Wetting of surfaces is ubiquitous in nature and technology. It depends on the surface energy of the material which is closely related to the surface properties, chemistry and microstructure. An interesting wetting behavior occurs, if the surface consists of a thin polymer film. To this end, surface wettability of covalently bonded graft polymer films, such as polymer brushes, can be tuned by the chemistry and swelling behavior of the attached macromolecules. Using surface initiated polymerization techniques, a large variety of chemical functions can be implemented into the polymer film, including those that are renowned as “smart” or “stimulus responsive” polymers. Another interesting class of surface-attached polymer films consist of chemically cross-linked layers. The swelling behavior of so called polymer brushes differs significantly from surface bonded polymer networks when in contact with solvents. Significant research has been carried-out to understand how<br/>molecular mass, graft density and cross-linking degree of the layers affect the wetting and swelling in contact with a solvent. Much less is known about the wetting, if patterned surfaces are considered: how does a drop of solvent behaves, if it wets a polymer brush that is located in direct contact with a polymer network, in particular, if both layers consist of a similar chemistry? In the presented work, we focus on this particular question. Polymer brushes were designed which consist of poly(<i>N</i>-isopropylacrylamide) (PNIPAm) with a light-activatable 2-ureido-4-pyrimidone (UPyA) as bimolecular cross-linking moiety. We show that the swelling behavior of the brush and the network, respectively, differs. In addition, we observe a strong imbibition zone of a drop placed on the polymer brush presumably due to swelling of the polymer chains. Such patterned polymer films may therefore be of interest for future microfluidic applications, where wetting and transport of droplets on surfaces can be controlled by surface-intrinsic and extrinsic parameters.

Wetting and transport on swellable, surface-immobilized polymer brush-network systems

2019 Spring National Meeting

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