The effect of polytetrafluoroethylene (PTFE) thin films deposited on aluminium surfaces on Phase Change Material (PCM) solidification

A thin film Polytetrafluoroethylene (PTFE) coating was applied to as-received (AR), manually polished (MP), and sandblasted (SB) surfaces of 60 mm diameter, 10 mm thick aluminium discs cut from a circular cross section rod to produce samples with different areal surface roughness parameters. This resulted in different water contact angles and different degrees of hydrophobicity. Experiments were performed to determine how the solidification behaviour of two PCMs; erythritol, a polar molecule, and polyethylene glycol 6000 (PEG 6000), a non-polar molecule were influenced by surface characteristics. The coated manually polished sample with measured areal surface roughness parameters, S_a = 1.02±1.30 μm, S_sk = 0.04, and S_ku = 2.69 increased the time to phase change onset of a 2 g sample of erythritol (placed on the surface and then melted) by 93% compared to the aluminium surface without a PTFE thin film. The fabricated surfaces which were superhydrophobic had a strong effect on the shape formed by hot erythritol liquid due to the polar characteristics of the erythritol molecule. Using superhydrophobic thin film coatings on heat exchanger surfaces to modify the solidification behaviour of polar molecules like erythritol, can have potential applications in Latent Heat Thermal Energy Storage (LHTES) systems by modifying charge/discharge performance.