Abstract
Self-cleaning of surfaces becomes challenging for energy harvesting devices because of the requirements of high optical transmittance of device surfaces. Surface texturing towards hydrophobizing can improve the self-cleaning ability of surfaces, yet lowers the optical transmittance. Introducing optical matching fluid, such as silicon oil, over the hydrophobized surface improves the optical transmittance. However, self-cleaning ability, such as dust mitigation, of the oil-impregnated hydrophobic surfaces needs to be investigated. Hence, solution crystallization of the polycarbonate surface towards creating hydrophobic texture is considered and silicon oil impregnation of the crystallized surface is explored for improved optical transmittance and self-cleaning ability. The condition for silicon oil spreading over the solution treated surface is assessed and silicon oil and water infusions on the dust particles are evaluated. The movement of the water droplet over the silicon oil-impregnated sample is examined utilizing the high-speed facility and the tracker program. The effect of oil film thickness and the tilting angle of the surface on the sliding droplet velocity is estimated for two droplet volumes. The mechanism for the dust particle mitigation from the oil film surface by the sliding water droplet is analyzed. The findings reveal that silicon oil impregnation of the crystallized sample surface improves the optical transmittance significantly. The sliding velocity of the water droplet over the thick film (~700 µm) remains higher than that of the small thickness oil film (~50 µm), which is attributed to the large interfacial resistance created between the moving droplet and the oil on the crystallized surface. The environmental dust particles can be mitigated from the oil film surface by the sliding water droplet. The droplet fluid infusion over the dust particle enables to reorient the particle inside the droplet fluid. As the dust particle settles at the trailing edge of the droplet, the sliding velocity decays on the oil-impregnated sample.
Highlights
Silicon oil impregnation improves the optical transmittance of the samples and enables water droplets to slide over the surface
Impregnated oil film thickness influences the sliding velocity of the droplet; the sliding velocity becomes lower for the small thickness oil film (~50 μm) than that corresponding to the large oil film thickness (~700 μm)
This is related to the interfacial resistance at the droplet bottom, i.e., slip velocity at the interface across the oil film and droplet fluid becomes small and it is likely that the droplet bottom becomes in contact with the crystallized surface rather than floating in the oil film
Summary
The examination of optically transparent textured surfaces and thin oil film impregnation towards dust particles mitigation from the textured surface becomes necessary. Several coating techniques have been developed towards hydrophobized surfaces for self-cleaning applications [14,17,22], yet further tests are needed for the assessment of dust adhesion and mitigation from these surfaces. The dust mitigation incorporating the oil film on optically transparent surfaces may become fruitful in terms of the effective self-cleaning process [10,19]. Towards the self-cleaning application of an oil-impregnated surface, a water droplet is used and the sliding velocity of the droplet over the oil film plays a major role in the mitigation of particles from the surface. The optical transmittance of the surface before and after silicon oil impregnation is evaluated
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