Translating Solid-Phase Conformational Memory in the Prophecy of Multi-stimuli Responsive Low Molecular Weight Gels.

Abstract

Polymorphism and its screening to select the best-performing form is in high demand. In low molecular weight organogels (LMWG), gelators are designed as they contain flexible groups, functionalities capable of varied H-bonding, and increased the potential to show polymorphism. We synthesized a bis-urea based LMWG G1 and isolated three distinct polymorphic phases (Form I, II, and III). G1 polymorphs showed noticeable differences in solubility; precisely, Form I is highly soluble compared to the other two. Gel screening was carried out for all three polymorphs using different stimuli like heat-cool, sonication, shaking, and grinding. Among the polymorphs, Form I was found to have better gelling ability which was reflected by the solvent scope, thermal stability (gel-sol transition temperature Tgel), minimum gelator concentration (M.G.C.), stimuli-responsiveness, morphology, and rheological properties. The differences in their gelation performance among the three polymorphs are associated with their solubility parameter. Stimuli like sonication, shaking, and grinding triggered Form I to form a gel.  Form II and III responded to heat-cool stimuli only due to poor solubility. Therefore, it is noted crucial to add polymorph screening as an integral part of the gel synthesis to avoid problems associated with reproducibility in the gel prophecy of LMWG systems.