title: The Role of Surfactants in the Stability of NiO Nanofluids: An Experimental and DFT Study.
abstract: This study shows an analysis of the stability of nanofluids based on a eutectic mixture of diphenyl oxide and biphenyl, which is used as a heat transfer fluid (HTF) in concentrating solar energy, and NiO nanoparticles. Two surfactants are used to analyse the stability of the nanofluids: benzalkonium chloride (BAC) and 1-octadecanethiol (ODT). From an experimental perspective, the stability is analysed by means of UV/Vis spectroscopy, particle size measurements through the dynamic light-scattering technique, and ζ-potential measurements. The results show that the stability of the nanofluids improves with the use of BAC. DFT calculations are performed to understand the role played by the surfactants. The interaction of the surfactants with both the fluid and the NiO (100) surface is studied. Quantum theory of atoms in molecules (QTAIM) analysis shows that hydrogen bridge interactions favour the stability of the fluid-surfactant mixture. The more stabilising NiO-surfactant interaction involves the Ni-H interaction of the -SH and -CH3groups of ODT and BAC. Also, nanofluids with BAC are favoured over those with ODT, which is in agreement with experimental results. The structural and electronic effects of incorporating the surfactant onto the NiO (100) surface are shown by using electron localisation function analysis, the non-covalent interaction index and projected density of states.
authors.affiliation: Physical Chemistry Department, Facultad de Farmacia, Universidad de Sevilla, 41012, Sevilla, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Sánchez-Coronilla
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Javier
authors.identifier: http://orcid.org/0000-0001-7569-0809
authors.initials: J
authors.lastname: Navas
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Aguilar
authors.affiliation: Chemical Engineering Department, Facultad de Química, Universidad de Sevilla, 41012, Sevilla, Spain.
authors.forename: Elisa I
authors.initials: EI
authors.lastname: Martín
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Juan Jesús
authors.initials: JJ
authors.lastname: Gallardo
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Mr Roberto
authors.initials: MR
authors.lastname: Gómez-Villarejo
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Mr Iván
authors.initials: MI
authors.lastname: Carrillo-Berdugo
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Alcántara
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Concha
authors.initials: C
authors.lastname: Fernández-Lorenzo
authors.affiliation: Physical Chemistry Department, Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
authors.forename: Joaquín
authors.initials: J
authors.lastname: Martín-Calleja
keywords: ELF (electron localization function); ab initio calculations; colloids; density functional calculations; nanofluids