Ömer Kantoğlu

The effect of external stimuli on the equilibrium swelling properties of poly(N-vinyl 2-pyrrolidone/itaconic acid) poly-electrolyte hydrogels

Hydrogels with varying crosslink densities and ionic moieties were prepared from the ternary systems N-vinyl 2-pyrrolidone/itaconic acid/water by irradiation with γ rays at ambient temperature. The influence of external stimuli such as pH, temperature and ionic strength of the swelling media and the type of buffer on the equilibrium swelling properties were investigated. Hydrogels showed typical pH response and temperature responses, such as high-pH and low-temperature swelling and low-pH and high-temperature deswelling. A change in the ionic strength of the swelling solution from 0.01 to 0.20 caused a decrease in the equilibrium degree of swelling of hydrogels. Oscillatory swelling behaviour was also observed and investigated in response to changes in the pH of the solution.

Biosynthesis and Characterization of Laccase Catalyzed Poly(Catechol)

Enzymatic polymerization of catechol was conducted batch-wise using laccase enzyme produced by the culture Trametes versicolor (ATCC 200801). The polymerization reaction was carried out in 1:1 (v/v) aqueous-acetone solution, buffered at pH 5.0 with sodium acetate (50 mM) in a sealed, temperature-controlled reactor at 25°C. The molecular weight of the produced polymer was determined with GPC. FT-IR, DSC, and TGA were employed to investigate the structure and thermal behavior of synthesized poly(catechol). It was found that catechol units were linked together with ether bonds and thermal stability of the catechol increased in the poly(catechol) polymeric structure effectively. The number average molecular weight of poly(catechol) was found as 813 ± 3 Da with a very narrow polydispersity value of 1.17 showing selective polymerization of catechol by the enzyme.

Effect of pH, ionic strength, and temperature on uranyl ion adsorption by poly(N‐vinyl 2‐pyrrolidone‐g‐tartaric acid) hydrogels

Poly-electrolyte N-vinyl 2-pyrrolidone-g-tartaric acid (PVP-g-TA) hydrogels with varying compositions were prepared in the form of rods from ternary mixtures of N-vinyl 2-pyrrolidone/tartaric acid/water. The effect of external stimuli, such as the solution pH, ionic strength, and temperature, on uranyl adsorption by these hydrogels was investigated. Uranyl adsorption capacities of the hydrogels were determined to be 53.2–72.2 (mg UO/g dry gel) at pH 1.8, and 35.3–60.7 (mg UO/g dry gel) at pH 3.8, depending on the amount of TA in the hydrogel. The adsorption studies have shown that the temperature and the ionic strength of the swelling solution also influence uranyl ion adsorption by PVP-g-TA hydrogels.

Equilibrium swelling behavior of pH- and temperature-sensitive poly(N-vinyl 2-pyrrolidone-g-citric acid) polyelectrolyte hydrogels

Hydrogels containing triprotic acid moieties sensitive to pH and ionic strength changes of the swelling medium were prepared from the ternary systems N-vinyl 2-pyrrolidone/citric acid/water by irradiation with g rays at ambient tempera- ture. Equilibrium swelling behavior of these hydrogels was studied using an equation, based on the phantom network theory of James-Guth and the approaches of Peppas et al., which was modified by the authors for determination of Mc and x parameter. The Mc and x parameters were related to equilibrium swelling behavior of the charged poly- meric network, pH, temperature, and ionic strength of the surrounding medium. The degree of swelling of these hydrogels decreases with these variables in accordance with expectation.

Thermal, Spectroscopic, and Mechanical Properties of Blend Films of Poly(N-Vinyl-2-Pyrrolidone) and Sodium Alginate

Blends of poly(N-vinyl-2-pyrrolidone) (PVP) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. These blends were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile strength test. The miscibility in the blends of PVP and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition-dependent glass transition temperatures (T g s), indicating that the blends are miscible in amorphous state. FT-IR studies indicate that there are the intermolecular hydrogen bonding interactions, i.e., –OH·····O=C in PVP/NaAlg blends. This blend films also exhibited the higher thermal stability and improved the elongation at break in dry states.

THE EFFECT OF EXTERNAL STIMULI ON THE URANYL IONS UPTAKE CAPACITY OF POLY(N-VINYL 2-PYRROLIDONE/ITACONIC ACID) HYDROGELS PREPARED BY GAMMA RAYS

The effect of external stimuli such as pH of the solution, ionic strength and temperature on the uranyl ions uptake capacity of poly(N-vinyl 2-pyrrolidone/itaconic acid) (P(VP/IA)) hydrogels was investigated. Polyelectrolyte P(VP/IA) hydrogels with varying compositions were prepared in the form of rods from ternary mixtures of N-vinyl 2-pyrrolidone/itaconic acid/water. Uranyl adsorption capacity of hydrogels were found to increase from 26.7 to 70 (mg UO22+ /g dry gel) with decreasing pH of the swelling solution. Adsorption studies have shown that other stimuli, such as temperature and ionic strength of the swelling solution have also influence on the uranyl ions uptake capacity of P(VP/IA) hydrogels.

Characterization of network structure of poly(N‐vinyl 2‐pyrrolidone/acrylic acid) polyelectrolyte hydrogels by swelling measurements

Poly(N-vinyl 2-pyrrolidone/acrylic acid) [P(VP/AA)] polyelectrolyte networks were prepared from the ternary mixtures N-vinyl 2-pyrrolidone/acrylic acid/water by using γ rays at ambient temperature. Equilibrium swelling behavior of these hydrogels was studied using an equation, based on the James–Guth phantom network theory and the approaches of Peppas et al., which was modified by the authors for determination of the Mc and χ parameters. The Mc and χ parameters were related to the equilibrium swelling behavior of the charged copolymeric network, pH, temperature, and ionic strength of the surrounding medium. The degree of swelling of these hydrogels was decreased with these variables, as expected. Oscillatory swelling behavior was also observed and investigated in response to changes in pH of the solution.

Polarographic determination of uranyl adsorption onto poly(acrylamide-g-ethylenediaminetetraacetic acid) hydrogels in the presence of cadmium and lead

Abstract Poly(acrylamide-g-ethylenediaminetetraacetic acid) [P(AAm-g-EDTA)] hydrogels with various compositions were prepared from ternary mixtures of acrylamide, ethylenediaminetetraacetic acid and water by using 60 Co γ-rays. This study showed that P(AAm-g-EDTA) hydrogels adsorb heavy metal ions such as UO 2 2+ in the presence of Pb 2+ and Cd 2+ selectively at certain pH’s. The external stimuli of pH, temperature and ionic strength play an important role on the adsorption behavior. Since a very sensitive electro-analytical technique, differential pulse polarography (DPP) was used for determination of UO 2 2+ adsorbed onto hydrogels (0.1–3.2 mg/g dry gel) from 5.0 mg/l aqueous solution without interfering Pb 2+ and Cd 2+ at certain pH’s. These hydrogels can be used directly as UO 2 2+ selective adsorbent for water and environmental pollutants without any pre-concentration techniques.

The Effect of Copolymer Composition on Surface Free‐Energy of Poly(2‐Hydroxyethyl Methacrylate–Crotonic Acid) Copolymers

Abstract Poly(2‐hydroxyethyl methacrylate–crotonic acid) P(HEMA/CrA) copolymers with varying compositions were prepared from ternary mixtures of 2‐hydroxyethyl methacrylate (HEMA)/crotonic acid (CrA)/water by using 60Co γ‐rays. The wetting forces were determined according to the Wilhelmy Plate Technique. Di‐iodomethane, ethylene glycol, and formamide were used as probe liquids. Lifshitz–van der Waals surface energy components, Lewis acid–base surface components, and total surface energies were calculated using van Oss et al. methodology. It was determined that Lifshitz–van der Waals component (γS LW) of the copolymers did not differ much from the copolymer composition. However, the electron‐donor surface free energy components (γS −) of the copolymers were decreased considerably with the increase of the CrA content of the copolymers, the surfaces of these copolymers were still found to have a basic character.