Hybrid surfaces combining electropolymerization and lithography: fabrication and wetting properties
We present here firstly a novel fabrication method in order to obtain hybrid surfaces consisting of mixed hydrophilic/superhydrophobic properties. These surfaces consist in a regular array of hydrophilic pillars (receding contact angle lower than 90°) surrounded by a superhydrophobic thinner layer made by electropolymerization of a fluorinated monomer. Secondly, we present the wetting properties of such complex surfaces by determining the advancing (θ_a) and receding (θ_r) contact angles as function of the surface properties. Two main parameters were varied: the pillar density (spacing d, from 25 to 45 micrometers corresponding to surface fraction from 21.2 % to 6.5 %) along with the polymer charge (from 0 to 100 mC/cm2). Here, we show that for low charges, only the ground surface is covered by hydrophobic polymers. For higher charges values, polymerization reaches higher levels on the lateral surfaces of the non-conductive cylindrical pillars eventually up to their top surfaces and covering them for the highest charges. This feature gives an additional parameter for the control of such surfaces wettability. We show that contact angles (advancing and receding) increase strongly with increased polymer charge above a critical charge value (that is higher for receding angles). We also measure that advancing and receding contact angle respectively increase and decrease with increasing pillar density. We interpret qualitatively these behaviors, the main point being how important is the impalement (null, partial or total).