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The University of Southampton
Engineering

Research project: Lubrication by Lamellar Liquid Crystals

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The development of environmentally friendly, low friction lubricants like based on biodegradable LCs, can be a game changer to meet increasingly strict environmental government regulations and efficiency standards.

Lamellar liquid crystals possess low shear strength between layers, solid-like elasticity and high load carrying capacity. As lubricants, they have significant potential for high fuel efficiency, longer lifespans of machinery, reduced maintenance, increased biodegradability - all important drivers for a global shift towards energy efficient systems. This project pioneers a breakthrough research concept of lamellar liquid crystals lubrication, supported by a bespoke microscopy technique for real time and in-situ visualisation of the tribological contact.

The visualization of LC inside and around high-pressure contacts is possible with a tailor-made modification of the EHD tribometer (Ultra-Thin Film Measurement System by PCS Instruments) and involves a polarised light microscopy set-up (PLM). The tribometer uses optical interferometry to measure ultra-thin films in a Hertzian contact made between a glass disc and a highly reflective steel ball/roller and is equipped with a monoscope mounted perpendicular to the contact plane for in-situ microscopy. Hence, it was a suitable testbed for mounting PLM to view LCs inside a tribological contact.

Figure 1 shows a schematic of the optical components required to image a birefringent sample such as LCs in a reflection mode. Light beam was split into two, ordinary and extraordinary components by passing through the sample and the resulting birefringence was captured. The quarter waveplate (QWP) was used to infer the shear alignment direction of the LCs. The high pressures and velocity gradients in EHD contacts produce shear stresses that can promote a high degree of alignment of LC molecules in the contact as seen in Fig 2 and Fig 3.

Fig 1. Schematic of PLM optical set-up on EHD tribometer
Fig 1. Schematic of PLM optical set-up on EHD tribometer
Fig. 2. Static elliptical Hertzian contact lubricated with 8CB at 20 N (Pmax 0.3 GPa); white line indicates the obscured contact
Fig. 2. Static elliptical Hertzian contact lubricated with 8CB at 20 N
Fig. 3. Images of 8CB in a circular contact at 20 N, 50% SRR at speeds of (a) 10 mms-1 (b) 100 mms-1 (c) 200 mms-1 (d) 500
Fig. 3. Images of 8CB in a circular contact at 20 N, 50% SRR
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