Institut Charles Sadron News

In the framework of a joint PhD student supervision, researchers from Institut Charles Sadron and Institut Laue Langevin used neutron scattering to determine the average conformation of individual deuterated polyelectrolyte chains within multilayer films composed of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). Deuterated coils of PSS are diluted with non-deuterated ones of the same molar mass thus reducing the coil-coil overlap of neighbouring deuterated coils and thus enabling to determine radii of gyration (Rg,x, Rg,y and Rg,z) by grazing incidence neutron scattering. Whereas in solution and in equilibrated polyelectrolyte complexes Rg,x = Rg,y = Rg,z, in LbL-films of solid-like polyelectrolytes (Rg,x = Rg,y) > Rg,z is observed. This work provides the first direct quantitative evidence that the conformation of individual PSS chains in a multilayer film prepared by dipping from 2 M NaCl solutions is of a flattened coil form with an asymmetry factor of more than seven. This structural asymmetry of polymer chains is higher for films assembled by spray- and spin-assisted assembly, testifying the memory effect of multilayer films in regard to the deposition process. Due to very high resolution of modern instruments it was also found that the charge stoichiometry between polyanions and polycations is locally disobeyed in Z-direction, a further indication that the polyelectrolyte complexes in the LbL-film is not at equilibrium. This study contributes to a better understanding of the formation of polyelectrolyte multilayer films, their internal structure and structure-dependent material properties. This work has been published in Nature Communications.