Dynamics of spreading of industrial oil-in-water emulsions on steel surfaces

The spreading of industrial oils, pure and emulsified in water, has been investigated on rough steel surfaces. Oils wet the surface regularly, the spreading remains circular and the contact area can be empirically correlated to timet by a power law similar to those of pure homogeneous liquids. Similar laws can also be found for oil-in-water emulsions, but in this case the spreading behaviour is quite different: first it is not circular, irregularities appear depending on the industrial oil; then retractions can occur and eventually, with some emulsions thinning of the central zone may occur after a certain time. All these effects might be due to the actual composition of these oils which are essentially esters of fatty acids dissolved in mineral oils with various added surfactants. This kind of experiment might be a very simple test to aid the choice of an appropriate rolling-oil.