Magnetically Tunable Adhesion of Magnetoactive Elastomers’ Surface Covered with Two-Level Newt-Inspired Microstructures

Abstract

As one of the new intelligent materials, controllable bionic adhesive materials have great application prospects in many fields, such as wearable electronic devices, wall climbing robot systems, and biomedical engineering. Inspired by the microstructure of the newt pad’s surface, this paper reports a bionic adhesive surface material with controllable adhesion on dry, wet acrylic, and iron sheet surfaces. The material is prepared by mixing the PDMS matrix with micron carbonyl iron powders (CIPs) and then pouring the mixture into a female mold prepared by Photo-curing 3D Printing for curing. As the mold interior is designed with a two-level microstructure array, the material’s surface not only coated a regular hexagonal column array with a side length of 250 μm and a height of 100 μm but also covered seven dome structures with a diameter of 70 μm on each column. In what follows, the adhesion force of the proposed materials contacted three different surfaces are tested with/without magnetic fields. The experimental results show that the MAEs covered with two-level bionic structures(2L-MAE) reported in this paper exhibit a stronger initial adhesion in the three types of surfaces compared to the normal one. Besides, we also found that the magnetic field will noticeably affect their adhesion performance. Generally, the 2L-MAE’s adhesion will increase with the external magnetic field. When the contact surface is an iron sheet, the material adhesion will be reduced by the magnetic field.

Adhesion performance of magnetically responsive surfaces under wet conditions

“…Particles commonly used in magnetically responsive surfaces include carbonyl iron particles (CIPs), 15,17,26 Fe 3 O 4 particles [30][31][32] and NdFeB particles. 9,14,18 The CIPs were chosen as the magnetizable particle source because of their excellent magnetic properties and ease of use.…”

“…At present, many schemes have realized reversible wettability and adhesion by external stimuli, such as photostimuli, 8,9 pH, 10 gas, 11,12 magnetic fields, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] etc. Among these stimuli, magnetic fields offering the advantages of remote controllability, instantaneous response and convenience have been widely investigated, and most studies have focused on the droplet manipulation and adhesion controlled by magnetic fields.…”

“…It was found that arrays of PDMS micropillars containing NdFeB microparticles with T-shaped terminals undergo strong bending in response to a magnetic field gradient, leading to the establishment of only a weak contact between the probe and the tilted pillars, which ultimately resulted in a decrease of the adhesion force. Meanwhile, Chen et al 15 found that the adhesion between magnetoactive elastomers' surface and wet acrylic increased with the external magnetic field, owing to the increase of the apparent contact angle of the capillary bridge. Therefore, the wet adhesion performance between a solid substrate and the magnetically responsive surface is related to both the contact area and the contact angle.…”