Patterned crystal growth and heat wave generation in hydrogels

• Published in: Nature communications Vol. 13; no. 1; p. 259
• Main Authors: Schroeder, Thomas B H, Aizenberg, Joanna
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 11.01.2022; Nature Publishing Group UK; Nature Portfolio
• Subjects: Acetic acid; Aqueous solutions; Crystal growth; Crystallization; Crystals; Heat; Heat transfer; Heat waves; Hydrogels; Internal energy; Latent heat; Liquid phases; Nucleation; Phase change materials; Photomasks; Polyacrylamide; Polymerization; Sodium; Sodium acetate; Temperature gradients; Wave generation; Wave propagation
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-27505-z

The crystallization of metastable liquid phase change materials releases stored energy as latent heat upon nucleation and may therefore provide a triggerable means of activating downstream processes that respond to changes in temperature. In this work, we describe a strategy for controlling the fast, exothermic crystallization of sodium acetate from a metastable aqueous solution into trihydrate crystals within a polyacrylamide hydrogel whose polymerization state has been patterned using photomasks. A comprehensive experimental study of crystal shapes, crystal growth front velocities and evolving thermal profiles showed that rapid growth of long needle-like crystals through unpolymerized solutions produced peak temperatures of up to 45˚C, while slower-crystallizing polymerized solutions produced polycrystalline composites and peaked at 30˚C due to lower rates of heat release relative to dissipation in these regions. This temperature difference in the propagating heat waves, which we describe using a proposed analytical model, enables the use of this strategy to selectively activate thermoresponsive processes in predefined areas.