatterned polymeric surfaces has been frequently demonstrated. Among the design parameters, the cap geometry plays an important role to improve their performance. In this work, we combined experiments on single polyurethane mushroom-shaped fibrils (with stalk diameter 80 µm and height 125 µm) against flat glass, with numerical simulations implementing a cohesive zone. We found that the geometry of the mushroom cap strongly affects the interfacial crack behavior and the pull-off stress. The experimental and numerical results suggest that optimal Adhesion was accompanied by the appearance of both edge and interior interfacial cracks during separation. Finite elemental analyses revealed the evolution of the interfacial stress distributions as a function of the cap thickness and confirmed the distinct detachment mechanisms. Furthermore, the effect of the stalk diameter and the Young's modulus on the adhesive force was established, resulting in an optimal design for mushroom-shaped fibrils.
-
Enhancing Dry Adhesion of Polymeric Micropatterns by Electric Fields.
ACS applied materials & interfaces, 2020Co-Authors: Vaishali Chopra, René Hensel, Maciej Chudak, Aa Anton Darhuber, Eduard ArztAbstract:Micropatterned Dry adhesives rely mainly on van der Waals interactions. In this paper, we explore the Adhesion strength increase that can be achieved by superimposing an electrostatic field through interdigitated subsurface electrodes. Micropatterns were produced by replica molding in silicone. The Adhesion forces were characterized systematically by means of experiments and numerical modeling. The force increased with the square of the applied voltage for electric fields up to 800 V. For larger fields, a less-than-quadratic scaling was observed, which is likely due to the small, field-dependent electrical conductivity of the materials involved. The additional Adhesion force was found to be up to twice of the field-free Adhesion. The results suggest an alternative method for the controlled handling of fragile or miniaturized objects.
-
Strong Wet and Dry Adhesion by Cupped Microstructures
ACS applied materials & interfaces, 2019Co-Authors: Yue Wang, Eduard Arzt, Victor Kang, Walter Federle, René HenselAbstract:Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater Adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design—cupped microstructures (CM)—that generates strong controllable Adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in Dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an Adhesion strength (f...
-
strong wet and Dry Adhesion by cupped microstructures
ACS Applied Materials & Interfaces, 2019Co-Authors: Yue Wang, Eduard Arzt, Victor Kang, Walter Federle, René HenselAbstract:Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are consid...
Yue Wang - One of the best experts on this subject based on the ideXlab platform.
-
A Design Strategy for Mushroom-Shaped Microfibrils with Optimized Dry Adhesion: Experiments and Finite Element Analyses
Journal of Applied Mechanics, 2020Co-Authors: Xuan Zhang, Yue Wang, René Hensel, Eduard ArztAbstract:Abstract Enhanced Dry Adhesion of micropatterned polymeric surfaces has been frequently demonstrated. Among the design parameters, the cap geometry plays an important role to improve their performance. In this work, we combined experiments on single polyurethane mushroom-shaped fibrils (with stalk diameter 80 µm and height 125 µm) against flat glass, with numerical simulations implementing a cohesive zone. We found that the geometry of the mushroom cap strongly affects the interfacial crack behavior and the pull-off stress. The experimental and numerical results suggest that optimal Adhesion was accompanied by the appearance of both edge and interior interfacial cracks during separation. Finite elemental analyses revealed the evolution of the interfacial stress distributions as a function of the cap thickness and confirmed the distinct detachment mechanisms. Furthermore, the effect of the stalk diameter and the Young's modulus on the adhesive force was established, resulting in an optimal design for mushroom-shaped fibrils.
-
Strong Wet and Dry Adhesion by Cupped Microstructures
ACS applied materials & interfaces, 2019Co-Authors: Yue Wang, Eduard Arzt, Victor Kang, Walter Federle, René HenselAbstract:Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater Adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design—cupped microstructures (CM)—that generates strong controllable Adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in Dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an Adhesion strength (f...
-
strong wet and Dry Adhesion by cupped microstructures
ACS Applied Materials & Interfaces, 2019Co-Authors: Yue Wang, Eduard Arzt, Victor Kang, Walter Federle, René HenselAbstract:Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are consid...
-
Switchable Dry Adhesion with Step-like Micropillars and Controllable Interfacial Contact
ACS Applied Materials & Interfaces, 2016Co-Authors: Yue Wang, Hongmiao Tian, Dan Sameoto, Hu Hong, Li Wang, Yucheng DingAbstract:Dry adhesives have attracted much attention because of their repeatable and reversible attachment. Many research groups have made fruitful achievements in fabricating and designing various Dry adhesives. However, most of these studies focus on imitating bioinspired geometry to achieve this smart Adhesion, neglecting the contact interface control through their peeling motion. Here, we present an alternative design to achieve this switchable Adhesion on the basis of controlling contact areas. This unique design includes micropillars array with large overhanging caps and a “step” located at the center line of the cap. When dragging the pillars in the direction of the upper surface of the step, the lower surface is brought into contact, rapidly yielding stronger Adhesion (switched-on state). Alternatively, when dragging the pillars in the direction of the lower surface of the step, the contact areas decrease sharply, leading to weak Adhesion (switched-off state). Such switchable property under strong Adhesion...
-
Effects of contact cap dimension on Dry Adhesion of bioinspired mushroom-shaped surfaces
Bioinspiration Biomimetics and Bioreplication 2015, 2015Co-Authors: Yue Wang, Hongmiao Tian, Yucheng Ding, Jinyou Shao, Hu HongAbstract:Dry Adhesion observed in small creatures, such as spiders, insects, and geckos, has many great advantages such as repeatability and strong adhesiveness. In order to mimic these unique performances, fibrillar surface with a mushroom shaped end has drawn lots of attentions because of its advantage in efficiently enhancing Adhesion compared with other sphere or simple flat ends. Here, in order to study the effects of contact cap dimension on Adhesion strength, patterned surfaces of mushroom-shaped micropillars with differing cap diameters are fabricated based on the conventional photolithography and molding. The normal Adhesion strength of these Dry adhesives with varying cap diameters is measured with home-built equipment. The strength increases with the rise of cap diameter, and interestingly it becomes strongest when the mushroom caps join together.
Hyunsik Yoon - One of the best experts on this subject based on the ideXlab platform.
-
Arrays of Lucius microprisms for directional allocation of light and autostereoscopic three-dimensional displays
Nature Communications, 2011Co-Authors: Hyunsik Yoon, Dae Shik Kang, Jong Myoung Park, Se Jin Choi, Kahp Y. Suh, Kookheon Char, Hong H. LeeAbstract:Directional and asymmetric properties are attractive features in nature that have proven useful for directional wetting, directional flow of liquids and artificial Dry Adhesion. Here we demonstrate that an optically asymmetric structure can be exploited to guide light with directionality. The Lucius prism array presented here has two distinct properties: the directional transmission of light and the disproportionation of light intensity. These allow the illumination of objects only in desired directions. Set up as an array, the Lucius prism can function as an autostereoscopic three-dimensional display. Autostereoscopic three-dimensional displays allow the perception of depth, by presenting offset images to the left and right eye, without the need for specialized glasses. Yoon et al propose a Lucius microprism array to control the directionality and intensity of light in three-dimensional displays.
-
Bio-inspired slanted polymer nanohairs for anisotropic wetting and directional Dry Adhesion
Soft Matter, 2010Co-Authors: Moon Kyu Kwak, Hoon Eui Jeong, Hyunsik YoonAbstract:Slanted polymer nanohairs possess a number of attractive properties in terms of anisotropic wetting and directional Adhesion. This highlight provides an overview of the recent progress in the development of bio-inspired slanted polymer nanohairs and their applications towards anisotropic wetting and directional Dry Adhesion properties. With the advanced nano-fabrication techniques, it is possible to fabricate angled, directionally bent polymer nanohairs in a highly reproducible and geometry-controllable manner. The fabrication methods can be categorized into two streams: direct replica molding from a master with slanted structure or nanofabrication (photolithography or molding) with post treatment such as e-beam exposure, thermal annealing and mechanical compression. In this highlight, the fabrication methods for angled, high aspect ratio polymer nanohairs are briefly described along with their potential applications in anisotropic wetting and directional Adhesion. Particular emphasis is given to recent achievements and future directions in biomimetic functional surfaces.
Seok Kim - One of the best experts on this subject based on the ideXlab platform.
-
LEGO-Like Microassembly Using Reversible Dry Adhesion
IEEE Potentials, 2016Co-Authors: Seok KimAbstract:When I was a kid, I was fascinated by watching water striders glide on the water and would wonder: why do they not drown but instead play, standing effortlessly on the water? This is undoubtedly a common question among curious children. The simplest answer would be "because the insect is very small and light." So then, why are smaller things better able to float on the water? An aircraft carrier can easily float on the sea too, although it is extremely large.
-
Micro-Masonry of MEMS Sensors and Actuators
Journal of Microelectromechanical Systems, 2014Co-Authors: Y. Zhang, H. Keum, Kidong Park, Rashid Bashir, Seok KimAbstract:Micro-masonry is a route to microassembly that involves elastomeric-stamp-based micromanipulation and direct bonding. This paper presents the assembly of MEMS mechanical sensors and actuators using micro-masonry, demonstrating its capability of constructing 3-D microdevices that are impossible or difficult to realize with monolithic microfabrication. Microfabrication processes for retrievable MEMS components (e.g., combs, spacers, and flexure beams) are developed. As micromanipulation tools, microtipped elastomeric stamps with reversible Dry Adhesion are also designed and fabricated to pick up and deterministically place those components. After the manipulation, the components are permanently bonded together via rapid thermal annealing without using any additional intermediate layers. The assembled MEMS device is modeled and analyzed in consideration of the microassembly misalignment. The sensing and actuating capabilities of the assembled MEMS devices are experimentally characterized.
-
Microstructured shape memory polymer surfaces with reversible Dry Adhesion
ACS Applied Materials and Interfaces, 2013Co-Authors: Jeffrey D. Eisenhaure, Stephen Varghese, Tao Xie, Seok KimAbstract:We present a shape memory polymer (SMP) surface with repeatable, very strong (>18 atm), and extremely reversible (strong to weak Adhesion ratio of >1 × 10(4)) Dry Adhesion to a glass substrate. This was achieved by exploiting bulk material properties of SMP and surface microstructuring. Its exceptional Dry adhesive performance is attributed to the SMP's rigidity change in response to temperature and its capabilities of temporary shape locking and permanent shape recovery, which when combined with a microtip surface design enables time-independent control of contact area.
-
Micro-Assembly using Elastomeric Surfaces with Switchable Dry Adhesion
2012Co-Authors: Seok KimAbstract:This work presents a micromanufacturing method for constructing microsystems, which we term ‘micro-masonry’ based on individual manipulation, influenced by strategies for deterministic materials assembly using advanced forms of transfer printing. Analogous to masonry in construction sites, micro-masonry consists of the preparation, manipulation, and binding of microscale units to assemble microcomponents and microsystems. We used microtipped elastomeric stamps as manipulators and built three dimensional silicon microstructures [1]. Silicon units of varied shapes were fabricated in a suspended format on donors, retrieved, delivered, and placed on a target location on a receiver using microtipped stamps. Annealing of the assembled silicon units permanently bound them and completed the micro-masonry procedure.
