When working with very small crystals (below 100 μm), dehydration is your worst enemy and time is of the essence. We recommend working in a humidified environment or a cold room, or else using a very slow flow of cooled and/or humidified air directed at your work area. If you've ever compared how quickly puddles evaporate in the summer and in the winter (on sunny days on equal side of the solstices), you know that evaporation rates vary strongly with temperature. The saturated vapor pressure of water at 4°C is 1/4 that at 25°C.
Some users have complained that the mounts seem to push small crystals away, as if they were too hydrophobic. That's not what's going on. What you see is a simple demonstration of laminar flow and Stoke's Law. When you move the mount through a crystal-containing drop, the liquid flows laminarly around it. If the crystal's density matched that of the liquid, it, too, would just flow around the mount, and it would nearly impossible to snag it.
If the crystal's density is larger than that of the liquid, the crystal will sediment under the influence gravity towards the mount. The crystal's sedimentation speed is determined by the balance between the gravitational force pulling down and the viscous drag force given by Stoke's law that opposes motion.
It's an easy matter to show that this sedimentation speed varies as the square of the crystal diameter. Thus, the time for the crystal to sediment onto the mount increases rapidly as the crystal gets smaller. You then need to move the mount very slowly to allow enough time for the crystal to sediment through the liquid around the mount and onto its surface. For the smallest crystals, you should probably hold the mount with some sort of micromanipulator unless you have very steady hands.
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MiTeGen
P. O. Box 3867
Ithaca, NY 14852
info@mitegen.com
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