Using neutron reflectivity, the internal structure of polyelectrolyte multilayers is described on the nanoscale. Each film consists of a protonated and a deuterated block, built from x protonated and y deuterated polycation/polyanion bilayers, respectively. The number of bilayers N = x + y is kept constant; the position of the interface between the blocks is varied systematically. The polyanion is poly(styrenesulfonate) (PSS), and the polycation is poly(allylamine hydrochloride) (PAH) or poly(diallyldimethylammonium chloride) (PDADMAC). Always, the first four to five bilayers are thinner than the average bilayer thickness, but the three terminating bilayers are sometimes thicker. In the core zone, the bilayer thickness is constant. The internal roughness is smallest next to the film/air interface and increases with the number of bilayers away from the film/air interface. This suggests that each deposition step promotes the interdiffusion of the supporting layers. At the selected preparation conditions, the internal roughness increases more for PDADMAC/PSS than for PAH/PSS; the diffusion constants differ by 2 orders of magnitude.

The internal interfaces of polyelectrolyte multilayers are investigated with neutron reflectivity. The films are made from poly(diallyldimethylammonium) (PDADMA), poly(styrenesulfonate) (PSS), and deuterated PSS-d. Each film consists of a protonated and a deuterated block. The internal roughness is smallest next to the film/air interface and increases with the number of layer pairs away from the film/air interface until a metastable state is reached. Both the final internal roughness and the interdiffusion constant increase with the salt concentration in the deposition solution and with PDADMA polymer weight. The increased mobility found with high molecular weight PDADMA is attributed to residual stresses occurring during film formation. The experiments suggest that PSS and PDADMA move partly as a complex. Postpreparation immersion in 1 M NaCl salt solutions has little effect if the multilayer is prepared from low salt solution and with high molecular weight PDADMA. However, almost complete intermixing is observed for multilayers prepared from 0.1 M NaCl and with low molecular weight PDADMA (diffusion length exceeds 30 nm).

A common feature of ionic liquids composed of cations with long aliphatic side chains is structural heterogeneities on the nanometer length scale. This so-called microphase separation arises from the clustering of aliphatic moieties. The temperature dependence of the liquid bulk structure was studied by small-angle X-ray and neutron scattering for a set of methylimidazolium ([CCim], [CCim]) based ionic liquids with tris(pentafluoroethyl)trifluorophosphate ([FAP]), bis(trifluoromethylsulfonyl)imide ([NTf]), and bis(nonafluorobutylsulfonyl)imide ([NNf]) anions. The experimental data is quantitatively analyzed using a generalized Teubner-Strey model. Discussion of the resulting periodicity d and correlation length ξ shows that the structural heterogeneities are governed by the interplay between the alkyl chain length, the geometry of the anion, and entropic effects. Connections between the mesoscopic correlation functions, density, and entropy of fusion are discussed in comparison to alcohols. The observed dependencies allow predictions on the mesoscopic correlation functions based on macroscopic bulk quantities.