Gold-nanoparticle/organic films were prepared via layer-by-layer self-assembly using dodecylamine-stabilised Au-nanoparticles and poly(propyleneimine) (PPI) dendrimers of generation one to five (G1-G5) or hexadecanedithiol (HDT) as linker compounds. TEM and FE-SEM images revealed that the bulk of the films consisted of nanoparticles with diameters of about 4 nm. XPS was used to study the chemical composition of the films. The C 1s and N 1s signals of an AuPPI-G4 film were interpreted qualitatively according to the dendrimer structure. The absence of the nitrogen signal in case of an AuHDT film indicated that the dodecylamine ligands were quantitatively exchanged during film assembly. About 76% of the sulfur atoms were bound to the nanoparticles. the remainder being present as free thiol (S H) groups. All films displayed linear current voltage characteristics and Arrhenius-type activation of charge transport. The conductivities of the AuPPI films decreased exponentially over approximately two orders of magnitude (6.8 x 10(-2) to 1.0 x 10(-3) ohms(-1) cm(-1)) with a five-fold increase of the dendrimer generation number. Dosing the films with solvent vapours caused their resistances to increase. Using different solvent vapours demonstrated that the sensitivity of this response was determined by the solubility properties of the linker compounds. Microgravimetric measurements showed that absorption of analyte was consistent with a Langmuir adsorption model. These measurements also revealed a linear correlation between the electrical response (deltaR/Rini) and the concentration of absorbed analyte. The absorption of d4-methanol from a saturated vapour atmosphere was studied by neutron reflectometry with an AuPPI-G4 film. This measurement indicated condensation of methanol on top of the film and a uniform distribution of the analyte across the film thickness.

Brewster angle microscopy (BAM) studies on dipalmitoyl phosphatidyl glycerol (DPPG, sodium salt) monolayers on water subphases containing different amounts of NaCl are presented. Inhomogeneities in the monolayer appear after spreading at large mean areas per lipid molecule and at electrolyte concentrations in the subphase lower than 0.15 M NaCl. It is assumed that (i) after spreading DPPG is completely hydrolyzed, (ii) dissociation of the resulting acid depends on the electrolyte concentration in the subphase, and (iii) nondissociated acid molecules form solidlike aggregates in the monolayer, while the dissociated part surrounds them. Image processing of the BAM images allows us to calculate the surface densities of the lipid in the coexisting states, and the dissociation constant of the lipid in the monolayer ( ). The electrostatic contribution to the surface pressure was estimated using the obtained value. Comparison with the experimental π/A isotherms shows satisfactory agreement, confirming the value of the determined dissociation constant. We concluded that the described procedure is useful for the determination of for monolayers of charged surfactant molecules.

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In the present work, specular neutron reflectometry was used to study the sorption of D2O and perdeuterated toluene in self-assembled Au nanoparticle/poly(amidoamine) composite films. The method provides information about analyte-induced film swelling and analyte distribution profiles across the films. Our data suggest that film swelling upon exposure to the analytes is negligible within the resolution of the method. Strong differences are observed between the distribution profiles of D 2O and toluene-d8. Water penetrates into the film with an exponentially decaying concentration profile. In contrast, toluened 8 forms a thin "wetting" layer on top of the film, while the bulk of the film remains essentially analyte free. These results are explained by taking into account the chemical structure of the dendritic polymer used for film preparation.

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There have been reports, originally by the Bristol group, and subsequently by others, of the preparation and properties of emulsions of stable, nearly monodisperse droplets of poly(dimethylsiloxane) (PDMS) in water, where no added surfactant is used. It has been assumed that their stability is due to the high density of surface-ionized hydroxyl groups, similar in fact to the closely related Stöber silica particles. In this study we confirm, from droplet lifetime studies, that droplets, prepared from such synthesized PDMS, are significantly more stable to coalescence than similar-sized droplets prepared from three types of commercially available PDMS, containing HO-, MeO-, or Me3-terminated chains, respectively. It is shown, however, that the zeta potentials of the synthesized PDMS and of the various commercial oils are all very similar (as indeed are their Hamaker constants). So some other explanation must be inferred for the enhanced stability to coalescence of the synthesized PDMS droplets compared to the commercial PDMS droplets. It is shown, for droplets formed from n-hexane and the synthesized oil, that stability to coalescence is conferred at PDMS volume fractions (phiPDMS) around 0.2 in the mixture. The synthesized PDMS is known to consist of mixtures of cyclic PDMS and short-chain linear species, with terminal -OH groups. There is some (indirect) evidence that in the interval 0.25 < phiPDMS < 0.35, the linear PDMS chains may be adsorbed close to a monolayer at the mixed oil/water interface, possibly conferring some enhanced Gibbs elasticity to the interface. This underpins the possibility that, in the synthesized oil droplets themselves, there is also preferential adsorption of the linear chains at the PDMS/water interface, and this leads to a value of the Gibbs elasticity, sufficient to significantly reduce coalescence. Unfortunately, the Gibbs elasticity could not be measured in this case. However, such preferential adsorption is unlikely to occur with the commercial PDMS oils, which are not so heterogeneous. Finally, it is shown that droplets of the three commercial PDMS oils could be stabilized against coalescence, if a sufficient, minimum amount of sodium dodecyl sulfate (SDS) is added. Gibbs elasticity values have been estimated in these cases, from plots of interfacial tension against ln(SDS concentration).

The permeability coefficients K for permeation of air through Newton black foam films (bilayer films) from sodium dodecyl sulfate plus sodium chloride aqueous solutions have been measured. The dependencies of the permeability coefficienta on surfactant concentration C at temperatures 23,25,27, and 30 O C have been obtained. The K values strongly depend on C at low concentrations, but they remain constant at higher C. The permeability increases with increasing temperature. The experimental data have been discussed on the basis of the nucleation theory of fluctuational formation of holes in amphiphile bilayers. The results are in favor of an essential contribution of hole-mediated permeability at low surfactant concentrations and higher temperatures.

The gas permeability of Newtonian black foam films, formed on the top of a small bubble at the solution surface, was studied experimentally. The aqueous solutions contained sodium dodecylsulphate with concentrations in the range 1.5 x 10 -4 to 3 • 10 -3 mol/dm 3 and sodium chloride (constant concentration of 0.5 mol/dm3). A dependence of the gas permeability coefficient on the surfactant concentration was obtained. The experimental results are discussed on the basis of a theory assuming the presence of clusters of molecule vacancies (holes) in the bilayer foam film, their number and size depending on the surfactant concentration. The experimental results are in agreement with this film structure and confirm the existence of flow through both the hole-free bilayer film and the holes. It was found that the holes of three molecule vacandes make the main contribution to gas permeability at low surfactant concentration. The diffusion coefficients through the hole-free film and through the three-vacancy holes are calculated.