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Subject: roughness × WGL Institute: INM ×

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Now showing 1 - 3 of 3
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    Composite pillars with a tunable interface for adhesion to rough substrates
    (Washington D.C. : American Chemical Society, 2017) Fischer, Sarah C.L.; Arzt, Eduard; Hensel, René
    The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young’s moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent.
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    Adhesion and Cellular Compatibility of Silicone-Based Skin Adhesives
    (Weinheim : Wiley-VCH, 2017) Fischer, Sarah C. L.; Kruttwig, Klaus; Bandmann, Vera; Hensel, René; Arzt, Eduard
    Pressure-sensitive adhesives based on silicone materials have emerging potential as adhesives in healthcare products, in particular for gentle skin adhesives. To this end, adhesion to rough skin and biocompatibility are crucial factors for a successful implementation. In this study, the mechanical, adhesive, and biological properties of the two-component poly(dimethylsiloxane) Soft Skin Adhesive MG 7-9800 (SSA, Dow Corning) have been investigated and compared to Sylgard 184. Different mixing ratios of SSA's components allow for tuning of the shear modulus, thereby modifying the adhesive properties of the polymer. To give a comprehensive insight, the authors have analyzed the interplay between pull-off stress, adhesion energy, and stretch of the adhesive films on smooth and rough surfaces. The focus is placed on the effects of substrate roughness and on low pressure oxygen plasma treatment of the adhesive films. SSA shows superior biocompatibility in in vitro cell culture experiments. High pull-off stresses in the range of 3 N cm−2 on a rough surface are achieved, promising broad application spectra for SSA-based healthcare products.
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    Perspective on statistical effects in the adhesion of micropatterned surfaces
    (Melville, NY : American Inst. of Physics, 2021) Booth, Jamie A.; Hensel, René
    Bioinspired micropatterned adhesives have attracted extensive research interest in the past two decades. In modeling the performance of these adhesives, the common assumption has been that the adhesive strength of each sub-contact is identical. Recent experiments, however, have shown that interfacial defects of different characters lead to a distribution of the adhesive strength within a fibrillar array. Based on experimental observations of detachment events, a statistical model for the distribution of the local adhesive strength and the resulting performance of a micropatterned adhesive are presented. This approach constitutes a paradigm shift, providing better understanding of micropatterned adhesives under real conditions. Examples presented include the prediction of unstable detachments in compliant systems. Future directions are discussed, including the extension of the statistical approach to non-uniform loading and rate-dependent effects, the contribution of suction to adhesion and aging of contacts over specific time periods, as well as the necessity for a more in-depth understanding of defect formation considering surface roughness and other imperfections in the system.