Supplementary Information
Tailoring normal adhesion of arrays of
thermoplastic, spring-like polymer nanorods by
shaping nanorod tips
Longjian Xue†,‡,*, Alexander Kovalev‡, Florian Thöle†, Gopalakrishnan Trichy Rengarajan†, Martin Steinhart†*, Stanislav N. Gorb‡*
†
Institut für Chemie, Universität Osnabrück, Barbarastrasse 7, 49069
Osnabrück, Germany
‡
Institut für Zoologie, Universität Kiel, Am Botanischen Garten 1-9,
24098 Kiel, Germany
* To whom correspondence should be addressed.
E-mail:
[email protected];
[email protected];
[email protected]
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(a)
(b)
Figure S1. Representative SEM images of AAO undersides. (a) Uncovered underside of
AAO after etching the aluminium substrate before the opening of the pore bottoms. The hemispherical pore bottoms consist of the barrier oxide. (b) Underside of AAO after opening of the
pore bottoms and partial etching of the AAO. PS nanorod tips protruding from the AAO pores
can clearly be seen. The scale bars correspond to 500 nm.
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Figure S2. Schematic illustration of the probability p of contact formation between contact
elements and sapphire sphere at a certain load Fl (not to scale). Each contact element is modeled as a spring with length l0 and contact area A. (a) Formation of partial contact with a certain probability p when the nanorods are compressed by ∆l under the loading force Fl. (b) All
contact elements have full contact with the sapphire sphere (p = 1) under the loading force Fl1
when the PS nanorods are compressed by ∆l1.
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(a)
1200
Force (µ N)
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0
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Piezo displacement (µm)
(b)
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1200
Force (µ N)
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(c)
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Piezo displacement (µm)
Figure S3. Properties of an array of collapsed PS nanorods prepared in the same way as the
PS nanorod arrays with foot-like tips (shear pressing) except that the pore diameter of the
AAO template was 180 nm (all other PS nanorod arrays were obtained with AAO having a
pore diameter of 270 nm) and except that the AAO was completely etched prior to rubbing. (a)
SEM image; (b) force-displacement curves with different loading forces; (c) successive forcedisplacement curves at a high loading force larger than 1200 µN. The curves are shifted horizontally by one micron from each other.
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(a)
(b)
Figure S4. Durability of PS nanorod arrays with (a) flat tips and (b) foot-like tips. (a) The
durability test on a PS nanorod array with flat tips was carried out by increasing Fl in 7 successive attachment/detachment cycles from ~220 µN to ~1000 µN (not shown). Then, 20 successive attachment/detachment cycles with Fl ≈ 400 µN were performed. As seen in panel (a),
Fad was about 130 µN. All measurements were carried out at the same position. (b) The durability test on a PS nanorod array with foot-like tips was carried out by increasing Fl in 9 successive attachment/detachment cycles from ~80 µN to ~1100 µN (not shown). Then, 20 successive attachment/detachment cycles with Fl ≈ 550 µN were performed. As seen in panel (b),
Fad amounted to about 325 µN. All measurements were carried out at the same position.
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