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Öğe Cation effects on phase transition of kappa-iota-carrageenan hybrids(Vsp Bv, 2007) Pekcan, Onder; Kara, Selim; Arda, ErtanPhase transitions of kappa-iota-carrageenan hybrid in various types of salts were studied using photon transmission technique: NaCl, KCI, MgCl2, CaCl2 and KCl+CaCl2 were chosen as the salt solutions for the carrageenan hybrid. Coil-to-helix (c-h), helix-to-dimer (h-d) and back to helix-to-coil (h-c), dimer-to-helix (d-h) phase transitions of carrageenan hybrid in these mono- and bivalent cation solutions were studied upon cooling and heating, respectively. Photon transmission intensity, It, was monitored against temperature to determine the (c-h), (h-d) and (h-c), (d-h) transition temperatures (T-ch, T-hd and T-hc, T-dh) and activation energies (Delta E-ch, Delta E-hd and Delta E-hc, Delta E-dh) of carrageenan hybrids. Two distinct transition regions were observed both during heating and cooling of the carrageenan-bivalent salt systems. During the heating process, at first dimers decompose into helices by making a (d-h) transition. Then at the high temperature region, a (h-c) transition takes place. During cooling, back transitions repeat themselves. However, the carrageenan-monovalent salt system presented only (c-h) and (h-c) transitions during the cooling and heating processes, respectively. A hysteresis was observed between (h-c)-(c-h) and (d-h)-(h-d) transitions for the monovalent and bivalent cation systems respectively.Öğe CMC/SWCNT biocomposites: A combined study on experiments, molecular simulations and continuum models(Elsevier, 2024) Mergen, Omer Bahadir; Gul, Ufuk; Kacar, Gokhan; Arda, Ertan; Aydogdu, MetinA comprehensive study is carried out including experimental, molecular dynamics (MD) simulations and continuum modelling of Carboxymethyl cellulose/Single walled carbon nanotube (CMC/SWCNT) biocomposites. The electrical, optical, and mechanical properties of CMC/SWCNT biocomposites were investigated in the experimental part of this work. In the result of measurements, it was determined that electrical conductivity (, d c ), absorbance level ( A ) and tensile modulus ( E ) of the composites increased significantly with the increase of SWCNT content in the CMC matrix. These physical changes in the CMC/SWCNT composites were explained by the percolation theory and the electrical and optical percolation thresholds ( R , and R op ) and the critical exponents ( fl , and fl op ) of these composites were calculated. In addition, MD simulations were performed to estimate the material properties for the polymer composite structures. The results of the tensile test experiments were found to qualitatively overlap with the experiments at low concentration range. Moreover, a homogenous distribution of SWCNTs were observed in the CMC matrix together with a strong level of interactions in between. In the continuum modelling a two parameters augmentation model is used. A coupled Mori -Tanaka -self consistent method is utilized when obtaining effective properties of composites. Experimental, MD and continuum modelling results of composites were compared and reasonable agreement was obtained between results.Öğe A comparative study on the AC/DC conductivity, dielectric and optical properties of polystyrene/graphene nanoplatelets (PS/GNP) and multi-walled carbon nanotube (PS/MWCNT) nanocomposites(Elsevier Sci Ltd, 2020) Mergen, Omer Bahadir; Umut, Evrim; Arda, Ertan; Kara, SelimPolystyrene/graphene nanoplatelets (PS/GNP) and polystyrene/multi-walled carbon nanotube (PS/MWCNT) nanocomposites were prepared through solution mixing processing. The effect of carbon filler (CF) (GNP or MWCNT) doping on the DC/AC electrical conductivity, dielectric characteristics and optical parameters (absorption coefficient, alpha and band gap energy, E-g) of nanocomposites were investigated and compared for similar doping concentrations. The observed behavior of the DC surface conductivity for PS/CF nanocomposites was explained according to the classical percolation theory, where the percolation thresholds (phi(c)) for PS/GNP and PS/MWCNT nanocomposites were determined as 12.0 vol% and 3.81 vol% and the critical exponents (t) were calculated as 2.19 and 2.13, respectively. These results indicate that CFs create three dimensional CF network in PS matrix. The dielectric relaxation properties and the AC conductivity studied by means of Broadband Dielectric Spectroscopy (BDS) measurements, showed that the presence of carbon fillers significantly enhanced the capacitive/charge storage capabilities of the nanocomposites. The optical band gap energies (E-g) of PS/GNP and PS/MWCNT nanocomposites were obtained by using Tauc method. From applicative point of view, with their enhanced dielectric and AC conductivity properties of the PS/GNP and PS/MWCNT nanocomposites have the potential to be used in energy storage and electromagnetic interference (EMI) shielding applications.Öğe A comparison of fluorescence and UV-visible spectrometry techniques for thermal phase transitions of agarose gels(Springer, 2015) Arda, Ertan; Kara, Selim; Mergen, Omer Bahadir; Pekcan, OnderIn this study, thermoreversible phase transitions of high (HMP) and low (LMP) melting point agarose gels were investigated by using the UV-vis and fluorescence spectroscopy techniques. Pyranine was added to the aqueous solution of agarose as a fluorescence-probe. Transmitted light (I (tr)) and fluorescence emission (I (fl)) intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. For the both techniques, gel-sol (T (gs)) and sol-gel (T (sg)) transition temperatures were determined from the first derivatives of the sigmoidal transition paths. It was observed that the critical transition temperatures obtained from UV-vis and fluorescence data slightly increased depending on the agarose type and concentration, and those values were found to be in accord with each other. Transition activation energies were determined using the Arrhenius type equation and were found to be strongly correlated with the agarose content in the gel system. The produced gel-sol (Delta E (gs)) and sol-gel (Delta E (sg)) transition energies from the fluorescence data were found to be lower than that of the UV-vis data, which was attributed to the temperature-dependent fluorescence quenching effect.Öğe Determination of electrical and optical behaviors of carboxymethyl cellulose/graphene nanocomposites(Springer, 2023) Mergen, Omer Bahadir; Arda, ErtanCarboxymethyl cellulose (CMC)/graphene nanoplatelet (GnP) nanocomposite films containing different volume fractions (0.00, 0.73, 1.46, 2.20, 2.94, and 3.68) were prepared by ultrasonication assisted solution casting method. The effect of GnPs on structural, electrical, optical properties, and dispersion parameters of the nanocomposite have been investigated by a fourier transform infrared (FTIR), scanning electron microscope (SEM), two-point probe resistivity measurement, UV-Vis absorbance, and reflectance spectroscopy. The direct (Ed) and indirect (Ei) optical band gap energies of nanocomposites were determined using Tauc and absorbance spectrum fitting (ASF) methods. The results demonstrated that the optical band gap energies could be adjusted by altering the GnP volume fraction. Additionally, it was found that the outcomes obtained through the Tauc and ASF methods were very close to each other. The electrical conductivity (& sigma;), Urbach energy (Eu), refractive index (n), dispersion energy (Edo), optical conductivity (& sigma;opt), and optical dielectric constant (& epsilon;) of CMC/GnP nanocomposite were found to increase with increasing GnP volume fraction (V). The improvements in structural, electrical, optical, dispersion parameters, and optical dielectric properties of these nanocomposites make them a potential candidate for many industrial applications.Öğe Effect of annealing rate on film formation from poly(vinyl acetate) latex particles(Taylor & Francis Ltd, 2008) Arda, Ertan; Kara, Selim; Pekcan, OenderThe photon transmission technique was used to monitor the time and temperature evolution of film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T-g) of PVAc. These films were annealed at various annealing rates above the Tg of PVAc. It was observed that transmitted photon intensity (I-tr) from these films increased at all annealing rates as the annealing time and temperature are increased. The increase in the I-tr is attributed to the increase in crossing density at the junction surface. The healing points (tau(H), T-H) were determined for various annealing rates and the healing activation energy (Delta H) was measured and found to be 43.4 kcal/mol. The interdiffusion (backbone) activation energies (Delta E) and reptation frequencies (nu) of PVAc chains were measured. The averaged value of Delta E was found to be 226.6 kcal/mol. It is observed that Delta E is unchanged but nu is increased as increasing the annealing rates.Öğe Effects of GNP addition on optical properties and band gap energies of PMMA films(Wiley, 2019) Mergen, Omer Bahadir; Arda, Ertan; Kara, Selim; Pekcan, OnderIn this study, the effects of graphene nanoplatelet (GNP) doping on the optical parameters (absorption coefficient, alpha and extinction coefficient, k) and the optical transition energies (optical band gap and Urbach energies) of poly(methyl methacrylate)/graphene nanoplatelet (PMMA/GNP) composite films were studied. PMMA/GNP composite films with various GNP mass fractions were prepared by spin coating technique. The absorbance (A) changes of the prepared composites were measured by using UV-Vis technique. The alpha and k values of the composites were obtained from UV-Vis data. The observed rapid increase in A values in UV-region were associated with the optical transitions of GNP electrons from valence to conduction band. The direct (E-d) and indirect (E-i) optical band gap energies of the composites were determined by using Tauc method. Both of the band gap energies were decreased when the GNP content in the PMMA matrix is increased. The decrease in the band gap energies was interpreted as evidence of increased conductivity of the composites. Additionally, energies of the band tails (Urbach energy) were calculated. It was seen that the Urbach energy levels were increased with GNP content. POLYM. COMPOS., 40:1862-1869, 2019. (c) 2018 Society of Plastics EngineersÖğe Electrical and optical percolations in PMMA/GNP composite films(Taylor & Francis Ltd, 2018) Arda, Ertan; Mergen, Omer Bahadir; Pekcan, OnderEffects of graphene nanoplatelet (GNP) addition on the electrical conductivity and optical absorbance of poly(methyl methacrylate)/graphene nanoplatelet (PMMA/GNP) composite films were studied. Optical absorbance and two point probe resistivity techniques were used to determine the variations of the optical and electrical properties of the composites, respectively. Absorbance intensity, A, and surface resistivity, R-s, of the composite films were monitored as a function of GNP mass fraction (M) at room temperature. Absorbance intensity values of the composites were increased and surface resistivity values were decreased by increasing the content of GNP in the composite. Electrical and optical percolation thresholds of composite films were determined as M-sigma = 27.5 wt.% and M-op = 26.6 wt.%, respectively. The conductivity and the optical results were attributed to the classical and site percolation theories, respectively. Optical ((op)) and electrical ((sigma)) critical exponents were calculated as 0.40 and 1.71, respectively.Öğe Electrical and optical percolations of polystyrene latex-multiwalled carbon nanotube composites(Academic Press Inc Elsevier Science, 2010) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, OenderElectrical conductivity and optical transmittance properties of polystyrene (PS)-multiwalled carbon nanotube (MWCNT) composite films were investigated. Composite films were prepared by mixing of various mass fractions of MWCNT in PS-water dispersions. After water evaporates, powder composite films were annealed at 175 degrees C above the glass transition of PS for 20 min. Photon transmission and two point probe resistivity techniques were employed to determine the variations of the optical and the electrical properties of composites. Transmitted light intensity, I(tr) and surface resistivity, R(s) were monitored as a function of MWCNT mass fraction (M). It was observed that, both the surface resistivity and the optical transparency were decreased by increasing the amount of MWCNT added to the polymeric system. Conductivity and optical results were interpreted according to the classical and site percolation theory, respectively. The electrical (sigma) and the optical (op) percolation threshold values and critical exponents were calculated as M(sigma) = 1.8 wt.%, M(op) = 0-0.13 wt.% and beta(sigma) = 2.25, beta(op) = 0.32, respectively. (C) 2010 Elsevier Inc. All rights reserved.Öğe Electrical, mechanical, and optical changes in MWCNT-doped PMMA composite films(Sage Publications Ltd, 2020) Mergen, Omer Bahadir; Arda, Ertan; Evingur, Gulsen AkinIn this study, we report the preparation of poly (methyl methacrylate)/multi-walled carbon nanotube (MWCNT) composite thin films by simple and efficient solution mixing and ultrasonic method and the electrical, optical, and mechanical characterizations. Scattered light intensity (I-sc), tensile modulus (E), and surface conductivity (sigma) of these composites have increased with the addition of MWCNT into the composite. The observed behavior in electrical, optical, and mechanical properties of the poly (methyl methacrylate)/MWCNT composites was interpreted by site and classical percolation theory. The optical mechanical and electrical percolation thresholds of poly (methyl methacrylate)/MWCNT composites were determined as phi(op)= 3 wt%, phi (m)= 0 wt%, and phi(sigma) = 5 wt%, respectively. The optical (t(op)), mechanical (t(m)), and electrical (t(sigma)) critical exponents were calculated as 2.23, 0.43, and 0.11, respectively. Both the tensile modulus and tensile strength of poly (methyl methacrylate)/MWCNT composites were increased with increasing MWCNT content until it reaches to 10 wt%. However, above phi = 10 wt%, the mechanical properties of the composites were decreased due to the aggregation of MWCNTs, while the toughness does not show a significant change until phi = 10 wt% MWCNT content, whereas it was decreased above this value.Öğe Electrical, optical and dielectric properties of polyvinylpyrrolidone/ graphene nanoplatelet nanocomposites(Elsevier, 2023) Mergen, Omer Bahadir; Arda, ErtanIn this study, polyvinylpyrrolidone (PVP) nanocomposite films containing GnP in four different volume fractions (phi = 0.00, 2.00, 4.08, and 5.91) were prepared by the solution casting method. UV-Vis absorbance spectroscopy, reflectance spectroscopy, and two-point probe resistivity measurement techniques were used to examine the optical, electrical, and dielectric properties of these films. Optical band gap energies of the PVP/GnP nano-composites were obtained using the most commonly used Tauc, Kubelka-Munk (K-M), Absorbance Spectrum Fitting (ASF), and Derivative (DM) methods. The results obtained by Tauc, K-M, and ASF methods were found to be consistent with each other. In addition, basic optical parameters such as Urbach energy (Eu), refractive index (n), optical conductivity (sigma opt) and dielectric constant (epsilon) of the PVP/GnP nanocomposites were investigated. As the GnP volume fraction increased in the nanocomposites, the electrical conductivity, Eu, n, sigma opt and epsilon increased whereas Eg decreased. These nanocomposites produced by varying the GnP volume fraction are promising for using optics, electricity, optoelectronics, and many other industrial applications.Öğe Electrical, optical and fluorescence percolations in P(VAc-co-BuA)/MWCNT composite films(Taylor & Francis Ltd, 2013) Arda, Ertan; Kara, Selim; Pekcan, OnderEffects of multiwall carbon nanotube (MWCNT) addition on the electrical conductivities, optical transparencies and fluorescence emissions of poly(vinyl acetate-co-butyl acrylate) (P(VAc-co-BuA))/MWCNT composite films were studied. Optical transmission, fluorescence emission and two point probe resistivity techniques were used to determine the variations of the optical, fluorescence and electrical properties of the composites, respectively. Transmitted photon intensity (I-tr), fluorescence emission intensity (I-fl) and surface resistivity ((s)) of the composite films were monitored as a function of MWCNT mass fraction (M) at room temperature. All these measured quantities of the composites were decreased by increasing the content of MWCNT in the composite. The conductivity and the optical results were attributed to the classical and site percolation theories, respectively. The fluorescence results, however, possessed both the site and classical percolation theories at low and high MWCNT content regions, respectively.Öğe Electrical, optical and mechanical properties of chitosan biocomposites(Sage Publications Ltd, 2020) Mergen, Omer Bahadir; Arda, Ertan; Evingur, Gulsen AkinIn this work, chitosan/graphene nanoplatelets (CS/GNP) and chitosan/multi-walled carbon nanotube (CS/MWCNT) biocomposite films were prepared using a simple, eco-friendly and low-cost method. The electrical, optical and mechanical properties of these composite films were investigated. The optical, mechanical and electrical properties of the biocomposites were significantly improved, which make them promising materials for food packaging, ultraviolet protection and biomedical applications. With the increase of carbon filler content (GNP or MWCNT) in CS biocomposites, the surface conductivity (sigma), the scattered light intensity (I (sc) ) and the tensile modulus (E) increased significantly. This behaviour in the electrical, optical and mechanical properties of the CS/carbon filler biocomposites was explained by percolation theory. The electrical percolation thresholds were determined as R (sigma) = 25.0 wt.% for CS/GNP and R (sigma) = 10.0 wt.% for CS/MWCNT biocomposites, while the optical percolation thresholds were found as R (op) =12.0 wt.% for CS/GNP and R (op) = 2.0 wt.% for CS/MWCNT biocomposites. Conversely, the mechanical percolation thresholds for both CS/GNP and CS/MWCNT biocomposites were found to be negligibly small (R (m) = 0.0 wt.%). The electrical (beta (sigma) ), optical (beta (op) ) and mechanical (beta (m) ) critical exponents were calculated for both CS/carbon filler biocomposites and found compatible with the applied percolation theory.Öğe Electrical, optical and mechanical properties of PS/GNP composite films(Taylor & Francis Ltd, 2018) Arda, Ertan; Mergen, Omer Bahadir; Evingur, Gulsen AkinIn this study, the electrical, optical and mechanical properties of polystyrene (PS) thin films added graphene nanoplatelet (GNP) have been investigated. Surface conductivity (sigma), absorbance intensity (A) and tensile modulus of these composite films have increased with increasing the content of GNP in the composite. The increase in the electrical and optical properties of the PS/GNP composite films has been interpreted by site and classical percolation theory, respectively. The electrical and the optical percolation thresholds of PS/GNP composite films were determined as R-sigma = 23.0 wt.% and R-op = 13.0 wt.%, respectively. While the conductivity results have been attributed to the classical percolation theory, the optical results have attributed to the site percolation theory. The electrical (beta(sigma)) and the optical (beta(op)) critical exponents were calculated as 2.54 and 0.40, respectively. The tensile modulus and the tensile strength of the PS/GNP composites increased with the increasing of GNP content in the PS. But, the toughness of the composites fluctuated with GNP addition.Öğe Electrical, optical, and mechanical percolations of multi-walled carbon nanotube and carbon mesoporous-doped polystyrene composites(Sage Publications Ltd, 2020) Mergen, Omer Bahadir; Arda, Ertan; Evingur, Gulsen AkinIn this study, we have investigated and compared electrical, optical, and mechanical properties of polystyrene thin films with added multi-walled carbon nanotube and carbon mesoporous. Surface conductivity (sigma), scattered light intensity (I-sc), and all the mechanical parameters of these composites have increased with increasing the content of carbon filler (multi-walled carbon nanotube or carbon mesoporous) in the polystyrene composites. This behavior in electrical, mechanical, and optical properties of the polystyrene/carbon fiber composites has been explained by classical and site percolation theory, respectively. The electrical percolation thresholds (R-sigma) were determined to be 8.0 wt% for polystyrene/multi-walled carbon nanotube and 25.0 wt% for polystyrene/carbon mesoporous composites. The optical percolation thresholds were found to be R-op = 0.8 wt.% for polystyrene/multi-walled carbon nanotube and R-op = 3.0 wt.% for polystyrene/carbon mesoporous composites. For the polystyrene/carbon mesoporous composite system, it was determined that the mechanical percolation threshold occurred at lower R values than the polystyrene/multi-walled carbon nanotube composite system. The electrical (beta(sigma)), optical (beta(op)), and mechanical (beta(m)) critical exponents have been calculated for both of the polystyrene/carbon fiber composites and obtained as compatible with used percolation theory.Öğe Evaluation of the fractal dimension of polyacrylamide during gelation and swelling(Elsevier, 2021) Arda, Ertan; Kara, Selim; Pekcan, Onder; Evingur, Gulsen AkinThe photon scattering method was performed to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) applied with N,N'-methylenebis (acrylamide) (Bis) in time. FCC experiments were conducted using different Bis contents to create fractal-like network structures in polyacrylamide (PAAm) gels. Higher intensity values of the scattered photons, Isc were observed with increasing Bis content, BC, at a given time, which was attributed to fractal-like macrogel formation from interconnected microgels. The same gels were used in swelling experiments after drying, and increased Isc intensities from the PAAm gels were observed during the swelling process. Fractal dimensions, d during the gelation and swelling processes were measured and found to be increased as gelation and swelling times increased. According to the results obtained from the gelation measurements, it was seen that the fractal size, d, increased from very small values to 3.00. A similar increase in the range 1.00-1.66 was observed during swelling experiments.Öğe Film formation stages for poly(vinyl acetate) latex particles(Springer, 2006) Kara, Selim; Pekcan, Onder; Sarac, Ayfer; Arda, ErtanPhoton transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T-g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T-g of PVAc. It is observed that transmitted photon intensity (I-tr) from these films increased as the annealing temperature is increased. It is seen from I (tr) curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (Delta H) and backbone motion (Delta E (b)) were obtained by using well-defined models. The averaged values of the backbone (Delta E (b)) and the viscous flow activation energies (Delta H) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (tau (M),T (M)) and healing points (tau (H),T (H)) were determined. Minimum film formation (Delta E (M)) and healing activation energies (Delta E (H)) were measured using these time-temperature pairs. Delta E (M) and Delta E (H) were found to be 32.5 and 28.3 kcal/mol, respectively.Öğe Fractal dimensions of kappa-carrageenan gels during gelation and swelling(Taylor & Francıs Inc, 2018) Kara, Selim; Arda, Ertan; Pekcan, OnderA photon scattering technique for research on the sol-gel and gel-sol transitions in kappa-carrageenan-water systems with various carrageenan contents (CC) was utilized for characterizing the fractal dimensions during gelation and swelling. It was observed that the scattered photon intensity, I-sc, increased at all temperatures with an increase in the CC when I-sc was monitored against temperature. Additionally, the sol-gel transition temperatures were found to be much lower than the gel-sol transition temperatures, causing hysteresis of the phase transition loops. I-sc increased with an increase in CC at all test temperatures, which is attributed to the formation of a fractal-like carrageenan gel. After drying, the gels were used in swelling experiments where the gels were immersed in water at room temperature, reswelling to the original structure. It was observed that I-sc from the carrageenan gels increased as the CC was increased. The fractal dimension, d, during gelation was found to increase as the gelation temperature was increased. On the other hand, the d values during swelling decreased as the swelling time was increased.Öğe Graphene Nanoplatelet and Multiwalled Carbon Nanotube Doping Effect on the Structural and Physical Properties of PolyVinyl Alcohol Composites(Taylor & Francis Inc, 2024) Mergen, Omer Bahadir; Arda, Ertan; Akin Evingur, Guelsen; Kurtulus Ozturk, Ozgul; Pietsch, UllrichPolyvinyl alcohol (PVA) composite thin films were prepared using graphene nanoplatelets (GNPs) and multiwalled carbon nanotubes (MWCNTs) as carbon fillers (CFs). The resulting electrical, optical, mechanical, and structural changes caused by adding the CFs to the pure PVA matrix were characterized. The improvement of electrical, optical, and mechanical properties was interpreted in terms of the percolation theory. Depending on this interpretation, the percolation threshold values, and the critical exponential values of the related properties were calculated. It turns out that the measured mechanical and optical changes were compatible with the site percolation theory while the electrical conductivity was compatible with the classical percolation theory. X-ray diffraction (XRD) measurements were performed to correlate the physical properties with the structure of the PVA composite films. They revealed that the degree of crystallinity of the composites increased with the CF reinforcement and that MWCNT was more effective in improvement of the crystallinity of the PVA composites than GNP.Öğe Monovalent and divalent cation effects on phase transitions of ?-carrageenan(Sage Publications Ltd, 2007) Kara, Selim; Arda, Ertan; Pekcan, OnderPhase transitions Of L-carrageenan in a variety of monovalent (Li, Na, K) and divalent (Mg, Ca, Sr) cation solutions were studied during heating and cooling by using photon transmission technique. Photon transmission intensity (I-tr) was monitored against temperature to determine the transition temperatures and activation energies during the heating and cooling processes in the monovalent and divalent systems. Three distinct transition regions were observed during the heating and cooling cycles for the carrageenan-divalent salt system. At the first step of the heating process, dimer groups were transformed into dimers that presented (g-d) transitions, then these dimers were directly converted into a double helix by undergoing a (d-h) transition. In the higher temperature region, a double helix-to-coil (h-c) transition took place. During the cooling process, these transitions are arranged in the order of (c-h), (h-d), and (d-g). The carrageenan-monovalent salt system presented only coil-to-rod-like helix (c-r) and rod-like helix-to-coil (r-c) transitions during the cooling and heating processes, respectively. A hysteresis was observed between (r-c)-(c-r) and (g-d)-(d-g) transitions for the monovalent and divalent cations, respectively.
