Person: ABDURRAHMANOĞLU, SUZAN
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ABDURRAHMANOĞLU
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SUZAN
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Publication Metadata only Preparation of homogeneous hydrogels by controlling the crosslinker reactivity and availability(TAYLOR & FRANCIS INC, 2008) ABDURRAHMANOĞLU, SUZAN; Abdurrahmanoglu, Suzan; Okay, OguzNetwork microstructures of polyacrylamide (PAAm) hydrogels were investigated by static light scattering measurements. The gels were prepared by free-radical crosslinking polymerization of acrylamide (AAm). To suppress the degree of gel inhomogeneity, the crosslinker reactivity during gelation was controlled by decreasing its availability in the reaction system. Our first approach was the addition of the crosslinker N,N'-methylenebis(acrylamide) (BAAm) in one or three portions during the course of the gelation reactions. As a second approach, a slightly water soluble crosslinker, namely ethylene glycol dimethacrylate (EGDM) was used as a crosslinker in AAm polymerization. Due to the low water solubility of EGDM, EGDM phase in the gelation system act as a reservoir of crosslinker so that the crosslinker can be supplied continuously to the aqueous reaction zone during the course of gelation. It was found that the delayed crosslinker addition technique further increases the degree of inhomogeneity of PAAm hydrogels. The results were explained with increasing viscosity of the reaction solution at the time of the crosslinker addition so that the crosslinking reactions are limited to local regions in the reaction system. The second approach, namely use of the slightly water soluble crosslinker EGDM significantly increases the degree of structural homogeneity of PAAm hydrogels.Publication Metadata only Unusual swelling behavior of polymer-clay nanocomposite hydrogels(ELSEVIER SCI LTD, 2007) ABDURRAHMANOĞLU, SUZAN; Can, Volkan; Abdurrahmanoglu, Suzan; Okay, OguzThe swelling behavior and the elastic properties of nanocomposite hydrogels have been investigated. The hydrogels were prepared by freeradical polymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA), and N-isopropylacrylamide (NIPA) in aqueous clay suspensions at 21 degrees C. Laponite with a radius of gyration in distilled water of 20 nm was used as clay particles in the hydrogel preparation. The reactions with AAm monomer were carried out in the presence of the chemical crosslinker N,N-methylenebis(acrylamide) (BAAm). It was found that the volume of nanocomposite hydrogels immersed in water rapidly increases and attains a maximum value after about one day. Surprisingly, further increase in the swelling time results in the deswelling of the gels until they reach a limiting swelling ratio after about 5 days. This unusual swelling behavior is observable only when the clay concentration in the hydrogel is above the overlap threshold c*. Swelling measurements combined with the elasticity tests show that the effective crosslink density first decreases, but then increases with increasing time of swelling of the hydrogels. The results were explained in terms of the rearrangements of the highly entangled polymer chains and clay particles during the gel volume change. (c) 2007 Elsevier Ltd. All rights reserved.Publication Metadata only Homogeneous Poly(acrylamide) Hydrogels Made by Large Size, Flexible Dimethacrylate Cross-Linkers(AMER CHEMICAL SOC, 2008) ABDURRAHMANOĞLU, SUZAN; Abdurrahmanoglu, Suzan; Okay, OguzPublication Metadata only Equilibrium swelling behavior and elastic properties of polymer-clay nanocomposite hydrogels(WILEY-BLACKWELL, 2008) ABDURRAHMANOĞLU, SUZAN; Abdurrahmanoglu, Suzan; Can, Volkan; Okay, OguzNanocomposite hydrogels were prepared by free-radical polymerization of the monomers acrylamide (AAm), NN-dimethylacrylamide (DMA), and N-iso-propylacrylamide (NIPA) in aqueous clay dispersions at 21 degrees C. Laponite XLS was used as clay nanoparticles in the hydrogel preparation. The hydrogels based on DMA or NIPA monomers exhibit much larger moduli of elasticity compared with the hydrogels based on AAm monomer. Calculations using the theory of rubber elasticity reveal that, in DMA-clay or NIPA-clay nanocomposites, both the effective crosslink density of the hydrogels and the functionality of the clay particles rapidly increase with increasing amount of Laponite up to 10% (w/v). The results suggest that DMA-clay and NIPA-clay attractive interactions are stronger than AAm-clay interactions due to the formation of multiple layers on the nanoparticles through hydrophobic associations. It was also shown that, although the nanocomposite hydrogels do not dissolve in good solvents such as water, they dissolve in dilute aqueous solutions of acetone or poly(ethylene oxide) of molecular weight 10,000 g/mol, demonstrating the physical nature of the crosslink points. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 109: 3714-3724,2008Publication Metadata only Dodecyl methacrylate as a crosslinker in the preparation of tough polyacrylamide hydrogels(ELSEVIER SCI LTD, 2011) ABDURRAHMANOĞLU, SUZAN; Abdurrahmanoglu, Suzan; Cilingir, Miray; Okay, OguzCopolymerization of acrylamide with dodecyl methacrylate (C12) solubilized in aqueous micelles of sodium dodecyl sulfate produces tough hydrogels exhibiting moduli of elasticity around 1 kPa. Swelling and gel fraction measurements show that the hydrophobic associations acting as temporary crosslinks are too strong to be destroyed in water during the expansion of the gel network. An order of magnitude larger value of loss factor tan delta of the hydrogels formed using the hydrophobe C12 as compared to the conventional hydrogels indicates the dynamic nature of their crosslink zones. The hydrogels are more homogeneous than the corresponding gels prepared by a chemical crosslinker, as determined by the static light scattering measurements. Mechanical tests indicate that, in addition to the dodecyl domains, permanent crosslinks are also needed to obtain hydrogels that are mechanically stable up to 250% elongation ratios. (C) 2010 Elsevier Ltd. All rights reserved.