Sprecher
Beschreibung
Wettability can be applied in many applications such as microfluidic devices, oil/water separation, water energy harvesting, etc. There are two known approaches to modify the wettability properties of different materials: changing their topography or chemical modification of the surface The topography of materials also can be modified by applying external stimuli such as temperature, magnetic field, electric field, light and others. One large group of materials with switchable topography is shape memory polymers. These materials can reversibly change their topography upon external stimuli. Their topography changing effect can be based on melting/crystallization processes of crystalline parts. For example, the lamellar structure of polyether-urethane with poly(1,10-decylene adipate) (PEU-PDA) bends in presence of capillary forces at 70°C [1]. However, temperature is not a local stimulus, and it is difficult to control specific areas of the material. On the other hand, laser exposure can be converted into thermal energy, although energy adsorption is better for dark surfaces. An approach was presented with coating polyester-urethane with poly(1,4-butylene adipate) black ink, which showed localized heating under laser exposure [2].
Here, we present a lamellar structure based on polymer composite by incorporation 0.2 wt.% graphene nanoplates (GN) or multi-walled carbon nanotubes (MWCNT) into PEU-PDA polymeric matrix. The particles in the polymer matrix increased the melting temperature up to 10°C, and the color of the composite materials became darker and could convert light energy into heat. The lamellar structure was fabricated by melt-electrowriting. The composite was heated to 210°C and a voltage of 3 kV was applied between the extruder and the glassslide. The lamellae were exposed to an infrared laser (808 nm). The exposed lamellae were heated up to 53°C and 74°C for GN and MWCNT composites respectively. The exposed area wrinkled due to melting of the soft segments and this process is reversible. Water droplets placed between two lamellae can help to determine the direction of their bending. Although in normal condition, the lamellae will not bend because the capillary forces are insufficient to overcome the elastic moduli of the lamellae and bend them. Local heating by IR radiation reduces the elastic modulus by almost 10 times, and the lamellae can be bent by a water droplet. After evaporation that position of lamellae can be reprogrammed by an additional droplet in a neighbor position, allowing topography changes due to capillary forces and local heating. Such adjustments can help us to create new types of topography in microfluidic devices or fabricate complex structure patterns.
[1] Sadilov I., Constante G., Dulle M., Schönfeld D., Pretsch T., Ionov L. Reversibly Switchable Topography Enabled by Melting and Crystallization of Melt-Electrowritten Polymer Fibers// ACS Materials Lett. 2025, 7, XXX, 401–408, DOI: 10.1021/acsmaterialslett.4c02057
[2] Constante G., Apsite I., Schönfeld D., Pretsch T., Ionov L. Reversibly Photoswitchable High-Aspect Ratio Surfaces// Small Struct. 2023, 4, 2300040, DOI: 10.1002/sstr.202300040