Strong and Facile Adhesives Based on Phase Transitional Poly(acrylic acid)/Poly(ethylenimine) Complexes

Polyelectrolyte complexes have demonstrated their potential application as adhesives to several substrates. However, it is unfortunate that the in-depth study focusing on polyelectrolyte phases as well as rheological analysis is insufficient to uncover the origin of the adhesive properties. Here, we precisely investigated the factors of polyelectrolyte adhesives in terms of electrostatic interaction using conventional rod coating and pH-induced phase transition, followed by a phase study between poly(acrylic acid) and branched poly(ethylenimine). The phase was systemically controlled by parameters such as polymer ratio, concentration of NaCl, and pH level. Then, the rheological modulus of each phase was studied to understand physical cross-linking. In relation to polyelectrolyte adhesives, it was found that a higher viscous phase led to more intensive adhesion strength. In addition, thermal treatment helped to obtain a dramatic increase in adhesion strength (2.4 MPa), which was accomplished by a conversion reaction from carboxylic acid to amide. This chemically cross-linked gel adhesive performance could compete with commercial grade adhesive, and this study creates a pathway to design polyelectrolyte adhesive regarding a facile process and applications

Highly Stretchable and Notch-Insensitive Hydrogel Based on Polyacrylamide and Milk Protein

Protein-based hydrogels have received attention for biomedical applications and tissue engineering because they are biocompatible and abundant. However, the poor mechanical properties of these hydrogels remain a hurdle for practical use. We have developed a highly stretchable and notch-insensitive hydrogel by integrating casein micelles into polyacrylamide (PAAm) networks. In the casein-PAAm hybrid gels, casein micelles and polyacrylamide chains synergistically enhance the mechanical properties. Casein-PAAm hybrid gels are highly stretchable, stretching to more than 35 times their initial length under uniaxial tension. The hybrid gels are notch-insensitive and tough with a fracture energy of approximately 3000 J/m². A new mechanism of energy dissipation that includes friction between casein micelles and plastic deformation of casein micelles was suggested

Dendrite-Free Lithium Deposition for Lithium Metal Anodes with Interconnected Microsphere Protection

A lithium (Li) metal anode is required to achieve a high-energy-density battery, but because of an undesirable growth of Li dendrites, it still has safety and cyclability issues. In this study, we have developed a microsphere-protected (MSP) Li metal anode to suppress the growth of Li dendrites. Microspheres could guide Li ions to selective areas and pressurize dendrites during their growth. Interconnections between microspheres improved the pressurization. By using an MSP Li metal anode in a 200 mAh pouch-type Li/NCA full cell at 4.2 V, dendrite-free Li deposits with a density of 0.4 g/cm³, which is 3 times greater than that in the case of bare Li metal, were obtained after charging at 2.9 mAh/cm². The MSP Li metal enhanced the cyclability to 190 cycles with a criterion of 90% capacity retention of the initial discharge capacity at a current density of 1.45 mA/cm²