We present Brownian motion-based sizing of individual submicron and nanoparticles in liquid samples. The advantage of our approach is that particles can freely diffuse in a 10 μm thin liquid film and are therefore always within the focal depth of a low numerical aperture objective. Particles are visualized with dark-field microscopy, and the resulting diffraction-limited spots are tracked over a wide field of view of several hundred micrometers. Consequently, it is ascertained that long 2D trajectories are acquired, which leads to significantly increased particle sizing precision. The hydrodynamic diameters of metal particles with nominal sizes ranging from 70 to 200 nm in aqueous solution were determined by tracking for up to 2 min, and it was investigated if the diffusion characteristics were influenced by the proximity of substrates. This was not the case, and the estimated diameters were in good agreement with the values obtained by electron microscopy, thus validating the particle sizing principle. Furthermore, we measured a sample mixture to demonstrate the distinction of close particle sizes and performed the conjugation of a model protein (BSA) on the nanoparticle surface. An average increase in the radius of 9 nm was determined, which corresponds to the size of the BSA protein.

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Purpose-This paper aims to investigate the wear behaviour of different materials for cylinder liners and piston rings in a linear reciprocating tribometer with special focus on the wear of the cylinder liner in the boundary lubrication regime. Design/methodology/approach-Conventional nitrided steel, as well as diamond-like carbon and chromium nitride-coated piston rings, were tested against cast iron, AlSi and Fe-coated AlSi cylinder liners. The experiments were carried out with samples produced from original engine parts to have the original surface topography available. Radioactive tracer isotopes were used to measure cylinder liner wear continuously, enabling separation of running-in and steady-state wear. Findings-A ranking of the material pairings with respect to wear behaviour of the cylinder liner was found. Post-test inspection of the cylinder samples by scanning electron microscopy (SEM) revealed differences in the wear mechanisms for the different material combinations. The results show that the running-in and steady-state wear of the liners can be reduced by choosing the appropriate material for the piston ring. Originality/value-The use of original engine parts in a closely controlled tribometer environment under realistic loading conditions, in conjunction with continuous and highly sensitive wear measurement methods and a detailed SEM analysis of the wear mechanisms, forms an intermediate step between engine testing and laboratory environment testing.

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