Smart Mechanically Tunable Surfaces with Shape Memory Behavior and Wetting-Programmable Topography

Abstract

This paper reports for the first time the fabrication and investigation of wetting properties of structured surfaces formed by lamellae with an exceptionally high aspect ratio of up to 57:1 and more. The lamellar surfaces were fabricated using a polymer with tunable mechanical properties and shape-memory behavior. It was found that wetting properties of such structured surfaces depend on temperature, and thermal treatment history-structured surfaces are wetted easier at elevated temperature or after cooling to room temperature when the polymer is soft because of the easier deformability of lamellae. The shape of lamellae deformed by droplets can be temporarily fixed at low temperature and remains fixed upon heating to room temperature. Heating above the transition temperature of the shape-memory polymer restores the original shape. The high aspect ratio allows tuning of geometry not only manually, as it is done in most works reported previously but can also be made by a liquid droplet and is controlled by temperature. This behavior opens new opportunities for the design of novel smart elements for microfluidic devices such as smart valves, whose state and behavior can be switched by thermal stimuli: valves that can or cannot be opened that are able to close or can be fixed in an open or closed states.

Reversibly Photoswitchable High‐Aspect Ratio Surfaces

“…As discussed in our previous article, [23] it is evidenced that the surface tension (F s % γ ⋅ dl), [25] elastic deformation (δ % F ⋅ H 3 =EI, where H is the height of lamella, I is the second moment of inertia I ¼ a ⋅ dl 3 =12, a is the thickness of a lamella, and dl is its length), and gravity (F g % ρ ⋅ g ⋅ h ⋅ b ⋅ dl, where h is the height of the droplet and S is the surface area) interact to deform the lamellae.…”

“…Synthesis of TPU: Poly(1,4-butylene)-based poly(ester urethane) (TPU PBA-75) was synthesized as previously described. [23] Briefly, 0.037 mol of dried PBA-diol Desmophen 2505 reacted at 120 °C with 0.157 mol of MDI for 90 min. The isocyanate prepolymer reacted with 0.12 mol dried BD.…”

“…Fabrication of the Surfaces: The lamellar surface was fabricated as previously described. [23] Briefly, the MEW of TPU PBA-75 was made in a 3D Discovery printer Regen Hu (Villaz-St-Pierre, Switzerland). The conditions for MEW were set at 215 °C, 3 kV of voltage, pneumatic pressure at 0.1 MPa, the distance between collector and nozzle was 2 mm, and the translation speed (F) was 100 mm s À1 .…”

“…[22] In our previous work, we demonstrate an approach for the fabrication of surfaces with switchable high-aspect ratio lamellae based on SMPs using melt-electrowriting (MEW). [23] The mechanical properties of the lamellae can be switched between soft and hard states. The high-aspect ratio lamellae demonstrated possibilities to switch their shape by surface tension of the water and temperature, and manual deformation was not required.…”

“…The high‐aspect ratio lamellae demonstrated possibilities to switch their shape by surface tension of the water and temperature, and manual deformation was not required. The temperature as a signal, used in our previous work, [ 23 ] can hardly be applied locally to achieve targeted switching of mechanical and wetting properties of surfaces. Using light as a signal presents more benefits.…”