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‐Healing Latex Containing Polyelectrolyte Multilayers

“…Water is an efficient plasticizer for PEMs, [47] causing a rheological transition from a rigid, glassy film to a viscous, liquid-like material. [48] After immersing the dry films in DI water, the storage modulus G′ and loss modulus G″ of all the films decreased, which is shown in Figure 8a. But G′ and G″ of the BPEI/PAA/latex film are always higher than the BPEI/PAA film at all times, no matter dry or wet.…”

“…The dry films were soaked in water and allowed to equilibrate for at least 15 min, and an axial force >20 N was applied to exclude the possible liquid influence. Water is an efficient plasticizer for PEMs, causing a rheological transition from a rigid, glassy film to a viscous, liquid‐like material . After immersing the dry films in DI water, the storage modulus G′ and loss modulus G″ of all the films decreased, which is shown in Figure a.…”

Coating Strategies Using Layer‐by‐layer Deposition for Cell Encapsulation

“…Most polyelectrolyte multilayer systems with self‐healing properties possess weak–weak and weak–strong polyelectrolyte interactions. For example, weak polyelectrolyte multilayers of poly(ethylenimine)/PAA (BPEI/PAA) showed self‐healing and adhesive properties that allowed their use as foldable devices to construct, for example, tubular structures . The self‐healing behavior of the multilayers is based on water‐induced mobility of polymer chains: in wet conditions, the swollen‐state surface allows defects to be eliminated by rearrangement of polymer chains.…”

“…The self‐healing behavior of the multilayers is based on water‐induced mobility of polymer chains: in wet conditions, the swollen‐state surface allows defects to be eliminated by rearrangement of polymer chains. In the BPEI/PAA films, the self‐healing transition was dependent on the transition of contact between organic solvents and hydration with water . Another work reported the preparation of self‐healing multilayer structures using non‐toxic chitosan and polyacrylic acid.…”

Fast Self‐Healing of Polyelectrolyte Multilayer Nanocoating and Restoration of Super Oxygen Barrier

“…Ionically bonded systems could be healed after reshuffling and relaxation of ionically clustered regions, which could solve the above mentioned challenge . The free volume and chain mobility of ionically bonded polymers are strongly influenced by ionic strength, pH, and water fraction, which could be used as stimuli to trigger healing. Rapid and efficient self‐healing behavior was observed in an ionically bonded complex of polyacrylic acid (PAA) and poly(allylamine hydrochloride) using sodium chloride as a promoter .…”