Adhesion of micropatterned adhesives to rough substrates and at elevated temperatures

The gecko is of high interest for scientists due to its ability to attach and to move on different surfaces with various roughnesses. To date, research groups worldwide aim to study adhesion mechanisms of gecko-like structures and to mimic gecko adhesion. However, most investigations have been performed in controlled environments and under near to ideal conditions, which present a significant constraint for transferring the results to applications. Therefore, two important parameters have been the subject of investigations in the present work, the surface roughness and elevated temperatures. For the first time, the impact of roughness on the adhesion of gecko-like, micropatterned structures was systematically studied. Two adhesive regimes, which are dependent on the pillar geometry and the roughness parameters, were discovered: an adhesive and a non –adhesive regime. The influence of the temperature on adhesion was studied on micropatterned samples fabricated out of three materials, which are interesting candidates for industrial applications. Promising correlations were determined between the temperature dependent mechanical properties and the adhesion values: the glass transition temperature was identified as the temperature of maximum adhesion. These results can support the improvement of bioinspired adhesives for industrial applications.Der Gecko ist für Wissenschaftler aufgrund seiner herausragenden Fähigkeit, sich an verschiedenen Oberflächen zu befestigen und fortzubewegen, ein besonderes Vorbild für temporäre Adhäsionssysteme. Bislang bezieht sich das Ziel vieler Forschungsgruppen darauf Geckostrukturen nachzuahmen und grundlegende Mechanismen zu studieren. Diese Untersuchungen finden jedoch bisher unter nahezu idealen Bedingungen und in einer kontrollierten Umgebung statt, was eine starke Einschränkung bei der Übertragung der Ergebnisse auf industrielle Anwendungen darstellt. Zwei wichtige Parameter waren Gegenstand der Untersuchungen in dieser Arbeit, die Rauigkeit und die Temperatur. Zum ersten Mal wurde der Einfluss der Rauigkeit auf das Adhäsionsverhalten einer großen Anzahl von mikrostrukturierten Strukturen systematisch untersucht. Hierbei wurden zwei Adhäsionsregime, die von der Pillargeometrie und den Rauigkeitsparametern abhängen, festgestellt: das adhäsive und das nicht-adhäsive Regime. Der Einfluss der Temperatur auf die Adhäsion wurde auf mikrostrukturierten Proben aus drei für industrielle Anwendungen sehr interessante Materialien erforscht. Hierbei wurden wichtige Korrelationen zwischen den temperaturabhängigen mechanischen Eigenschaften und den ermittelten Rauigkeitswerten festgestellt. So wurde die Glasübergangstemperatur als die Temperatur der maximalen Adhäsion identifiziert. Diese Ergebnisse können dazu beitragen, bioinspirierte Strukturen für industrielle Anwendungen zu optimieren

Elevated temperature adhesion of bioinspired polymeric micropatterns to glass

Micropatterned polymer surfaces that operate at various temperatures are required for emerging technical applications such as handling of objects or space debris. As the mechanical properties of polymers can vary significantly with temperature, adhesion performance can exhibit large variability. In the present paper, we experimentally study temperature effects on the adhesion of micropatterned adhesives (pillar length 20 μm, aspect ratios 0.4 and 2) made from three different polymers, i.e., polydimethylsiloxane (PDMS), perfluoropolyether dimethacrylate (PFPEdma), and polyurethane (PU-ht). PU specimens showed the highest pull-off stresses of about 57 kPa at 60 °C, i.e., more than twice the value of unpatterned control samples. The work of separation similarly showed a maximum at that temperature, which was identified as the glass transition temperature, Tg. PDMS and PFPEdma specimens were tested above their Tg. As a result, the adhesion properties decreased monotonically (about 50% for both materials) for temperature elevation from 20 to 120 °C. Overall, the results obtained in our study indicate that the operating temperature related to the glass transition temperature should be considered as a significant parameter for assessing the adhesion performance of micropatterned adhesives and in the technical design of adhesion devices

Fibrillar Elastomeric Micropatterns Create Tunable Adhesion Even to Rough Surfaces

Acknowledgements V.B., N.K.G., and E.A. contributed with conception and experimental design. V.B. performed the experiments. V.B., R.H., A.G., and R.M.M. carried out analysis and interpretation of data. V.B., R.H., A.G., and E.A. wrote the manuscript. V.B. and R.H. contributed equally to this work. V.B. acknowledges funding by SPP 1420 of the German Science Foundation DFG. E.A., N.K.G., and R.H. acknowledge funding from the European Research Council under the European Union/ERC Advanced Grant “Switch2Stick,” Agreement No. 340929.Peer reviewedPublisher PD

Fibrillar elastomeric micropatterns create tunable adhesion even to rough surfaces

Biologically inspired, fibrillar dry adhesives continue to attract much attention as they are instrumental for emerging applications and technologies. To date, the adhesion of micropatterned gecko-inspired surfaces has predominantly been tested on stiff, smooth substrates. However, all natural and almost all artificial surfaces have roughnesses on one or more different length scales. In the present approach, micropillar-patterned PDMS surfaces with superior adhesion to glass substrates with different roughnesses are designed and analyzed. The results reveal for the first time adhesive and nonadhesive states depending on the micropillar geometry relative to the surface roughness profile. The data obtained further demonstrate that, in the adhesive regime, fibrillar gecko-inspired adhesive structures can be used with advantage on rough surfaces; this finding may open up new applications in the fields of robotics, biomedicine, and space exploration