Controlling Hierarchical Self-Assembly in Supramolecular Tailed-Dendron Systems

We study the self-assembly of a dendritic macromolecular system formed by a second-generation dendron with pH-responsive end groups and with a polymer chain emanating from its focal point, typically referred to as dendron-coil system. We use supramolecular ionic interactions to attach to the periphery of the dendrons sulfate-terminated alkyl tails of various lengths. The resulting ionic complexes have a molecular architecture similar to a four-arm dendritic pitchfork with varying arms and holder lengths. The bulk morphologies observed by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) show thermodynamically stable, hierarchical “inverted” hexagonal or lamellar structures. In addition, for a specific range of volume fractions, we show order-to-order transitions associated with the melting of the crystalline alkyl tails. The structural models for the molecular packing emerging from TEM and SAXS analysis are benchmarked to available self-consistent field theories (SCFTs) developed for identical systems and experiments and theoretical predictions are found in perfect agreement. With respect to our previous work on inverted dendron and dendrimer-surfactant self-assembled morphologies (Mezzenga et al. Soft Matter. 2009, 5, 92−97), the present findings show that keeping the same dendritic molecular architecture but adding a polymer chain emanating from the focal point enables the scale up of the structural organization from the liquid crystalline length scale (100 nm) to the block copolymer length scale (101 nm) while preserving the inverted unconventional morphologies. Because the length of the holder and the arms of the dendritic pitchfork can be finely tuned, these systems offer new possibilities in the design of nanostructured organic materials and their use in templating applications.