Extended Data Fig. 1: Comparison of three classes of polymeric materials.
a,b, Schematics (a) and tensile stress-strain curves (b) illustrating the role of identical solvent loading in gel and glassy gel. Adding solvent improves extensibility of glassy polymers, but usually weakens the mechanical properties (for example, hydrogel). In contrast, glassy gel is extensible like a gel, but stiff like the glassy polymer due to strong solvent-polymer interactions that non-covalently crosslink the polymer. Insets in b show individual tensile stress-strain curves. As an example, consider poly(acrylic acid) (PAA). In the absence of solvent, the polymer is glassy and stiff, yet brittle. Swelling in water produces a hydrogel (56 wt% water) that is many orders of magnitude softer, weaker, and extensible than the glassy polymer. In contrast, replacing water with an ionic liquid solvent (58 wt% ionic liquid) is nearly as stiff as a glass, while maintaining extensibility of a gel. c, A spider plot summary in terms of liquid content, toughness, recovery, fracture strength, and elongation. The experimental data is for PAA and the values in a are from tensile tests reported in b, c, and Supplementary Fig. 4.
