Scrolling in Supramolecular Gels: A Designer's Guide.

Area of Science:

• Supramolecular chemistry
• Materials science
• Chemical engineering

Background:

• Small molecule gelation is crucial for applications in catalysis, nanomaterials, drug delivery, and pharmaceutical crystallization.
• The precise mechanisms governing the self-organization of gelators into fibrous networks remain largely unexplained.

Purpose of the Study:

• To elucidate the self-assembly mechanism of bis(urea) compounds leading to gel formation.
• To correlate molecular features with the ability of compounds to form supramolecular fibrous networks.

Main Methods:

• Synthesis and characterization of a library of bis(urea) compounds.
• Investigation of gelation properties.
• Molecular dynamics simulations to model the aggregation process from molecular motifs to fiber networks.

Main Results:

• Observed distinct self-assembly pathways for lamellae with asymmetric versus symmetric surfaces.
• Asymmetric lamellae were shown to scroll into uniform, unbranched fibrils.
• Symmetric lamellae were observed to stack and form crystals.
• Identified specific molecular features, including narrow, flexible end groups and high packing densities, associated with asymmetric lamellae scrolling.

Conclusions:

• The scrolling of asymmetric lamellae represents a general mechanism for small molecule gel formation.
• Understanding these self-assembly pathways can guide the design of novel gelators for various applications.
• The findings provide fundamental insights into supramolecular assembly driving gelation.