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Materialwissenschaft und Werkstofftechnik
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Materialwissenschaft und Werkstofftechnik
Article . 2010 . Peer-reviewed
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Lotus‐Effect and inverse Lotus‐Effect in connection with extremely rough titanium surfaces

Authors: Jennissen, Herbert; Lüers, S.;

Lotus‐Effect and inverse Lotus‐Effect in connection with extremely rough titanium surfaces

Abstract

Abstract Titanium alloys are frequently surface‐modified by plasma vapor deposition of cp titanium (titanium plasma spraying, TPS; Ti‐PVD surface) for clinical use. Such surfaces are extremely rough with Ra values of 30 μm. Unmodified surfaces of Ti‐PVD display apparent static contact angles of θ S ˜ 145° which are in the ultra‐/super‐hydrophobic range and in agreement with contact angles of plant leaves displaying the Lotus‐Effect. On the same surfaces a static contact angle of θ S Oil ˜ 0° is found for mineral oil, characterizing the surface as ultra‐/superlipophilic in agreement with ultrahydrophobicity (θ S /θ S Oil = 145°/0°). At an inclination angle of 45° droplets of water roll off the Ti‐PVD surface with a running rate of ˜20 mm/s. For a classical Lotus‐Effect however a roll‐off angle of <10° is required. Wilhelmy plate measurements reveal an apparent dynamic advancing contact angle of θ A ′ = 98.8°, which is 46° lower than the static angle. The large contact angle hysteresis of Δθ ′ ˜ 62° (θ A ′/θ R ′ = 98.8°/36.7°) explains the high roll‐off angle on Ti‐PVD surfaces. The surfaces also display a type of so‐called “responsive switching” between the ultrahydrophobic and ultrahydrophilic states. When they are chemically treated with chromosulfuric acid the surface becomes ultrahydrophilic (θ A ′/θ R ′ = 0°/0°) in agreement with the inverse Lotus‐Effect. Mineral oil (θ S Oil ˜ 0°) and n‐hexane spread completely on the ultrahydrophilic surface indicating superamphiphilicity (θ S /θ S Oil = 0°/0°). A switching back from the ultrahydrophilic state to the hydrophobic state occurs spontaneously if the surface is not conserved e. g. by an exsiccation layer of salt. The phenomena Lotus‐Effect and inverse Lotus effect are theoretically considered. Titanlegierungen werden häufig für den Einsatz im klinischen Bereich über ein physikalisches Gasphasenabscheidungsverfahren (PVD; Titanplasmabeschichtung, TPS; Ti‐PVD Oberfläche) mit cp Titan beschichtet. Solche Oberflächen sind extrem rau mit Ra‐Werten von 30 μm. Unmodifizierte Oberflächen von Ti‐PVD weisen einen apparenten statischen Kontaktwinkel von θ S ˜ 145° auf, der dem ultrahydrophoben Bereich zuzuordnen ist und im Bereich der Kontaktwinkel liegt, die Pflanzenblätter mit Lotus‐Effekt kennzeichnen. Auf den gleichen Oberflächen findet man bei Messungen mit Mineralöl statische Kontaktwinkel von θ S Oil ˜ 0°, die charakteristisch sind für ultra‐/superlipophile Oberflächen und mit der Ultrahydrophobie übereinstimmen (θ S /θ S Oil = 145°/0°). Bei einem Neigungswinkel von 45° rollen die Wassertröpfchen von der Ti‐PVD Oberfläche herunter mit einer Laufgeschwindigkeit von ˜20 mm/s. Für den klassischen Lotus‐Effekt sind jedoch Abrollwinkel von <10° erforderlich. Wilhelmy Plate Messungen ergeben einen apparenten dynamischen Vorrückwinkel von θ A ′ = 98.8°, der um 46° niedriger ist als der statische Winkel. Die ausgeprägte Kontaktwinkelhysterese von Δθ ′ ˜ 62° (θ A ′/θ R ′ = 98.8°/36.7°) erklärt den hohen Abrollwinkel auf Ti‐PVD Oberflächen. Darüber hinaus zeigen die Ti‐PVD Oberflächen eine Art von “Responsive Switching” zwischen dem ultrahydrophoben und dem ultrahydrophilen Zustand. Wenn die Oberflächen chemisch mit Chromschwefelsäure behandelt werden, wird die Oberfläche ultrahydrophil (θ A ′/θ R ′ = 0°/0°) in Übereinstimmung mit dem inversen Lotus‐Effekt. Mineralöl (θ S Oil ˜ 0°) und n‐hexan spreiten vollständig auf der ultrahydrophilen Oberfläche, was auf Superamphiphilizität hinweist (θ S /θ S Oil = 0°/0°). Ein “switching back” vom ultrahydrophilen Zustand in den hydrophoben Zustand erfolgt spontan, wenn die Oberfläche nicht z. B. durch eine Exsikkationsschicht geschützt wird. Die Phänomene Lotus‐Effekt und inverser Lotus‐Effekt werden theoretisch dargelegt.

Keywords

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
7
Average
Average
Average
bronze