Emulsion layer

When completed, the solution is merely dumped into 1L of dH20 and extracted 3 x lOOmL Et20 or DCM or benzene. BUT when that solution hits the solvent, the biggest, ugliest emulsion Strike has ever hypothesized occurs. It is wicked The chemists can try all the usual tricks to get rid of that bitch, but when it comes down to it, there is only one way that works. The chemist is going to have to extract with hundreds upon hundreds of mLs of solvent. The idea here is to saturate both the aqueous and emulsion layer with so much solvent that a separate solvent layer can form. Once saturated, the entire mix can then be properly extracted. 

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

To maintain color isolation, it is important for the exposed grains of each emulsion layer to be substantially developed before a dye developer assigned to a different emulsion layer reaches them. Both the auxiUary developer and the barrier interlayers assist in such isolation. Color isolation may also be assisted by the release of low solubiUty silver ligands, such as mercaptans (65). 

A (macro)emulsion is formed when two immiscible Hquids, usually water and a hydrophobic organic solvent, an oil, are mechanically agitated (5) so that one Hquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both Hquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water (o /w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitation ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible Hquids, one of them becomes continuous and the other one remains in droplet form. 

Fig. 2.3.5 Profiles recorded from a drying alkyd left. The Peclet number is defined as HE/D emulsion layer are shown on the right. At low where H is the film height, the evaporation Peclet number (upper set of profiles), drying is rate and D the particle diffusivity. The upper set...

Withdraw the slide immediately or wait a few seconds to derive a thicker emulsion layer (DO NOT dip each slide repeatedly to achieve a thicker emulsion instead, reduce withdrawal rate or emulsion temperature). Consult Rogers (7) for selecting an appropriate emulsion thickness (1.5-2.0 pm but depends on emulsion and isotope in question), especially if one is contemplating quantitative autoradiography. Move slide away from the emulsion so that excess emulsion does not drip back onto the surface of the emulsion creating bubbles. 

Note The dipped slide can be placed vertically for drying but results in an emulsion layer that varies in thickness from top to bottom of the slide and is, therefore, not recommended. 

Difficult to obtain an emulsion layer of constant and reproducible thickness making comparisons of radioactivity with different structures very tenuous [see ref. (7) for a thorough discussion of such comparisons as a function of isotope employed]... 

Halation can be prevented by coating dyes either on the back of the film support or between the film support and the emulsion layer to absorb the harmful radiation. These antihalation (or filter) dyes are only required during the camera exposure of the sensitive... 

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