Gold nanoparticles (NPs) were prepared by reduction with salicylic acid in aqueous solution. The resulting dispersions were found to contain a mixture of flat triangular/hexagonal and smaller close-to-spherical NPs. As expected from theoretical considerations, such nanocolloids display two clearly differentiated surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively. Layer-by-layer (LBL) assembly was used to deposit thin films of the Au colloids. UVvisible data indicate preferential adsorption of the flat particles on polyelectrolyte films. Importantly, a new band developed at 650 nm as the number of the Au NPs bilayers increased. This finding indicates that there exists a strong interaction between the NPs in adjacent layers, resulting in the surface plasmon absorption at a new wavelength. The insertion of extra polyelectrolyte or montmorillonite layers between the Au bilayers was shown to gradually reduce the interlayer interaction and resulted in the NP composite films with absorption spectra virtually identical to those of the original dispersion. The bilayer deposition sequence in LBL assembly, i.e. multilayer architecture, can be used to control the strength of NP-NP coupling in the layered composites.

The interlayer configuration proposed by Moore and Reynolds and commonly used to reproduce the 00ℓ reflections of bi-hydrated smectite is shown to be inconsistent with experimental X-ray diffraction data. 1 The alternative configuration of interlayer species with cations located in the mid-plane of the interlayer and one sheet of H 2 O molecules on each side of this plane is also shown to imperfectly describe the actual structure of bi-hydrated smectites. Specifically, the thermal fluctuation of atomic positions (Debye-Waller factor) used to describe the positional disorder of interlayer H 2 O molecules has to be increased to unrealistic values to satisfactorily reproduce experimental X-ray diffraction data when using this model. A new configuration is thus proposed for the interlayer structure of bi-hydrated smectite. Cations are located in the mid-plane of the interlayer whereas H 2 O molecules are scattered about two main positions according to Gaussian-shaped distributions. This configuration allows reproducing all 00ℓ reflections with a high precision, with only one new variable parameter (width of the Gaussian function). The proposed configuration is consistent with those derived from Monte-Carlo calculations and allows matching more closely the amount of interlayer water that can be determined independently from water vapor adsorption/desorption isotherm experiments. In addition, the proposed configuration of interlayer species appears valid for both dioctahedral and trioctahedral smectites exhibiting octahedral and tetrahedral substitutions, respectively, thus not allowing to differentiate these expandable 2:1 phyllosilicates from their respective interlayer configuration.