Sample Cooling Procedures

Abstract

At the end of the previous chapter we discussed the different strategies we might adopt to successfully convert water and aqueous solutions to a solid state suitable for microscopy and analysis. There are two main advantages to be gained from this phase change: the provision of a solid matrix suitable for manipulation and microscopy, and an effective immobilization of dynamic processes. It should now be clear that if our purpose is to convert the water in a sample to a vitreous or even a microcrystalline state, solely by lowering the temperature, then we must limit ourselves to small samples, which should be cooled as rapidly as possible. The low thermal conductivity of water prevents high cooling rates in the center of a specimen much thicker than 25 μm, and adequate preservation will be achieved throughout larger specimens only if the properties of water are changed either by physical or chemical means.