Influence of water vapor on Nujol adsorption and desorption on quartz and calcite surfaces: A near-ambient pressure X-ray photoelectron spectroscopy and ambient atomic force microscopy study

Abstract

The stability of oil/substrate interaction upon external stimuli is a critical issue for enhanced oil recovery (EOR) processes and catalytic applications. In this study, we address how the Nujol films behaves on well-defined SiO₂(001) and CaCO${}_3$(104) surfaces against water vapor pressure (2 mbar) and ultra-high vacuum (UHV) environment (10⁻¹⁰ mbar) by in-situ near-ambient pressure X-ray photoelectron spectroscopy measurement (NAP-XPS) and ex-situ by atomic force microscopy (AFM). The specimen conditioning with Nujol resulted in a film of $\sim$ 2 nm on SiO₂ and up 4 nm on CaCO${}_3$. The chemical composition of Nujol/SiO₂ interface does not vary significantly against treatment, although its topography passes from continuous to cluster like in DW/Nujol/SiO₂ interface. In Nujol/CaCO${}_3$ interface oil component reduces by: (i) 20% in UHV and (ii) $\sim$ 60% after controlled exposure to DW vapor pressure (2 mbar). The modification of interface chemical composition is reflected into the alteration of Nujol film topography on CaCO${}_3$ that varies from continuous to fragmented film after 12 h in UHV and substantially reorganizes itself after exposure to p(H${}_2$O) = 2 mbar. Our results highlight the role of water in reshaping the oil-oxide interface under controlled environmental conditions and its relevance in oil removal process.