Premium
Validation of convection‐limited cooling of samples for freeze‐fracture electron microscopy
Author(s) -
Bailey Stuart M.,
Zasadzinski Joseph A. N.
Publication year - 1991
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1991.tb03182.x
Subject(s) - biot number , materials science , convection , liquid nitrogen , thermal conduction , thermal conductivity , heat transfer , fracture (geology) , thermodynamics , composite material , chemistry , physics , organic chemistry
SUMMARY Rapid freezing is the most important step in sample preparation for freeze‐fracture and other cryotechniques for electron microscopy. A simple heat transfer model is experimentally validated to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples [Biot modulus, ( hd/k ) < 1] by measuring cooling rates in a variety of samples, materials, and cryogens. In comparison to the commonly accepted conduction‐limited model, the convection‐limited model predicts, and our experiments show, that cooling rates are proportional to the surface area to volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. We show that almost any material can be frozen at similar rates if the sample thickness, the cryogen, and the method and velocity of contact with cryogen are similar. Liquid ethane or propane cooled to liquid nitrogen temperature are shown to give the best results.