Geometrical Deposits on Microstructured Surfaces

Abstract

Research into evaporating droplets on patterned surfaces has grown exponentially, since the capacity to control droplet morphology has proven to have significant technological utility in emerging areas of fundamental research and industrial applications. Here, we incorporate two interest domains-complex wetting patterns of droplets on structured surfaces and the ubiquitous coffee-ring phenomenon of nanofluids containing dispersed aluminium oxide particles. We lay out the surface design criteria by quantifying the effect of pillar density and shape on the wetting footprint of droplets, yielding complex polygon droplet geometries. Our work is not constrained to pure liquids only, as we delve into the shape selection of particle-laden droplets of different concentrations. We visualise the deposition patterns through microscopy on surfaces exhibiting different features and further establish the ordering of particles on microscale surface asperities. At a high nanofluid concentration, we observe intriguing self-assembly of particles into highly ordered intricate structures. The collective findings of this work have the potential to enhance many industrial technologies, particularly attractive for high performance optical and electrical devices.

Binary mixture droplet wetting on micro-structure decorated surfaces

“…This work expands on earlier works where one single microstructure configuration 27 , cavities instead of pillars 51 , limited binary mixture concentrations (0% and 30%) on a single micro-pyramid structured configuration 38 or pure fluids varying in surface tension 41,44 . We note that single structure configuration as in 27 and 38 or the use of pure fluids 38,44,45 did not allow for the wide range of interactions and the regime map further extended and proposed in this work, of eventual concern to wider range of applications and communities. Future work suggests adopting other experimental techniques and characterisation such as internal total reflection 64 and electrochemical impedance 65 as well as other binary mixtures 66 to better elucidate the intimate interactions between the wide ranges of surface tension fluids and solid structures presented in this work.…”

“…Two contact angles were reported depending on the azimuthal direction of the droplet and the observation. Moreover, geometrical shapes for pure water have also been found in the work of spacings between pillars on a hydrophobic coated pillared surface 45 . The study showed that varying the spacing between pillars and the shape of the pillars, the shape of the droplets for the low surface tension fluids could be controlled, which eventually dictated the final shape and distribution of the deposits 45 .…”

Geometrically-controlled evaporation-driven deposition of conductive carbon nanotube patterns on inclined surfaces

“…Although there have been a number of studies concerning the physics involved in the edge effect 19,24 and the evaporation characteristics of pinned asymmetric drops, 25–27 the contact line deposition has not yet been fully investigated for them. 23,28…”

Surfactant Control of Coffee Ring Formation in Carbon Nanotube Suspensions

“…These depend on atmospheric conditions like temperature , and humidity . Furthermore, external factors, such as the characteristics of the substrate like surface wettability, , adhesive nature, texture, , and viscoelastic nature are critically important. These factors and the interplay between them play a key role in influencing the thermodynamic interactions and processes that govern the mass transport that, ultimately, determines the final morphology of the solid matter.…”