Fouling behaviour of zwitterionic DLC surfaces

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In the proposed project the validity of the following two hypotheses about the formation of fouling deposits on coated surfaces for applications in chemical process engineering shall be studied experimentally and the obtained results shall be incorporated in a comprehensive model: 1.) Surfaces of modified diamond-like carbon coatings (DLC) show an exceptionally favourable fouling behaviour, i.e., especially low adsorption of proteins and salts from supersaturated aqueous solutions, if, under conditions of use, these surfaces furnish identical and significant densities of positively and negatively charged surface functional groups (so-called zwitterionic surfaces). 2.) Coatings with such surfaces are not only accessible - as already known - by plasma-based modification after deposition, but also by the incorporation of suitable elements or compounds during deposition, such as oxygen and nitrogen or sulfur dioxide and nitrogen. In order to evaluate these hypotheses DLC coatings will be prepared by plasma-activated chemical vapour deposition. Functional surface groups which are ionized under conditions of use, i.e., in aqueous solutions with typically 6 < pH < 8, will be prepared by incorporation of hetero-atoms (O, N, S) into the growing film by the addition of suitable gases or vapours during film deposition from low hydrocarbons. Thus obtained surfaces will be characterised physico-chemically; particularly zeta potentials und LW-AB components of surface free energies will be studied. Coating compositions will be investigated using XPS and to some extent EPMA, fouling-relevant surface functional groups primarily by FTIR-ATR spectroscopy. After suitable conditioning the surfaces will be exposed to typical cleaning and fouling conditions, respectively, using whey protein isolates (WPI) and milk salts (simulated milk ultra filtrate, SMUF) as fouling systems. The data and insights obtained in the experiments will be used as the basis for a description in terms of a mathematical model. An in-depth understanding of the interactions between surface, fouling deposit, and cleaning mechanisms will enable improved opportunities of tailor-made surface design as well as an adapted cleaning strategy.