A new salt-free approach was developed for fabricating conductive paper by layer-by-layer (LBL) assembly of conductive indium tin oxide (ITO) nanoparticles and polyelectrolytes onto wood fibers. Subsequent to the coating procedure, the fibers were manufactured into conductive paper using traditional paper making methods. The wood fibers were first coated with polyethyleneimine (PEI) and then LBL assembled with poly(sodium 4-styrenesulfonate) (PSS) and ITO for several bilayers. The surface charge intensity of both the ITO nanoparticles and the coated wood fibers were evaluated by measuring the zeta-potential of the nanoparticles and short fibers, respectively. The ITO nanoparticles were found to preferentially aggregate on defects on the fiber surfaces and formed interconnected paths, which led to the formation of conductive percolation paths throughout the whole paper. With ten bilayer coatings, the as-made paper was made DC conductive, and its sigma(dc) was measured to be 5.2 x 10(-6) S cm(-1) in the in-plane (IP) direction, while the conductivity was 1.9 x 10(-8) S cm(-1) in the through-the-thickness (TT) direction. The percolation phenomena in these LBL-assembled ITO-coated paper fibers was evaluated using scanning electron microscopy (SEM), current atomic force microscopy (I-AFM), and impedance measurements. The AC electrical properties are reported for frequencies ranging from 0.01 Hz to 1 MHz. A clear transition from insulating to conducting behavior is observed in the AC conductivity.

Exponential growth of layer-by-layer (LbL) assembled films is desirable because this method considerably increases the growth rate, resulting in much thicker films in a shorter period of time than is the case with normally linearly grown LbL thin films. For the first time, we demonstrate the exponential LbL (e-LbL) growth of poly(ethyleneimine)/SiO2 nanoparticles (PEI/SiO2) bicomponent thin films that consist mostly of SiO2 nanoparticles (over 90 wt % obtained by thermogravimetric analysis). These results are in contrast to earlier e-LbL studies, where the film thickness was made up mostly of the polyelectrolyte, with a very small percentage coming from the inorganic nanoparticles. Here, we show that the LbL growth of the PEI/SiO2 system significantly depends on the pH of the PEI and the SiO2 solutions. The e-LbL growth will only occur when the film is deposited with PEI at a high pH and SiO2 at a low pH. The exponential growth was characterized using a quartz crystal microbalance, atomic force microscopy and scanning electron microscopy imaging, and neutron reflectometry. It is demonstrated that e-LbL films can grow to thicknesses as large as 2–3 μm within just 10 bilayers. The findings reported in this article emphasize new opportunities for the e-LbL growth of organic/inorganic bicomponent composite thin films that may have applications as electrically conducting films, hydrophobic films, and brick-and-mortar biomimetic films.

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We demonstrate that polyethyleneimine (PEI) stabilizes indium tin oxide (ITO) colloidal suspensions to a wider pH range and enhances the growth rate of the nanoparticle thin film during a layer-by-layer (LBL) assembly process. The interaction between the PEI and the ITO nanoparticle surface was determined by Fourier transform infrared spectroscopy to be mainly due to the electrostatic force between the amine groups of PEI and the ITO particle surface. The enhanced growth rate of ITO thin films was evaluated using a quartz crystal microbalance, atomic force microscopy, impedance spectroscopy, and thermogravimetric analysis. Results were found to be dependent on the PEI/ITO ratio used. Using the PEI-modified ITO suspension at a PEI/ITO ratio of 0.5 wt %, more than twice the amount of ITO was deposited onto model surfaces, such as cellulose fibers, silicon wafers, and gold electrodes of quartz crystals, when compared against the unmodified suspension. A 2 orders of magnitude higher conductivity was obtained for conductive paper made from PEI-modified, ITO-coated cellulose fibers as compared with paper made from unmodified, ITO-coated cellulose fibers. This enhanced assembly rate is attributed to (1) the relatively constant electrostatic attraction forces between the PEI-modified ITO and PSS maintained during the LBL assembly process, (2) the large number of interaction sites and strong polymer chain entanglement between the PEI-modified ITO and the PSS assembly layers, and (3) the relatively modest interparticle repulsive forces between the PEI-modified ITO nanoparticles.

In this Article, we investigate the effect of a precursor layer, which is composed of four bilayers of polyethyleneimine (PEI) and poly(sodium styrene sulfonate) (PSS), on the subsequent LBL assembly of hybrid films composed of indium tin oxide (ITO) nanoparticles and PSS. A precursor polyelectrolyte layer is usually deposited to minimize interference by the substrate. It is shown here that the "effective" surface charge of the precursor layer can significantly affect the subsequent assembly behavior of [ITO/PSS](9.5) hybrid thin films. Depending on the surface charge of the precursor layer, the subsequent LbL assembly of [ITO/PSS](9.5) hybrid films can exhibit either one or two regimes. When two growth regimes are present, the first one consists of a "recovery regime", and the second is the expected "linear growth regime." The length of the "recovery regime" is dependent on how much positive charge the precursor layer possesses and how fast this surface charge can be compensated. This work reveals for the first time that changes in the surface charge of the precursor layer can have a significant effect on the subsequent LBL assembly process. The surface charge of the precursor layer was investigated using ζ-potential measurements on model silica microspheres. These experiments showed that the surface charge of the precursor layer, [PEI/PSS](4), is dependent on the pH of the solution in which it is immersed, and that it can reverse from a negatively charged surface to a positively charged one, at sufficiently low pH due to the protonation of PEI, despite having the negatively charged PSS layer as the outermost layer.

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Rational design of electrocatalysts with unique morphological structure and chemical composition was crucial for the electrochemical performance and the capacity of energy storage. In this work, Fe-doped NiCoP hybrid hollow...

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