Dilution-induced gel-sol-gel-sol transitions by competitive supramolecular pathways in water

• Published in: Science (American Association for the Advancement of Science) Vol. 377; no. 6602; pp. 213 - 218
• Main Authors: Su, Lu, Mosquera, Jesús, Mabesoone, Mathijs F. J., Schoenmakers, Sandra M. C., Muller, Cyprien, Vleugels, Marle E. J., Dhiman, Shikha, Wijker, Stefan, Palmans, Anja R. A., Meijer, E. W.
• Format: Journal Article
• Language: English
• Published: Washington The American Association for the Advancement of Science 08-07-2022
• Subjects: Benzene; Dilution; Elongated structure; Hydrogels; Sol-gel processes; Surfactants
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abn3438

Fascinating properties are displayed by synthetic multicomponent supramolecular systems that comprise a manifold of competitive interactions, thereby mimicking natural processes. We present the integration of two reentrant phase transitions based on an unexpected dilution-induced assembly process using supramolecular polymers and surfactants. The co-assembly of the water-soluble benzene-1,3,5-tricarboxamide (BTA-EG
4
) and a surfactant at a specific ratio yielded small-sized aggregates. These interactions were modeled using the competition between self-sorting and co-assembly of both components. The small-sized aggregates were transformed into supramolecular polymer networks by a twofold dilution in water without changing their ratio. Kinetic experiments show the in situ growth of micrometer-long fibers in the dilution process. We were able to create systems that undergo fully reversible hydrogel-solution-hydrogel-solution transitions upon dilution by introducing another orthogonal interaction.
Dilution-induced ordering
Many molecules, such as surfactants, can form ordered structures when placed in solution. Typically, the systems become more ordered and the structures change from spheres to elongated shapes as the concentration is increased. Su
et al
. studied a system of benzene-1,3,5-tricarboxamide) (BTA-EG4) with the cationic surfactant octyltrimethylammonium bromide (OTAB), in water (see the Perspective by Webber). BTA-EG4 undergoes supramolecular polymerization in water and will form hydrogels at higher concentrations, whereas OTAB will form small aggregates. However, when combined, the OTAB initially disrupts the BTA-EG4 hydrogels, but these can be reestablished upon dilution because this lessens the effect of the surfactant. With careful engineering, this can be expanded to a gel-sol-gel-sol system as a function of concentration. —MSL
Dilution-induced gelation in multicomponent supramolecular systems leads to highly adaptive hydrogel materials.