Spinning discs Thin films

Figure 20.19. View of sheared thin films on a spinning disc reactor 28 ...

Polycondensation reactions that are equilibrium controlled, such as polyesters, could benefit from the thin films generated in the RPB or spinning disc. In these reactions, removal of the coproduct of polymerization, e.g., ethylene glycol, is necessary in order to advance the polymerization, a task that becomes increasingly difficult as the reaction proceeds. The thin films and short residence time of high-gravity devices aid the evaporation and may permit operation at higher temperatures than conventional reactors (50). 

Thin films of a blend of poly(sebaic acid) and PLA (Polysciences) on glass are prepared by spin-coating from 1 w/v % solutions in chloroform onto cleaned glass slides. The glass slides are glued with epoxy to the metallic sample holder disc. 

We will not discuss the last method since it is merely a mechanical procedure which uses centripetal force on a spinning disc to disperse the slurry material. All of the other techniques require a substantial vacuum in order to form the thin film and to prevent oxidation and contamination of the film during its formation on a selected substrate. The history of vacuum pumps covers many years. Both incandescent and gas-discharge lamps would not have been developed and made a part of our life if the vacuum pump had not been invented and made practical. Nor would we have the color television if vacuum pumps had not been invented. AU three of these devices use thin films in one form or another. The past 12 years have accelerated the use of thin films for AMLCD s, OLED s, PDF s, LED s and LCD s, to the degree that the vacuum pump is Indispensable. 

Thin, uniform polymer films can be formed by casting a polymer solution onto a rotating disc. Investigations of spin casting have, to date, focused on the process at a macroscopic level. Of primary concern has been the ability to predict the final film thickness and any radial dependence of the thickness induced by spinning. Various models have been derived to relate the spinning and solution characteristics to film thickness and uniformity. These parameters are of very practical importance in the present applications of spin casting, especially for resists. 

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