Dynamic Spreading of Fountain Solution onto Lithographic Anodized Aluminum Oxide.

The dynamic wettability of the non-image area of the plate is of prime importance within the context of the search for isopropanol substitutes in the Fountain Solution. The device constructed in the laboratory and described at TAGA 95 (Paris) is able to follow the spreading behavior of liquids onto solid surfaces within time scales going from 5 milliseconds to several minutes. Results related to the kinetics of fast spreading of droplets of various aqueous solutions onto anodized aluminum oxide are reported. One set of experiments dealt with the acid-base interactions between aqueous solutions of varying pH and the substrate and showed its amphiphilic character (albeit more basic) indicated by a higher tendency to spread at non-neutral pHs. The other set of runs dealt with the different roles of aliphatic alcohols added to water at different concentrations. The specific structure and vapor pressure of the additive were qualitatively and quantitatively related to the changes occurring in the spreading behavior, and interpreted in term of a Marangoni effect. Indeed, the onset of the Marangoni flow manifested itself within a few tenths of a second, when the added alcohol had a vapor pressure higher than that of water. Finally, the role of different non-ionic surfactants was also studied. Ease of spreading onto the non-image areas of the plate was drastically decreased because of surfactant specific adsorption onto the plate. Some interpretation of the Water Window problem encountered with surfactant-based Fountain Solutions are given.