From the conformation of a single molecule to physical networks in highly interacting polymers: A small-angle neutron study

Small-angle neutron scattering has been used to study the conformation and structure of highly interacting macromolecules in complex fluids. The evolution of the structure has been investigated from the conformation of a single molecule through an association process to the formation of physical networks. Two highly interacting polymers, an ionic polymer (consisting of a perfluorinated backbone and an ionizable hydrophilic side chain dissolved in water/alcohol mixtures) and rodlike, highly conjugated phenylene ethylene molecules (dissolved in toluene), have been studied. Highly interacting polymers often form relatively long lasting physical networks with increasing polymer concentration. The driving force, however, is system-specific, and so are the micellar systems and physical networks formed. Although the two families of polymers under consideration are entirely different chemically, their strong interaction, either ionic or through π-π coupling, results in similarities in the complex fluids formed when they are dissolved in solutions. These include elongated configurations in dilute solutions, association into micelles, and eventually coalescence into physical networks. The ionic polymers form durable stable networks, whereas the rodlike polymers form a fragile, gel-like phase.