Contact angles, work of adhesion, and interfacial tensions at a dissolving Hydrocarbon surface

Fluorinated substrates like Teflon w (poly(tetrafluoroethylene); PTFE) are well known for their role in creating non-stick surfaces. We showed previously that even geckos, which can stick to most surfaces under a wide variety of conditions, slip on PTFE. Surprisingly, however, geckos can stick reasonably well to PTFE if it is wet. In an effort to explain this effect, we have turned our attention to the role of substrate surface energy and roughness when shear adhesion occurs in media other than air. In this study, we removed the roughness component inherent to commercially available PTFE and tested geckos on relatively smooth wet and dry fluoropolymer substrates. We found that roughness had very little effect on shear adhesion in air or in water and that the level of fluorination was most important for shear adhesion, particularly in air. Surface energy calculations of the two fluorinated substrates and one control substrate using the Tabor-Winterton approximation and the Young-Dupré equation were used to determine the interfacial energy of the substrates. Using these interfacial energies we estimated the ratio of wet and dry normal adhesion for geckos clinging to the three substrates. Consistent with the results for rough PTFE, our predictions show a qualitative trend in shear adhesion based on fluorination, and the quantitative experimental differences highlight the unusually low shear adhesion of geckos on dry smooth fluorinated substrates, which is not captured by surface energy calculations. Our work has implications for bioinspired design of synthetics that can preferentially stick in water but not in air.

show abstract

“…where u is the contact angle of water on the substrate and g l is the interfacial tension of water, taken as 72.8 mJ m 22 [43].…”

Section: Theoretical Modelling Proceduresmentioning

confidence: 99%

Adhesive interactions of geckos with wet and dry fluoropolymer substrates

Stark

Dryden

Olderman

et al. 2015

J. R. Soc. Interface.

View full text Add to dashboard Cite

show abstract

“…The contact angle is measured by placing the droplet on the surface of the polymer using the integrated dispenser system; the angle which this drop makes with the surface is then measured using the associated high resolution camera and computer software. The liquid drop properties are extracted using the Strom et al [17,18] technique. In order to determine the surface energy it is necessary to dispense three liquids of different polarities.…”

Section: Characterisationmentioning

confidence: 99%

Atmospheric pressure plasma treatment of amorphous polyethylene terephthalate for enhanced heatsealing properties

Dowling

Tynan

Ward³

et al. 2012

International Journal of Adhesion and Adhesives

View full text Add to dashboard Cite

An atmospheric pressure plasma system has been used to treat amorphous polyethylene terephthalate (APET) to enhance its healseal properties to a polyethylene terephthalate (PET) film. The plasma treated APET sheet material was thermoformed into trays for use in the food packaging industry and heatsealed to a PET film. The heatsealing properties of the resulting package were assessed using the burst test technique. It was found that the plasma treatment significantly enhanced the adhesive properties and an increase in burst pressure from 18 to 35 kPa was observed for plasma treated food trays. The APET surface chemistry was assessed after plasma treatment where it was found that the plasma treatment had affected an increase in oxygen and an addition of nitrogen species to the polymer surface. The surface roughness (R a ) of the plasma treated samples was also observed to increase from 0.4 to 0.9 nm after plasma treatment. IntroductionHeatsealed polymer trays are widely used for packaging food products, particularly meat and fish [1]. In the heat sealing process a polymer top film is applied to the polymer tray under elevated temperature and pressure in order to enclose the food product in an airtight environment [2]. The conventional method for creating a strong bond between a food tray and a top film is to use a co-extruded heatseal layer ( Figure 1).

show abstract

“…According to the geometric mean method, the solid surface tension components were evaluated with Eqn. (1), (Van Oss et al, 1989) using the known surface tension components, (Erbil, 1997;Rankl et al, 2003;Strom et al, 1987) of different liquids from Table 3 and the contact angles from γ increases from 9.1 to 10.7 mN/m). Table 5 shows the contribution of the polar component to the total surface tension obtained from the geometric mean method GM for untreated and plasma treated polyurethanes.…”

Section: Wwwintechopencommentioning

confidence: 99%