Mechano-responsive and dynamic electro-wetting of replica-casted laser-induced periodic surface structures

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The present research proposal combines material synthesis aspects (laser processing, replica casting, and surface functionalization) with the mechano-responsive wetting of elastomers and the electro-, pyro-, and piezo-wetting of ferroelectric polymers.Our research proposal focuses on the dynamic wetting of flexible polymer substrates. For this purpose we will realize specific micro- and nanostructures on the surface of stretchable polymers. The wetting behavior is controlled by surface functionalization and various external triggers. The micro- and nanostructures are produced on a metallic master substrate in the form of so-called laser-induced periodic surface structures (LIPSS) using an fs-laser. The LIPSS model is then transferred to flexible and stretchable polymer samples in a replica casting process.In a first approach, hydrophilic and hydrophobic surface groups are coupled to the structured surface by a sequential process of hydroxylation and selective silanization. In contact with water the prepared samples show superhydrophobic behaviour due to roughness induced air inclusions. Stretching the specimen reduces the contact angle as roughness is reduced and an increasing number of hydrophilic functional groups come into contact with the water drop. With prolonged elongation, the surface becomes hydrophilic due to the increasing specific amount of polar groups. In this way, the wettability of the polymer can be reversibly adjusted over a wide range by mechanical deformation.Our second approach is based on the electro-wetting of polarized ferroelectric polymers. Here the contact angle can be controlled by an external voltage between the water drop and the substrate. Based on the pyro or piezoelectric effect of the selected polymer, the contact angle can be adjusted by temperature or mechanical stress as an external trigger. The starting point of the contact angle and thus the maximum working range is determined by the LIPSS model, which is transferred to the polymer by the replica casting process.