COMBINED FLOW AND EVAPORATION DURING SPIN-COATING OF COMPLEX SOLUTIONS

The flow and evaporation behavior from complex solutions during spin c oating have been measured. Methanol/butanol mixtures where chosen as a controlled case-study for intensive evaluation. In addition, a sample sol-gel was evaluated using the same techniques. It was found that bi nary solutions had two identifiable thinning regions. At first, the th inning behavior is governed by the viscosity and evaporation rate of t he starting mixture. However, near the end of the spinning process, th e evaporation of the more volatile component has caused the fluid comp osition to change (toward the less volatile solution member). Therefor e, the thinning behavior at the end displays a transition which approa ches that of the pure end-member. The thinning behavior for the sol-ge l precursor solution was linear until quite close to the gelation poin t, suggesting that further analysis of sol-gel solutions would be frui tful using this technique. (C) 1997 Elsevier Science B.V.