Neutron reflectometry has been used to study the adsorption of the anionic surfactant bis(2-ethylhexyl) sulfosuccinate cesium salt on the anionic surface of mica. Evidence of significant adsorption is reported. The adsorption is reversible and changes little with pH. This unexpected adsorption behavior of an anionic molecule on an anionic surface is discussed in terms of recent models for surfactant adsorption such as cation bridging, where adsorption has been reported with the divalent ion calcium but not previously observed with monovalent ions.

Surfactants, which contain phenol and amine groups, are commonly used in industry to protect metallic surfaces and their efficiency depends strongly on factors such as pressure and temperature, solvent properties, and the presence of other surfactants in the system. In this work, we present a molecular simulation study of the competitive adsorption between a multi-functional phenol and amine surfactant model and ethanol at the oil/solid interface formed between iso-octane and a model hematite (α -Fe 2 O 3 ) slab. We show that the surfactant strongly adsorbs at the iso-octane/hematite interface in the absence of ethanol at moderate temperatures. As the concentration of ethanol is increased, the ethanol molecules compete effectively for the adsorption sites on the iron oxide surface. This competition drives the surfactant molecules to remain in the bulk-solution while ethanol forms an ordered and strongly coordinated layers at the oil/solid interface, despite the well-known complete miscibility of ethanol in iso-octane in bulk at standard conditions. Potential of mean force calculations show that the free energy of adsorption of the surfactant is approximately two times larger than for a single ethanol molecule, but the simulations also reveal that a single surfactant chain needs to displace up to five ethanol molecules to adsorb onto the surface. The end result is a more favorable ethanol adsorption which agrees with the experimental analysis of similar oil/iron oxide systems also reported in this work.

Fouling of oil-exposed surfaces remains a crucial issue due to the continued importance of oil as the world's primary energy source. The key perpetrators in crude oil fouling have been identified as asphaltenes, a poorly-described mixture of diverse polyfunctional molecules that form part of the heaviest fractions of oil.Asphaltenes are responsible for a decrease in oil production and energy efficiency, and an increase in the risk of environmental hazards. Hence, understanding and managing systems that are prone to fouling is of great value but constitutes a 2 Confidential challenge due to their complexity. In an effort to reduce that complexity, a study of a synthesised foulant of archipelago structure is presented. An alternative perspective on previously described solubility and aggregation mechanisms (eg. Critical Nanoaggrerate Concentration, Critical Clustering Concentration) is offered since the characterised system favours a continuous distribution of n-mers instead.A battery of experimental and modelling techniques have been employed to link the bulk and interfacial behaviour of a representative foulant monomer to effective fouling mitigation strategies. This systematic approach defines a new multiscale methodology in the investigation of fouling systems.

The adsorption of 4-n-nonylphenol (4NP), carvacrol, and ethanol onto the surface of iron oxide from nonaqueous solutions is presented. It is found that adsorption of 4NP from alkanes is strong and proceeds to monolayer formation, where the molecules are essentially "upright". However, at high relative concentrations, ethanol successfully outcompetes 4NP for the iron oxide surface. Estimates of the enthalpy and entropy of binding of 4NP were found to be exothermic and entropically disfavored. Sum frequency generation vibrational spectroscopy data indicate some evidence of binding through a phenolate anion, despite the nonpolar, nonaqueous solvent. Carvacrol is also found to adsorb as a monolayer where the molecules are lying "flat". The adsorption of ethanol onto iron oxide from dodecane was investigated through the use of quantitative NMR, which is a convenient analytical technique for measuring adsorption isotherms. It was concluded that ethanol does not form adsorbed monolayers on the surface. Instead, it partitions onto the surface as a surface-enhanced local phase separation related to its poor solubility in alkane solvents.