University of Cambridge
Ethoxylated amine surfactants as model additives for engine friction reduction
Abstract
dc:description.abstractThe exact mechanism by which organic friction modifiers (OFMs) adsorb onto metallic surfaces and reduce friction remains debated. To optimise the use of these compounds, a precise understanding of their mechanism is essential. This knowledge will drive the development of next-generation additives, which could significantly extend engine lifespans and reduce fuel emissions. Hindered tertiary amine surfactants are promising candidates as OFMs. In this thesis, the self-assembly and adsorption behaviour of an industrially relevant OFM, 2,2’-(Octadecylazanediyl)diethanol (E1812), is investigated both in bulk dodecane and at the hematite/dodecane interface, to shed light on its friction-reducing mechanism. Chapter 3 examines the self-assembly of E1812 in dodecane through pendant drop tensiometry and small angle neutron scattering (SANS). The surfactant was found to form spherical aggregates with a radius of ∼ 11 Å at 25 °C, and its behaviour was influenced by solvent changes and dopant addition. As explored by SANS in Chapter 4, addition of 2.5−20 : 1 molar ratios of acetic acid (AcOH) to E1812 solutions caused the formation of worm-like micelles (WLMs) that were both concentration- and time-dependent. These were hypothesised to lack a well-defined global energy minimum, due to the hydrogen-bonding interaction of E1812 headgroups, AcOH, and native dissolved water, as well as the formation of trialkylammonium acetate salt. Chapter 5 investigates the adsorption of E1812 at the hematite/dodecane interface under static conditions, by neutron reflectometry (NR). The surfactant exhibited multilayer adsorption, as described by Freundlich isotherms, with the onset occurring above a concentration of 2.5 mM. E1812 formed strongly-bound protective films with a thickness of ∼ 20 Å , effectively screening the interface from water and competing with oleic acid (OA) for surface adsorption. As discussed in Chapter 6, the addition of AcOH largely induced off-specular scattering in NR studies, suggesting surface-correlated roughness likely linked to WLM formation in the bulk. It is hypothesised that E1812-AcOH mixtures adsorb as double-layer structures, with E1812 strongly bound to the surface and the laterally correlated, AcOH-containing species weakly adsorbed. To investigate conditions relevant to engine operation, Chapter 7 explores the adsorption of E1812 at the hematite/dodecane interface under shear, by NR. E1812 films remained stable under applied shear rates of 7.9×10³ s⁻¹, presenting a marginally increased thickness of ∼ 24 Å . The surfactant effectively shielded the interface from water adsorption under the same dynamic conditions and, under shear of 6.6×10³ s⁻¹, its co-adsorption with OA indicated that ΔHads,OA ≤ ΔHads,E1812 at the interface under study. Additionally, E1812 protected the interface from direct AcOH adsorption at a shear rate of 7.9×10³ s⁻¹, where off-specular scattering was removed. As discussed in Chapter 8, mini-traction machine (MTM) testing showed that E1812 enhanced the boundary lubrication of pure dodecane, particularly when mixed with AcOH, highlighting the role of WLMs in improving friction performance.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2024
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Boggio-Robutti, Beatrice
- Advisor dc:contributor.advisor
-
- Routh, Alexander
Subjects
dc:subject × 6Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.116741
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/381615