Investigations Electrochimiques des Systemes Redox: Fe3+, Fe(lll)-Complexe, Cu2+, Cu(ll)-Complexe - meta-Bisulfite de Sodium, Initiateurs de Polymerisation de l\u27 Acrylamide en Milieu Aqueux

Plusieurs systemes redox du type: Fe3+, Fe(III)-complexe, Cu2+, Cu(II)-complexe - meta-bisulfite de sodium (Na2S20 5), ont ete etudies, potentiometriquement et potentiodynamiquement en vue de la possibilite d\u27initier la polymerisation de l\u27acrylamide dans un milieu aqueux. A titre de complexant (reactifs de complexation), a ete utilise un ensemble d\u27amines carboxyles avec un groupe iminodiacetique comme element principal, et on a pu constater !\u27influence de !\u27introduction de substituants nouveaux et surtout de nouveaux groupes iminodiacetiques, ainsi que !\u27influence de certaines particularites dans la structure ou de facteurs steriques sur la capacite des complexants a produire des complexes, et sur la stabilite des complexes ainsi formes. Dans toutes ces recherches on a remarque une dependance, en general reguliere et clairement manifestee, de la stabilite des complexes. Les methodes electrochimiques susmentionnees et !\u27electrolyse a potentiel contr6le ont permis de proposer le mecanisme reactionnel le plus probable dans les systemes initiateurs. Several redox systems of the type: Fe3+, Fe(III)-complex, Cu"+, Cu(II)-complex - Na2S20 5, were studied using p0tentiodynamic and potentiometric techniques, in order to evaluate their potential to initiate acrylamide polymerisation in aqueous media. A group of carboxylate amines, with the iminodiacetate group as a basic structural unit, were used as complexing agents in order to follow the effect of the increased coordination ability resulting from the new substituents involved, especially the new iminodiacetate groups. In addition the effects of structural and steric factors on the ability of an agent to form complexes and on the strength of the resulting complexes were examined. In all cases a clear effect of the complex strength factor was found; electrolysis at controlled potential and electrochemical methods allow the most probable reaction mechanism of the initiator systems to be proposed

The Kinetics of Polyacrylamide Adsorption on Polycrystalline Gold

Fast potential step measurements (0.9 ® 1.9 ® 0.9 V, E vs. she) with simultaneous monitoring of the double layer capacity were applied in the study of the kinetics of PAA adsorption on gold from 0.5 M H2SO4, at 293 K. It was shown that the addition of PAA to the solution at 1.9 V (in the presence of a very thin oxide layer at the gold surface of 1 nm) does not affect the value of the capacity of the Au/Au2O3/PAA-solution interface, which was also confirmed by Electrochemical Impedance Spectroscopy. After the very fast cathodic reduction of the thin oxide layer (step 1.9 ® 0.9 V) for several milliseconds, the initial adsorption of PAA molecules at the bare gold surface reappeared in approx. 10 ms, causing exhaustion of the metal/solution boundary layer. The induction region (dq/dt = 0) as well as the diffusion controlled region (dq/dt = const. = f Mn((PAA); cPAA) are characteristic of low concentrations in the solution. According to the experimentally obtained linear parts of the (q / logt)-dependences, values of the diffusion coefficient of PAA-molecules with different molecular weights were calculated. These values follow fairly well the empirical equation: DPAA = 7.03 × 10–4 Mn–0.66 cm2 s–1. Using the same procedure, the diffusion coefficient of 9 × 10–6 cm2 s–1 for adsorption of »small« organic molecules, such as HMBT, was calculated

Poli(laktid-ko-glikolid) mikročestice kao sustav za kontrolirano oslobađanje proteina: priprava i karakterizacija

Poly(DL-lactide-co-glycolide) (PDLLGA) and poly(L-lactide-co-glycolide) (PLLGA) copolymers were prepared by bulk ring opening polymerization of lactide and glycolide and characterized by GPC, FTIR, 1H NMR and DSC. Copolymers with different molar masses at a constant lactide/glycolide ratio were used for preparation of bovine serum albumin (BSA)-loaded microparticles by the double emulsion w/o/w method. The influence of the copolymer molar mass and composition on the microparticle morphology, size, yield, degradation rate, BSA-loading efficiency and BSA release profile were studied. For microparticles prepared from PDLLGA copolymers, a biphasic profile for BSA release was found and for those made from PLLGA copolymers the release profile was typically triphasic; both of them were characterized by high initial burst release. Possible reasons for such behavior are discussed.Poli(DL-laktid-ko-glikolid) (PDLLGA) i poli(L-laktid-ko-glikolid) (PLLGA) kopolimeri priređeni su polimerizacijom laktida i glikolida uz otvaranje prstenova i karakterizirani pomoću GPC, FTIR, 1H NMR i DSC. Kopolimeri različitih molarnih masa i stalnog omjera laktida i glikolida upotrebljeni su za pripravu mikročestica s goveđim serumskim albuminom (BSA) metodom dvostruke emulzije tipa voda/ulje/voda. Proučavan je utjecaj molarne mase i sastava kopolimera na oblik, veličinu, iskorištenje i stupanj razgradnje mikročestica, uklapanje i oslobađanje BSA. Za mikročestice pripravljene s PDLLGA kopolimerom utvrđen je bifazični profil oslobađanja BSA, a za mikročestice s PLLGA kopolimerom trifazičan profil. Za obje vrste karakteristično je brzo početno oslobađanje. Razmatrani su mogući uzroci takvog ponašanja

Biocompatible Polymer Blends of Poly(D,L-lactic acid-co-glycolic acid) and Triblock PCL-PDMS-PCL Copolymers: Their Characterizations and Degradations

Polymer blends of poly(D,L-lactic-co-glycolic acid), PDLLGA, and triblock polycaprolactonepoly(dimethylsiloxane)-polycaprolactone (PCL-PDMS-PCL) copolymer, TEGOMER, were obtained by coprecipitation from their chloroform mixed solutions into methanol and were characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), degradation tests and scanning electron microscopy (SEM). Binary blends of PDLLGA/TEGOMER were found to be partially miscible according to DSC measurements and FTIR analysis. Stressstrain results showed that addition of TEGOMER improved significantly the overall toughness of PDLLGA. Degradation of PDLLGA/TEGOMER blends was investigated in phosphate buffered saline at pH = 7.4 and 37 °C, and the morphology of the blends during degradation was examined by scanning electron microscopy

Corrosion inhibition of iron in hydrochloric acid by polyacrylamide

The corrosion protection and/or adsorption of polyacrylamide (PAA) of number average molecular weight, , between 15,000 – 1,350,000 g mol-1 on mild steel and iron (99.99 % Fe) in 3 M HCl at room temperature was studied using spectrophotometry (the phenanthroline method), the weight loss method and EIS (Electrochemical Impedance Spectroscopy). It was found that the corrosion protect­tion efficiency of the PAA – adsorbed layers strongly depends on both the molar concentration of PAA in the solution and its molecular weight, reaching limiting values between 85 and 96 %. Simultaneously, it was also concluded that a relatively high surface coverage could be obtained with very low PAA concentrations (0.5 – 2 ppm), indicating the good adsorption characteristics of PAA on mild steel and iron in hydrochloride acid. The experimentally obtained results follow a Lan­gmuir adsorption isotherm. According to the best fitting parameters, the adsorption coef­f­i­cient B ranged between 2×107 and 4×108 mol-1 and depended strongly on the mole­cular weight of the PAA: B = k (for a ≈ 0.67 and k = 2.95×104) or the size of the polymer coil. As was found by EIS, the thickness of the adsorbed PAA layer was approx. 1.1 nm (for er = 15) and corresponded only to the polymer segments attached to the metal surface. On the other hand, as was found by ellipsometry, the limiting layer of the adsorbed PAA molecules was highly voluminous and relatively thick (100 – 200 nm), containing entangled polymer coils