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5631 articles

T0029 – Thermal behavior of ferroelectric polyamide 11 in a relation to pyroelectric properties

The pyroelectric properties of oriented thin films of ferroelectric Polyamide 11 have been studied in the temperature range of -100°C up to +140°C. The temperature dependence of the experimental pyroelectric coefficient has been analyzed. Three changes of slope of the pyroelectric coefficient are observed at -20, +50, and +100°C. The origin of the lower temperature event has not yet been defined. The upper transition is attributed to chain movements in crystalline regions, and more precisely, to a crystalline phase transition. The intermediate event is close to the glass transition temperature Tg observed by DSC. It is attributed to the manifestation of the glass transition. Below Tg, the variations of the pyroelectric coefficient are very small. For higher temperatures, it increases rapidly, attesting to a major contribution of secondary pyroelectricity and dimensional effects above Tg. The breaking of hydrogen bonds occurring at the glass transition temperature observed on DSC thermograms does not affect pyroelectric properties. Pyroelectric properties are mildly reduced after annealing at temperatures up to +140°C. A comparative study of oriented ferroelectric films prepared by quenching from the melt and nonoriented slowly cooled samples has been carried out by means of DSC
L. Ibos, C. Maraval, A. Bernès, G. Teyssèdre, C. Lacabanne, S-L. Wu and J.I. Scheinbeim, Journal of Polymer Sciences 37 (1999) 715-723

T0018 – Dielectric relaxation properties of filled ethylene propylene rubber

Thermally stimulated discharge currents and time domain dielectric spectroscopy were employed to characterize the behavior of clay-filled ethylene propylene rubber. Measurements were made on samples with different clay concentrations and particle sizes. The main effect of the clay filler on the electrical properties is on interfacial polarization which occurs at the clay polymer interface. The experimental results are sensitive to the shape of the clay particles. A few results indicate that other mechanisms also affect the electrical behavior of this material
A.M. Jeffery and D.H. Damon, IEEE Transactions on Dielectrics and Electrical Insulation 2 (1995) 394-408

T0039 – Thermal behaviour and slow molecular mobility in two isomers of biphenylmethanol DSC and TSDC study

The thermal behaviour of 2- and 4-biphenylmethanol were studied by differential scanning calorimetry (DSC). It was found that the 2-isomer shows a relatively strong resistance to crystallisation, and that it easily vitrifies on cooling. Oppositely, 4-biphenylmethanol readily crystallizes on cooling. The slow molecular mobility of 2-biphenylmethanol in the amorphous solid state was studied by DSC and by thermally stimulated depolarisation currents (TSDC). Both techniques indicate that 2-biphenylmethanol is a relatively strong glass-former, with a fragility index of ~50 in the Angell's scale.
H.P. Diogo, S.S. Pinto and J.J. Moura Ramos, Journal of Thermal Analysis and Calorimetry 83 (2006) 361-366

T0028 – Effect of water on the molecular mobility of elastin

Purified and hydrated elastin is studied by both thermal and dielectric techniques to have insight into the chain dynamics of this protein. By differential scanning calorimetry, the glassy behavior of elastin is highlighted; the glass transition temperature (Tg) of elastin is found to be widely dependent on hydration, falling from 200°C in the dehydrated state to 30°C for 30% hydration. A limit of Tg at around 0°C is found when crystallizable water is present in the system, that is, when the formation of ice prevents motions of some 10 nm along the polypeptidic chains. The technique of thermally stimulated currents, carried out in the -180 to 0°C temperature range, is useful to detect localized motions. In this case, too, the localized motions vary considerably according to hydration: a first relaxation mode is observed at -145°C and it is associated with the reorientation of crystallizable water in ice I; a second relaxation mode, more complex and cooperative, occurs at around -80°C and could be attributed to the complex constituted by the dipolar groups of the polypeptidic chain and noncrystallizable water, behaving as a glassy system
V. Samouilllan, C. André, J. Dandurand and C. Lacabanne, Biomacromolecules 5 (2004) 958-964

T0017 – Origins of Thermally Stimulated Current in polyethersulfone

In order to understand the dominant carrier species in electrical conduction in polyethersulfone (PES), thermally stimulated current (TSC) measurements were carried out under various conditions. It was found that PES has two TSC peaks in the temperature range from 20 to 220°C, consisting of an alpha peak at ~210°C and a beta peak whose peak temperature moves towards a higher temperature with an increasing poling temperature. Even when the sample was not poled, PES shows a spontaneous current with its peak at ~210°C. Both the spontaneous current peak and the alpha peak were found to disappear when the sample had been heated to 230°C, keeping the external circuit closed. From such similarity of appearance and disappearance between the two peaks, it is concluded that they have the same origin. From the change in the spatial distribution of space charges inside the sample measured simultaneously with the TSC measurements, positive charges, probably due to K+ ions, existed nonuniformly in the sample from the beginning, and are thought to be responsible for the two peaks. From a similar study, the beta peak is considered to be due to polarization of ionic space charges during the poling process
E.J. Kim, T. Takeda and Y. Ohki, IEEE Transactions on Dielectrics and Electrical Insulation 3 (1996) 386-391

T0038 – Intrinsic compensation phenomenon in thermally stimulated depolarisation studies

The compensation behaviour as observed in thermally stimulated depolarisation currents (TSDC) corresponds to the linear relationship found between the Arrhenius (or Eyring) apparent thermokinetic parameters obtained in a series of thermal sampling (TS) experiments performed in the region of cooperative relaxation processes, particularly around the glass transition of glass forming materials. The compensation effect exhibits the same features of the intrinsic compensation found for any given TS curve, where the values of Ea and t0, in the region where the sum of square residues is low, are highly correlated, being this correlation similar to the conventional compensation. This intrinsic compensation is a result, and exhibits the same features, of the compensation found in the description of a given set of points obtained with the Arrhenius equation with the own Arrhenius equation. This compensation is transmitted directly to the equation that describes the temperature dependence of the depolarisation currents, J(T), as a nearly direct relationship exists between J(T) and t(T). In fact, it was shown that J(T) for an elementary process could be approximated by P0 exp[-c/t(T)]/t(T), c being a constant.
J.F. Mano, Thermochimica Acta 430 (2005) 135-141

T0027 – Relaxations in amorphous and semi-crystalline polyesters. A study by thermally stimulated depolarization currents

Thermally stimulated depolarization currents and differential scanning calorimetry are performed on thermoplastic polyesters to characterize both and relaxations. The influence on the different relaxations phenomena of the chemical structure (size of the naphthalene groups, presence of cyclohexane, length of the aliphatic group, ) as well as the influence of the crystallinity are discussed. The three phases model with a crystalline part, a rigid amorphous part unable to relax and an amorphous phase able to relax at various temperatures depending on the distribution of the relaxation times is used to explain the evolution of the main relaxation while the standard two-phases model is sufficient to explain the variations of the relaxation mode. Elementary analysis of both and relaxations show that the relaxation characterized by a continuous variation of activation energies as a function of temperature follows the activated state equation with a zero activation entropy while the cooperative a relaxation exhibits a prominent maximum of the activation energies at the glass transition temperature.
M. Kattan, E. Dargent, J. Grenet, Journal of Thermal Analysis and Calorimetry 76 (2004) 379-394

T0016 – Analysis of the experimental distribution of relaxation times around the liquid-glass transition of poly(vinylidene fluoride)

The dielectric relaxation mode associated with the liquid-glass transition of a semicrystalline polymer, polyvinylidene fluoride, has been analyzed by the technique of fractional polarizations. A discrete distribution of relaxation times following an Arrhenius law has been obtained experimentally. The activation energy of the "single'' relaxation processes are distributed according to a Gaussian function. Moreover, these relaxation times follow a compensation law. These results allowed us to introduce a continuous distribution of relaxation times whose parameters are temperature dependent. The validity of the method was verified for the thermally stimulated current spectra. Use is made of this distribution to compute the temperature and frequency dependence of the complex dielectric permittivity.
G. Teyssèdre, P. Demond and C. Lacabanne, Journal of Applied Physics 79 (1996) 9258-9267

T0037 – Weak solid-solid transitions in pharmaceutical crystalline solids detected via thermally stimulated current

To demonstrate the ability of thermally stimulated current (TSC), normally used to study amorphous systems, in detecting weak solid-solid transitions in crystalline pharmaceutical compound. Methods: Polymorphs of a new chemical entity, LAU254, were generated and characterized using conventional and hot plate X-ray diffraction, DSC and TSC. Equilibration of 50:50 mixtures of the different polymorphs and solubility studies were conducted in aqueous and organic solvent at 25 and 50°C and then analyzed by X-ray and DSC. Results: Four crystalline forms (A-D) were isolated. Form B showed one single endotherm at 180°C while the other forms showed lower melting endotherms, a crystallization exotherm and eventually a final melting endotherm corresponding to that of form B (180°C). The heat of fusion of form B was the highest. In contrast, solubility as well as mixture equilibration studies resulted in all forms converting to form A. TSC analysis revealed a well-defined reproducible peak with a maximum at 130°C which was suspected to be a solid-solid transition. This was confirmed by hot plate X-ray diffraction where careful probing around 120-130°C revealed three different forms; form A (the initial form), a second form that appears above 150°C, melts, crystallizes and produces form B. Careful inspection of larger sample sizes in DSC showed a small endotherm at 130°C. Conclusions: TSC, normally used to study amorphous systems, proved to be useful in detecting weak solid-solid transitions in crystalline pharmaceuticals, an application that has never been explored or reported previously. This resulted in identifying a form, obtainable only at temperatures above the transition temperature (related enantiotropically to the form that is most stable at ambient temperatures) and in reconciling the DSC and solubility data. TSC can be very useful in detecting and probing those transitions that occur in the solid state due to subtle dipolar motion and are not associated with large changes in global motion and heat capacity that is needed for detection by DSC and therefore can be complementary to DSC in obtaining a more complete assessment of the polymorphism behavior of crystalline solids.
R.A. Shmeis and S.L. Krill, Thermochimica Acta 427(2005) 61-68

T0026 – Thermally stimulated measurements on polycrystalline Pbl2 layers

Thermally stimulated current measurements have been performed on polycrystalline layers of lead iodide grown from solution. Several TSC peaks or bands have been observed at temperatures of 100 K, 195-220 K, 230-240 K and 270-300 K. Comparison with PbI 2 single crystal shows that the polycrystalline structure of the material introduces additional defects. In contrast the defect currently found in single crystal and attributed to the lead vacancy has not been clearly evidenced in the polycrystalline layers. The position and relative intensity of the peaks can be modified by Ag doping and thermal annealing. On the other hand, only small differences resulting from the anisotropy of the material have been observed depending on the orientation of the electric field with regards to the grains orientation.
J.P. Ponpon and M. Amann, Eur. Phys. J. Applied Physics 18 (2002) 25-31

T0015 – Comparison of chemical treatments on the chain dynamics and thermal stability of bovine pericardium collagen

A new approach for the replacement of heart valves consists of obtaining an acellular matrix from animal aortic valves that performs mechanically, is nonantigenic, and is free from calcification and fibroblast proliferation. Novel biochemical treatments must be developed for this purpose. In this work, we focus on the characterization of collagen in acellular bovine cardiovascular tissues, fresh or glutaraldehyde treated, and stored in different solutions [phosphate-buffered saline (PBS), ethanol, octanol, and glutaraldehyde], to determine whether the resulting fibrous material is structurally preserved. The preservation of the triple helical structure of collagen is checked by differential scanning calorimetry (DSC), which is a well suited technique to analyze thermal transitions in proteins, such as denaturation. To get insight into the molecular dynamics of collagen in the nanometric range, we used thermally stimulated currents, a dielectric technique running at low frequency, that measure the dipolar reorientations in proteins submitted to a static electrical field. The combined use of these two techniques allowed us to evaluate the physical structure and conformation of collagen after the different chemical treatments. We have found that the glutaraldehyde treatment followed by octanol storage preserves the triple helical conformation of the polypeptidic chains of collagen, contrary to the ethanol and PBS storage that induce drastic changes in the thermal and dielectric behavior of the protein. Moreover, this particular chemical treatment stabilizes the collagen structure (shift toward high temperature of the collagen denaturation and stiffening of the chains by a cross-linking action) when compared to the control sample, and so could provide interesting fibrous material for the conception of bioprosthetic heart valve.
V. Samouillan, J. Dandurand, C. Lacabanne, R.J. Thoma, A. Adams, M. Moore, Journal of biomedical materials research 64 (2003) 330-338

T0036 – The determination of the activation energy of a relaxational process from thermally stimulated depolarisation currents (TSDC) data: an illustration with the beta-relaxation of maltitol

Three different and independent procedures to obtain the activation energy of a motional process from thermally stimulated depolarisation currents (TSDC) data are reported. One of the procedures requires a single thermal sampling (TS) experiment: the activation energy is calculated from the temperature dependence of the relaxation time associated with this TS peak. The other two procedures are based on the influence of the heating rate on the features of the TS peak namely, on the temperature location Tm and on the intensity of the maximum I(Tm) of the peak. The illustration with the case of an elementary component of the beta-relaxation of maltitol shows that the values of the activation energy provided by these procedures are in good mutual agreement. The fact that the TSDC technique provides different and independent procedures to obtain the kinetic parameters of a motional process is a unique feature in the context of the experimental techniques most often used to study molecular mobility.
J.J. Moura Ramos and N.T. Correia, Thermochimica Acta 426 (2005) 185-190

T0025 – Thermally stimulated current in SiO2

Thermally stimulated current (TSC) techniques provide information about oxide-trap charge densities and energy distributions in MOS (metal-oxide-semiconductor) capacitors exposed to ionizing radiation or high-field stress that is difficult or impossible to obtain via standard capacitance-voltage or current-voltage techniques. The precision and reproducibility of measurements through repeated irradiation/TSC cycles on a single capacitor is demonstrated with a radiation-hardened oxide, and small sample-to-sample variations are observed. A small increase in Edelta' center density may occur in some non-radiation-hardened oxides during repeated irradiation/TSC measurement cycles. The importance of choosing an appropriate bias to obtain accurate measurements of trapped charge densities and energy distributions is emphasized. A 10 nm deposited oxide with no subsequent annealing above 400°C shows a different trapped-hole energy distribution than thermally grown oxides, but a similar distribution to thermal oxides is found for deposited oxides annealed at higher temperatures. Charge neutralization during switched-bias irradiation is found to occur both because of hole-electron annihilation and increased electron trapping in the near-interfacial SiO2. Limitations in applying TSC to oxides thinner than 5 nm are discussed.
D.M. Fleetwood, R.A. Reber Jr, L.C. Riewe and P.S. Winokur, Microelectronics Reliability 39 (1999) 1323-1336

T0014 – Molecular stability of elastin : effect of molecular architecture

The thermal and dielectric properties of elastin and two soluble derivatives ( k-elastin and derived elastin peptides from enzymatic elastolysis) were investigated in the freeze-dried state in a wide temperature range (from -180 to +220°C). The glass transition of these amorphous proteins was studied by differential scanning calorimetry (DSC). The dielectric relaxations of both proteins were followed by thermally stimulated currents (TSC), an isochronal dielectric spectrometry running at variable temperature, analogous to a lowfrequency spectroscopy (10^(-3) - 10^(-2) Hz) and by dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10^(-2) to 3 x 10^6 Hz. The combination of TSC and DDS experiments and the determination of the activation parameters of the relaxation times inform about the molecular mobility of the proteins, both in the glassy state and in the liquid state. Major differences between the relaxation behavior of elastin and its soluble derivatives have been discussed and correlated with the molecular architecture of the proteins.
V. Samouillan, J. Dandurand, C. Lacabanne and W. Hornebeck, Biomacromolecules 3 (2002) 531-537

T0035 – Low frequency chain dynamic of cross-linked poly(acrylic acid)

Cross-linked poly(acrylic acid) (PAA) synthesized by radical polymerization in inverse suspension is a swelling gel. The physical structure of PAA has been analyzed using low frequency chain dynamic given by the analysis of thermo stimulated currents (TSC). The alpha primary dielectric relaxation mode observed around the glass transition temperature (Tg=+38°C) corresponds to the slowest dynamic. The relaxation times of the constituting processes show that it is due to a delocalized cooperative molecular mobility involving nanometric sequences of the hydrocarbon skeleton. The beta secondary dielectric relaxation mode observed at lower temperature (Tbeta=-35°C) corresponds to a higher frequency molecular mobility. It has been assigned to the cooperative mobility of hydrogen bonded COOH groups. In fact, the hydrogen bonded side chains behave as an hydrophilic matrix in which nanometric domains constituted by sequences of the main chain are embedded. Such a picture might explain the specific swelling properties of cross-linked PAA.
Ch. Mayoux, J. Dandurand and C. Lacabanne, Thermochimica Acta 421 (2004) 43-49.

T0024 – Thermally-stimulated current and dielectric loss measurement of polypropylene and teflon-FEP films immersed in diarylethane

Some properties of oil/PP (biaxially stretched polypropylene) and oil/FEP (Teflon FEP) composite insulators have been investigated with TSC (thermally stimulated current) techniques. The oil/PP system showed three TSC peaks originating from carriers captured in the swollen surface region of the PP. The TSC spectra depended strongly on the polarity of the poling voltage and on the impregnating temperature. Their analysis yielded information on the carrier traps existing near the PP surface in the oil/PP interface region. On the other hand, the TSC spectrum of the oil/FEP system has a small impregnating temperature dependence and a small effect of the poling voltage polarity. The difference in TSC between oil/PP and oil/FEP systems is closely related to the difference in the oil-polymer interaction. The TSC is a useful method for investigating carrier traps in the surface region and their change due to the oil-polymer interaction. To investigate further the relation between the carrier traps and tan delta, collecting bias TSC was measured on a specimen to which an ac voltage was applied. The results indicate that the decrease in tan(delta) during the ac voltage application depends on the amount of trapped carriers near the polymer's surface or, the decrease in carriers in the oil
S. Ochiai, H. Iwasaki, M. Ieda and T. Mizutani, IEEE Transactions on Dielectrics and Electrical Insulation 1 (1994) 487-495

T0046 – Process-structure-property relationships of erodable polymeric biomaterials: II–long range order in poly(desaminotyrosyl arylates)

The long-range order of some bioerodable polyesteramides based on a desaminotyrosyl [Thermochim Acta 396 (2003) 141; Polym Adv Technol 13 (2002) 926; J Am Chem Soc 119 (1997) 4553] diol monomer has been investigated. The order is mesogenic, best described as a 'condis crystal' or smectic-like. In all cases where long-range order is present, ordered H bonds between amide groups are observed. The order stabilizes the polymer to dimensional change and mechanical relaxation under biorelevant conditions.
M. Jaffe, Z. Ophir, G. Collins, A. Recber, S-U. Yoo, J.J. Rafalko, Polymer 44 (2003) 6033-6042

T0013 – Study by thermostimulated currents of dielectric relaxations through the glass transition in an amorphous polymer : poly(n-butyl methacylate)

The study of poly(n-butyl methacrylate) (PnBMA) by thermostimulated currents has been performed in order to give a better definition of the molecular mobility when crossing the glass transition. It reveals the existence of two dipolar relaxation modes: alpha, ascribed to the glass-rubber relaxation, and alpha', which might be the dielectric manifestation of the liquid-liquid transition. The distribution of relaxation times and the evolution of the activation enthalpies when increasing the temperature have been studied by the fractional polarizations technique. It appears that the alpha and alpha' modes behave differently, showing the crossover from an Arrhenian to a Vogelian behavior. Furthermore, up to T, the cooperativity of molecular mobility is highlighted by the existence of a compensation law in agreement with Starkweather's criterion, and above T, results might be explained by the existence of an intermediate state neither glassy nor completely liquid.
E. Dudognon, A. Bernès and C. Lacabanne, Macromolecules 34 (2001) 3988-3992

T0034 – Analysis of Thermally Stimulated Current and effect of rubbery annealing around glass-rubber transition temperature in polyethylene terephtalate

Thermally stimulated currents (TSC) in amorphous polyethylene terephthalate films have been investigated in the temperature range of -180 to 140°C. This material shows a very weak intensity peak at approximately -95°C and another around 80°C originated from dipolar process (alpha-peak), as evidenced from the variation of polarizing conditions such as applied electric field and polarizing time. The effect of isochronal rubbery annealing starts to appear from a temperature of annealing of 90°C, it then appears in a TSC spectrum two components around 88 and 108°C allotted, respectively to the true and rigid amorphous phases. The first component tends to disappear in an irreversible way to the detriment of the second which implies the establishment of an order within material during annealing by the formation and growth of nodules. The thermostimulated currents technique allowed to calculate with good precision the activation parameters of each process as well as the evaluation of the crystallinity rate by an established empirical formula.
N. Benrekaa , A. Gourari, M. Bendaoud and K. Ait-hamouda, Thermochimica Acta 413 (2004) 39-46

T0023 – Simulation of thermally stimulated curents in dielectric : effects of thermal expansion

The influence of thermal expansion on thermally stimulated currents has been studied by means of model calculations based on the bistable model of Fröhlich, considering especially the case of materials characterized by expansion coefficients markedly different above and below the relaxation range. A good qualitative and quantitative agreement has been obtained between theory and experiment in elastomeric materials (styrene-isoprene-styrene and isoprene-styrene-isoprene block copolymers) showing that thermal expansion is the main factor responsible for the appearance of current reversals in thermally stimulated polarization processes
J. Vanderschueren, M. Ladang, J. Niezette and M. Corapci, Journal of Applied Physics 58 (1985) 4654-4657

T0045 – Characterisation of EVA encapsulant material by thermally stimulated current technique

The purpose of this investigation is to better define the thermal behaviour of EVA-based encapsulant during photovoltaic module encapsulation process and also in field exposure in desert climate using the thermally stimulated current (TSC) technique. TSC experiments were conducted on EVA in the temperature range from -150°C to 70°C, the measurements were carried out on uncured and cured specimens of EVA and on EVA samples especially prepared using the laminator equipment. When performing the measurements with the TSC instrument it was noted that the EVA exhibits two peaks assigned to dipole relaxation processes. The peak maximum current and the area under the TSC current peak were used for the determination of the glass transition temperature, activation energy and relaxation frequency. For original EVA, we found that glass transition temperature at constant polarisation voltage and under different polarisation temperatures remain unchanged and is located around -38°C. Also, the activation energy has been determined using initial rise method to be about 0.32 eV. At gel content of 70%, the cured EVA shows a reduced integrated area under the depolarisation peak, especially for the high temperature. The combined change in TSC peak parameters of EVA encapsulant is correlated with the degree of curing.
K. Agroui, G. Collins, Solar Energy Materials & Solar Cells 80 (2003) 33-45

T0033 – The use of thermal methods for predicting glass-former fragility

Glass-former fragility describes the changing dynamics of a supercooled liquid with temperature and so dictates the temperature of glass transition as well as the dynamics of the non-equilibrium glassy state. Fragility parameters can be calculated from either experimental relaxation time or viscosity data. Predictions of fragility can also be made using thermal methods. The objectives of this manuscript are to evaluate three thermal methods of fragility prediction and, using these methods, to predict the fragility of a number of pharmaceutical glass-formers. Using differential scanning calorimetry, fragility predictions were performed by extrapolating configurational entropy to zero and by calculating an activation enthalpy of structural relaxation at the glass transition (?ETg) from the scanning rate dependency of the glass transition temperature, and glass transition width. On comparison with experimental Vogel-Tammann-Fulcher (VTF) fragility parameters for four glass-formers, all thermal methods were found to have reasonable predictive ability. Characterisation of pharmaceutical glass-formers by all thermal methods yielded predicted VTF D parameters in the range of 7-15. Predictions for a further 10 pharmaceutical glass-formers using only the configurational entropy method were within this range suggesting that moderately 'fragile' behaviour may be a common feature of such materials.
K.J. Crowley and G.Zografi, Thermochimica Acta 380 (2001) 79-93

T0022 – Thermally Stimulated Currents from corona-charged polypropylene films : a thermal effect of vacuum deposition of metallic electrodes

It is demonstrated that the thermally stimulated currents (TSC) from positively or negatively corona-charged polypropylene strongly depend on the order of the following two processes: a process of vacuum deposition of Al electrodes on the sample polymer and a process of heat-treatment of the polymer. Observed results are explained by a thermal effect which is introduced during the vacuum deposition of metallic electrodes. This thermal effect of the vacuum deposition of metallic electrodes is the largest for Al and the smallest for Bi among Al, Au, Ag, and Bi. Observed TSC spectra have three peaks at about 68, 142, and above 147°C for positively charged samples and four peaks at about 48, 90, 142, and above 147°C for negatively charged samples, respectively. Origins of these TSC peaks are discussed in some detail.
A. Baba and K. Ikezaki, Journal of Applied Physics 57 (1985) 359-365

T0044 – A mechanistic investigation of an amorphous pharmaceutical and its solid dispersions. Part II: Molecular mobility and activation thermodynamic parameters

The ability of TSDC to characterize further amorphous materials beyond that possible with DSC was presented in part I (16) of this work. The purpose of part II presented here is to detect and quantitatively characterize time-scales of molecular motions (relaxation times) in amorphous solids at and below the glass transition temperature, to determine distributions of relaxation times associated with different modes of molecular mobility and their temperature dependence, and to determine experimentally the impact upon these parameters of combining the drug with excipients (i.e., solid dispersions at different drug to polymer ratios). The knowledge gleaned may be applied toward a more realistic correlation with physical stability of an amorphous drug within a formulation during storage. Methods. Preparation of amorphous drug and its solid dispersions with PVPK-30 was described in part I (16). Molecular mobility and dynamics of glass transition for these systems were studied using TSDC in the thermal windowing mode. Results. Relaxation maps and thermodynamic activation parameters show the effect of formulating the drug in a solid dispersion on converting the system (drug alone) from one with a wide distribution of motional processes extending over a wide temperature range at and below Tg to one that is homogeneous with very few modes of motion (20% dispersion) that becomes increasingly less homogeneous as the drug load increases (40% dispersion). This is confirmed by the high activation enthalpy (due to extensive intra- and intermolecular interactions) as well as high activation entropy (due to higher extent of freedom) for the drug alone vs. a close to an ideal system (lower enthalpy), with less extent of freedom (low entropy) especially for the 20% dispersion. The polymer PVPK-30 exhibited two distinct modes of motion, one with higher values of activation enthalpies and entropy corresponding to -relaxations, the other with lower values corresponding to -relaxations characterized by local noncooperative motional processes. Conclusions. Using thermal windowing, a distribution of temperature- dependent relaxation times encountered in real systems was obtained as opposed to a single average value routinely acquired by other techniques. Relevant kinetic parameters were obtained and used in mechanistically delineating the effects on molecular mobility of temperature and incorporating the drug in a polymer. This allows for appropriate choices to be made regarding drug loading, storage temperature, and type of polymer that would realistically correlate to physical stability.
R.A. Shmeis, Z. Wang and S.L. Krill, Pharmaceutical Research 21 (2004) 2031-2039

T0032 – Characterization of structural heterogeneity of polyurethane coatings

The thermal analysis techniques - Differential Scanning Calorimetry and ThermoStimulated Current - have been used to characterize a polyurethane high solid coating. The glass transition temperature, as determined by DSC, is 60°C. Below this glass transition temperature, an sub dielectric relaxation mode has been observed; it corresponds to cooperative movements precursor of the glass transition. The ss dielectric relaxation mode, located at Tg has been attributed to movements of soft sequences of the amorphous phase liberated at the glass transition temperature. The analysis of the fine structure shows that they are constituted of elementary processes characterized by relaxation times following a compensation law. Above Tg, the hs dielectric relaxation of hard sequences has been shown. It corresponds to hard sequences hydrogen bonded in polyurethane
P. Paolpi, C. Lacabanne, Journal of Applied Polymer Science 81 (2001) 2786 - 2790

T0052 – Comparison of HPMC based polymers performance as carriers for manufacture of solid dispersions using the melt extruder

Preparation of amorphous solid dispersions using hot-melt extrusion process for poorly water soluble compounds which degrade on melting remains a challenge due to exposure to high temperatures. The aim of this study was to develop a physically and chemically stable amorphous solid dispersion of a poorly water-soluble compound, NVS981, which is highly thermal sensitive and degrades upon melting at 165 °C. Hydroxypropyl Methyl Cellulose (HPMC) based polymers; HPMC 3cps, HPMC phthalate (HPMCP) and HPMC acetyl succinate (HPMCAS) were selected as carriers to prepare solid dispersions using hot melt extrusion because of their relatively low glass transition temperatures. The solid dispersions were compared for their ease of manufacturing, physical stability such as recrystallization potential, phase separation, molecular mobility and enhancement of drug dissolution. Two different drug loads of 20 and 50% (w/w) were studied in each polymer system. It was interesting to note that solid dispersions with 50% (w/w) drug load were easier to process in the melt extruder compared to 20% (w/w) drug load in all three carriers, which was attributed to the plasticizing behavior of the drug substance. Upon storage at accelerated stability conditions, no phase separation was observed in HPMC 3cps and HPMCAS solid dispersions at the lower and higher drug load, whereas for HPMCP, phase separation was observed at higher drug load after 3 months. The pharmaceutical performance of these solid dispersions was evaluated by studying drug dissolution in pH 6.8 phosphate buffer. Drug release from solid dispersion prepared from polymers used for enteric coating, i.e. HPMCP and HPMCAS was faster compared with the water soluble polymer HPMC 3cps. In conclusion, of the 3 polymers studied for preparing solid dispersions of thermally sensitive compound using hot melt extrusion, HPMCAS was found to be the most promising as it was easily processible and provided stable solid dispersions with enhanced dissolution.
Indrajit Ghosh, Jennifer Snyder, Radha Vippagunta, Marilyn Alvine, Ronak Vakil, Wei-Qin (Tony) Tong, Sudha Vippagunta, International Journal of Pharmaceutics 419 (2011) 12– 19

T0051 – Self-assembling peptide-enriched electrospun polycaprolactone scaffolds promote the h-osteoblast adhesion and modulate differentiation-associated gene expression

Electrospun polycaprolactone (PCL) is able to support the adhesion and growth of h-osteoblasts and to delay their degradation rate to a greater extent with respect to other polyesters. The drawbacks linked to its employment in regenerative medicine arise fromits hydrophobic nature and the lack of biochemical signals linked to it. This work reports on the attempt to add five different self-assembling (SA) peptides to PCL solutions before electrospinning. The hybrid scaffolds obtained had regular fibers (SEM analysis) whose diameters were similar to those of the extracellularmatrix, more stable hydrophilic (contact angle measurement) surfaces, and anamorphous phase constrained by peptides (DSC analysis). They appeared to have a notable capacity to promote the h-osteoblast adhesion and differentiation process by increasing the gene expression of alkaline phosphatase, bone sialoprotein, and osteopontin. Adding an Arg-Gly-Asp (RGD) motif to a self-assembling sequence was found to enhance cell adhesion, while the same motif condensed with a scrambled sequence did not, indicating that there is a cooperative effect between RGD and 3D architecture created by the self-assembling peptides. The study demonstrates that self-assembling peptide scaffolds are still able to promote beneficial effects on h-osteoblasts even after they have been included in electrospun polycaprolactone. The possibility of linking biochemical messages to self-assembling peptides could lead the way to a 3D decoration of fibrous scaffolds.
Roberta Danesin, Paola Brun, Martina Roso, Florian Delaunay, Valérie Samouillan, Katya Brunelli, Giovanna Iucci, Francesca Ghezzo, Michele Modesti, Ignazio Castagliuolo, Monica Dettin, Bone 51 (2012) 851–859

T0050 – Local motions in L-iditol glass: Identifying different types of secondary relaxations

The sub-Tg relaxations in amorphous L-iditol have been studied by Thermally Stimulated Depolarisation Current (TSDC). The effect of aging on these motional processes was analyzed during annealing at 253K and 243K, respectively 19K and 29K below its calorimetric glass tranaition at Tg=272K.
Joaquim J. Moura Ramos, Herminio P. Diogo, Susanna S. Pinto, Thermochimica Acta 467 (2008) 107-112

T0049 – The nature of crystal disorder in milled pharmaceutical materials

The purpose of this study was to study the nature of disorder in milled crystalline materials. Specifically to elucidate if the induced disorder represents crystal defects or amorphous regions. Felodipine and griseofulvin were chosen as model drugs and subjected to milling. Cryomilling was chosen in order to mitigate the influence of heat generated by the process. Amorphous drug samples were produced by quenching the melt. Crystalline, amorphous and cryomilled drug samples were characterized by powder X-ray diffraction (PXRD), thermal analysis (DSC), thermal polarization (thermally stimulated polarization current), and surface energy (inverse gas chromatography). The PXRD analysis shows that cryomilling reduces the crystallinity of the two drugs, while maintaining the same crystal form. Heat capacity measurements (DSC) show that milled material for either drug does not exhibit a glass transition but shows instead an exothermic (crystallization like) event. The thermal polarization profiles revealed that none of the modes of molecular motion (polarization peaks) characteristic of the amorphous formwere observed in either the unmilled crystalline or milled forms for either drug. For each drug, the polarization spectra of milled forms were similar, but not identical, to those of the corresponding unmilled crystalline materials. Inverse gas chromatography (IGC) measurements showed that the surface energy of cryomilled samples was higher than those of the unmilled and amorphous forms for both drugs. The polarization and heat capacity measurements show that the disorder induced by milling either griseofulvin or folodipine consists of crystal defects rather than amorphous regions. The exothermic event in the milled samples is attributed to the crystallization of defects in the crystal. These results when combined with the IGC measurements indicate that the milled material retains its crystalline character, making it more stable (at the core) than the amorphous form. However, the milled material has also the most active surface, making itthe more interactive with other surfaces as an activated powder.
Sai Prasanth Chamarthy, Rodolfo Pinal, Colloids and Surfaces A: Physicochem. Eng. Aspects 331 (2008) 68–75

T0048 – Weak solid–solid transitions in pharmaceutical crystalline solids detected via thermally stimulated current

To demonstrate the ability of thermally stimulated current (TSC), normally used to study amorphous systems, in detecting weak solid–solid transitions in crystalline pharmaceutical compound. Methods: Polymorphs of a new chemical entity, LAU254, were generated and characterized using conventional and hot plate X-ray diffraction, DSC and TSC. Equilibration of 50:50 mixtures of the different polymorphs and solubility studies were conducted in aqueous and organic solvent at 25 and 50 ?C and then analyzed by X-ray and DSC. Results: Four crystalline forms (A–D) were isolated. formBshowed one single endotherm at 180 ?Cwhile the other forms showed lower melting endotherms, a crystallization exotherm and eventually a final melting endotherm corresponding to that of form B (180 ?C). The heat of fusion of form B was the highest. In contrast, solubility as well as mixture equilibration studies resulted in all forms converting to form A. TSC analysis revealed a well-defined reproducible peak with a maximum at ?130 ?C which was suspected to be a solid–solid transition. This was confirmed by hot plate X-ray diffraction where careful probing around 120–130 ?C revealed three different forms; form A (the initial form), a second form that appears above 150 ?C, melts, crystallizes and produces form B. Careful inspection of larger sample sizes in DSC showed a small endotherm at ?130 ?C. Conclusions: TSC, normally used to study amorphous systems, proved to be useful in detecting weak solid–solid transitions in crystalline pharmaceuticals, an application that has never been explored or reported previously. This resulted in identifying a form, obtainable only at temperatures above the transition temperature (related enantiotropically to the form that is most stable at ambient temperatures) and in reconciling the DSC and solubility data. TSC can be very useful in detecting and probing those transitions that occur in the solid state due to subtle dipolar motion and are not associated with large changes in global motion and heat capacity that is needed for detection by DSC and therefore can be complementary to DSC in obtaining a more complete assessment of the polymorphism behavior of crystalline solids.
Rama A. Shmeis, Steven L. Krill Thermochimica acta (2004) article in press

T0047 – Thermal analysis of complex relaxation processes in poly(desaminotyrosyl-tyrosine arylates)

The goal of this study is to better understand the thermal characteristics and molecular behavior of two poly(desaminotyrosyl-tyrosine arylates). These two polymers were chosen from a combinatorial library of polymers developed by changing the type and size of the two substitutable chain locations. The objective of this work was to describe the origin of the complex relaxation processes that have been observed by thermal analysis methods. DSC, TMA and TSC studies were conducted on poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DT 12,10), and poly(desaminotyrosyl-tyrosine ethyl succinate), poly(DT 2,2), in film and fiber form. DSC experiments on poly(DT 2,2) show only a glass transition at about 80°C which is characteristic of an amorphous polymer. The DSC of poly(DT 12,10) shows multiple thermal events indicative of a more complex internal structure. The thermally stimulated current (TSC) analysis results for poly(DT 2,2) indicate a region of molecular mobility at about 80°C consistent with the Tg from DSC. For poly(DT 12,10) there is a dipole relaxation process observed at about 40°C. An additional region of mobility at 60°C for poly(DT 12,10) fibers is observed. The comparison of conventional TSC with a modified TSC procedure suggests that this process represents a spontaneous reorganization of the internal structure of the solid. The comparison of DSC and TSC results suggests that poly(DT 12,10) has two distinct modes of organization with a transition between these modes at about 60°C. Previously published results indicate that solid state structure formation is related to two different modes of hydrogen bonding in the internal structure of the solid.
G. Collins, S-U. Yoo, A. Recber, M. Jaffe, Polymer 48 (2007) 975-988