RESUMO
Surfaces that stay clean when immersed in water are important for an enormous range of applications from ships and buildings to marine, medical, and other equipment. Up until now the main strategy for designing self-cleaning surfaces has been to combine hydrophilic/hydrophobic coatings with a high aspect ratio structuring (typically micron scale pillars) to trap a (semi)static water/air layer for drag and adhesion reduction. However, such coating and structuring can distort optical properties and get damaged in harsh environments, and contamination, i.e., particles, oil droplets, and biofouling, can get trapped and aggregate in the structure. Here we present a radically different strategy for self-cleaning surface design: We show that a surface can be made self-cleaning by structuring with a pattern of very low aspect ratio pillars ("pancakes"). Now the water is not trapped. It can flow freely around the pancakes thus creating a dynamic water layer. We have applied the new pancake design to sapphire windows and made the first surfaces that are self-cleaning through structuring alone without the application of any coating. An offshore installation has now been running continuously with structured windows for more than one year. The previous uptime for unstructured windows was 7 days.
RESUMO
We present an experimental protocol for fast determination of hydrate stability in porous media for a range of pressure and temperature (P, T) conditions. Using a lab-on-a-chip approach, we gain direct optical access to dynamic pore-scale hydrate formation and dissociation events to study the hydrate phase equilibria in sediments. Optical pore-scale observations of phase behavior reproduce the theoretical hydrate stability line with methane gas and distilled water, and demonstrate the accuracy of the new method. The procedure is applicable for any kind of hydrate transitions in sediments, and may be used to map gas hydrate stability zones in nature.
