We report here on the influence of changes in the solution salt concentration on the structure of multilayers
of weak polyelectrolytes. For poly(acrylic acid) (PAA) and poly(allylamine) (PAH) multilayers assembled
by the layer-by-layer process in the presence of sodium chloride, washing with pure water after deposition
of each layer produces films with considerable surface roughness (root-mean-squared (rms) roughness ∼17
nm for a 10 layer film), as assessed by scanning force microscopy. In contrast, relatively smooth (rms
roughness ∼1 nm) and homogeneous PAH/PAA multilayer films are formed when the salt concentration
is kept constant both during the assembly process and in the washing steps. For such smooth films,
subsequent exposure to pure water leads to the introduction of regular, discrete, nanometer-sized pores,
thus providing a means of introducing lateral structure into the PAH/PAA multilayer films. Electrochemical
measurements revealed that the pores formed in less than 10 min. The sensitivity of the multilayer films
to salt as well as the subsequent creation of nanopores potentially makes them attractive candidates for
use in controlled-release applications where defined permeability characteristics are desired.
Ultrathin films have been prepared by self-assembling trioctylphosphine oxide, TOPO, capped n-type 20-40 Å diameter CdSe nanoparticles and 1,6-hexadecanethiol, HDT, onto p-doped semiconducting polymers, chemically deposited poly(3-methylthiophene), PMeT (for DeWice A), and electrochemically deposited poly-(pyrrole), Ppy (for DeWice B). The semiconducting polymers have, in turn, been electrochemically layered (for DeWice A) or layer-by-layer chemically assembled (for DeWice B) onto derivatized conducting substrates. The ultrathin films have been characterized by absorption and emission spectroscopy, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy, and by electrochemical measurements. By controlling the level of doping into the p-type junction, it was possible to prepare dissymmetrical junctions and observe a rectifying behavior in the forward direction and a Zener breakdown in the reverse direction for Au/PMeT/(HDT/CdSe) 3 , DeWice A, and for Au/MEA/Ppy/(HDT/CdSe) 3 , DeWice B. Additionally, Au/MeA/PAH/CdSe (PAH ) poly(allylamine hydrochloride)), Au/MEA/Ppy/PSS/CdSe (PSS ) polystyrene sulfonate), and Au/MEA/Ppy/R-ZrP/CdSe (R-ZrP ) R zirconium phosphate) films have been prepared and characterized.
The construction of a high‐capacity intercalating cathode via an entirely new approach is reported—the self‐assembly of nanometer‐thick polyelectrolytes and graphite/graphite oxide nanoplatelets on a conducting substrate. The advantages of this approach as well as the charging and discharging behavior of a high‐density (1232 mAhg–1 of graphitic carbon) rechargeable lithium‐ion battery based on this cathode are described. This electrochemical cell holds commercial promise as it may be readily scaled up to an economically viable battery.
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