Adhesion of façade coating colonisers, as mediated by physico-chemical properties

The adhesion of Klebsormidium flaccidum, Stichococcus bacillaris and Chlorella cf. mirabilis, three strains of green microalgae isolated from biofilms on façade coatings were investigated in a parallel plate flow chamber. The model surfaces tested were glass slides, and -CH(3) (mediated by octadecyltrichlorosilane [OTS] and hexamethyldisilazane [HMDZ] modification) and -NH(2) (aminopropyltriethoxysilane [APS] modification) terminated self-assembled monolayers. Algal physicochemical properties were evaluated by the microbial adhesion to solvents (MATS) assay and by contact angle measurements. The model surfaces were characterised by X-ray photoelectron spectroscopy analysis and by contact angle measurements. Predicted adhesion trends were then compared to in vitro measurements. The adhesion strength of the three algal strains followed the trend: APS > OTS > HMDZ > glass. The adhesion process thus seemed to be mediated by hydrophobic and electrostatic interactions, and was shown to be influenced by the algal culture age and the initial contact time.