Effect of non-associated electrolyte solutions on the behaviour of poly(vinyl alcohol)-based hydrogels

The aim of this paper is to present the behaviour of the poly(vinyl alcohol) hydrogels [PVA-HG] in sodium and potassium chlorides aqueous solutions, due to their interactions. The tested [PVA-HG]-s have been obtained by repeated freezing and thawing cycles. White, heterogeneous hydrogels have been obtained. These hydrogels exhibit a mechanical active behaviour at their contact with electrolytes aqueous solutions, manifested by important changing in mass, volume and density of the hydrogel samples. These modifications could be explained by water elimination from the hydrogels that initially reached the equilibrium of swelling. The kinetic of the water desorption and the reversibility of this process, have been studied and some of the factors that influence this behaviour have been evidenced. The sensitivity of PVA hydrogels to electrolyte nature and concentration could be used in sensors design and also could explain some aspects of electrolytes diffusion through PVA membranes and targeted drugs delivery.     

Study of some properties of poly(N-vinyl imidazole) partially quaternized with n-butyl bromide aqueous solutions

This paper presents a study of the properties of aqueous solutions of poly(N-vinyl imidazole) quaternized with n-butyl bromide (PVIQ3). The influence of the temperature and polymer concentration on refractive index, electrical conductivity and surface tension was studied. The critical micelar concentration of PVIQ3 in aqueous solution was determined and correlated with the polymer solubility in water.All the PVIQ3 aqueous solutions properties were compared with those of poly(N-vinyl imidazole) (PNVI) and the influence of the quaternization process on the polymer properties was evidenced.     

Effect of alkylimidazolium based ionic liquids on the structure of UV-irradiated cellulose

In this paper, the influence of three alkylimidazolium-based ionic liquids with the same cation (1-ethyl-3-methylimidazolium) and different anions (chloride, tetrafluoroborate and hexafluorophosphate) on the structure and properties of cellulose, have been studied by using Fourier transform infrared spectroscopy measurements, fluorescence microscopy imaging, viscometric and methylene blue sorption tests. Cellulose treated with ionic liquids showed better stability to UV light, as demonstrated by the lower variations of the polymerization degree, carboxyl groups content, moisture index, crystallinity index, lateral order index and allomorph index, with the increase of the UV exposure period, by comparing to non-treated cellulose. The results show that the tested ionic liquids could be effective as “green” plasticizers and UV stabilizers for cellulose-based materials.     

Evaluation of ammonia absorption coefficients by photoacoustic spectroscopy for detection of ammonia levels in human breath

Photoacoustic spectroscopy represents a powerful technique for measuring extremely low absorptions independent of the path length and offers a degree of parameter control that cannot be attained by other methods. We report precise measurements of the ammonia absorption coefficients at the CO₂ laser wavelengths by using a photoacoustic (PA) cell in an extracavity configuration and we compare our results with other values reported in the literature. Ammonia presents a clear fingerprint spectrum and high absorption strengths in the CO₂ wavelengths region. Because more than 250 molecular gases of environmental concern for atmospheric, industrial, medical, military, and scientific spheres exhibit strong absorption bands in the region 9.2–10.8 μm, we have chosen a frequency tunable CO₂ laser. In the present work, ammonia absorption coefficients were measured at both branches of the CO₂ laser lines by using a calibrated mixture of 10 ppm NH₃ in N₂. We found the maximum absorption in the 9 μm region, at 9R(30) line of the CO₂ laser. One of the applications based on the ammonia absorption coefficients is used to measure the ammonia levels in exhaled human breath. This can be used to determine the exact time necessary at every session for an optimal degree of dialysis at patients with end-stage renal disease.     

Bioleaching of UO2 2+ ions from a Romanian poor uranium ore

The present paper deals with an experimental study on the bioleaching of a poor uranium ore by means of hydrophytic plants Lemna minor and Riccia fluitans, under various operating conditions. The maximum degree of bioleaching (42%) of the reduced uranium species to U(VI) has been attained for the ore-Lemna minor-alkaline carbonate solution system. The UO₂ ²⁺ ions amount accumulated in the plants is negligible as compared to the dissolved quantity, owing to the ionic competition between uranyl ions and the cations necessary to the mineral nutrition. The X-ray diffraction patterns prove that the uranium species in pyrochlore mineral are completely oxidized to U(VI), while thucolite is only partially turned into UO₂ ²⁺ ions, in the presence of living plants.     

PVA-DNA cryogel membranes: characterization, swelling, and transport studies

Double-stranded (ds) DNA from salmon testes has been incorporated into PVA hydrogels obtained by a technique of repeated freezing and thawing. The cryogels obtained are free of potential toxic species like chemical cross-linkers, and consequently, they can be used in pharmaceutical or medical applications. These cryogels show a good mechanical resistance and a white and opaque appearance caused by a heterogeneous porous structure. Encapsulated DNA molecules can be in a compacted or an extended conformation in the PVA matrix and can be controlled by tailoring the degree of crystallinity of the PVA network; this is supported by fluorescence microscopy and UV and FTIR spectroscopic studies. The two forms of encapsulated DNA were observed for different types of matrixes: an extended one in a more crystalline network and a globular one in a more amorphous one. Different associations of base pairs have also been observed. PVA cryogel crystallinity could be tailored by the cryogel contact with different salt solutions. Cryogel surface (scanning electron microscopy) and bulk morphology (porosimetry), swelling, DNA retention, and delivery kinetics have also been studied. All these investigations clearly show strong interactions between PVA and DNA.     

Effect of different electrolytes on the swelling properties of calyx[4]pyrrole-containing polyacrylamide membranes

Calix[4]pyrrole (1) was synthesized and characterized and this macrocycle was incorporated in polyacrylamide gels. The presence of meso-octamethyl-porphyrinogen inside of gel was checked using infrared spectroscopy, differential scanning calorimetry, and swelling studies. The swelling degree of these hydrogels in equilibrium with different electrolytes (NaCl, LiCl, KCl, CaCl₂ and AlCl₃) was measured in a concentration range 0.1-0.5 mol dm⁻³. Although no significant alterations in the swelling degree can be found for the different 1:1 electrolytes, when the cation charge of unsymmetrical electrolytes increases, the gel swells in a significant way. This swelling process is enhanced by the presence of calyx[4]pyrrole. The effect of alkaline hydrolysis of polaycrylamide-based hydrogels was also studied. The hydrolysed hydrogels collapse in the presence of the electrolytes; this behavior is dependent on the hydrolysis degree, electrolyte charge and calyx[4]pyrrole presence and concentration; the latter leads to polyacrylamide with tailor-made properties.