Dielectric study of the antiplasticization of trehalose by glycerol (original) (raw)
Related papers
Journal of Non-Crystalline Solids, 2010
We utilize dielectric relaxation spectroscopy for the quantitative characterization of antiplasticization of glassy-trehalose by glycerol. The high frequency Johari-Goldstein relaxation time (s) was obtained by analyzing the complex permittivity data in terms of the distribution function of relaxation times and a regularization technique. We analyzed the dielectric spectrum without prior assumptions about a spectral function and the number of the relaxation processes. The ratio of s values for the mixture and pure trehalose, an antiplasticization factor (H), is found to provide a useful measure of the extent of antiplasticization. We observe that increasing the glycerol mass fraction (x w) at fixed temperature increases s, extending antiplasticization until a temperature dependent critical plasticization concentration is reached. At a fixed concentration, we find an antiplasticization temperature at which antiplasticization first occurs upon cooling. At a temperature of 293 K the antiplasticization factor peak value is about 1.6 when x w of glycerol is about 0.24. At 323 K a mild antiplasticization maximum occurs when x w decrease to about 0.05. Above 323 K, H < 1, glycerol plasticizes trehalose, thus the antiplasticizing effect apparently no longer exists. The antiplasticization factor that we describe in terms of Arrhenius functions is a convenient predictive model to characterize antiplasticization in glassy sugar formulations and other glass-formers.
Dynamic mechanical and dielectric characterisation of amylose–glycerol films
Carbohydrate Polymers, 2001
The dynamic mechanical, dielectric and calorimetric behaviour of amylose ®lms, plasticised with glycerol, was examined as a function of temperature and glycerol content. Two separate relaxation processes were observed. Whereas the temperature of the lower temperature transition, in the vicinity of 2508C, showed a weak dependence on composition, the temperature of the upper transition, in the range 150± 508C, decreased with increasing glycerol content. The activation energy of the lower temperature transition, obtained from the dependence of the frequency of the relaxation peak upon temperature, was typical of a primary a-relaxation or glass transition process. This indicated that although glycerol was an effective plasticiser of amylose, amylose±glycerol mixtures are only partially miscible. q
Physical Review B, 1990
Brief Reports Brief Reports are short papers which report on completed research which, while meeting the usual physical Review standards of scientific qualityd, oes not warrant a regular article (A. ddenda to papers previously published in the physical Review by the same authors are included in Brief Reports)& B.rief Report may be no longer than 3Yz printed pages and must be accompanied by an abstract Th.e same publication schedule as for regular articles is followed, and page proofs are sent to authors Comparison between frequency-dependent specific heat and dielectric relaxation of glycerol and propylene glycol
Journal of Pharmaceutical Sciences
The bioprotective properties of 2 disaccharides (sucrose and trehalose) were analyzed during the freezedrying (FD) process and at the end of the process, to better understand the stabilization mechanisms of proteins in the solid state. In situ Raman investigations, performed during the FD process, have revealed that sucrose was more efficient than trehalose for preserving the secondary structure of lysozyme during FD, especially during the primary drying stage. The lower bioprotective effect of trehalose was interpreted as a consequence of a stronger affinity of this disaccharide to water, responsible for a severe phase separation phenomenon during the freezing stage. Dielectric spectroscopy investigations on the freezedried state of protein formulations have shown the capabilities of trehalose assisted by residual water to reduce the molecular mobility of the vitreous matrix, suggesting that trehalose is more efficient to preserve the protein structure during long-term storage.
Dielectric properties of glycerol/water mixtures at temperatures between 10 and 50°C
The Journal of Chemical Physics, 2006
At six temperatures T between 10 and 50°C and at mole fractions xg of glycerol (0<xg⩽0.9) the complex (electric) permittivity ϵ(ν) of glycerol/water mixtures has been measured as a function of frequency ν between 1MHz and 40GHz. The spectra of the glycerol/water mixtures can be well represented by a Davidson-Cole [J. Chem. Phys. 18, 1417 (1950)] relaxation function that reveals an unsymmetric relaxation time distribution. The effective dipole orientation correlation factor derived from the static permittivity displays an unspectacular behavior upon mixture composition. The dielectric relaxation time reveals a simple relation to the shear viscosity of the mixtures, but both quantities are not proportional to one another. The relaxation times at high temperatures nicely complement previously determined low temperature data, following a Vogel-Fulcher-Tammann-Hesse [Z. Phys. 22, 645 (1925); J. Am. Chem. Ceram. Soc. 8, 339 (1923); Z. Anorg. Allg. Chem. 156, 245 (1926)] (VFTH) temperat...
Dielectric and conductivity relaxation in mixtures of glycerol with LiCl
The European Physical Journal E, 2008
We report a thorough dielectric characterization of the α relaxation of glass forming glycerol with varying additions of LiCl. Nine salt concentrations from 0.1-20 mol% are investigated in a frequency range of 20 Hz-3 GHz and analyzed in the dielectric loss and modulus representation. Information on the dc conductivity, the dielectric relaxation time (from the loss) and the conductivity relaxation time (from the modulus) is provided. Overall, with increasing ion concentration, a transition from reorientationally to translationally dominated behavior is observed and the translational ion dynamics and the dipolar reorientational dynamics become successively coupled. This gives rise to the prospect that by adding ions to dipolar glass formers, dielectric spectroscopy may directly couple to the translational degrees of freedom determining the glass transition, even in frequency regimes where usually strong decoupling is observed.
A study of dielectric relaxations in galactose–water mixtures
Journal of Non-Crystalline Solids, 2010
We studied the frequency dependent dielectric loss spectra of galactose-water mixtures with different water contents in the temperature range which covers the supercooled and glassy states. In the frequency range from 10 mHz to 100 MHz, first we observed the α-relaxation, then slow extra relaxation, and then fast extra relaxation with increasing frequency. The temperature dependent relaxation times of slow and fast extra relaxations were consistent with τ JG in the coupling model and that of the γ-relaxation (S. Capaccioli et al., 2006). The relaxation time difference and the relaxation strength of the fast extra relaxations relative to the αrelaxation respectively decreased and increased as the water content increased, indicating that the fast extra relaxation in galactose-water mixtures might be strongly related to the coupling between galactose and water molecules. We also observed crossover phenomena at temperatures close to the glass transition temperatures in the temperature dependent relaxation times of two extra relaxations.
The Journal of Physical Chemistry B, 2001
The interaction between amylopectin, a starch polysaccharide, and ethylene glycol (EG) was investigated using broad-band dielectric relaxation spectroscopy. Water-free amylopectin (AP) was mixed with 21 wt % ethylene glycol. This resulted in a continuous ethylene glycol phase, as well as a molecularly mixed AP/EG fraction. After storage at room temperature or annealing, the mixture shows dynamic properties typical of a polymer with weak intermolecular interactions, suggesting that EG binds preferentially to AP and forms intrachain H-bridges leading to increased chain stiffness and thus an increased glass transition temperature. This structure evolution is accompanied by a sharp reduction in the size of the ethylene glycol droplets to a few nanometers, as revealed by pronounced confinement effects in the R-relaxation of the dispersed EG.
Evidence of growing spatial correlations during the aging of glassy glycerol
2012
We have measured, as a function of the age ta, the aging of the nonlinear dielectric susceptibility χ3 of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time τα(ta), this scaling breaks down for χ3, suggesting an increase of the amplitude of χ3. This is a strong indication that the number Ncorr of molecules involved in relaxation events increases with ta. For T = 0.96 × Tg, we find that Ncorr increases by ∼ 10% when ta varies from 1ks to 100ks. This sheds new light on the relation between length scales and time scales in glasses.