Self-healing actuating adhesive based on polyelectrolyte multilayers

Abstract

Creating actuators capable of mechanical motion in response to external stimuli is a key for design and preparation of smart materials. The lifetime of such materials is limited by their eventual wear. Here, self-healable and adhesive actuating materials are demonstrated by taking advantage of the solvent responsive of weak polyelectrolyte multilayers consisting of branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA). BPEI/PAA multilayers are dehydrated and contract upon contact with organic solvent and become sticky when wetted with water. By constructing an asymmetric heterostructure consisting of a responsive BPEI/PAA multilayer block and a nonresponsive component through either layer-by-layer assembly or the paste-to-curl process, smart films that actuate upon exposure to alcohol are realized. The curl degree, defined as degrees from horizontal that the actuated material reaches, can be as high as ≈228.9°. With evaporation of the ethanol, the curled film returns to its initial state, and water triggers fast self-healing extends the actuator's lifetime. Meanwhile, the adhesive nature of the wet material allows it to be attached to various substrates for possible combination with hydrophobic functional surfaces and/or applications in biological environments. This self-healable adhesive for controlled fast actuation represents a considerable advance in polyelectrolyte multilayers for design and fabrication of robust smart advanced materials. Self-healable adhesive that actuates upon exposure to ethanol is developed by layer-by-layer assembly and paste-to-curl approaches. The degree of curling is easily controlled by controlling exposure to the organic solvent stimulus as well as engineering the thickness and modulus of the inert part of the actuator. The branched poly(ethylenimine)/poly(acrylic acid) film, which is the active component, can easily be self-healed in water, prolonging lifetime of the actuator.