Shock cooling

The polymer is not easy to process and in injection moulding melt temperatures of 300°C are employed. In order to prevent excess embrittlement by shock cooling of the melt, mould temperatures as high as 150°C may be used. The polymer may also be compression moulded at temperatures of 250-260°C. 

The three common methods in use for performing crystal cryoprotection prior to shock-cooling are... 

Table 4.1 Antifreeze agents used in the shock cooling of macromolecular crystals...

Preparation of a shock-cooled macromolecular crystal involves the rapid introduction of a loop-mounted sample into a cryogen. Introduction into the cryogen must be rapid in order to ensure that aqueous solvent within the crystal cools as a vitreous... 

Shock-cooling into freshly thawed liquid propane... 

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

Using a gaseous nitrogen stream as a cryogen is the simplest of the three methods of preparing shock-cooled crystals, since it requires no special equipment other than that to be used for the measurement of X-ray diffraction. Of special note is that gaseous... 

Figure 4.4 Procedure for shock-cooling a crystal using a gaseous cryogen. (a) The goniometer head is assembled on the X-ray camera and the cold gaseous nitrogen stream is centred on the eucentric point of the camera, (b) The stream is deflected with some appropriate obstruction.

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

Protocol 4.6 Recovery of shock-cooled crystals from the X-ray diffraction camera ... 

The above reaction is reversible above 1,850°C. The metal produced as vapor must be cooled rapidly to prevent any reversible reactions. Rapid cooling (shock cooling) can quench the reaction giving finely divided pyrophoric dust... 

Follow steps 2 through 5 in the section about stopper bioburden method for heat shocking, cooling, shaking, and sonicating samples (one container containing 20 small vials 20 half-filled vials). 

Most actual crystals are imperfect different portions of the lattice are not quite parallel, and the crystal behaves as if it consisted of a number of blocks (of the order of 10 5 cm in diameter) whose orientation varies over several minutes or even in some cases up to half a degree. This imperfection is perhaps connected with the manner of growth in thin layers (see Chapter II and Plates I and II) each layer may be slightly wavy, and there may be cracks or impurities between the layers. Most crystals are imperfect in this way, and in structure determination it is usually safe to assume that the intensity of any reflection is proportional to the square of the structure amplitude. To make quite sure that a crystal is ideally imperfect , it may be dipped in liquid air the shock-cooling produces imperfections. 

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