Sticky pad

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Sticky pads are friction devices used to prevent objects from sliding on a surface, by effectively increasing the friction between the object and the surface.

Contents

Sticky pads are used to fix items to otherwise smooth surface that are leaned or that moves, so that objects put on that surface could off due to insufficient friction when the surface inclines or moves. [1] The pad has large friction coefficient both with the base surface and with the item laid on it, which prevent both the sticky pad from moving with respect to the surface, and objects laid on the pad from moving relative to the pad. Sticky pads are commonly used on car dashboards where forces caused by acceleration of the vehicle would cause objects put on dashboards slip off the otherwise smooth surface of the dashboard.

Contrary to fasteners, sticky pads do not affix objects to the surface. They merely prevent objects from slipping on the surface until the threshold acceleration or inclination angle is exceeded. Sticky pads also usually don't make use of adhesives. Because of this they are easily detached form the surface, and they need gravity to serve their purpose. In particular, the force acting on the object must have a component perpendicular on the surface and directed towards it. This is different from Microsuction tape where adhesion of object is achieved by microscopic bubbles on the surface that function as small suction cups. Sticky pads are made of rubber-like materials. This help dissipate kinetic energy when the base surface vibrates, such that object on the pad keep maintaining large enough contact surface with the pad and tangential friction forces keep preventing objects from slipping relative to the pad.

Principle of operation

Although basic principles of sticky pads are simple, physics behind may be complex due to many specific and sometimes conflicting requirements arising from practical use. Mechanisms involved in high friction materials go beyond simple Coulomb friction. [2] [3] These can be combined by other mechanisms such as energy dissipation in viscous materials or adhesion.

The above requirements impose many design challenges. To operate well on vibrating surfaces, pads are usually made of soft, rubber like materials with very high friction coefficients. Designs seek to achieve certain level of adhesion (e.g. for use on vertical or very steep surfaces) without compromising easy detachment and continuous use without residual left-over. Some applications (such as sticking smartphones or tablets to vertical surface) require high degree of reliability, which is difficult to achieve without strong sticking to the surfaces.

Various innovative approaches and engineered materials are used to keep in line with requirements. Some designs apply sticking based on vacuum in addition to high friction and softness (see e.g. micro-suction tapes). [4] Other development includes designs that find inspiration in nature, especially in animals that are able to climb walls and ceilings such as geckos, [5] [6] [7] [8] [9] various species of insects [10] , tree frogs [11] , or chameleons. [12]

Mechanisms of insects that can scale walls and ceilings help understand how to produce surfaces with extremely high friction that don't exhibit too much sticking for practical applications. [10] Abilities of geckos have been intensively studied to find out how sticking of vertical walls or ceilings can be joined with ability of easy and quick detachment that enables geckos quick movement. [5] It has been discovered that Van der Waals force rather than friction or adhesion is the most important mechanism behind gecko's abilities. [6] This implies that artificial designs mimicking geckos' feet should rely on maximizing surface contact between object and the pad, which is less practical in some situations, for example when pads are used on non-flat surfaces or when objects put on the pad don't have flat surfaces. On the other hand, mechanisms in geckos' feet help design materials with reliable sticking and easy detachment at the same time. [5] Mechanisms used in geckos, tree frogs and some insects were also studied for self-cleaning ability, which would enable artificial materials retain the ability to prevent sliding after continuous use in dirty environments. [10] [11]

See also

Related Research Articles

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<span class="mw-page-title-main">Friction</span> Force resisting sliding motion

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Arthropods, including insects and spiders, make use of smooth adhesive pads as well as hairy pads for climbing and locomotion along non-horizontal surfaces. Both types of pads in insects make use of liquid secretions and are considered 'wet'. Dry adhesive mechanisms primarily rely on Van der Waals' forces and are also used by organisms other than insects. The fluid provides capillary and viscous adhesion and appears to be present in all insect adhesive pads. Little is known about the chemical properties of the adhesive fluids and the ultrastructure of the fluid-producing cells is currently not extensively studied. Additionally, both hairy and smooth types of adhesion have evolved separately numerous times in insects. Few comparative studies between the two types of adhesion mechanisms have been done and there is a lack of information regarding the forces that can be supported by these systems in insects. Additionally, tree frogs and some mammals such as the arboreal possum and bats also make use of smooth adhesive pads. The use of adhesive pads for locomotion across non-horizontal surfaces is a trait that evolved separately in different species, making it an example of convergent evolution. The power of adhesion allows these organisms to be able to climb on almost any substance.

Microsuction tape is a material for sticking objects to surfaces such as furniture, dashboards, walls, etc. One side is usually attached to the base surface by a classical adhesive. Objects are attached to the other side by pressing them against the tape. They stick to the tape due to small bubbles (cavities) on the surface of the tape. These contain air, which is squeezed out when the surface of an object is pressed against the surface of the tape. Due to sealing properties of the material, when the object is pulled off the surface, a vacuum is created in the cavities. Due to external air pressure, this creates a force that prevents the object from being removed from the surface, a mechanism similar to that of a suction cup.

<span class="mw-page-title-main">Nano tape</span>

Nano tape, also called gecko tape; marketed under the name Alien Tape, is a synthetic adhesive tape consisting of arrays of carbon nanotubes transferred onto a backing material of flexible polymer tape. These arrays are called synthetic setae and mimic the nanostructures found on the toes of a gecko; this is an example of biomimicry. The adhesion is achieved not with chemical adhesives, but via van der Waals forces, which are weak electric forces generated between two atoms or molecules that are very close to each other.

References

  1. ↑ Carolyn Shearlock (Jan 2012). "Sticky Pads". The Boat Galley. Archived from the original on 2017-09-02. Retrieved 2017-09-02.
  2. ↑ Elena Loredana Deladi (2006). Static Friction in Rubber-metal Contacts with Application to Rubber Pad Forming Process (PDF) (Thesis). University of Twente. Archived from the original (PDF) on 2017-09-05. Retrieved 2017-09-05.
  3. ↑ Ulrika Petterson (2005). Surface design for High and Low friction (PDF) (Thesis). University of Uppsala. Archived from the original (PDF) on 2017-09-05. Retrieved 2017-09-05.
  4. ↑ Ozcanli, Osman Can (March 16, 2010). "Looking For The Next Post-It". Forbes. Archived from the original on 2017-09-08. Retrieved 2017-09-02.
  5. 1 2 3 Quan Xu, Yiyang Wan, Travis Shihao Hu, Tony X. Liu, Dashuai Tao, Peter H. Niewiarowski, Yu Tian, Yue Liu, Liming Dai, Yanqing Yang & Zhenhai Xia (20 November 2015). "Robust self-cleaning and micromanipulation capabilities of gecko spatulae and their bio-mimics". Nature Communications. Archived from the original on 2017-09-05. Retrieved 2017-09-05.{{cite web}}: CS1 maint: multiple names: authors list (link)
  6. 1 2 Mena R. Klittich, Michael C. Wilson, Craig Bernard, Rochelle M. Rodrigo, Austin J. Keith, Peter H. Niewiarowski & Ali Dhinojwala (13 March 2017). "Influence of substrate modulus on gecko adhesion". Nature. Archived from the original on 2017-09-05. Retrieved 2017-09-05.{{cite web}}: CS1 maint: multiple names: authors list (link)
  7. ↑ "Gecko Tape". University of Stanford. Archived from the original on 2017-09-05. Retrieved 2017-09-05.
  8. ↑ Richard Black (June 1, 2003). "Gecko inspires sticky tape". BBC. Archived from the original on 2017-09-05. Retrieved 2017-09-05.
  9. ↑ A. K. GEIM, S. V. DUBONOS1, I. V. GRIGORIEVA, K. S. NOVOSELOV, A. A. ZHUKOV and S. YU. SHAPOVAL (1 June 2003). "Microfabricated adhesive mimicking gecko foot-hair" (PDF). Nature Materials. 2 (7): 461–463. Bibcode:2003NatMa...2..461G. doi:10.1038/nmat917. PMID   12776092. S2CID   19995111. Archived from the original (PDF) on 2017-09-05. Retrieved 2017-09-05.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. 1 2 3 "How stick insects honed friction to grip without sticking". Phys.org News. Phys.org. February 19, 2014. Archived from the original on 2017-09-05. Retrieved 2017-09-05.
  11. 1 2 "Frog feet could solve a sticky problem". Phys.org News. Phys.org. July 3, 2011. Retrieved 2017-09-05.
  12. ↑ Marlene Spinner, Guido Westhoff and Stanislav N. Gorb. "Subdigital setae of chameleon feet: Friction-enhancing microstructures for a wide range of substrate roughness". Nature. Archived from the original on 2017-09-05. Retrieved 2017-09-05.
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