Referenzen
- Vorführexperimente, Videos
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Crystal Critters
Presentation and some basic explanations of the phenomenon
- Wissenschaftliche Artikel
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Crystal critters
Paper associated with the video "Crystal Critters".
https://www.researchgate.net/publication/346886734_Crystal_critters
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Crystal critters: Self-ejection of crystals from heated, superhydrophobic surfaces
They present the phenomenon in which crystals self-eject from heated, nanotextured superhydrophobic materials during evaporation of saline water drops. These crystal structures have exceedingly minimal contact with the substrate and thus pre-empt crystal fouling. This phenomenon is caused by cooperative effects of crystallization, evaporative flows, and nanoscale effects. The temperature dependence of the critter effect can be predicted using principles of mass conservation, and they demonstrate that self-propulsion can be generated via temperature gradients, which promote asymmetric growth.
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Rings, Igloos, and Pebbles of Salt Formed by Drying Saline Drops
They show that ordered three-dimensional structures can be built via evaporation of saline drops on highly hydrophobic substrates like polypropylene. These observations lead them to conclude that combined effects of solubility, evaporation rate, and mobility of the contact line determine the final three-dimensional shape of the salt precipitate.
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Salt creeping as a self-amplifying crystallization process
They report an experimental approach that allows to quantitatively describe the salt creeping mechanism and demonstrate its universality with respect to different salts. They show that there exists a critical contact angle below which salt creeping occurs, provided also the nucleation of multiple crystals is favored. The self-amplifying process results in a three-dimensional crystal network at macroscopic distances from the solution reservoir.
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Salt stains from evaporating droplets
They show that crystallization patterns of evaporating of water drops containing dissolved salts are different from the stains reported for evaporating colloidal suspensions. This happens because during the solvent evaporation, the salts crystallize and grow during the drying. Their results show that the patterns of the resulting salt crystal stains are mainly governed by wetting properties of the emerging crystal as well as the pathway of nucleation and growth and are independent of the evaporation rate and thermal conductivity of the substrates.
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Self-Lifting NaCl Crystals
they show that macroscopic crystals of NaCl that form from evaporating drops of aqueous salt solutions can spontaneously lift themselves up and away from a hydrophobic surface. At the end of the evaporation process, tiny crystals of NaCl grow onto larger ones and form “legs” that push the large crystals away from the surface. The temperature dependence of the lifting speed is found to exhibit Arrhenius behavior with an activation energy similar to that of crystals growing in solution. They show that surface hydrophobicity is a necessary but not a sufficient condition to obtain this “self-lifting” behavior.
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The dependence of evaporation and crystallization kinetics on dynamic and thermal background
They describe both non-stationary evaporation and non-stationary crystallization of droplets and films. Evaporation and crystallization of a drop are shown to fundamentally differ from those of a thin layer. For correct simulation of evaporation, it is necessary to take into account the thicknesses of the thermal, diffusion and concentration boundary layers.
https://aiche.onlinelibrary.wiley.com/doi/abs/10.1002/aic.16282