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Title: Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

Abstract

Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of 3 and a water contact angle of ~15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (~2.2) and becomes hydrophobic (contact angle of ~104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. In conclusion, this study provides insight into the role of surface relaxation on themore » wettability of REOs.« less

Authors:
 [1];  [2];  [1];  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Univ. of Toronto, Toronto, ON (Canada)
Publication Date:
Research Org.:
Northwest Energy Innovations, Portland, OR (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Water Power Technologies Office (EE-4WP)
Contributing Org.:
Hydro Research Foundation
OSTI Identifier:
1483685
Grant/Contract Number:  
EE0006056
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 106; Journal Issue: 6; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
13 HYDRO ENERGY

Citation Formats

Khan, Sami, Azimi, Gisele, Yildiz, Bilge, and Varanasi, Kripa K. Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides. United States: N. p., 2015. Web. doi:10.1063/1.4907756.
Khan, Sami, Azimi, Gisele, Yildiz, Bilge, & Varanasi, Kripa K. Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides. United States. doi:10.1063/1.4907756.
Khan, Sami, Azimi, Gisele, Yildiz, Bilge, and Varanasi, Kripa K. Mon . "Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides". United States. doi:10.1063/1.4907756. https://www.osti.gov/servlets/purl/1483685.
@article{osti_1483685,
title = {Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides},
author = {Khan, Sami and Azimi, Gisele and Yildiz, Bilge and Varanasi, Kripa K.},
abstractNote = {Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of 3 and a water contact angle of ~15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (~2.2) and becomes hydrophobic (contact angle of ~104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. In conclusion, this study provides insight into the role of surface relaxation on the wettability of REOs.},
doi = {10.1063/1.4907756},
journal = {Applied Physics Letters},
number = 6,
volume = 106,
place = {United States},
year = {Mon Feb 09 00:00:00 EST 2015},
month = {Mon Feb 09 00:00:00 EST 2015}
}

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Cited by: 21 works
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Works referenced in this record:

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