Learn about how nature has inspired technological innovations with this book on the similarities between gecko feet and a new adhesive tape. Integrating both historical and scientific perspectives, this book explains how gecko feet inspired the invention of an adhesive. Readers will make connections and examine the relationship between the two concepts. Sidebars, photographs, a glossary, and a concluding chapter on important people in the field add detail and depth to this informational text on biomimicry.
Abstract: Several creatures including insects, spiders, and lizards, have developed a unique clinging ability that utilizes dry adhesion. Geckos, in particular, have developed the most complex adhesive structures capable of smart adhesion--the ability to cling on different smooth and rough surfaces and detach at will. These animals make use of on the order of a million microscale hairs (setae) (about 14000/mm2) that branch off into hundreds of nanoscale spatulae. This hierarchical surface construction gives the gecko the adaptability to create a large real area of contact with surfaces. van der Waals forces are the primary mechanism utilized to adhere to surfaces and capillary forces are a secondary effect that can further increase adhesive force. Although a gecko is capable of producing on the order of 20 N of adhesive force, it retains the ability to remove its feet from an attachment surface at will. A man-made fibrillar structure capable of replicating gecko adhesion has the potential for use in dry, superadhesive tapes that would be of use in a wide range of applications. These adhesives could be created using micro/nanofabrication techniques or self-assembly. A fibrillar polyvinylsiloxane (PVS) sample consisting of an array pillars (about 230/mm2) approximately 50 um in diameter, 70 um in height and 60 um center-to-center was compared to an unstructured sample. Structured roughness was found to be more important than random roughness in adhesion. The added roughness of the structured sample increased the hydrophobicity of the surface.
The last 20 years have seen considerable interest in bioinspired dry adhesives, based on discoveries regarding the adhesive system of the gecko and some arthropods. Such adhesives typically have the advantage of being reusable, leaving no residue, and allowing control of the adhesion through loading states. However, the number of practical applications of these adhesives remains small. One possible reason is that unlike in mechanical design, where design, simulation, and testing methodologies are all well established, there are significant gaps in all of these phases of engineering as applied to gecko-inspired adhesives. There are a variety of methods and metrics used for evaluating adhesives, often giving differing results, and even in some cases results that do not accurately reflect those observed in practical applications. Even with an accurate evaluation of an adhesive material, refining the design is challenging, as the design and manufacturing methods are typically time-consuming, highly constraining, or both. At the same time, there continues to be growing interest in the use of these adhesives in wide-ranging applications including reusable tapes and bandages; improved and more gentle industrial grippers; and grasping objects in space, where the combination of large objects, low contact forces, and lack of atmosphere make adhesives of particular interest. To address this growing need for improved ability to design and manufacture adhesives tailored to these applications, a three-pronged approach is taken. An improved method for testing gecko-inspired adhesives is presented. Unlike the common testing paradigms published in the literature, which impose a fixed displacement between the adhesive material and a test surface, the proposed testing method uses a series elastic configuration to apply forces to the adhesive. This shift in test control from displacement-space to force-space allows the testing conditions to be aligned to those seen in applications; whether for climbing, grasping, or adhesive tapes, nearly all applications of gecko-inspired adhesives fundamentally involve force-space constraints in normal conditions. It is shown that by testing the adhesives in similar conditions to those observed in use, the measured limit curves better reflect those seen in practice. Further, in cases where the adhesive structures are more complicated, or more integral to the performance of the adhesive--such as the directional, controllable adhesives at the core of this work--force-space testing enables measuring the full capabilities of the adhesive, which in many cases are impossible to measure in displacement-space. With the ability to accurately measure more complex limit curves, spatial variation is investigated as a means to improve the ability to create adhesives with novel parameters. In this case, the property of interest is a high friction ratio, the ratio of friction in a preferred direction to friction in the opposite direction, a property of the natural gecko adhesive system. Taking inspiration from the spatial variation found on the gecko's feet, an adhesive structure with wedges of varying length is developed, modeled, and analyzed. The friction ratio of this adhesive is measured, indicating an improvement of orders of magnitude over the current state of the art. Further, this adhesive structure also demonstrates the possibility of simplifying the adhesive design problem. Rather than developing a single complex feature to provide all of the desired properties, spatial variation permits the development of multiple features that are individually simpler but interact to provide more complex behavior. A discussion of the manufacturing process and associated fabrication constraints for these designed adhesive geometries follows. The process is an extension of a previous manufacturing process developed for making uniform adhesives. This is coupled with methods for directly incorporating adhesives into larger assemblies to create tightly coupled adhesive and sensing systems. Finally, a simplified design framework is presented, synthesizing many of the concepts from the prior sections. The current state of the art in adhesive simulation and modeling, while useful for understanding and explaining various specific aspects of adhesive design, is not adequate for directly analyzing the adhesion of complex adhesive geometries. The framework is intended to be a heuristic that synthesizes concepts from the various models of adhesion to provide useful guidance for thinking about adhesive designs for particular applications.
You are surrounded by stickiness. With every step you take, air molecules cling to you and slow you down; the effect is harder to ignore in water. When you hit the road, whether powered by pedal or engine, you rely on grip to keep you safe. The Post-it note and glue in your desk drawer. The non-stick pan on your stove. The fingerprints linked to your identity. The rumbling of the Earth deep beneath your feet, and the ice that transforms waterways each winter. All of these things are controlled by tiny forces that operate on and between surfaces, with friction playing the leading role. In Sticky, Laurie Winkless explores some of the ways that friction shapes both the manufactured and natural worlds, and describes how our understanding of surface science has given us an ability to manipulate stickiness, down to the level of a single atom. But this apparent success doesn't tell the whole story. Each time humanity has pushed the boundaries of science and engineering, we've discovered that friction still has a few surprises up its sleeve. So do we really understand this force? Can we say with certainty that we know how a gecko climbs, what's behind our sense of touch, or why golf balls, boats and aircraft move as they do? Join Laurie as she seeks out the answers from experts scattered across the globe, uncovering a stack of scientific mysteries along the way.
The comprehensive reference and textbook serves as a timely, practical introduction to the principles of nanotribology and nanomechanics. Assuming some familiarity with macroscopic tribology, the book comprises chapters by internationally recognized experts, who integrate knowledge of the field from the mechanics and materials-science perspectives. They cover key measurement techniques, their applications, and theoretical modelling of interfaces, each beginning their contributions with macro- and progressing to microconcepts.
In 1974 when I published my book, Biological Mechanism of Attachment, not many pages were required to report on the attachment devices of insect cuticles. As in most fields of research, our knowledge on this specific subject has simply exploded. Dr. Stanislav N. Gorb now describes the present day level of our knowledge, to which he has personally contributed so much, and a research team working on biological microtribology has gradually developed, also. With modern methods of measurement it is possible to enter the structure – function relationship much more deeply, even down to a molecular level, which was not possible two and a half decades ago. It is a well known fact that, in biology, the more sophisticated the measuring method, the greater the achievement of biological fundamental research, and its resulting evidence. Our knowledge remains at a certain level until new methods once more permit a forward leap. Biological knowledge develops in the form of a stepped curve rather than linear, as reflected in the studies carried out on the attachment devices of insect cuticles.
Geckos' feet consist of an array of millions of keratin hairs that are hierarchically split at their ends into hundreds of contact elements called "spatula(e)". Spatulae make intimate contacts with surface and the attractive van der Waals (vdW) interactions are strong enough to support up to 100 times the animals' bodyweight. Tremendous efforts have been made to mimic this adhesion with polymeric materials and carbon nanotubes (CNT). However, most of these fall short of the performance of geckos. "Contact splitting principle", based on Johnson-Kendall-Roberts (JKR) theory, predicts that a vertically aligned carbon nanotube array (VA-CNT) will be at least 50 times stronger than gecko feet. Although 160 times higher adhesion was recorded in atomic force microscopy (AFM) measurements, macroscopic VA-CNT patches often show low or even no adhesion to substrates. The behavior of VA-CNT hairs near the contact interface has been explored using a combination of mechanical, electrical contact resistance, and scanning electron microscopic (SEM) measurements. Instead of making the expected end contacts, carbon nanotubes make significant side-wall contacts that increase with preload. Adhesion of side-wall contact CNTs is determined by the balance of adhesion in the contact region and the bending stiffness of the CNTs, thus a compliant VA-CNT array is required to make adhesive patches. Macroscopic patches of compliant VA-CNT array have been fabricated. Patches of uniform array have adhesive strength similar to that of geckos (10 N/cm2) on a variety of substrates and can be removed easily by peeling. When the array is patterned to mimic the hierarchical structures of gecko foot-hairs, strength increases up to four times. VA-CNT-based gecko adhesives are self-cleaning, non-viscoelasticity and give good strength in vacuum. These properties are desired in robotics, microelectronics, thermal management and outer space operations. Current theory still cannot completely explain adhesion of gecko feet. A series of experiments have been carried out to measure adhesion at different temperatures using a single protocol with two species of gecko that had been previously studied (G. gecko and P. dubia). Strong evidence of an effect of temperature was found but the trend was counterintuitive given the thermal biology of geckos and it violated the prediction by van der Waals interactions. Consequently, other factors (e.g., humidity) that could explain the variation in the observed clinging performance were examined. Evidence was found, unexpectedly, that humidity is likely an important determinant of clinging force in geckos. Both van der Waals and capillary forces fail to explain the shear adhesion data at the whole animal scale. Resolution of this paradox will require examination of the physical and chemical interaction at the interface and particular way in which water interacts with substrate and setae at the nanometer scale.
This major work has established itself as the definitive reference in the nanoscience and nanotechnology area in one volume. In presents nanostructures, micro/nanofabrication, and micro/nanodevices. Special emphasis is on scanning probe microscopy, nanotribology and nanomechanics, molecularly thick films, industrial applications and microdevice reliability, and on social aspects. Reflecting further developments, the new edition has grown from six to eight parts. The latest information is added to fields such as bionanotechnology, nanorobotics, and NEMS/MEMS reliability. This classic reference book is orchestrated by a highly experienced editor and written by a team of distinguished experts for those learning about the field of nanotechnology.
Memory, morality, and immortality merge in this “haunting and lyrical triumph” from the bestselling author of Schismatrix Plus (Time). In the late twenty-first century, technology has lengthened lifespans far beyond what was once medically possible. Existence itself has become relatively easy—if boring. In this futuristic paradise, ninety-four-year-old Mia Ziemann longs for something different and undergoes a radical new treatment that restores both her body and mind to that of a twenty-year-old. After her dramatic transformation, Mia finds herself lost in an avant-garde world of passion, designer drugs, and creative expression . . . “Ideas—big ideas—lurk beneath Mia’s romp through Sterling’s delightfully imagined newly post-human Earth. Art, artifice, the pursuit of immortality, and youth and aging bounce around the story, the characters, and their conversations in imaginative, engaging fashion. . . . In the end, Holy Fire is one of the most interesting, imaginative, and subtly humorous—and relevant for it—novels the cyberpunk/post-human era has produced. . . . Holy Fire may very well be [Sterling’s] best work.” —Speculiction “An intellectual feat, it is also a treat for the spirit and the senses.” —Wired “A patented Sterling extra-special.” —Newsday “The future Sterling traces is plausible and provocative, particularly his consideration of several contrasting cultures, and of the disenfranchised who are unable to become ‘post-human.’ Those interested in serious speculative conversation set within a very strange near-future will find this much to their taste.” —Publishers Weekly
