No abstract

The intercalation of poly(allylamine) (PAA) into a synthetic fluoromica (Na-TSM) was studied in order to understand the subsquent process of gold nanoparticle intercalation into the interlayer galleries. The composition and structure of the PAA intercalation compound (PAA/Na-TSM) was strongly influenced by the pH of its synthesis. At pH 3.0, the fully protonated form of the polymer was intercalated as a single layer (d ) 1.42-1.46 nm), accompanied by 0.2-0.4 chloride ions per PAA monomer unit. The role of chloride appears to be to screen the electrostatic repulsion of polycations within the gallery. At pH 12.0, a partially protonated form of PAA intercalates as an expanded layer (d ) 1.50-1.61 nm) with no chloride ions. From equilibrium PAA adsorption data, the standard free energy for PAA intercalation at pH 12.0 was -35 kJ/mol. At pH 3.0 and low PAA loading, the corresponding ∆G°is -64 kJ/mol, consistent with the stronger interaction of protonated PAA chains with the anionic clay sheets. Au nanoparticles (<10 nm diameter) intercalated into PAA/Na-TSM composites made at pH 12.0, but not those made at pH 3.0. The most effective pH for intercalation of well-dispersed Au nanoparticles was 11.0. potential measurements show that, at pH 11.0, the PAA/Na-TSM and Au colloids have nearly neutral and negative surface charges, respectively. From this result, it was concluded that electrostatic interactions as well as covalent bonding between free amine groups and intercalated Au nanoparticles are important for optimal intercalation. A red shoulder extending from 570 to 730 nm on the plasmon resonance absorption of Au/PAA/Na-TSM was observed and was attributed to close interactions between nanoparticles in adjacent galleries.

The transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.