RESUMO
A water droplet's behavior on an inclined hydrophobic surface in the presence of environmental dust particles is considered and the droplet's dynamics are analyzed pertinent to self-cleaning applications. A polycarbonate wafer is crystallized using the solution-crystallization method to generate hierarchically distributed micro/nano-sized spherules and pillars on the surface. To improve the wetting state and lower the contact angle hysteresis, functionalized silica particles are synthesized and, later, deposited on the crystallized surface. Environmental dust particles are collected and characterized in terms of elemental composition, size and shape. A high-speed camera is used to monitor a water droplet's behavior on the inclined hydrophobic surface with and without the presence of dust particles. The influence of droplet volume on the dust particle removal rate from the inclined hydrophobic surface is assessed. It is found that the functionalized silica particles deposited on the surface result in a droplet contact angle in the order of 158 ± 2° and contact angle hysteresis of 2 ± 1°. The water droplet mainly rolls on the inclined hydrophobic surface and the sliding velocity remains almost 13% of the transverse velocity of the droplet. Droplet wobbling is influenced by the dust particles and the droplet size; in which case, increasing the droplet volume enhances the droplet puddle thickness on the hydrophobic surface. The cloaking of the droplet fluid onto the dust particles causes mixing of the dust particles with the droplet fluid while enhancing the particle removal from the hydrophobic surface. Increasing the droplet volume slightly enhances the size of the area of the cleaned surface.
RESUMO
The removal of environmental dust particles from optically transparent glass surfaces is considered, and the dynamics of the dust particles on the inclined hydrophobic glass surface is examined. The glass surfaces are coated by functionalized nano-sized silica particles to create a hydrophobic wetting state on the surface. A thin layer of environmental dust particles, collected from the local area of Dammam in the Kingdom of Saudi Arabia (KSA), is deposited on the surface while mimicking the dust accumulation on the surfaces in the dusty days of KSA. In order to increase the removal rate of the dust particles from the inclined hydrophobic glass surfaces, high density particles, which are higher than the density of the dust particles, are locally distributed on the dust particle-deposited surface while generating the avalanche influence on the inclined surface. The motion of the dust and high density particles on the inclined surface is monitored using a high speed camera. The predictions of the dust particles' acceleration and velocity are compared to those obtained from the high speed camera data. It is found that the predictions of velocity and acceleration of the dust particles agree well with the experimental data. Local insertion of the high density particles generates avalanche influence on the inclined surface while initiating the removal of the dust particles from the hydrophobic surface at small inclination angles. The size of the area where the dust particles are removed from the inclined surface increases with enlarging coverage area of the high density particles. The dust-removed surface, under the avalanche influence, improves the UV-visible transmittance of the hydrophobic glass.