Lubrication of surfaces by modification with polymer films has proven an efficient method of frictional reduction. Bio-inspired bottle-brush copolymers containing a linear block with surface affinity, and a soluble polymer brush block have shown to be effective lubricants in aqueous systems. We have synthesised bottle-brush copolymers with hydrophilic linear blocks and oil-soluble polymer brushes. These copolymers adsorb to the steel-oil interface leading to a large frictional reduction for oil-based applications. Here, we propose to use polarised neutron reflectometry, exploiting both isotopic and magnetic sensitivity, to determine the structure of bottle-brush copolymer films at the steel-oil interface. This information will allow us to understand the interfacial structure-function relationship of these materials, further directing the design of polymeric lubricants.