Shock-cooling liquid nitrogen

Protocol 4.2 Shock-cooling into liquid nitrogen Materials... 

A vial containing a shock-cooled crystal is placed in a bath of liquid nitrogen, which is housed in a shallow Dewar flask. 

In the first method,freeze etching, a drop of solution is rapidly frozen by shock-cooling with liquid nitrogen. Solvent is then allowed to evaporate off from a freshly microtomed surface of the droplet. Finally a replica is made of collapsed micelles left proud of the frozen surface. In one report results are reported for four copolymers a poly sty rene-h/ocfc-polyisoprene copolymer, a (poly-styrene-h/ock-polyisoprene)4Si star copolymer and two polystyrene- ra/t-polyisoprene copolymers M , M /Mn and the wt % polystyrene contents for the unassociated copolymers were respectively (51000,1.12,25.2), (188 000,1.10,24.9), (550000,1.18,29.2) and (420000,1.22,38.1). Technical white oil, which is a selectively bad solvent for polystyrene, was used for the study. Within experimental error the micelles formed by the two block copolymers were monodisperse in size. The graft copolymer micelles on the other hand showed measurable size distributions. 

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