RESUMEN
Environmental air monitoring is of great interest due to the large number of people concerned and exposed to different possible risks. From the most common particles in our environment (e.g. by-products of combustion or pollens) to more specific and dangerous agents (e.g. pathogenic micro-organisms), there are a large range of particles that need to be controlled. In this article we propose an original study on the collection of electrostatically deposited particles using electrowetting droplet displacement. A variety of particles were studied, from synthetic particles (e.g. Polystyrene Latex (PSL) microsphere) to different classes of biological particle (proteins, bacterial spores and a viral simulant). Furthermore, we have compared ElectroWetting-On-Dielectric (EWOD) collecting efficiency using either a hydrophobic or a superhydrophobic counter electrode. We observe different cleaning efficiencies, depending on the hydrophobicity of the substrate (varying from 45% to 99%). Superhydrophobic surfaces show the best cleaning efficiency with water droplets for all investigated particles (MS2 bacteriophage, BG (Bacillus atrophaeus) spores, OA (ovalbumin) proteins, and PSL).
Asunto(s)
Electrohumectación/métodos , Monitoreo del Ambiente/métodos , Interacciones Hidrofóbicas e Hidrofílicas , Aire/análisis , Polvo/análisis , Nanoestructuras/química , Tamaño de la Partícula , Poliestirenos/química , Proteínas/aislamiento & purificación , Esporas Bacterianas/aislamiento & purificación , AguaRESUMEN
The reversible actuation of droplets on superhydrophobic surfaces under ambient conditions is currently an important field of research due to its potential applicability in microfluidic lab-on-a-chip devices. We have recently shown that Si-nanowire (NW) surfaces allow for reversible actuation provided that the surface structures show certain characteristics. In particular it appears that, for such surfaces, the presence of structures with multiple specific length scales is indeed needed to have a robust reversibility of contact angle changes. Here we report on electrowetting (EW) and impalement experiments on double-scale structured surfaces prepared by a combination of silicon micropillars prepared by an association of optical lithography and silicon etching, and nanowire growth on top of these surfaces. We show that while micropillar surfaces have a low impalement threshold and irreversible EW behaviour, a surface with double-scale texture can show both a very high resistance to impalement and a limited reversibility under EW, provided that the roughness of the micro-scale is large enough--i.e. that the pillars are tall enough. The optimal performance is obtained for a space between pillars that is comparable to the height of the nanostructure.
RESUMEN
The paper reports on the comparison of the wetting properties of superhydrophobic silicon nanowires (NWs), using drop impact impalement and electrowetting (EW) experiments. A correlation between the resistance to impalement on both EW and drop impact is shown. From the results, it is evident that when increasing the length and density of NWs (i) the thresholds for drop impact and EW irreversibility increase and (ii) the contact-angle hysteresis after impalement decreases. This suggests that the structure of the NW network could allow for partial impalement, hence preserving the reversibility, and that EW acts the same way as an external pressure. The most robust of our surfaces shows a threshold to impalement higher than 35 kPa, while most of the superhydrophobic surfaces tested so far have impalement thresholds smaller than 10 kPa.
RESUMEN
The oscillatory motion of a fluid carrying micron-sized particles inside a capillary tube is investigated experimentally. It is found that initially uniformly distributed particles can segregate and accumulate to form regularly spaced micron-sized particle clusters. The wavelength of the microclusters is compared to data for macroscale sand-ripple patterns and found to obey the same universal scaling as these. A dimensional analysis is performed that confirms the universality of the experimentally observed scaling. The experimental data for the microripple clusters further suggest the existence of a minimum particle length scale for which patterns can form and below which the Brownian motion associated with the molecules of the matrix fluid inhibits pattern formation.