Swelling of iota-carrageenan gels prepared with various CaCl2 content: A fluorescence study

Iota carrageenan gels prepared with various CaCl2 content were completely dried and then swelled in water vapor. Steady-state fluorescence ( SSF) technique was used to monitor the swelling process of each iota carrageenan gels at various temperatures. Pyranine was used as a fluorescence probe. Apparent fluorescence intensity, I increased as swelling time increased for all gel samples. The increase in I was modelled using Li-Tanaka equation from which the swelling time constants, tau(1) and cooperative diffusion coefficients, D-c were determined. It was observed that D-c increased as the swelling temperature was increased. On the other hand at each temperature, it was seen that D-c decreased as CaCl2 content was increased. Activation energies for swelling were obtained and found to be 60.5, 61.0, 61.5 and 62.8 kJmol(-1) for the gels prepared with increasing amount of CaCl2 content.Publisher's Versio

Thermal And Volumetric Phase Transitionsin Carrageenan Gels

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2009Bu çalışmada kappa ve iota karagenan jellerinin termal ve hacimsel faz geçişleri floresans tekniği kullanılarak incelendi. Floresans ajan olarak piranin kulanıldı. Karagenan jellerinin sol-jel (soğutma) ve jel-sol (ısıtma) faz geçişleri sürecinde floresans şiddet ve saçılan ışık şiddeti sıcaklığın fonksiyonu olarak takip edildi ve histerezis gözlendi. Faz geçiş bölgesinde kritik sıcaklık değerleri bulundu ve jel kesrini tanımlayan kritik üs hesaplandı. Kritik üslerin Flory-Stockmayer teorisi ile uyum içerisinde olduğu gözlendi. Ayrıca sıcaklık ve konsantrasyonun kappa ve iota karagenan jellerinin kuruma ve şişme süreçlerine etkisi çalışıldı. Kuruma boyunca floresans şiddetinin lineer bir şekilde azalması Case II difuzyon modeli ile açıklanırken, şişme olayı ise Li - Tanaka modeli kullanılarak yorumlandı ve kooperatif difüzyon katsayısı hesaplandı. Kullanılan floresans tekniğin jellerin fiziksel yapısını incelemede etkili ve kullanışlı bir yöntem olduğu sonucuna varıldı. Elde edilen sonuçların diğer deneysel tekniklerle yapılan benzer çalışmalarla belirli bir uyum içinde oldukları görüldü.In this study, thermal and volumetric phase transitions of kappa and iota carrageenan gels were studied by using fluorescence technique. Pyranine was used as a fluorescence probe. Fluorescence intensity and scattered light intensity were monitored during sol-to-gel (cooling) and gel-to-sol (heating) phase transitions of carrageenan gels as a function of temperature and hysteresis was observed. Critical temperatures were found at phase transition regions and critical exponent at all phase transition temperatures was calculated, and it was found to be in accord with the Flory-Stockmayer theory. Also the effects of temperature and concentration on drying and swelling of kappa and iota carrageenan gels were studied. While the linear relation of the fluorescence intensity curve with the drying time was explained by using the Case II diffusion model, the swelling process was interpreted by using the Li-Tanaka equation and the cooperative diffusion coefficient was calculated. It is found that the fluorescence technique that was used in this study is an effective and useful method to study the physical structures of the gels. The values obtained in the experiments are in agreement with similar studies in which other experimental techniques were used.DoktoraPh

Calculation of the Raman frequencies as a function of temperature in phase I of benzene

Tarı, Özlem (Arel Author)This study gives our calculation of the Raman frequencies of the lattice modes A (A1g), B (AgB2g) and C (B1gB3g) as a function of temperature at constant pressures of 0, 1.4 and 3.05 GPa for the solid phase I of benzene. The Raman frequencies of those lattice modes are calculated using the volume data from the literature through the mode Grüneisen parameters for the solid phase I of this molecular crystal. It is shown here that the Raman frequencies of the lattice modes studied decrease with increasing temperature, as expected and they also decrease as the pressure increases in the solid phase I of benzene

Modelling of swelling by the fluorescence technique in kappa carrageenan gels

Conference: International Congress on Advances in Applied Physics and Materials Science -- Location: Antalya, (Turkey) -- Conference date: 12–15 May 2011 -- Published in: AIP Conference Proceedings (2011)Kappa (-) carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in water vapor. Steady state fluorescence measurements were performed using a spectrometer equipped with temperature controller. Pyranine was embedded in -carrageenan gels as a fluorescence probe during gel preparation. The fluorescence intensity, I, increased exponentially as swelling time is increased for all gel samples. The increase in I was modelled using Li-Tanaka equation from which swelling time constants, c and cooperative diffusion coefficients, Dc were determined. It was observed that Dc increased as the swelling temperature was increased. On the other hand at each temperature, it was seen that Dc decreased as kappa carrageenan concentration was increased. Activation energies for swelling were obtained and found to be 57.4, 58.3 and 62.73kJ mol-1 for the gels with increasing amount of - K-carrageenan content

Raman frequencies calculated at various pressures in phase I of benzene

Tarı, Özlem (Arel Author)We calculate in this study the pressure dependence of the frequencies for the Raman modes of A (Ag), B (Ag, B2g) and C (B1g, B3g) at constant temperatures of 274 and 294K (room temperature) for the solid phase I of benzene. Using the mode Grüneisen parameter of each lattice mode, which correlates the pressure dependence of the crystal volume and the frequency, the Raman frequencies of those modes are computed for phase I of benzene. Our results show that the Raman frequencies of the three lattice modes (A, B and C) increase as the pressure increases, as expected. The temperature effect on the Raman frequencies is not significant, which can be explained by the experimental measurements

Calculation of the C-P-C-V as a function of temperature close to the melting point in benzene

Tarı İlgin, Özlem (Arel Author)The temperature dependence of the C-P - C-V is calculated at constant pressures using the observed volume data from the literature for solid and liquid benzene near the melting point. Our calculated values are compared with some earlier treatments and we find that they disagree at constant pressures for the solid benzene, whereas for the liquid benzene agreement is reasonable in terms of the order of magnitude between our calculated C-P - C-V and those predicted from the Peng-Robinson equation of state. Our calculated C-P also agrees with the experimental data at normal pressure and has lower values at higher pressures in liquid benzene. Our treatment given here indicates that the C-P - C-V and the heat capacity C-P can be calculated from the molar volume as a function of temperature at constant pressures using the thermodynamic relations for the solid and liquid benzene near the melting point

Variation of the molar volume with the temperature and the Pippard relations near the melting point in benzene

Tarı İlgin, Özlem (Arel Author)In this study, we calculate variation of the molar volume with the temperature at constant pressures (70.5, 85.2, 128 and 175.2 MPa) using the experimental data from the literature for the solid and liquid phases of benzene near the melting point. The calculated molar volume decreases in the solid phase as the temperature increases toward the melting temperature, whereas in the liquid phase just above the melting temperature it increases abruptly, as expected. By calculating the specific heat, thermal expansion and the isothermal compressibility from the molar volume, which increase with increasing temperature (at constant pressures), we construct the Pippard relations for the solid and liquid phases of benzene near the melting point. Our calculated molar volume and the thermodynamic quantities (specific heat, thermal expansion and the isothermal compressibility) agree to some extend with those experimental measurements from the literature for the molar volume (at 1 atm and constant pressures studied here) and the specific heat (at 0.1, 0.9 and 1.5 GPa), which also increase with increasing temperature for the solid and liquid phases near the melting point in benzene. Our calculated thermodynamic quantities and the Pippard relations can also be examined with the measurements at various temperatures at constant pressures given here near the melting point in benzene

Calculation of the thermodynamic quantities of perovskite metal organics DMAKCr and perovskite HyFe close to the weakly first-order relaxor-like structural transformation using the mean field theory

#nofulltext# -- Tarı, Özlem (Arel Author)Weakly first-order or nearly second-order phase transitions occurring in metal{organic frameworks (MOFs), particularly in DMAKCr and perovskite HyFe, are studied under the mean field model by using the observed data from the literature. In this work, mainly thermal and magnetic properties among various physical properties which have been reported in the literature for those MOFs are studied by the mean field theory. By expanding the free energy in terms of the magnetization (order parameter), the excess heat capacity (Delta C-P) and entropy (Delta S), latent heat (L), magnetization (M) and the inverse susceptibility (chi(-1)) are calculated as a function of temperature close to the weakly first-order phase transition within the Landau phenomenological model which is fitted to the experimental data from the literature for C-P (DMAKCr and perovskite HyFe) and for magnetization M (HyFe).Our predictions of the excess heat capacity (Delta C-P) and entropy (Delta S) agree below T-c with the observed data within the temperature intervals studied for DMAKCr and perovskite HyFe. From our predictions, we find that magnetization decreases continuously whereas the inverse susceptibility decreases linearly with increasing temperature toward the transition temperature in those MOFs as expected for a weakly first-order transition from the mean field model