A Direct Method of Studying Adsorption of a Surfactant at Solid-Liquid Interfaces

Haïdara, Hamidou; Chaudhury, Manoj K.; Owen, Michael J.

doi:10.1021/j100021a037

Cited by 27 publications

(36 citation statements)

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“…Our experimental results also are supported by our model, and ratios of wet to dry adhesion are near 1 (wet adhesion is not different from dry adhesion) in case 1, in which the gecko hair-like surface remains dry before and during contact. The maintenance of dry contact is interesting because when two surfaces become separated, water likely will penetrate the separation crack forming between the two surfaces and even propagate further growth (46). This may be what occurs when testing normal and frictional (shear) adhesion of a patch of setae, where normal adhesion in water is much lower, as the result of water penetration, than frictional adhesion in water under high loads that presumably keep water from separating the two surfaces (37).…”

Section: Discussionmentioning

confidence: 99%

Surface wettability plays a significant role in gecko adhesion underwater

Stark

Badge

Wucinich

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

128

192

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Although we now have thousands of studies focused on the nano-, micro-, and whole-animal mechanics of gecko adhesion on clean, dry substrates, we know relatively little about the effects of water on gecko adhesion. For many gecko species, however, rainfall frequently wets the natural surfaces they navigate. In an effort to begin closing this gap, we tested the adhesion of geckos on submerged substrates that vary in their wettability. When tested on a wet hydrophilic surface, geckos produced a significantly lower shear adhesive force (5.4 ± 1.33 N) compared with a dry hydrophilic surface (17.1 ± 3.93 N). In tests on an intermediate wetting surface and a hydrophobic surface, we found no difference in shear adhesion between dry and wet contact. Finally, in tests on polytetrafluoroethylene (PTFE), we found that geckos clung significantly better to wet PTFE (8.0 ± 1.09 N) than dry PTFE (1.6 ± 0.66 N). To help explain our results, we developed models based on thermodynamic theory of adhesion for contacting surfaces in different media and found that we can predict the ratio of shear adhesion in water to that in air. Our findings provide insight into how geckos may function in wet environments and also have significant implications for the development of a synthetic gecko mimic that retains adhesion in water.contact angle | superhydrophobicity | van der Waals | friction | bioinspired adhesive O ver the past decade, researchers have made extraordinary progress in understanding how the gecko adhesive system works (1-8). Indeed, many laboratories have tested hundreds of synthetic mimics for potential use in robotics, medicine, space, and everyday life (9-21). Although the range and performance of synthetic "gecko-tapes" are impressive, important gaps remain in our knowledge of the system and its capabilities in natural environments. Geckos are extremely diverse, constituting more than 1,400 species worldwide (22, 23). However, knowledge of the natural substrates and conditions geckos use is very limited. For example, it is likely that many species move across leaves and other plant structures that are not perfectly smooth and have variable surface chemistries (24,25). In principle, the interaction of gecko feet with such surfaces may have a significant effect on adhesion, yet gecko research has only just begun to tackle such questions (26-28). Additionally, natural surfaces are likely to become wet (especially in the tropics) and dirty, potentially reducing adhesion. Although research on the ability of geckos to remove dirt from their toes has received some attention (29,30), studies on wetting and the effect of water are limited, despite the well-known antiwetting properties of the toes, which are superhydrophobic and have a low-contact-angle hysteresis (31, 32).Somewhat surprisingly, geckos cannot stick to hydrophilic glass when it is covered with a layer of water (33). Anecdotally, this effect has been long and widely appreciated; nevertheless, the effect of water on gecko adhesion is complex. For example, a thin water ...

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Section: Discussionmentioning

confidence: 99%

Surface wettability plays a significant role in gecko adhesion underwater

Stark

Badge

Wucinich

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

128

192

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“…A promising approach has recently been published by Chaudhury. 12 He studied the dynamic adsorption of hydrocarbonbased surfactants to a PDMS sheet/PDMS halfsphere system. Alternatively we developed a modified Wilhelmy method.…”

Section: Introductionmentioning

confidence: 99%

Silicon-modified surfactants and wetting: I. Synthesis of the single components of Silwet L77 and their spreading performance on a low-energy solid surface

Wagner

Czichocki

et al. 1999

Appl. Organometal. Chem.

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Defined surfactants of general formula [(CH3)3SiO]2CH3Si(CH2)3(OCH2CH2)3–9OCH3, have been synthesized from the corresponding oligoethylene glycol monoallyl monomethyl ethers via hydrosilylation. The concentration‐dependent spreading performance on hydrophobized silicon wafers has been investigated and compared with that of Silwet L77. For the hexaethylene glycol derivative the highest initial spreading velocities and largest spreading areas were found. Since Silwet L77 spreads faster than all the other derivatives under investigation, a synergistic effect of different compounds is unlikely. Minor differences were found for handshaken and sonicated solutions. Copyright © 1999 John Wiley & Sons, Ltd.

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“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In this method, a semispherical object is brought into contact with another flat or a semispherical object under controlled loads. If one of the contacting materials is deformable and if their surfaces are smooth, then deformation occurs in the zone of contact, the magnitude of which depends on the work of adhesion between surfaces and any external loads applied on them.…”

Section: Introductionmentioning

confidence: 99%

Adhesive contact of cylindrical lens and a flat sheet

Chaudhury

Weaver

Hui

et al. 1996

Journal of Applied Physics

201

144

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Methods are developed to estimate the adhesion and surface free energies of compliant materials from the contact deformations of cylindrical lenses with flat sheets. Some important differences are found between the cylindrical contact studied here and the widely studied geometry of spherical contact. For example, while the pull-off force is completely independent of the elastic constants (K) of the materials for spherical contacts, the pull-off force for cylindrical contact is proportional to K 1/3 . Furthermore, for cylindrical contacts the contact width at separation reaches to a value of 39% of the width ͑a 0 ͒ at zero load, whereas the corresponding value is 0.63a 0 for spherical contact. The feasibility of using cylindrical contacts to estimate the surface and adhesive energies of polymers was investigated using elastomeric polydimethylsiloxane ͑PDMS͒ as a model system. PDMS was used in two ways: ͑1͒ unmodified and ͑2͒ with its surface hydrolyzed with dilute hydrochloric acid. Significant hysteresis of adhesion was observed with the hydrolyzed PDMS surfaces due to H-bonding interactions, which appeared to depend on normal stress.

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A Direct Method of Studying Adsorption of a Surfactant at Solid-Liquid Interfaces

Cited by 27 publications

References 1 publication

Surface wettability plays a significant role in gecko adhesion underwater

Surface wettability plays a significant role in gecko adhesion underwater

Silicon-modified surfactants and wetting: I. Synthesis of the single components of Silwet L77 and their spreading performance on a low-energy solid surface

Adhesive contact of cylindrical lens and a flat sheet

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