Diffusion in Model Networks as Studied by NMR and Fluorescence Correlation Spectroscopy

We have studied the diffusion of small solvent molecules (octane) and larger hydrophobic dye probes in octane-swollen poly(dimethyl siloxane) linear-chain solutions and end-linked model networks, using pulsed-gradient nuclear magnetic resonance (NMR) and fluorescence correlation spectroscopy (FCS), respectively, focusing on diffusion in the bulk polymer up to the equilibrium degree of swelling of the networks, that is, 4.8 at most. The combination of these results allows for new conclusions on the feasibility of different theories describing probe diffusion in concentrated polymer systems. While octane diffusion shows no cross-link dependence, the larger dyes are increasingly restricted by fixed chemical meshes. The simple Fujita free-volume theory proved most feasible to describe probe diffusion in linear long-chain solutions with realistic parameters, while better fits were obtained assuming a stretched exponential dependence on concentration. Importantly, we have analyzed the cross-link specific effect on probe diffusion independently of any specific model by comparing the best-fit interpolation of the solution data with the diffusion in the networks. The most reasonable description is obtained by assuming that the cross-link effect is additive in the effective friction coefficient of the probes. The concentration dependences as well as the data compared at the equilibrium degrees of swelling indicate that swelling heterogeneities and diffusant shape have a substantial influence on small-molecule diffusion in networks.

Surfactant foam flushing for in situ removal of DNAPLs in shallow soils

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Assessment of a new foam-based technology for enhanced oxidation of anisotropic unsaturated soils contaminated by hydrocarbons

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Surfactant foam technology for in situ removal of heavy chlorinated compounds-DNAPLs

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Retention of Cu(II)- and Ni(II)-polyaminocarboxylate complexes by ultrafiltration assisted with polyamines

International audienceThe retention of Cu(II)– and Ni(II)–nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) complexes in dilute solutions ([M-chelate] = 0.5 mM) by ultrafiltration in presence of polyethylenimine (PEI) or chitosan 10 mM was studied. Metal retentions larger than 98% were observed for PEI in the pH-range of 4–9. The excellent metal retention resulted from the combination of covalent binding and electrostatic interactions. The metal retention was studied at pH 7 as a function of the Cu-chelate/PEI ratio and has shown that the more encapsulating the chelate was, the lower was the retention.Electrolysis at pH 2 was used to precipitate Cu ions and to regenerate PEI with electrolytic yields in the range of 40–50% depending on the mixture composition

Reusing chelating agents to wash metal-contaminated soils

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PAH contaminated soil remediation by reusing an aqueous solution of cyclodextrins

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