Complete Dynamic Phase Diagram of a Supramolecular Polymer

We revisit the equilibrium phase diagram of themuch-studied model supramolecular polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT) in nonpolar solvents andprovide unambiguous evidence of a much richer behavior,characterized by four distinct regimes. Typically, two types ofself-assembled structures are formed: tubes (filaments) at higher(lower) concentrations and lower (higher) temperatures. The tubestructure forms viscoelastic solutions that had been characterized byrheology, however, without detailed analysis of the experimentalsignals. Here, we combine rheology and microrheology to establishthe complete dynamic phase diagram of EHUT in dodecane. It stillcomprises two structures, tubes andfilaments, with the transitiontemperature being almost constant over the examined wide concentration range, as confirmed with the help of complementarydifferential scanning calorimetry measurements. The tubes are found to exist in three dynamic states with increasing concentration,unentangled, partially entangled, and well entangled, which are separated by isolength lines. We present criteria for unambiguouslyidentifying these phases and discuss their distinct concentration and temperature dependencies. The new, complete phase diagrammay serve as a guide for investigating other supramolecular polymers with tunable rheology and, more importantly, providinginsights into a universal description of one-dimensional self-assembled structures by linking this class of materials with the classicwormlike surfactant micelles, for which the partially and well-entangled regimes were recently elucidated