Sanitär- und Kommunaltechnik; Umwelttechnik
The initial attachment and subsequent biofilm formation of electroactive bac-teriaShewanella putrefaciensCN32 was investigated to clarify the influence oforganic conditioning layers. A selection of macromolecules and self-assembledmonolayers (SAMs) of different chain lengths and functional groups were pre-pared and characterized by means of infrared spectroscopy in terms of theirchemistry. Surface energy and Zeta (ζ-) potential of the conditioning layers wasdetermined with contact angle and streaming current measurements. Amongthe studied surface parameters, a high polar component and a high ratio ofpolar-to-disperse components of the surface energy has emerged as a successfulindicator for the inhibition of the initial settlement ofS. putrefacienson stainlesssteel AISI 304 surfaces. Considering the negative surface charge of planktonicS. putrefacienscells, and the strong inhibition of cell attachment by positivelycharged polyethylenimine (PEI) conditioning layers, our results indicate thatelectrostatic interactions do play a subordinate role in controlling the attach-ment of this microorganism on stainless steel AISI 304 surfaces. For the biofilmformation, the organization of the SAMs affected the local distribution of thebiofilms. The formation of three-dimensional and patchy biofilm networks waspromoted with increasing disorder of the SAMs.
Nebulizing of polymer solutions, in a high-voltage field under atmospheric conditions by electrospray ionization (ESI), is a comfortable way to deposit ultra-thin layers of polar or ionic polymers onto any conductive substrate materials. The substrate is grounded and the polymer solution is sprayed through a powered capillary. The formed charged droplets shrink by solvent evaporation during their way to the grounded substrate, the charges close ranks and the droplets collapse consecutively by charge repulsion, thus forming finally charged single macromolecules. After their discharging at the grounded substrate, an ultrathin ‘quasi-monomolecular’ polymer layer is formed. It could be shown by imaging of scratches through the polymer layer by atomic force microscopy that the deposited polymer layers are dense at a thickness of about 10 nm. Carbon fibre bundles were coated with poly (allylamine) (PAAm) or poly(acrylic acid) (PAA) as potential adhesion-promoting layers in fibre–polymer composites. The polymer deposition is self-inhibiting after formation of a continuous coverage of about 200 nm for PAAm and 30 nm for PAA as result of surface charging. Continuous deposition onto such isolating layers or polymers without charging can be achieved by using current of alternating polarity. The film formation is self-healing because of the electrophoretic effect, i.e. the ion discharging occurs preferentially at noncoated areas. This electrophoretic effect of ESI was demonstrated by completely enwrapping all the carbon fibres of the roving within a distance of about 100 μm far from its outside and also at the backside of the fibre bundle with about 80% of the topside coverage, as measured by X-ray photoelectron spectroscopy and visualized using scanning electron microscopy.