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Crosslinked poly(N,N-dimethylacrylamide) hydrogel samples were synthesized with various total comonomer concentrations and crosslinker ratios in the reacting mixture, and at two different temperatures: room temperature and the boiling point of the reacting mixture, about 80 • C. During gelation of samples prepared at the higher temperature, the bubbles of the boiling system were trapped in positions homogeneously distributed, and post-gel reactions fixed them. These samples were macroporous, showing about three times the swelling capacity of conventional hydrogels synthesized at room temperature with the same composition. Both types of hydrogel swollen at equilibrium in water deswelled exponentially with time when they were immersed in acetone or dioxane. The rate of shrinking was higher for macroporous than for conventional samples and it was smaller in dioxane, the solvent with higher viscosity (η), although there was no proportionality to the solvent fluidity, η −1 . The morphology, which was in the scale of micrometres (as revealed by scanning electron microscopy), played a minor role in the shrinking rates of both types of gels. The excess swelling and the faster solvent response of macroporous gels were ascribed to the store and draining capacity of macropores at the millimetre scale.

This work attempts to study the interaction of two ionic liquids (1-ethyl-3-methylimidazolium tosylate and 1-hexyl-3-methylimidazolium chloride) with chemically crosslinked poly(N-vinylimidazole) in aqueous media, and to compare it with that of NaCl, a typical salting-out electrolyte. The three salts show a salting-in effect whose intensity was measured on the basis of the decrease of the polymer-solvent interaction parameter and the increase of swelling with increasing ionic strength. It was thus found that the salting-in effect is the same for the two salts with the same anion (chloride), while the intensity of the salting-in effect exerted by the tosylate ionic liquid is larger. The coefficient of selective sorption, which expresses the salt excess inside the swollen gel with respect to the external solution was determined by comparing the initial and equilibrium compositions of the immersion bath. These results are discussed in terms of the hydrophobic character of the ions involved.

Abstract:Water absorption of an epoxy resin was studied by steady-state fluorescence spectroscopy and gravimetry. It was found that the intrinsic emission of the epoxy resin could be modified selecting an adequate excitation wavelength. The epoxy component of the resin was labelled with a trans-4-nitro-4' -aminostilbene fluorescent probe. Using an excitation wavelength of340nm it was possible to induce energy transfer to the suitable acceptor trans-4-nitro-4' -dialkylaminostilbene (NDAS). The relative fluorescence intensity / 433 /1 596 was used as a convenient means to follow the quenching effect of water on the emission ofNDAS when excited via energy transfer. It was found that both the relative intensity and the water content increase linearly with the square root of diffusion time in the early stages of the process. The apparent Stem-Volmer constants for the quenching of the fluorophore, when excited directly in a fluid THF solution or in the polymer matrix, were very similar but lower than when the fluorophore was excited via energy transfer. It was concluded that, at least in the early stages of the water diffusion process, the interchromophoric distance should increase.

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