Designing Deep Eutectic Solvents with Crystalline Features: A New-Generation Green Crystallization-Induced Porogen

Abstract

Freeze-casting offers a simple method to prepare super-macroporous materials. However, research on inexpensive, low-toxic, and devisable deep eutectic solvents (DESs) as potential crystallization-induced porogens remains a great challenge. In this work, we used three organics (1,6-hexanediol, 1,8-octanediol, and 1,9-nonanediol) as the hydrogen bond donors along with a hydrogen bond acceptor (tetrabutylammonium chloride, TBAC) to form the DESs. COSMOtherm was used to predict the solid–liquid phase diagram of the DESs, and the DES molar ratios [TBAC/1,6-hexanediol (1:1), TBAC/1,8-octanediol (1:2.125), and TBAC/1,9-nonanediol (1.5:1)] were screened with suitable melting points (−14.77, 22.25, and 8.34 °C). The differences in melting point, viscosity, and crystal morphology of DESs caused the hydrophobic polymethylmethacrylate cryogels (contact angle > 120°) to exhibit smaller pore sizes (a reduction of 20–50%) and a higher specific surface area (an increase of 160–390 times) relative to conventional porogens. The absorption capacities of the cryogels in dichloromethane, ethyl acetate, and liquid paraffin were 39.3, 20.4, and 13.3 g g–1, respectively. This study presented a strategy that combined COSMOtherm-assisted screening and experimental validation to design DESs with a suitable melting point and cocrystal behavior. Green and devisable DESs provided more potential for achieving an adjustable pore structure of hydrophobic cryogels.