Ductile "Ice": frozen hydrogels with high ductility and compressive yielding strength

Abstract

Ice, the solid state of water, which mainly consists of a hexagonal crystal structure in bulk, is usually very brittle. Although ice appears less brittle under compression or shear at a relatively low strain rate, it is by no means a ductile material as metal and is seldom considered as an engineering material in applications other than igloos. We report herein the astonishing ductility and high compressive yielding strength of a polymeric hydrogel in a frozen state. Containing 88 wt. % of water, the hydrogel appears like ice when frozen, and embraces most other physical properties of ice. Meanwhile, the frozen hydrogel not only shows a high compressive modulus (∼1 GPa at -25 °C) and yielding strength (∼20 MPa at -25 °C), but is also ductile enough to sustain extremely large deformation such as bending, twisting, stretching, extensive shaping, and even machining in a large low temperature range. The ductility at a high strain rate also makes it a material with a significant impact resistivity. Moreover, the frozen gel also exhibits the repeatable ductility - the large plastic deformation is completely recoverable at an elevated temperature. These results will be important towards developing low-cost and environment-friendly engineering materials used in a low temperature range when ductility and reusability is required.