Compact Nanoparticle Polyethyleneimine Multilayers

Figure 4 shows the assembly QCM monitoring and scanning electron micrographs of film cross-sections and a partial top view of a film with architecture PDDA/PSS/PDDA+ (MnO2/PDDA)9 and 190 nm thick SnO2/PDDA multilayer.

MnO2-film has a remarkably smooth surface and uniform thickness. The total frequency shift by QCM was 11,000 Hz and film thickness from SEM was 170 nm. Dividing the film thickness by the number of manganese oxide/PDDA bilay-ers, we obtain values slightly less than the 23-nm bilayer thickness found above from QCM because the first two layers of manganese oxide are thinner. We cannot detect separate layers in the film by SEM, but individual structures of about 20 nm dimensions are clearly visible and may be attached to nanoparticles.

We analyzed the chemical composition and the chemical state of Mn and N atoms on the surface of a film with architecture PDDA/PSS/PDDA + (MnO2/PDDA)9 by XPS. Spectra revealed a surface rich in carbon and oxygen with manganese and nitrogen present in concentrations less than 7% and trace amounts of chlorine. The Mn (2p) region consists of a spin-orbit doublet with a Mn (2p1/2) binding energy of 653.30 eV and Mn (2p3/2) binding energy of 641.63 eV. This doublet can be assigned to a mixed valent manganese system, most likely Mn (4+) and Mn (3+) since the average oxidation state of Mn in the nanoparticles is 3.7. The N 1s region showed two peaks at 402.04 eV and 399.12 eV, indicating two different chemical environments for the nitrogen atoms. The difference in the chemical environment may reflect the formation of contact ion pairs and long-distance charge pairs between the MnO2 particles and the polycation PDDA.

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