Double-network hydrogels are an extremely useful type of soft matter due to their high toughness and high water content. However, during their fabrication process they undergo significant swelling, making them difficult to utilize in composite applications or preventing their fabrication into complex shapes. By firstly preparing a sacrificial network out of gel particles, we can synthesize double-network hydrogels through a one-step process. This allows us to incorporate these types of gels into composites, as surface coatings, and as interfacial glues.

Publications:

• Takahashi, R.; Shimano, K.; Okazaki, H.; Kurokawa, T.; Nakajima, T.; Nonoyama, T.; King, D. R.; Gong, J. P. “Tough Particle-Based Double Network Hydrogels for Functional Solid Surface Coatings” Advanced Materials Interfaces. 2018, 5 (23): 1801018.

The first network of a double-network hydrogel provides sacrificial bonds that dissipate energy and prevent crack growth, significantly increasing toughness. The sacrificial network is generally formed by swelling the polymer network until it approaches the fully extended state. Rather than requiring this swelling process to extend the network chains, we can incorporate inherently stiff polyelectrolytes into a soft polymer network, then form a supramolecular sacrificial network by immersion in multivalent metal ions. The benefits of this method include a simpler, one step synthesis process, and the incorporation of self-healing properties. Furthermore, we can orient the sacrificial network by applying mechanical stimulus during the supramolecular network formation, allowing us to develop anisotropic hydrogels with tunable mechanical properties based on the orientation. Because many biological materials have anisotropic properties, we envision this method could be useful for developing synthetic biomaterials.

Publications:

• King, D. R.*,‡; Takahashi‡, R.; Ikai, T.‡; Fukao, K.; Kurokawa, T.; Gong, J. P.* “Anisotropic Double Network Hydrogels via Controlled Orientation of a Physical Sacrificial Network.” ACS Applied Polymer Materials. 2020, 2 (6): 2350-2358.

• Takahashi, R.; Ikai, T.; Kurokawa, T.; King, D. R.*; Gong, J. P.* “Double Network Hydrogels Based on Semi-rigid Polyelectrolyte Physical Networks.” Journal of Materials Chemistry B. 2019, 7 (41), 6347–6354.

Fiber reinforced polymers are commonly used in industrial applications, such as in materials that make up modern airplanes. Developing fiber-reinforced soft composites is very difficult, because these types of composites generally fail either due to interfacial delamination, or by the fibers rupturing the soft matrix. We have determined that three requirements exist that enable the fabrication of fiber-reinforced soft composites with extremely high toughness: 1) The fibers must be extremely stiff, 2) the matrix must be very tough, and 3) the interphase between these two components must be strong. By following these design parameters, we have developed soft composites with toughness greater than steel.

Publications:

• Cui, W.; King, D. R.; Huang, Y.; Chen, L.; Sun, T. L.; Guo, Y. Z.; Saruwatari, Y.; Hui, C.-Y.; Kurokawa, T.; Gong, J. P. “Fiber-reinforced Viscoelastomers Show Extraordinary Crack Resistance that Exceeds Metals.” Advanced Materials. 2020, 32 (31): 1907180.

• Huang, Y.; King, D. R.; Cui, W.; Sun, T. L.; Guo, H.; Kurokawa, T.; Brown, H. R.; Hui, C.-Y.; Gong, J. P.* “Superior Fracture Resistance of Fiber Reinforced Polyampholyte Hydrogels Achieved by Extraordinarily Large Energy-Dissipative Process Zones.” Journal of Materials Chemistry A. 2019, 7 (22): 13431–13440.

• Huang, Y.; King, D. R.; Sun, T. L.; Nonoyama, T.; Kurokawa, T.; Nakajima, T.; Gong, J. P. “Energy-Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft Composites.” Advanced Functional Materials. 2017, 27 (9): 1605350.

• King, D. R.; Sun, T. L.; Huang, Y.; Kurokawa, T.; Nonoyama, T.; Crosby, A. J.; Gong, J. P. “Extremely Tough Composites from Fabric Reinforced Polyampholyte Hydrogels.” Materials Horizons. 2015, 2: 584-591.

Traditional double-network gels consist of two interpenetrating polymer networks, where sacrificial bonds exist on the molecular scale. By understanding the essence of this design, we have developed macroscale double-network composite materials. In this system, the sacrificial bonds are provided by a fabricated network on the millimeter scale. During deformation, the macroscale sacrificial network fractures dissipating energy, and the bulk matrix prevents global failure and enables high stretch. Force transmission occurs due to topological interlocking between the two phases, due to the interpenetrating structure. Since preferential interfacial interactions are not required, any material can be used to form a sacrificial network, from biomaterials such as wood, to synthetic plastics, to metal.

Publications:

• Okumura, T., Takahashi, R., Hagita, K., King, D.R.*, and Gong, J.P.* (2021). “Improving the strength and toughness of macroscale double networks by exploiting Poisson's ratio mismatch.” Scientific Reports. 11, 13280.

• King, D. R.*,‡; Okumura, T.‡; Takahashi, R.; Kurokawa, T.; Gong, J. P.* “Macroscale Double Networks: Design Criteria for Optimizing Strength and Toughness.” ACS Applied Materials & Interfaces. 2019, 11 (38): 35343-35353.

• Takahashi, R.; Sun, T. L.; Saruwatari, Y.; Kurokawa, T.; King, D. R.*; Gong, J. P.* “Creating Stiff, Tough, and Functional Hydrogel Composites with Low-Melting-Point Alloys” Advanced Materials. 2018, 30 (16): 1706885.