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.