Volkan Can - Academia.edu (original) (raw)
Papers by Volkan Can
ACS Applied Bio Materials
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) ... more Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalısma kapsamında, nanokompozit hidrojellerin sisme ve elastik davranısları arastırılmıstır. Hidrojeller, sulu kil süspansiyonu içerisinde akrilamid (AAm) monomerinin serbest radikal polimerizasyonu ile 5 0C‘de sentezlenmistir. Reaksiyonlar kimyasal bir çapraz baglayıcı olan N,N’-metilenbis(akrilamid) (BAAm) varlıgında gerçeklestirilmistir. Bulgular, hidrofilik polimer bileseni olan PAAm ve kil bileseni olan Laponit XLS ile sentezlenen nanokompozit hidrojellerin normal jellerde görülmeyen bir sisme davranısına sahip oldugunu göstermistir. Buna göre jeller suya atıldıklarında, yaklasık bir gün süreyle siserek bir maksimum degere ulasmaktadır. Jellerin su içerisinde kalma süreleri arttırıldıgında ise sisme degerleri azalarak, yaklasık 5 gün içinde bir sınır degere ulasmaktadırlar. Bu sisme davranısı sadece kil k...
Macromolecules, 2016
Materials. n-octadecyl acrylate (C18A, Sigma-Aldrich), sodium dodecylsulfate (SDS, Sigma-Aldrich)... more Materials. n-octadecyl acrylate (C18A, Sigma-Aldrich), sodium dodecylsulfate (SDS, Sigma-Aldrich), NaCl (Merck), ammonium persulfate (APS, Sigma-Aldrich), and sodium metabisulfite (SMS, Merck) were used as received. Acrylic acid (AAc, Merck) was freed from its inhibitor by passing through an inhibitor removal column (Sigma-Aldrich). The supramolecular hydrogels were prepared by conducting the micellar copolymerization of AAc and C18A at 55 °C in aqueous 1.5 M NaCl solutions containing 22 w/v% SDS. Because C18A is insoluble in SDS solutions, we added NaCl into the surfactant solution to induce the micellar growth and thus, to solubilize C18A in the grown SDS micelles. 1 C18A content in the comonomer feed was varied between 20 and 50 mol% C18A while the total monomer concentration was fixed at 1.0 M. The polymerization reaction was initiated using a redox initiator system consisting of 0.79 mM APS and 1 mM SMS. The reactions were conducted for 24 h in plastic syringes of 4.8 mm internal diameter as well as between two glass plates (5x5 cm) separated by a 0.5 mm Teflon spacer. Swelling and gel fraction measurements. Hydrogel samples were immersed first in ethanol for 3 days and then in a large excess of water at 24 °C for 1 month by replacing water every day to extract any
RSC Advances, 2016
A photo-decomposable hydrophobic crosslinker was synthesized and utilized to obtain photo-tunable... more A photo-decomposable hydrophobic crosslinker was synthesized and utilized to obtain photo-tunable hydrogelsviafree radical micellar copolymerization.
Soft Matter, 2015
Triple network hydrogels based on hyaluronan and poly(N,N-dimethylacrylamide) containing 81–91% w... more Triple network hydrogels based on hyaluronan and poly(N,N-dimethylacrylamide) containing 81–91% water sustain compressive stresses above 20 MPa and exhibit Young's moduli of up to 1 MPa.
The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigate... more The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigated. The hydrogels were prepared by free- radical polymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA), and N-isopropylacrylamide (NIPA) in aqueous clay suspensions at 21 � C. Laponite with a radius of gyration in distilled water of 20 nm was used as clay particles in the hydrogel preparation.
Macromolecules, 2014
Among the hydrogels prepared in recent years, double network (DN) hydrogels exhibit the highest c... more Among the hydrogels prepared in recent years, double network (DN) hydrogels exhibit the highest compression strength, toughness, and fracture energies. However, synthesis of DN hydrogels with extraordinary mechanical properties is limited to polyelectrolyte networks, which hinders their widespread applications. Herein, we prepared nonionic DN and triple network (TN) hydrogels based on polyacrylamide (PAAm) and poly(N,N-dimethylacrylamide) (PDMA) with a high mechanical strength by sequential polymerization reactions. The TN approach is based on the decrease of the translational entropy of the second monomer upon its polymerization in the first network, so that additional solvent (third monomer) can enter into DN hydrogel to assume its new thermodynamic equilibrium. The first network of TN hydrogels comprises chemically cross-linked PAAm or PDMA while the second and third networks are linear polymers. To increase the degree of inhomogeneity of the first network hydrogel, an oligomeric ethylene glycol dimethacrylate was used as a cross-linker in the gel preparation. Depending on the concentration of the first network cross-linker and on the molar ratio of the second and third to the first network units, TN hydrogels contain 89−92% water and exhibit high compressive fracture stresses (up to 19 MPa) and compressive moduli (up to 1.9 MPa).
Journal of Macromolecular Science, Part A, 2006
The swelling behavior of acrylamide (AAm)-based polyampholyte hydrogels in water and in aqueous s... more The swelling behavior of acrylamide (AAm)-based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. [(Methacrylamido)propyl]trimethyl-ammonium chloride (MAPTAC) and acrylic acid (AAc) were used as the ionic comonomer in the hydrogel preparation. Three sets of hydrogels containing 70 mol% AAm and 30 mol% ionic comonomers of varying mole ratios were prepared. The variations of the hydrogel volume in response to changes in pH, and salt concentration were measured. As pH increases from 1, the hydrogel volume V eq in water first increases and reaches a maximum value at a certain pH. Then, it decreases again with a further increase in pH and attains a minimum value around the isoelectric point (IEP). After passing the collapsed plateau region, the gel reswells again up to pH ¼ 7.1. The reswelling of the collapsed gels containing 10 and 4% MAPTAC occurs as a first-order phase transition at pH ¼ 5.85 and 4.35, respectively, while the hydrogel with 1% MAPTAC reswells continuously beyond its IEP. Depending on pH of the solution, the hydrogels immersed in salt solutions exhibit typical polyelectrolyte or antipolyelectrolye behavior. The experimental swelling data were compared with the predictions of the Flory-Rehner theory of swelling equilibrium including the ideal Donnan equilibria. It was shown that the equilibrium swelling theory qualitatively predicts the experimental behavior of polyampholyte hydrogels.
Thiol-ene networks were synthesized at different monomer concentrations by using difunctional tri... more Thiol-ene networks were synthesized at different monomer concentrations by using difunctional triethyleneglycol divinylether monomer and tetrafunctional pentaerithritol trimercaptopropionate crosslinker. The studied network is thought to have a homogenous structure due to the stepgrowth nature of the polymerization mechanism during synthesis. The aim of this thesis was to investigate this idea with the help of various methods such as rheology and dynamic light scattering. Measurements are conducted during and after synthesis of thiol-ene networks. Rheological measurements showed that the gelation reaction via the thiol-ene mechanism is quite rapid and the gels synthesized have a relatively high crosslinking efficiency up to 60% with respect to the predictions of phantom network model. This was explained by the high monomer conversion at the gel point. Syneresis is observed for the networks below 20% (w/v) monomer concentration due to the contraction of the network as the clusters me...
Designed Monomers and Polymers, 2005
Disc-shaped clay particles (Laponite) with a thickness of 1 nm and a diameter of 25 nm were bridg... more Disc-shaped clay particles (Laponite) with a thickness of 1 nm and a diameter of 25 nm were bridged into a physical gel (shake gel) by poly(ethylene oxide) (PEO) chains under shear. The shake gels formed transformed again into a liquid when the shear stopped. The critical concentrations of Laponite and PEO required for the shake gel formation were determined. The results show that the molecular weight of the polymer chains significantly affects the critical concentrations, as well as the mechanical properties of gels. Shake gels form under certain concentrations of Laponite and PEO, corresponding to a critical surface coverage valuen PEO of the Laponite particles by the polymer chains. The value ofn PEO decreases as the molecular weight of PEO is increased. It was shown that strong gels with a relaxation time longer than 30 min form if the polymer molecular weight is in the range of 2 × 10 5-3 × 10 5 g/mol.
ACS Applied Bio Materials
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) ... more Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalısma kapsamında, nanokompozit hidrojellerin sisme ve elastik davranısları arastırılmıstır. Hidrojeller, sulu kil süspansiyonu içerisinde akrilamid (AAm) monomerinin serbest radikal polimerizasyonu ile 5 0C‘de sentezlenmistir. Reaksiyonlar kimyasal bir çapraz baglayıcı olan N,N’-metilenbis(akrilamid) (BAAm) varlıgında gerçeklestirilmistir. Bulgular, hidrofilik polimer bileseni olan PAAm ve kil bileseni olan Laponit XLS ile sentezlenen nanokompozit hidrojellerin normal jellerde görülmeyen bir sisme davranısına sahip oldugunu göstermistir. Buna göre jeller suya atıldıklarında, yaklasık bir gün süreyle siserek bir maksimum degere ulasmaktadır. Jellerin su içerisinde kalma süreleri arttırıldıgında ise sisme degerleri azalarak, yaklasık 5 gün içinde bir sınır degere ulasmaktadırlar. Bu sisme davranısı sadece kil k...
Macromolecules, 2016
Materials. n-octadecyl acrylate (C18A, Sigma-Aldrich), sodium dodecylsulfate (SDS, Sigma-Aldrich)... more Materials. n-octadecyl acrylate (C18A, Sigma-Aldrich), sodium dodecylsulfate (SDS, Sigma-Aldrich), NaCl (Merck), ammonium persulfate (APS, Sigma-Aldrich), and sodium metabisulfite (SMS, Merck) were used as received. Acrylic acid (AAc, Merck) was freed from its inhibitor by passing through an inhibitor removal column (Sigma-Aldrich). The supramolecular hydrogels were prepared by conducting the micellar copolymerization of AAc and C18A at 55 °C in aqueous 1.5 M NaCl solutions containing 22 w/v% SDS. Because C18A is insoluble in SDS solutions, we added NaCl into the surfactant solution to induce the micellar growth and thus, to solubilize C18A in the grown SDS micelles. 1 C18A content in the comonomer feed was varied between 20 and 50 mol% C18A while the total monomer concentration was fixed at 1.0 M. The polymerization reaction was initiated using a redox initiator system consisting of 0.79 mM APS and 1 mM SMS. The reactions were conducted for 24 h in plastic syringes of 4.8 mm internal diameter as well as between two glass plates (5x5 cm) separated by a 0.5 mm Teflon spacer. Swelling and gel fraction measurements. Hydrogel samples were immersed first in ethanol for 3 days and then in a large excess of water at 24 °C for 1 month by replacing water every day to extract any
RSC Advances, 2016
A photo-decomposable hydrophobic crosslinker was synthesized and utilized to obtain photo-tunable... more A photo-decomposable hydrophobic crosslinker was synthesized and utilized to obtain photo-tunable hydrogelsviafree radical micellar copolymerization.
Soft Matter, 2015
Triple network hydrogels based on hyaluronan and poly(N,N-dimethylacrylamide) containing 81–91% w... more Triple network hydrogels based on hyaluronan and poly(N,N-dimethylacrylamide) containing 81–91% water sustain compressive stresses above 20 MPa and exhibit Young's moduli of up to 1 MPa.
The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigate... more The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigated. The hydrogels were prepared by free- radical polymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA), and N-isopropylacrylamide (NIPA) in aqueous clay suspensions at 21 � C. Laponite with a radius of gyration in distilled water of 20 nm was used as clay particles in the hydrogel preparation.
Macromolecules, 2014
Among the hydrogels prepared in recent years, double network (DN) hydrogels exhibit the highest c... more Among the hydrogels prepared in recent years, double network (DN) hydrogels exhibit the highest compression strength, toughness, and fracture energies. However, synthesis of DN hydrogels with extraordinary mechanical properties is limited to polyelectrolyte networks, which hinders their widespread applications. Herein, we prepared nonionic DN and triple network (TN) hydrogels based on polyacrylamide (PAAm) and poly(N,N-dimethylacrylamide) (PDMA) with a high mechanical strength by sequential polymerization reactions. The TN approach is based on the decrease of the translational entropy of the second monomer upon its polymerization in the first network, so that additional solvent (third monomer) can enter into DN hydrogel to assume its new thermodynamic equilibrium. The first network of TN hydrogels comprises chemically cross-linked PAAm or PDMA while the second and third networks are linear polymers. To increase the degree of inhomogeneity of the first network hydrogel, an oligomeric ethylene glycol dimethacrylate was used as a cross-linker in the gel preparation. Depending on the concentration of the first network cross-linker and on the molar ratio of the second and third to the first network units, TN hydrogels contain 89−92% water and exhibit high compressive fracture stresses (up to 19 MPa) and compressive moduli (up to 1.9 MPa).
Journal of Macromolecular Science, Part A, 2006
The swelling behavior of acrylamide (AAm)-based polyampholyte hydrogels in water and in aqueous s... more The swelling behavior of acrylamide (AAm)-based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. [(Methacrylamido)propyl]trimethyl-ammonium chloride (MAPTAC) and acrylic acid (AAc) were used as the ionic comonomer in the hydrogel preparation. Three sets of hydrogels containing 70 mol% AAm and 30 mol% ionic comonomers of varying mole ratios were prepared. The variations of the hydrogel volume in response to changes in pH, and salt concentration were measured. As pH increases from 1, the hydrogel volume V eq in water first increases and reaches a maximum value at a certain pH. Then, it decreases again with a further increase in pH and attains a minimum value around the isoelectric point (IEP). After passing the collapsed plateau region, the gel reswells again up to pH ¼ 7.1. The reswelling of the collapsed gels containing 10 and 4% MAPTAC occurs as a first-order phase transition at pH ¼ 5.85 and 4.35, respectively, while the hydrogel with 1% MAPTAC reswells continuously beyond its IEP. Depending on pH of the solution, the hydrogels immersed in salt solutions exhibit typical polyelectrolyte or antipolyelectrolye behavior. The experimental swelling data were compared with the predictions of the Flory-Rehner theory of swelling equilibrium including the ideal Donnan equilibria. It was shown that the equilibrium swelling theory qualitatively predicts the experimental behavior of polyampholyte hydrogels.
Thiol-ene networks were synthesized at different monomer concentrations by using difunctional tri... more Thiol-ene networks were synthesized at different monomer concentrations by using difunctional triethyleneglycol divinylether monomer and tetrafunctional pentaerithritol trimercaptopropionate crosslinker. The studied network is thought to have a homogenous structure due to the stepgrowth nature of the polymerization mechanism during synthesis. The aim of this thesis was to investigate this idea with the help of various methods such as rheology and dynamic light scattering. Measurements are conducted during and after synthesis of thiol-ene networks. Rheological measurements showed that the gelation reaction via the thiol-ene mechanism is quite rapid and the gels synthesized have a relatively high crosslinking efficiency up to 60% with respect to the predictions of phantom network model. This was explained by the high monomer conversion at the gel point. Syneresis is observed for the networks below 20% (w/v) monomer concentration due to the contraction of the network as the clusters me...
Designed Monomers and Polymers, 2005
Disc-shaped clay particles (Laponite) with a thickness of 1 nm and a diameter of 25 nm were bridg... more Disc-shaped clay particles (Laponite) with a thickness of 1 nm and a diameter of 25 nm were bridged into a physical gel (shake gel) by poly(ethylene oxide) (PEO) chains under shear. The shake gels formed transformed again into a liquid when the shear stopped. The critical concentrations of Laponite and PEO required for the shake gel formation were determined. The results show that the molecular weight of the polymer chains significantly affects the critical concentrations, as well as the mechanical properties of gels. Shake gels form under certain concentrations of Laponite and PEO, corresponding to a critical surface coverage valuen PEO of the Laponite particles by the polymer chains. The value ofn PEO decreases as the molecular weight of PEO is increased. It was shown that strong gels with a relaxation time longer than 30 min form if the polymer molecular weight is in the range of 2 × 10 5-3 × 10 5 g/mol.