Sol–gel coatings with lime repellent properties

Calcification of surfaces by hard water represents a major issue for sanitary installations. Calcium carbonate precipitates forming crusts of lime that are difficult to remove. Much effort has been undertaken to avoid scaling, most methods require chemicals or create waste. We constructed a test rig which allows for the controlled calcification of various substrates. It is found that all solid surfaces investigated calcify more or less evenly. On the other hand, surface bound poly(ethylene glycol), PEG, is known to prevent the non-specific adsorption of biomolecules. PEG coated surfaces find their use in a variety of applications. Here we show that glass and plastics, such as polyethylene, polypropylene and acrylonitrile–butadiene–styrene, can be efficiently made lime repellent by the use of sol–gel coatings containing a PEG bearing silane. It is shown that the amount of scaling is drastically reduced. Prior to coating, plastics have to be pretreated by oxygen plasma and an adhesion promoter has to be employed.