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1. The Effect of Dust Hygroscopicity on Soiling and Self-Cleaning Processes in a Condensing Environment

   https://doi.org/10.1109/PVSC48317.2022.9938585  

   Eidlisz, Jordan; Sultana, Nadera; Nayshevsky, Illya; Xu, QianFeng; Lyons, Alan M. (June 2022, The Effect of Dust Hygroscopicity on Soiling and Self-Cleaning Processes in a Condensing Environment)

   Dew promotes chemical interactions between soilants and glass that lead to increased soiling rates and cleaning costs. Anti-soiling coatings have been developed to address these issues, and prior experiments have quantified the soiling impact of several categories of particle chemistries. In this paper, the impact that the hygroscopicity of a soilant has on soiling and cleaning values was measured on hydrophobic coated glass and compared to bare glass samples. Results will be presented from UV -visible direct transmittance and optical image processing measurements to characterize soiling and self-cleaning of surfaces as a function of particle hygroscopicity in a condensing environment, mimicking natural dew conditions. 

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2. An active self-cleaning surface system for photovoltaic modules using anisotropic ratchet conveyors and mechanical vibration

   https://doi.org/10.1038/s41378-020-00197-z  

   Sun, Di; Böhringer, Karl F. (September 2020, Microsystems & Nanoengineering)

   Abstract The purpose of this work is to develop an active self-cleaning system that removes contaminants from a solar module surface by means of an automatic, water-saving, and labor-free process. The output efficiency of a solar module can be degraded over time by dust accumulation on top of the cover glass, which is often referred to as “soiling”. This paper focuses on creating an active self-cleaning surface system using a combination of microsized features and mechanical vibration. The features, which are termed anisotropic ratchet conveyors (ARCs), consist of hydrophilic curved rungs on a hydrophobic background. Two different ARC systems have been designed and fabricated with self-assembled monolayer (SAM) silane and fluoropolymer thin film (Cytop). Fabrication processes were established to fabricate these two systems, including patterning Cytop without degrading the original Cytop hydrophobicity. Water droplet transport characteristics, including anisotropic driving force, droplet resonance mode, cleaning mechanisms, and system power consumption, were studied with the help of a high-speed camera and custom-made test benches. The droplet can be transported on the ARC surface at a speed of 27 mm/s and can clean a variety of dust particles, either water-soluble or insoluble. Optical transmission was measured to show that Cytop can improve transmittance by 2.5~3.5% across the entire visible wavelength range. Real-time demonstrations of droplet transport and surface cleaning were performed, in which the solar modules achieved a 23 percentage-point gain after cleaning. 

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3. BIOMIMICKING HYDROPHOBICITY USING MICROSCALE STRUCTURES FOR BIOMEDICAL APPLICATIONS

   https://doi.org/10.34107/LWWJ5713177  

   Desai, Roma; Cordeiro, Jhonatam; Bastakoti, Bishnu; Dellinger, Kristen (July 2022, Biomedical Sciences Instrumentation)

   Hydrophobic surfaces provide special characteristics for biomedical applications ranging from tunable protein adsorption, cellular interactions, and hemocompatibility to antibacterial coatings. In this research, we biomimic the hair-like micro-whisker structures of magnolia leaf using a synthetic polymeric formulation. Optical and scanning electron microscopy images revealed the presence of micro-whiskers resulting in higher water contact angles. The top layer of the magnolia leaf had a contact angle of 50º as compared to the hydrophobic bottom layer at 98º. A synthetic polymeric formulation was coated on different materials to study its effect on hydrophobicity. The coating was replicated (n=3) on each of the materials used such as glass, polymer, fabric, wood, and stainless steel. A surface tensiometer was used to measure the transition from hydrophilic to hydrophobic interactions between water and the substrate materials. Contact angle measurements revealed an increase in hydrophobicity for all the materials from their original uncoated surface. Glass displayed the highest increase in contact angle from 37º to 90º. Phase analysis of the coated region was performed to characterize the surface exposure of glass substrate to the synthetic polymeric formulation. An increase in the coated region showed a significant increase in contact angle from 50º to 95º. This research lays the foundation to develop and understand hydrophobic coatings for several biomedical applications including non-fouling implant surfaces, lab-on-chip devices, and other diagnostic tools. 

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4. Field tests of a self-sintering, anti-soiling, self-cleaning, nanoporous metal oxide, transparent thin film coating for solar photovoltaic modules

   https://doi.org/10.1016/j.solmat.2023.112560  

   Walz, Kenneth A.; Hoege, Timothy D.; Duensing, Joel W.; Zeltner, Walter A.; Anderson, Marc A. (October 2023, Solar Energy Materials and Solar Cells)

   Nanoporous metal oxide ceramic coatings, deposited using sol-gel techniques, have the potential to impart self-sintering and self-cleaning coatings to silicon oxide glass. When used on solar photovoltaic modules, these coatings can impart anti-static properties, improve wetting behavior, and degrade soiling deposits through photocatalytic activity. This paper reports on a field trial of a mixed silicon and titanium oxide thin film coating conducted in the upper midwestern U.S. Coated modules demonstrated increased electrical generation relative to uncoated controls. The results are encouraging for the commercialization of this coating technology, and provide a strong motivation for further research and development efforts. 

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5. On predicting the performance of different silicas on key property enhancements of fine APIs, blends, and tablets

   https://doi.org/10.1016/j.powtec.2023.119104  

   Kim, Sangah S.; Seetahal, Ameera; Kossor, Christopher; Davé, Rajesh N. (January 2024, Powder Technology)

   Predictive selection of silica size, type (hydrophobic/hydrophilic), and amount is addressed for achieving significant property enhancements of fine active pharmaceutical ingredients (APIs). Four models, Chen’s multiasperity particle-adhesion, total surface energy-based guest-host compatibility, dispersive surface energy-based tablet tensile strength, and stick-bounce-based silica aggregation on coated particles, are invoked. The impact on the bulk properties of four APIs cohesive API powders (~10 μm) and 40 wt% (wt%) blends of one API, drycoated at 50% and 100% surface area coverage (SAC) of four nano-silicas (7–20 nm), hydrophobic (R972P), hydrophilic (M5P, A200, A300) is assessed. Significant enhancements in flowability, bulk density, compactability, agglomeration reduction, and dissolution for API or blend are achieved with all silicas. The experimental and model-based outcomes demonstrate that silica performance is impacted by multiple factors, silica size and coating effectiveness being most critical. In conclusion, R972P and A200 at lower 50% SAC present two excellent choices. 

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