title: Slippery when sticky: Lubricating properties of thin films of Taxus baccata aril mucilage.
abstract: Mucilage is hydrogel produced from succulent plants and microorganisms displaying unique adhesiveness and slipperiness simultaneously. The objective of this study is to establish an understanding on the lubricating mechanisms of the mucilage from Taxus baccata aril as thin, viscous lubricant films. Oscillation and flow rheological studies revealed that T. baccata mucilage is shear-thinning, thixotropic, and weak hydrogel that is highly stretchable under shear stress due to its high density physical crosslinking characteristics. In addition, T. baccata mucilage showed a distinct Weissenberg effect, i.e., increasing normal force with increasing shear rate, and thus it contributes to deplete the lubricant from tribological interfaces. Lubrication studies with a number of tribopairs with varying mechanical properties and surface wettability have shown that the lubricity of T. baccata mucilage is most effectively manifested at soft, hydrophilic, and rolling tribological contacts. Based on tenacious spreading on highly wetting surfaces, slip plane can be formed within mucilage hydrogel network even when the lubricating films cannot completely separate the opposing surfaces. Moreover, highly stretchable characteristics of mucilage under high shear enhance smooth shearing of two opposing surfaces as lubricating film.
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Troels
authors.initials: T
authors.lastname: Røn
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Sankaranarayanan
authors.initials: S
authors.lastname: Rishikesan
authors.affiliation: Nano-BioScience Research Group, DTU-Food, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Ioannis S
authors.initials: IS
authors.lastname: Chronakis
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Seunghwan
authors.initials: S
authors.lastname: Lee
mesh_terms: D000269:Adhesives / Q000302:isolation & purification*; D055598:Chemical Phenomena; D005638:Fruit / Q000737:chemistry*; D054327:Lubricants / Q000302:isolation & purification*; D012212:Rheology; D020946:Taxus / Q000737:chemistry*
chemical_list: D000269:Adhesives; D054327:Lubricants