Noncontact All‐In‐Situ Reversible Reconfiguration of Femtosecond Laser‐Induced Shape Memory Magnetic Microcones for Multifunctional Liquid Droplet Manipulation and Information Encryption

Abstract

Shape memory polymers can change their shapes in a controlled way under external stimuli and thus promote the development of smart devices, soft robotics, and microfluidics. Here, a kind of iron particles (IPs) doped shape memory microcone is developed for noncontact all‐in‐situ reversible tuning between the tilted and upright state under near‐infrared (NIR) irradiation and magnetic field (MF) actuation. The magnetic microcones are simply fabricated by a laser‐ablated replica‐molding strategy so that their height can be precisely controlled by adjusting the laser machining parameters. In addition, it is found that the droplets can be transported unidirectionally on the tilted microcones, which is related to the variation of the adhesion force induced by the length of the triple contact line (TCL). Finally, other multifunctional applications have also been realized, such as, selective droplet release, information encryption, rewritable display, and reusable temperature switch. This work may provide a facile strategy for developing multiresponsive smart devices based on shape memory polymers.

Pancake Jumping of Sessile Droplets

“…Coalescence‐induced droplet jumping occurs on superhydrophobic surfaces caused by the release of surface energy during the condensation process, [ 22 , 23 , 24 , 25 , 26 ] but it is limited by the low energy transfer efficiency and thus suffers from a small jumping velocity. [ 27 , 28 ] The directional movement of sessile droplets can be achieved on responsive surfaces through constructing energy gradient, or resorting to stimuli such as temperature, [ 29 , 31 ] pressure, [ 32 , 33 , 34 , 35 ] optical, [ 36 , 37 ] electrical [ 38 , 39 ] or magnetic fields, [ 40 , 41 , 42 , 43 , 44 , 45 , 46 ] etc. In particular, owing to its advantages of instantaneous response, [ 42 ] low energy consumption, flexible/convenient/safe controllability, and good biocompatibility, magnetic actuation has emerged as a promising approach to manipulate droplet motion.…”

Laser Micromachining of Magnetoactive Elastomers as Enabling Technology for Magnetoresponsive Surfaces

“…[49] Strategies for controlling liquid flow with MAEs typically include surface structures, such as micropillars and microplates arrays, with a large aspect ratio and local elastic surface deformation. [35] Current structuring techniques rely mainly on replica molding, [41,[50][51][52][53] magnetic particle-assisted molding, [26,[54][55][56] and magnetic micropillar bonding to the substrate. [57,58] These techniques require multiple and often intricate manufacturing steps and/or dedicated tools to achieve the desired features.…”

Magneto‐Responsive Shutter for On‐Demand Droplet Manipulation

“…[ 2 , 20 , 21 , 23 ] To lower the structure stiffness, MRSS always utilize magneto‐responsive microstructures with large aspect ratios to allow bending deformation. [ 1 , 28 , 29 , 36 ] However, such magneto‐responsive bendable microstructures suffer from highly restricted deformation range as well as single transformation mode, which severely limit the multifunctional droplet manipulation capability. Moreover, it is also difficult to accurately control the bending degree of the microstructures in a predesigned way, resulting in failure of high‐precision liquid manipulation.…”