scholarly journals Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

2015 ◽  
Vol 12 (104) ◽  
pp. 20141346 ◽  
Author(s):  
Saurabh Das ◽  
Nicholas Cadirov ◽  
Sathya Chary ◽  
Yair Kaufman ◽  
Jack Hogan ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Silica Surface ◽  
Surface Forces ◽  
Surface Forces Apparatus ◽  
Stick Slip ◽  
Theoretical Approaches ◽  
Frictional Forces ◽  
Modified Surface ◽  
Glass Surfaces ◽  
Effect Of Surface

The discovery and understanding of gecko ‘frictional-adhesion’ adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick–slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick–slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick–slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

scholarly journals When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs

2016 ◽  
Vol 7 ◽  
pp. 2116-2131 ◽  
Author(s):  
Niall Crawford ◽  
Thomas Endlein ◽  
Jonathan T Pham ◽  
Mathis Riehle ◽  
W Jon P Barnes
Keyword(s):  
Surface Roughness ◽  
Real Contact Area ◽  
Small Scale ◽  
Tree Frog ◽  
Natural Habitats ◽  
Litoria Caerulea ◽  
Frictional Forces ◽  
Tree Frogs ◽  
Air Pockets ◽  
Effect Of Surface

Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low elastic modulus, making it highly deformable.

Effect of Solvent Condition on the Dynamic Response of Polymer Brushes

1998 ◽  
Vol 543 ◽  
Author(s):  
S. M. Kilbey ◽  
P. Schorr ◽  
M. Tirrell
Keyword(s):  
Polymer Brushes ◽  
Surface Forces ◽  
Polymer Chains ◽  
Lateral Motion ◽  
Dilute Solution ◽  
Surface Forces Apparatus ◽  
Effect Of Solvent ◽  
Preferential Adsorption ◽  
Frictional Forces ◽  
Theta Solvent

AbstractThe frictional response of two opposing polymer brushes subjected to steady shear was studied as a function of solvent condition and degree of compression using the Surface Forces Apparatus (SFA). The brushes were made by preferential adsorption of polyvinylpryridinepolystyrene (PVP-PS) block copolymers adsorbed onto atomically smooth surfaces from a dilute solution of toluene. Extremely parallel lateral motion was imparted to one surface and the response was detected at the opposing brush-covered surface. When the brushes were bathed in a good solvent, it was necessary to strongly compress the layers in order to observe frictional forces transmitted between the surfaces. However, when the solvent was changed to a near-theta solvent, large frictional forces were measured at weaker compressions. The onset of these frictional forces occurred at distances comparable to the distance at which the opposing layers contact one another and rapidly increase as the brushes are compressed. Arguments are advanced that this behavior is attributable to frictional interactions between the polymer chains and the solvent.

scholarly journals Effect of Surface Roughness on the Stick-slip Behavior of Magnetic Field Controlled-dipolar Suspensions in Simple Linear Shear Mode

2016 ◽  
Vol 67 ◽  
pp. 03032
Author(s):  
Jile Jiang ◽  
Zhimin Zhang ◽  
Gang Hu ◽  
Yonggang Meng ◽  
Yu Tian
Keyword(s):  
Magnetic Field ◽  
Surface Roughness ◽  
Shear Mode ◽  
Stick Slip ◽  
Linear Shear ◽  
Effect Of Surface

Triboelectrification Between Dissimilar Smooth Metal Surfaces With Self-Assembled Monolayers

2005 ◽  
Author(s):  
Mustafa Akbulut ◽  
Anna R. Godfrey Alig ◽  
Jacob Israelachvili
Keyword(s):  
Metal Surfaces ◽  
Surface Forces ◽  
Self Assembled Monolayers ◽  
Surface Forces Apparatus ◽  
Static Contact ◽  
Large Fluctuations ◽  
Assembled Monolayers ◽  
Modified Surface ◽  
The Mean ◽  
Sliding Distance

We have simultaneously measured the friction and triboelectrification between two adhering SAM-coated molecularly smooth dissimilar metal surfaces using a modified surface forces apparatus. As the pressure is increased, triboelectrification increases drastically with large fluctuations about the mean. When the surfaces are in static contact, none of these effects is observed. Triboelectrification strongly depends on the friction type and force, sliding distance, contact area and sliding history. We also show that both SAMs and metal substrates contribute to the charge transfer mechanism.

High-Speed Friction Measurements Using a Modified Surface Forces Apparatus

2011 ◽  
Vol 42 (1) ◽  
pp. 117-127 ◽  
Author(s):  
D. D. Lowrey ◽  
K. Tasaka ◽  
J. H. Kindt ◽  
X. Banquy ◽  
N. Belman ◽  
...  
Keyword(s):  
High Speed ◽  
Surface Forces ◽  
Surface Forces Apparatus ◽  
Modified Surface ◽  
Friction Measurements

A study of structure and properties of molecularly thin methanol film using the modified surface forces apparatus

2014 ◽  
Vol 77 (11) ◽  
pp. 851-856 ◽  
Author(s):  
Gutian Zhao ◽  
Di Cai ◽  
Gensheng Wu ◽  
Qiyan Tan ◽  
Li Xiang ◽  
...  
Keyword(s):  
Surface Forces ◽  
Structure And Properties ◽  
Surface Forces Apparatus ◽  
Modified Surface

Incorporation of Multi Wall Carbon Nanotubes into Glass-Surfaces via Laser-Treatment

2003 ◽  
Vol 772 ◽  
Author(s):  
T. Seeger ◽  
G. de la Fuente ◽  
W.K. Maser ◽  
A.M. Benito ◽  
A. Righi ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Continuous Wave ◽  
Silica Surface ◽  
Multi Wall Carbon Nanotubes ◽  
Composite Formation ◽  
Multi Walled Carbon Nanotubes ◽  
Glass Surfaces ◽  
Walled Carbon Nanotubes ◽  
First Time ◽  
Scanning Electron

AbstractCarbon nanotubes (CNT) are interesting candidates for the reinforcement in robust composites and for conducting fillers in polymers due to their fascinating electronic and mechanical properties. For the first time, we report the incorporation of multi walled carbon nanotubes (MWNTs) into silica-glass surfaces by means of partial surface-melting caused by a continuous wave Nd:YAG laser. MWNTs were detected being well incorporated in the silica-surface. The composites are characterized using scanning electron microscopy (SEM) and Raman-spectroscopy. A model for the composite-formation is proposed based on heatabsorption by MWNTs and a partial melting of the silica-surface.

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