Thermosolutal Self-Organization of Supramolecular Polymers into Nanocraters

The ability of two complementary molecular modules bearing H-bonding uracilic and 2,6-(diacetylamino)pyridyl moieties to self-assemble and self-organize into submicrometer morphologies has been investigated by means of spectroscopic, thermogravimetric, and microscopic methods. Using uracilic ³<i>N</i>-BOC-protected modules, it has been possible to thermally trigger the self-assembly/self-organization process of the two molecular modules, inducing the formation of objects on a mica surface that exhibit crater-like morphology and a very homogeneous size distribution. Confirmation of the presence of the hydrogen-bonding-driven self-assembly/self-organization process in solution was obtained by variable-temperature (VT) steady-state UV−vis absorption and emission measurements. The variation of the geometric and spatial features of the morphologies was monitored at different <i>T</i> by means of atomic force microscopy (AFM) and was interpreted by a nonequilibrium diffusion model for two chemical species in solution. The formation of nanostructures turned out to be affected by the solid substrate (molecular interactions at a solid−liquid interface), by the matter-momentum transport in solution (solute diffusivity <i>D</i>₀ and solvent kinematic viscosity ν), and the thermally dependent cleavage reaction of the BOC functions (<i>T</i>-dependent differential weight loss, θ = θ(<i>Τ</i>)) in a <i>T</i> interval extrapolated to ∼60 K. A scaling function, <i><i>f</i> = f</i> (<i>νD</i>₀, <i>ν</i>/<i>D</i>₀, θ), relying on the onset condition of a concentration-driven thermosolutal instability has been established to simulate the <i>T</i>-dependent behavior of the structural dimension (i.e., height and radius) of the self-organized nanostructures as ⟨<i>h</i>⟩ ≈ <i>f</i> (<i>T</i>) and ⟨<i>r</i>⟩ ≈ 1/<i>f</i> (<i>T</i>).