Now showing items 21-31 of 31

  • Optical energy band gap of PAAm-GO composites 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Elsevier Science, 2018)
    Graphene oxide (GO) can be used as an electron acceptor for polymers. The generation of the exciton in such materials is intimately related to the optical band gap. Polyacrylamide (PAAm) - graphene oxide (GO) composites were prepared via free radical crosslinking copolymerization with GO content varying in the range between 5 and 40 mu l of GO. The influence of the GO content on the optical properties of the composites is characterized by ultraviolet visible spectrophotometer. The optical band gap ...

  • Phase Transitions in Pure and Hybrid Hydrogels: A Fluorescence Study 

    Authors:Aktas, Demet Kaya; Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Wiley, 2009)
    Recent observations on phase transitions around the critical point showed that the critical exponents differed drastically from percolation results and classical results for pure hydrogel systems depending on monomer concentration. in addition to pure hydrogels the sol-gel phase transition during radical crosslinking copolymerization of acrylamide (AAm) and N-isopropylacrylamide (NIPA) hybrid was studied by using the steady state fluorescence (SSF) technique. NN'-methylenebis(acrylamide) (BIS) and ...

  • Steady state fluorescence technique for studying phase transitions in PAAm-PNIPA mixture 

    The steady state fluorescence (SSF) technique was used to study the sol-gel phase transition during free radical crosslinking copolymerisation of various amounts of acrylamide (AAm) and N-isopropylacrylamide (NIPA) mixtures. NN'-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator respectively. Pyranine (8-hydroxypyrene-1 3 6-trisulfonic acid trisodium salt HPTS) was added as a fluoroprobe for monitoring the polymerisation. It was observed that ...

  • Studies on Drying and Swelling of PAAm-NIPA Composites in Various Compositions 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Wiley-Blackwell, 2011)
    The steady-state fluorescence technique was introduced for studying the drying and swelling of disc-shaped PAAm-NIPA composites. Disc-shaped gels were formed with various acrylamides (AAm) and N-isopropylacrylamides (NIPA) by free radical crosslinking copolymerization in water. Composites were prepared with pyranine (Py) doped as a fluorescence probe. Scattered light I(sc) and fluorescence intensities I were monitored during drying of these gels. The fluorescence intensity of pyranine increased ...

  • Superelastic percolation network of polyacrylamide (PAAm)-kappa carrageenan (kappa C) composite 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Springer, 2013)
    The elasticity of the polyacrylamide (PAAm)-kappa carrageenan (kappa C) composite was determined as a function of (w/v-%) kappa C content at 40 A degrees C. The gel composites studied contained various percentages (w/v-%) of kappa C. The elasticity of the swollen PAAm-kappa C composite was characterized by using the tensile testing technique. This study investigated the elasticity and the percolation threshold of PAAm-kappa C composite as a function of kappa C content. It is understood that the ...

  • Surfactant and Metal Ion Effects on the Mechanical Properties of Alginate Hydrogels 

    This paper addresses the controlled variation of the mechanical properties of alginate gel beads by changing the alginate concentration or by adding different surfactants or cross-linking cations. Alginate beads containing nonionic Brij 35 or anionic sodium dodecyl sulfate (SDS) surfactants were prepared with two different types of cations (Ca2+ Ba2+) as crosslinkers. Compression measurements were performed to investigate the effect of the surfactant and cation types and their concentrations on ...

  • Swelling Kinetics of PAAm-kappa-Carrageenan Composites: A Fluorescence Technique 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Taylor & Francis Inc, 2011)
    The steady-state fluorescence (SSF) technique was introduced for studying swelling of disc-shaped polyacrylamide (PAAm) gels containing various amount of kappa-carrageenan (kappa C). They were prepared by free-radical cross-linking copolymerization. N N'-methylenebisacrylamide (BIS) and ammonium persulfate (APS) were added as a crosslinker and an initiator respectively. Composite gels were prepared at 80 degrees C with pyranine as a fluorescence probe. After drying of these gels swelling kinetics ...

  • Temperature Effect on the Elasticity of Acrylamide-n-Isopropylacrylamide Copolymers 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Taylor & Francis Inc, 2018)
    Acrylamide (AAm) - N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with various weight percentages (wt%) of AAm and NIPA. The temperature dependence of the compressive elastic modulus G and toughness U-TU- of the PAAm- NIPA copolymers due to a volume phase transition was found using a compressive testing technique. It was observed that the compressive elastic modulus increased comprehensively when the temperature was increased between 30 degrees ...

  • Temperature effect on the swelling of PAAm-kappa-carrageenan composites 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(Wiley-Blackwell, 2012)
    The steady-state fluorescence (SSF) technique was used for studying swelling of disc-shaped polyacrylamide (PAAm)-kappa-carrageenan (kappa C) composites which were prepared by free-radical crosslinking copolymerization at 80 degrees C. Pyranine was introduced as a fluorescence probe during polymerization. Swelling experiments were performed in water at various temperatures by real-time monitoring of the pyranine (Py) fluorescence intensity I which decreased as swelling proceeded. Stern-Volmer ...

  • The Role of Pyranine in Characterization of PAAm-kappa C Composites by Using Fluorescence Technique 

    Polyacrylamide (PAAm) doped by kappa-carrageenan (kappa C) gels were prepared with various amounts of kappa C varying in the range between 0 wt.% and 3 wt.%. Steady-state fluorescence (SSF) technique was employed for studying sol-gel transition and swelling of PAAm-kappa C composite gels which were prepared by free-radical crosslinking copolymerization. Pyranine was introduced as a fluorescence probe. Pyranine molecules start to bind to acrylamide polymer chains upon the initiation of the ...

  • Universality of elasticity on PAAM-NIPA copolymer gels 

    Authors:Evingür, Gülşen Akin; Pekcan, Önder
    Publisher and Date:(EDP Sciences, 2015)
    Polyacrylamide (PAAm)-N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with different molar of NIPA varying in the range between 0 and 2 M. The mechanical properties of swollen PAAm-NIPA copolymers were characterized by the compressive testing technique. It is understood that the compressive elastic modulus was found to increase by increasing NIPA contents keeping temperature constant at 30 degrees C. The critical exponent of elasticity y above ...