Magneto-Responsive Actuating Surfaces with Controlled Wettability and Optical Transmittance

Abstract

The wettability of surfaces can be manipulated using actuating micro/nanostructures, as in the manipulation of water droplets with magnetic forces. Controlling water droplets with magneto-responsive surfaces is limited to optical applications, however, because these surfaces are normally opaque. Herein, we introduce a magneto-responsive actuating surface that is capable of controlling not only the wettability but also the optical transmittance. The magneto-responsive actuating surface is fabricated using a composite of iron particles with polydimethylsiloxane (PDMS). Thanks to the elastic properties of PDMS, fabricated microstructures’ bending is induced by applying magnetic force. Therefore, the static/dynamic water contact angle and the optical transmittance can be controlled. Furthermore, as a feasible application, a sliding angle control system that depends on the magnet location is implemented. On the basis of the interesting characteristics of not only wettability but also optical transmittance, this study is expected to be widely used in various fields such as optics, surface self-cleaning systems of solar cells, and smart windows.

Recent Progress on the Development of Magnetically‐Responsive Micropillars: Actuation, Fabrication, and Applications

“…Due to the incomparable advantages of the micro-pillared structures such as higher flexibility and large surface area, many fabrication methods for polymer micropillars have been developed in the past decades. Distinguishing from the pure polymer pillars, embedding magnetic media (such as the iron microparticles, [90] NeFeB particles, [58] Fe 3 O 4 nanoparticles, [42] carbonyl iron particles, [60] and Co nanoparticles [74] ) into the micropillars is the critical aspect for magnetic micropillars. Magnetic media act as engines to transform the magnetic field energy into kinetic energy to drive the deformations and movements of the micropillars.…”

Magnetic Responsive On‐Site Switching of the Directional Droplet Self‐Transport in Shape Memory Slippery Tube

“…PDMS, on the other hand, possesses high elasticity and a low Young's modulus. [64,65] When a magnetic field of ≈0.5 T was applied, micro-cones appeared on the surface of the PDMS/Fe gel, resulting in a notable increase in R a (R a ≈ 40.05 μm, Figure 1f) and SA (SA ≈ 41°, Figure 1i). When the magnetic field was removed, the micro-cones disappeared, and the PDMS/Fe surface returned to its original smooth state (R a ≈ 0.33 μm, Figure 1g), enabling the droplet to slide again (SA ≈ 1°, Figure 1j).…”

Bioinspired Wire-on-Pillar Magneto-Responsive Superhydrophobic Arrays

“…For example, the lotus leaf with discrete, hierarchical, and low-surface-energy (hydrophobic) structures has inspired the design of water-repellent surfaces for applications such as self-cleaning surfaces, anti-icing surfaces, and thermal management (Figure a). − One of the optimal manifestations of water repellency is the pancake-bouncing of impacting droplets with a greatly reduced droplet–substrate contact time (<5 ms) compared to the inertia-capillary time . The butterfly wing with anisotropic structures has inspired the design of surfaces with directional lateral adhesion forces (Figure b), leading to applications such as droplet directional manipulation. − Moreover, the respiratory cilia with highly flexible microstructures have inspired the design of active or stimuli-responsive surfaces, , leading to applications such as active surface cleaning and transport of small objects (Figure c). − Given such intriguing applications, a versatile surface mimicking lotus leaf, butterfly wing, and respiratory cilia by simultaneously possessing interfacial properties such as structural superhydrophobicity, anisotropicity, stimuli responsiveness, and flexibility is highly desired.…”