Thermally Active Liquid Crystal Network Gripper Mimicking the Self-Peeling of Gecko Toe Pads

Significance Statement

The ability of geckos to climb on surfaces is mainly pegged on their adhesive toe pads. The pads are designed with hair-like structures. These hierarchical structures enhance compliance, intimate contact and promote van der Waals interactions with the surfaces. It has been confirmed that a unique configuration of the gecko toes is key in their locomotion, which happens in two modes namely; gripping and release modes.

During the gripping mode, two diagonally opposite toes are in action and are pulled inwards towards the center of mass of the body. The other two pads are normally detached during the attachment mode, which can be termed as the Y-configuration. The gecko applies both lateral and normal forces to drag the setae array against the surfaces they move on. In the release mode, the setae are configured in a critical angle to enhance the release of the pads. The toe pads scroll upward from the mating surface and reduce the adhesion using the setal shaft, which functions like a lever for perpendicular peeling the spatulae off the substrates.

Gecko-inspired adhesives, which are normally based on micropillars terminated by flaps, have, therefore, received numerous research works in the recent past. However, active control of the adhesives imitating the switchable properties of gecko’s toe pads is still an outstanding challenge. A collaborative research between Professor Antal Jákli at Kent State University and Professor Boxin Zhao at Waterloo Institute of Nanotechnology with experiments carried out by graduate students Hamed Shahsavan and Muhammad Salili (by now both received their PhD) reported the integration of gecko imitating adhesives to cantilevers form liquid crystal network in a bid to design multi-legged gecko grippers with thermally-induced peeling capabilities. Their work is published in Advanced Materials.

The authors developed a multilegged gripper and the pick-and-place mechanism. They made each leg by a hybrid liquid crystal polymer cantilever attached to one edge, and a film terminated fibrillar on the other end. They also fabricated two forms of film-terminated adhesive structures, one fully elastic and the other with viscoelastic top-coat.

In order to achieve adequate preload stress, the authors attached small magnetic patches on the upper surface of the cantilevers. The preload stress was, therefore, provided via the applied magnetic field which was created by an electromagnet placed below the specimen. During the experiment, the release mode was triggered by the bending of the liquid crystal polymers, which initiated the self-peeling of the adhesive patch. The authors realized that for the attachment mode, the applied magnetic force should be adequate in order to impose the required preload stress.

The researchers observed that the adhesion as well as the bending energy of the liquid crystal polymers was dictated by the temperature on the surface. Higher temperature caused a larger bending, which further induced self-peeling of the liquid crystal network cantilever.

The authors concluded that the liquid crystal polymer cantilevers with cross-linking provided adequate work output to detach film adhesive patches from smooth and flat surfaces. They implemented the self-peeling mechanism of the structures in pick and place handling of smooth 2-dimensional objects. This study demonstrated the possible implementation of the gecko-inspired gripping and release mechanism for developing switchable adhesives, which can be used as grippers.

Thermally Active Liquid Crystal Network Gripper Mimicking the Self-Peeling of Gecko Toe Pads - Advances in Engineering

About The Author

Antal Jákli has obtained his PhD in Statistical Physics from the Loránd Eötvös University in Budapest, Hungary in 1986 and his Doctor of Science Degree from the Hungarian Academy of Sciences in 2000. Currently he is Professor of Chemical Physics at the Liquid Crystal Institute of Kent State University in Kent, OH, USA. His research focuses on the physical properties of soft matter with special emphasis on bent-core liquid crystals, piezoelectricity and ferroelectricity.

He has developed two new graduate courses for the Chemical Physics Interdisciplinary Program at Kent State University and incorporated them into a textbook “One and two dimensional fluids” co-authored with A. Saupe (Taylor&Francis, 2006). He co-authored about 250 peer-reviewed papers and 10 book chapters, and holds over 15 US patents. Since 2009 he is an associate Editor of Phys. Rev. E handling liquid crystal papers.

About The Author

Dr. Boxin Zhao is a tenured associate professor in chemical engineering at the University of Waterloo. He is also affiliated with Waterloo Institute for Nanotechnology, Centre for Bioengineering and Biotechnology, and Institute for Polymer Research. Dr. Zhao obtained his PhD in Chemical Engineering from McMaster University in 2004. Before joining the University of Waterloo, Dr. Zhao had worked as a NSERC postdoctoral fellow at the University of California, Santa Barbara. At Waterloo, Professor Zhao has established the Laboratory of Surface Science and Bionanomaterials, working on both fundamental and applied research to meet the growing need of bionanotechnologies in advanced manufacturing, e.g. multifunctional green and smart materials and processes, additive manufacture or 3D printing.

He have 165 publications in total; 79 are peer-refereed papers on the top journals including Macromolecules, Langmuir, J. Materials Chemistry, Carbon, Advanced Materials, and Advanced Functional Materials. His research work has been well recognized in the field and has been invited to deliver talks and lectures to Celestica, Xerox and Magna and other national and international conferences. He was awarded the Early Researcher Award from the Province of Ontario in 2012 and was awarded a prestigious Fulbright Visiting Research Chair at UCSB from Fulbright Canada in 2015.

The current research interests of his group are in the areas of multifunctional composites, interfacial technologies and surface science, biomimetic adhesion and adhesives, biopolymers, 3D printing, interfacial phenomena and contact dynamics (e.g., wetting, adhesion, friction, lubrication, wear, fracture) in polymers and biological systems.

About The Author

Dr. Hamed Shahsavan is a post-doctoral fellow in department of chemical engineering at University of Waterloo. He is also affiliated with Liquid Crystal Institute at Kent State University in Kent, OH, USA, as a visiting scholar. Dr. Shahsavan obtained his PhD in Chemical Engineering (Nanotechnology) from University of Waterloo in 2017. He was awarded the Early Stage Career Award from International Liquid Crystal Elastomer Conference held in Erice, Italy in 2016.

His research interests include biomimetics, smart surfaces, interfaces and miniature devices, liquid crystal elastomers, bio-inspired topographical and chemical modification of polymeric surfaces, contact mechanics studies (adhesion, friction, and wetting), and interfacial phenomena at micro/nanoscales.

Reference

Hamed Shahsavan1,2, Seyyed Muhammad Salili2, Antal Jákli2,3, and Boxin Zhao1. Thermally Active Liquid Crystal Network Gripper Mimicking the Self-Peeling of Gecko Toe Pads. Advanced Materials, volume 29 (2017), 1604021.

Show Affiliations
  1. Department of Chemical Engineering, Waterloo Institute for Nanotechnology, Institute for Polymer Research, and Centre for Bioengineering and Biotechnology, Waterloo, ON, Canada
  2. Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH, USA
  3. Complex Fluids Group, Wigner Research Centre, Budapest, Hungary

 

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