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Author: Frensemeier, Mareike × Publisher: Hoboken, NJ : Wiley ×

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    Temperature-induced switchable adhesion using nickel-titanium-polydimethylsiloxane hybrid surfaces
    (Hoboken, NJ : Wiley, 2015) Frensemeier, Mareike; Kaiser, Jessica S.; Frick, Carl P.; Schneider, Andreas S.; Arzt, Eduard; Fertig III, Ray S.; Kroner, Elmar
    A switchable dry adhesive based on a nickel–titanium (NiTi) shape-memory alloy with an adhesive silicone rubber surface has been developed. Although several studies investigate micropatterned, bioinspired adhesive surfaces, very few focus on reversible adhesion. The system here is based on the indentation-induced two-way shape-memory effect in NiTi alloys. NiTi is trained by mechanical deformation through indentation and grinding to elicit a temperature-induced switchable topography with protrusions at high temperature and a flat surface at low temperature. The trained surfaces are coated with either a smooth or a patterned adhesive polydimethylsiloxane (PDMS) layer, resulting in a temperature-induced switchable surface, used for dry adhesion. Adhesion tests show that the temperature-induced topographical change of the NiTi influences the adhesive performance of the hybrid system. For samples with a smooth PDMS layer the transition from flat to structured state reduces adhesion by 56%, and for samples with a micropatterned PDMS layer adhesion is switchable by nearly 100%. Both hybrid systems reveal strong reversibility related to the NiTi martensitic phase transformation, allowing repeated switching between an adhesive and a nonadhesive state. These effects have been discussed in terms of reversible changes in contact area and varying tilt angles of the pillars with respect to the substrate surface.
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    Shape-memory topographies on nickel–titanium alloys trained by embossing and pulse electrochemical machining
    (Hoboken, NJ : Wiley, 2016) Frensemeier, Mareike; Schirra, Dominik; Weinmann, Martin; Weber, Oliver; Kroner, Elmar K.
    The two-way shape-memory effect (TWSME) in Nickel–titanium (NiTi) alloys is of interest for applications in aerospace, biomedicine, and microengineering due to its reversible shape recovery. In this study, the authors demonstrate two approaches to obtain switchable surface structures using the TWSME. Samples are structured using two surface geometries by either cold embossing, or pulse electrochemical machining (PECM). After planarization, a change from optically smooth to structured and vice versa is observed. The switch is induced through heating and cooling the sample above and below the phase transformation temperature. The protrusions reflect the pattern applied by the two processes. Both methods are promising for preparation of switchable metallic surfaces on larger areas.