Adhesion performance of magnetically responsive surfaces under wet conditions

Adhesion is the key functionality to pick-and-place objects in wet environments. Recently, various micropillars and external stimuli have been proposed to achieve reversible wet adhesion. However, their underlying mechanisms of liquid/solid regulations have not been sufficiently revealed. Herein, two kinds of magnetically responsive micropillar arrays with different terminals (pointed and flat) are developed using a spray self-assembly method. The coupling effect of geometric structures and external stimuli on the wet adhesion performance between a solid substrate and the developed surface is discussed. In situ observation and analysis of theoretical models demonstrate that changes in adhesive forces are mainly caused by the length of the liquid bridge and the apparent contact angle of the developed surface. The adhesion conversion efficiency in the presence of an on/off magnetic field can achieve a highest value of 72% for the micropillar arrays with flat terminals, which exceeds 3 times that of the micropillar arrays with pointed terminals. In addition, wet adhesion measurements during the process of repeatedly switching the magnetic field demonstrate the durability and cyclic reversibility of the magnetically responsive surface. Furthermore, the transportation of microcomponents verifies the application potential of the magnetically responsive surface, which may provide inspiration for transfer printing systems and wet climbing robots.