Temperature calibration of differential scanning calorimeters

Price, Duncan M.

doi:10.1007/bf02547423

Cited by 42 publications

(13 citation statements)

References 23 publications

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“…Hysteresis in the transition between crystal structures is not unusual and has been observed in other systems [13,14]. One approach to establishing the absolute limit of this discrepancy between the transition point on cooling and that seen on heating is to observe the transition at progressively slower rates of temperature change and extrapolating the measurements to zero heating and cooling rates [15]. Figure 2 shows stepwise isothermal modulated temperature DSC measurements on silver iodide.…”

Section: Methodsmentioning

confidence: 85%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

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IntroductionSilver iodide can exist in three crystal polymorphs at atmospheric pressure [1]. Below 147°C the b-phase is stable; this has a wurtzite structure with the iodide ions arranged in a hexagonal close packed structure and with the silver ions occupying a sublattice of interstitial tetrahedral sites. Above 147°C silver iodide undergoes a crystalline transition to the high temperature a-phase, which has a body centred cubic arrangement of iodine ions with the silver ions distributed over a sublattice of interstitial sites whose number exceeds the occupancy of silver ions. This phase is stable up to the melting temperature of 555°C. Also present below 147°C is the metastable g-phase which differs from the b-phase in that it has a zinc blende structure with the iodide ions occupying a cubic close packed lattice. This can be viewed as a defect b-phase structure in which the iodide ions are layered ABABAB rather than ABCABC. Migration of Ag + though the disordered cationic lattice gives rise to exceptionally high ionic conductivity of the a-AgI phase [2]. The ordering of Ag + has been studied using computer simulations and it is the tendency of the cations to condense into a locally monoclinic arrangement which is unstable relative to the hexagonal (wurtzite) structure which is proposed as the driving force for the a-b phase transition [3].Previous investigators have reported the heat capacity of silver iodide using conventional and AC calorimetry [4,5]. These measurements have been carried out in heating only whereas Hanaya et al. have reported DSC studies on heating and cooling of the stabilisation of a-AgI by incorporating AgI inside porous silica [6]. In this work the nucleation of the low temperature phase is claimed to be inhibited by the reduction in AgI particle size. For bulk AgI claims have been made that the b-a phase transition can be made to occur around 100°C when the specimen is heated by microwave radiation rather than be conventional heating [7]. In this particular case, multi-phonon coupling between the electromagnetic field and vibrational motions within the AgI crystal are conjectured to stabilise the high temperature form in the same way that mechanical stress by reduction in particle size might also achieve the same effect. An alternative mechanism is the so-called 'ponderomotive effect' whereby microwave-excited ionic currents become locally rectified at interfaces (such as grain boundaries) so as to promote mass transport [8]. In the case of AgI there is no bulk diffusion of material during its structural transformation but it is not unreasonable to propose that this process might promote the formation of a-AgI.This work reports studies on the silver iodide a-b phase transition by conventional and modulated-temperature calorimetry. We also report dielectric property measurements under conventional and microwave heating. ExperimentalThe silver iodide powder (99.999%, Acros Organics) used for these studies was made into pellets with a density of 4.9±0.3 g cm -3 , i.e. 83% of theoretical d...

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Section: Methodsmentioning

confidence: 85%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

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“…A baseline was subtracted, and the temperatures of phase coexistence onset and completion were determined using the model-free tangent construction method [40,41]. Additional analysis details are found in Supplementary Materials S2.…”

Section: Methodsmentioning

confidence: 99%

Phase behavior and domain size in sphingomyelin-containing lipid bilayers

Petruzielo

Heberle

Drazba

et al. 2013

Biochimica et Biophysica Acta (BBA) - Biomembranes

117

153

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Membrane raft size measurements are crucial to understanding the stability and functionality of rafts in cells. The challenge of accurately measuring raft size is evidenced by the disparate reports of domain sizes, which range from nanometers to microns for the ternary model membrane system sphingomyelin (SM)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). Using Förster resonance energy transfer (FRET) and differential scanning calorimetry (DSC), we established phase diagrams for porcine brain SM (bSM)/dioleoyl-sn-glycero-3-phosphocholine (DOPC)/Chol and bSM/POPC/Chol at 15 and 25°C. By combining two techniques with different spatial sensitivities, namely FRET and small-angle neutron scattering (SANS), we have significantly narrowed the uncertainty in domain size estimates for bSM/POPC/Chol mixtures. Compositional trends in FRET data revealed coexisting domains at 15 and 25°C for both mixtures, while SANS measurements detected no domain formation for bSM/POPC/Chol. Together these results indicate that liquid domains in bSM/POPC/Chol are between 2 and 7 nm in radius at 25°C: that is, domains must be on the order of the 2–6 nm Förster distance of the FRET probes, but smaller than the ~7 nm minimum cluster size detectable with SANS. However, for palmitoyl SM (PSM)/POPC/Chol at a similar composition, SANS detected coexisting liquid domains. This increase in domain size upon replacing the natural SM component (which consists of a mixture of chain lengths) with synthetic PSM, suggests a role for SM chain length in modulating raft size in vivo.

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“…As they emerge from the bottom of the column, they are detected by a differential refractometer. Since the molecular size in solution (hydrodynamic volume) is related to M w (molecular weight), a picture of the entire M w distribution is obtained quickly and simply [13]. …”

Section: Methodsmentioning

confidence: 99%

Manilkara zapota (Linn.) Seeds: A Potential Source of Natural Gum

Singh¹,

Bothara

2014

ISRN Pharmaceutics

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Mucilage isolated from seeds of Manilkara zapota (Linn.) P. Royen syn. is a plant growing naturally in the forests of India. This mucilage is yet to be commercially exploited, and characterized as polymer. Various physicochemical methods like particle size analysis, scanning electron microscopy, thermal analysis, gel permeation chromatography, X-ray diffraction spectrometry, zeta potential, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy have been employed to characterize this gum in the present study. Particle size analyses suggest that mucilage has particle size in nanometer. Scanning electron microscopy analysis suggests that the mucilage has irregular particle size. The glass transition temperature of the gum was observed to be 138°C and 136°C by differential scanning calorimetry and differential thermal analysis, respectively. The thermogravimetric analysis suggested that mucilage had good thermal stability. The average molecular weight of mucilage was determined to be 379180, by gel permeation chromatography, while the viscosity of mucilage was observed to be 219.1 cP. The X-ray diffraction spectrometry pattern of the mucilage indicates a completely amorphous structure. Elemental analysis of the gum revealed the contents of carbon, hydrogen, nitrogen, and sulfur to be 80.9 (%), 10.1 (%), 1.58 (%), and 512 (mg/kg), respectively. Mucilage had specific content of calcium, magnesium, potassium, lower concentrations of aluminum, cadmium, cobalt, lead, and nickel. The major functional groups identified from FT-IR spectrum include 3441 cm−1 (–OH), 1660 cm−1 (Alkenyl C–H & C=C Stretch), 1632 cm−1 (–COO–), 1414 cm−1 (–COO–), and 1219 cm−1 (–CH3CO). Analysis of mucilage by paper chromatography and 1D NMR, indicated the presence of rhamnose, xylose, arabinose, mannose, and fructose.

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Temperature calibration of differential scanning calorimeters

Cited by 42 publications

References 23 publications

Hysteresis in the β–α phase transition in silver iodide

Hysteresis in the β–α phase transition in silver iodide

Phase behavior and domain size in sphingomyelin-containing lipid bilayers

Manilkara zapota (Linn.) Seeds: A Potential Source of Natural Gum

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