Wetting and fouling on polymeric films

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Various polymer surfaces have been studied in the current project with regard to their wetting and scaling behavior. The impact of surface roughness and pre-treatment techniques (plasma/corona) have been quantified and can be used for estimation of an industrial application potential. The observed positive wetting characteristics of Ionic Liquids (IL) are an incentive for further investigations, because of the high potential in process intensification of e.g. absorption chillers with alternate working pairs (IL/water instead of LiBr/water). An increased wettability of the high viscous fluids results in enhanced heat transfer due to the formation of thin and stable liquid films. The simple contact angle measurements gave a profound basis to predict the performance of falling film wetting. Existing correlations for the critical liquid load of falling films (relevant for layout) on plane surfaces were successfully adapted to that of polymeric surfaces. The expected low scaling affinity of the polymeric surfaces could be quantified with stainless steel as benchmark. A relation between deposition quantity and surface free energy as well as adhesive force of the deposit was established. A demand for future investigations exists to verify the low scaling propensity of the polymer surfaces also for mixed salt solutions relevant for real industrial processes. A stepwise adaption of the experimental methodology to describe the complex mechanisms of mixed salt deposition on polymeric surfaces is planned within the time frame of the one year project extension. The improved wetting performance of the polymer surfaces due to conditioning could be explained by changes in polymer conformation, also validated by molecular dynamics simulation. It could be shown that coarse grained dissipative particle dynamics (DPD) simulations can be used to analyze the local conditions for wetting enhancement. However, in addition to the already obtained DPD interaction parameters of water and polymer an exemplary validation of the methodology using an alternative solvent (e.g. isopropanol as organic one) is still necessary.