title: Wetting properties of phospholipid dispersion on tunable hydrophobic SiO2-glass plates.
abstract: We study the wetting properties of very small droplets of salty aqueous suspensions of unilamellar liposomes of DMPC (dimyristoylphosphatidylcholine), situated on SiO2-glass surfaces with different levels of hydrophobicity. We evaluated two different measures of hydrophobicity of solid surfaces - receding contact angles and the thickness of wetting films trapped between an air bubble and the solid surface at different levels of hydrophobicity. We established a good correlation between methods which differ significantly in measurement difficulty and experimental setup. We also reveal details of the mechanism of wetting of different surfaces by the DMPC liposome suspension. Hydrophilic surfaces with water contact angles in the range of 0° to 35° are readily hydrophobized by the liposomes and only showed corresponding contact angles in the range 27°-43°. For same range of surface hydrophobicities, there was a clear reduction of the thickness of the wetting films between the surface and a bubble, reaching a minimum in the 35°-40° range. At higher levels of hydrophobicity both pure water and the liposome suspension show similar contact angles, and the thickness of wetting films between a bubble and those surfaces increases in parallel. Our analysis showed that the only force able to stabilize the film under these experimental conditions is steric repulsion. The latter suggests that nanobubbles adsorbed on hydrophobic parts of the surface, and coated with a DMPC layer, may be the cause of the 40-70 nm thickness of wetting films we observe.
authors.affiliation: (a)Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. Electronic address: lalex@chem.uni-sofia.bg.
authors.forename: Lidia
authors.initials: L
authors.lastname: Alexandrova
authors.affiliation: (b)Department of Physical Chemistry, Sofia University, 1164 Sofia, Bulgaria. Electronic address: fhsk@chem.uni-sofia.bg.
authors.forename: Stoyan I
authors.initials: SI
authors.lastname: Karakashev
authors.affiliation: Department of Inorganic Chemistry, Sofia University, 1164 Sofia, Bulgaria. Electronic address: ljudmil.grigorov@abv.bg.
authors.forename: L
authors.initials: L
authors.lastname: Grigorov
authors.affiliation: Curtin University, Department of Chemical Engineering, Perth, WA 6845, Australia. Electronic address: C.Phan@curtin.edu.au.
authors.forename: Chi M
authors.initials: CM
authors.lastname: Phan
authors.affiliation: (e)Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom. Electronic address: sks46@cam.ac.uk.
authors.forename: Stoyan K
authors.initials: SK
authors.lastname: Smoukov
mesh_terms: D000327:Adsorption; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D017155:Wettability
chemical_list: D008081:Liposomes; D012822:Silicon Dioxide; D004134:Dimyristoylphosphatidylcholine
keywords: DMPC; Phospholipid vesicles; Thin wetting film; Wetting contact angle