Droplet manipulation and mobility on non-wetting surfaces is of practical importance for diverse applications ranging from micro-fluidic devices, anti-icing, dropwise condensation, and biomedical devices. The use of active external fields has been explored via electric, acoustic, and vibrational, yet moving highly conductive and viscous fluids remains a challenge. Magnetic fields have been used for droplet manipulation; however, usually, the fluid is functionalized to be magnetic, and requires enormous fields of superconducting magnets when transitioning to diamagnetic materials such as water. Here we present a class of active surfaces by stably impregnating active fluids such as ferrofluids into a textured surface. Droplets on such ferrofluid-impregnated surfaces have extremely low hysteresis and high mobility such that they can be propelled by applying relatively low magnetic fields. Our surface is able to manipulate a variety of materials including diamagnetic, conductive and highly viscous fluids, and additionally solid particles. V

Recent developments in climate change have increased the frequency of dust storms in the Middle East. Dust storms significantly influence the performances of solar energy harvesting systems, particularly (photovoltaic) PV systems. The characteristics of the dust and the mud formed from this dust are examined using various analytical tools, including optical, scanning electron, and atomic force microscopies, X-ray diffraction, energy spectroscopy, and Fourier transform infrared spectroscopy. The adhesion, cohesion and frictional forces present during the removal of dry mud from the glass surface are determined using a microtribometer. Alkali and alkaline earth metal compounds in the dust dissolve in water to form a chemically active solution at the glass surface. This solution modifies the texture of the glass surface, thereby increasing the microhardness and decreasing the transmittance of the incident optical radiation. The force required to remove the dry mud from the glass surface is high due to the cohesive forces that result from the dried mud solution at the interface between the mud and the glass. The ability altering the characteristics of the glass surface could address the dust/mud-related limitations of protective surfaces and has implications for efficiency enhancements in solar energy systems.

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Owing to recent climate changes, dust storms are increasingly common, particularly in the Middle East region. Dust accumulation and subsequent mud formation on solid surfaces in humid environments typically have adverse effects on surface properties such as optical transmittance, surface texture, and microhardness. This is usually because the mud, which contains alkaline and ionic species, adheres strongly to the surface, often through chemical bonds, and is therefore difficult to remove. In this study, environmental dust and the after-effects of mud formed on a polycarbonate sheet, which is commonly used as a protective glass in photovoltaic cells. Ionic compounds (OH−) are shown to significantly affect the optical, mechanical, and textural characteristics of the polycarbonate surface, and to increase the adhesion work required to remove the dry mud from the polycarbonate surface upon drying. Such ability to modify characteristics of the polycarbonate surface could address the dust/mud-related limitations of superhydrophobic surfaces.

Electrospinning is used to prepare hydrophobic and self-cleaning polysulfone (PSf) surfaces. The effects of PSf concentration in Dimethylformamide (DMF) solvent and electrospinning process parameters on the surface structure and hydrophobicity are investigated. The experimental results show that depending on PSf concentration, three types of morphologies are obtained: beads, beads-on-strings, and free-beads fibers. The surface hydrophobicity depends mainly on the resultant surface morphology, and the existence of beads increases hydrophobicity. The contact angle (CA) is found to increase from 73°for smooth PSf surface to more than 160°for surfaces formed by electrospinning. Moreover, the contact angle hysteresis (CAH) was generally less than 10°f or all the chemistries. It is noted that increasing the PSf concentration leads to the formation of beads-on-string and freebeads fiber structures; this morphological change is accompanied by a reduction in the contact angle. Surface structures are found to be more sensitive to electrospinning feed rate than to electrospinning voltage; however, these two parameters have a negligible influence on the hydrophobicity. Porosity measurements of different chemistries show an average pore size in the range 3-8 microns. The thickness of PSf mats was variable, from as low as 10 μm to as high as 70 μm.

The influence of the immersion period on the crystallization of polycarbonate (PC) was investigated, and the resulting texture configurations of the crystal structures were reconstructed with polydimethylsiloxane (PDMS). Analytical tools, including optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, the sessile drop technique, Fourier transform infrared spectroscopy, microtribometry, and ultraviolet-visible spectrophotometry, were used to characterize crystallized PC and PDMS surfaces. We found that the crystallized PC surface possessed microsize/nanosize spherulites, voids, and fibrils, and the increasing immersion period increased the texture height and spherulite concentration at the surface. The residual stress in the crystallized PC wafer was compressive, and it was on the order of 230 MPa. The friction coefficient of the crystallized PC surface remained lower than that of the as-received PC wafer, and the increase in the immersion period lowered the friction coefficient. The crystallized PC surface demonstrated superhydrophobic characteristics, and the maximum contact angle occurred with 6 min of immersion. The PDMS exactly reconstructed the texture of the crystallized PC surface, except those of the nanofibrils and subnanofibrils. The droplet contact angle attained a higher values for the PDMS replicated surfaces than for those corresponding to the crystallized PC wafer.

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The behavior of environmental dust particles on a silicone oil impregnated glass surface is examined in relation to optical transparent surfaces for self-cleaning applications.