Ultracentrifugation Studies on the Solution Properties of Supramolecular Building Blocks for Polymers: Potential, Problems, and Solutions

Suitable supramolecular building blocks can assemble via non-covalent interactions into large, often regular structures, such as surface films. Uniformity of the state of association of the building blocks seems to be a prerequisite for the success of the assembly process. The paper shows how the association behavior of the compounds can be characterized by analytical ultracentrifugation. In addition to describing the potential of the method, two major problems are addressed: the determination of the partial specific volume of the compounds, ν, and disturbancies due to their electric charge. ν is found to be strongly dependent on the solvent, but can be reliably determined by a special solvent density variation technique ("buoyant density method"). The latter procedure also seems to correct for the secondary charge effect.