Probing weak intermolecular interactions in self-assembled nanotubes.

Extreme confinement affects the physical properties of fluids, but little quantitative data is available. We report on studies of a bisurea compound that self-assembles into nanotubes to probe solvent confinement on the angstrom scale. By applying a statistical model to calorimetric data obtained on solvent mixtures, we show that the thermodynamic stability of the nanotubes is an extremely sensitive function of the solvent composition because solvent interactions inside and outside of the nanotubes are different. We are able to measure energetic effects as small as 0.01 kT and relate them to the differences in molecular structure of the solvents.