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Silver nanoparticles (4.5 nm average radius) are used as the first negatively charged layer of a polyelectrolyte multilayer prepared subsequently from poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) solutions with 1 M KCl. After adsorption of a PAH layer on top of the silver nanoparticle monolayer, particle aggregation occurs, as evidenced by the double peak of the UV−vis absorption spectrum and by the decreased number of the objects found with AFM. On adsorption of the first PSS layer on top of the Ag/PAH sandwich, the nanoparticles remain close as is indicated by a the reduced object count and the changed absorption spectrum. If the PAH layer covering the Ag nanoparticles is adsorbed from salt-free solution, the nanoparticles remain isolated. Apparently, the aggregation is mediated by the PAH adsorbing in coiled conformation. Additionally, UV−vis and X-ray reflectivity evidence is found for lateral yet not vertical nanoparticle movement when polyelectrolytes adsorb, even if the adsorbing coils do not touch the nanoparticles directly. [ABSTRACT FROM AUTHOR]

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 xprotonated and ydeuterated polycation/polyanion bilayers, respectively. The number of bilayers N= x+ yis 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. [ABSTRACT FROM AUTHOR]

To describe the swelling of polyelectrolyte multilayers (PEMs) on a molecular scale, the PEM architecture is varied. The polyanion is poly(styrenesulfonate) (PSS) and the polycation poly(allylamine hydrochloride) (PAH). PEM either consists of 10 protonated polyelectrolyte bilayers (p 10), 10 deuterated bilayers (d 10), or two different blocks, p 5d 5or d 5p 5. Prior to the exposure to 100% relative humidity (RH) D 2O or H 2O, the PEM is immersed in liquid D 2O or H 2O, respectively. The obtained scattering length density profiles provide insight into the exchange rates of the constituent molecules: The data indicate that three mobile protons of each PAH monomer are replaced by deuterium ions, yet most of the H 2O molecules found in PEM at 0% RH remain bound at 100% RH D 2O. This is in consistency with the fact that the core of PEM is in a glassy state. At 0% RH, the amount of bound water in the deuterated layers does not depend on the film architecture, whereas in the protonated layers it does. [ABSTRACT FROM AUTHOR]