Frozen-drop method

Figure 1. Drop sampler for frozen-drop method (Longwell)...

The frozen-drop technique was naturally adopted in measuring molten metal droplet size before any other methods became available. Similarly to the methods for normal liquids, the freeze-up and collection of molten metal droplets may be carried out in many different ways. For example, metal droplets can solidify during flight in gaseous or liquid medium in a spray chamber. 13H51 The solidified particles are subsequently sieved to obtain the size distribution. 

The frozen-drop and the wax methods eliminate the tedious and time-consuming operations of microscopic counting of the larger droplets, and sampling errors are less likely because all of a large increment of spray can be collected and handled by employing screens and gravimetric methods of analysis. The chief limitation is that screens are not available to obtain data on particles smaller than 75 microns. Some form of microscopic count or air elutriation procedure is necessary for the smaller droplets. 

Transmission electron micrography has, remarkably, been successfully used to image micelles formed by block copolymers in dilute solutions. Price and coworkers used two preparation methods. In the first method (Price and Woods 1973), f reeze etching, a drop of solution was rapidly frozen by quenching in liquid nitrogen. Solvent was then allowed to evaporate from a freshly microtomed surface of the droplet. Finally, a replica was made of collapsed micelles raised proud from the frozen surface. In the second method (Booth et al. 1978), a drop of micellar solution was allowed to spread and evaporate on a carbon substrate, and 0s04 was used to selectively stain one of the blocks. 

Extraction. A modification of the Shell method for extracting animal products proved highly effective (13). The tissue should be cut quickly and extracted while still frozen to ensure good dispersion of the sample. The recovery of insecticide drops markedly when samples are allowed to thaw before the initial blending. 

Special techniques must be used to avoid glass formation [131] and zone melting usually results in a sizable drop in yield. If reliable methods can be developed to produce a small, completely melted zone within the frozen IL, zone melting represents one of the most promising techniques being developed for the purification of ILs. 

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