Drops Favoring the Cold

Brzoska has studied the movement of PDMS drops placed on silanized silicon wafers (OTS) subjected to a horizontal temperature gradient. The crucial element of the experiment was the preparation of the substrate, since high hysteresis would prevent drops from moving. 

In the following experiments, the advancing and receding angles were 13° and 11°, respectively [S = 7(cos h — cos a) 10 ]. Under such conditions, drops can be made to move even in weak thermal gradients. This could never be done with chemical gradients because of their greater hysteresis. 

The wettability gradient, which tends to drive drops toward regions of higher S  

It is impossible to predict a priori the direction in which the drops will end up moving. 

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