Differential scanning calorimetry

About: Differential scanning calorimetry is a research topic. Over the lifetime, 50315 publications have been published within this topic receiving 1152335 citations. The topic is also known as: DSC.

The phase behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals

Abstract: Air- and water-stable 1-alkyl-3-methylimidazolium tetrafluoroborate salts with the general formula [Cn-mim][BF4] (n = 0–18) have been prepared by metathesis from the corresponding chloride or bromide salts. The salts have been characterised by 1H NMR and IR spectroscopy, microanalysis, polarising optical microscopy and differential scanning calorimetry. Those with short alkyl chains (n = 2–10) are isotropic ionic liquids at room temperature and exhibit a wide liquid range, whereas the longer chain analogues are low melting mesomorphic crystalline solids which display an enantiotropic smectic A mesophase. The thermal range of the mesophase increases with increasing chain length and in the case of the longest chain salt prepared, [C18-mim][BF4], the mesophase range is ca. 150 °C.

Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: 2H nuclear magnetic resonance and differential scanning calorimetry.

Abstract: Deuterium nuclear magnetic resonance spectroscopy and differential scanning calorimetry are used to map the phase boundaries of mixtures of cholesterol and chain-perdeuteriated 1,2-dipalmitoyl-sn- glycero-3-phosphocholine at concentrations from 0 to 25 mol % cholesterol. Three distinct phases can be identified: the La or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the 0 phase. The liquid-crystalline phase is characterized by highly flexible phospholipid chains with rapid axially symmetric reorientation; the gel phase has much more rigid lipid chains, and the motions are no longer axially symmetric on the 2H NMR time scale; the 0 phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, we identify three regions of two-phase coexistence. The first of these is a narrow La/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospho- lipid/water dispersions, at 37.75 OC. The dramatic changes in the *H NMR line shape which occur on passing through the phase transition are used to map out the boundaries of this narrow two-phase region. The boundaries of the second two-phase region are determined by 2H NMR difference spectroscopy, one boundary lying near 7.5 mol 5% cholesterol and running from 37 down to at least 30 OC; the other boundary lies near 22 mol 5% cholesterol and covers the same temperature range. Within this region, the gel and /3 phases coexist. As the temperature is lowered below about 30 "C, the phospholipid motions reach the intermediate time scale regime of 2H NMR so that spectral subtractions become difficult and unreliable. The third two-phase region lies above 37 OC, beginning at a eutectic point somewhere between 7.5 and 10 mol % cholesterol and ending at about 20 mol %. In this region, the La and /3 phases are in equilibrium. The boundaries for this region are inferred from differential scanning calorimetry traces, for the boundary between the La- and the two-phase region, and from a dramatic sharpening of the NMR peaks on crossing the boundary between the two-phase region and the &phase region. In this region, the technique of difference spectroscopy fails, presumably because the diffusion rate in both the La- and P-phase domains is so rapid that phospholipid molecules exchange rapidly between domains on the experimental time scale.

Dependence of the Fictive Temperature of Glass on Cooling Rate

Abstract: An equation derived by Ritland relating the cooling rate and fictive temperature for glasses without memory is extended to those with memory, i.e. those which exhibit a spectrum of relaxation times. Provided that the spectrum of relaxation times is temperature-independent, the limiting fictive temperature, T′f, obtained when a glass is cooled through the transition region, is shown to be related to the cooling rate, q, by d In |q|/d(1/T'f)=-Δh★/R where R is the ideal gas constant and Δh★ the activation enthalpy for the relaxation times controlling the structural relaxation. Values of T′f vs q obtained from enthalpy measurements by differential scanning calorimetry are presented for B2O3, 0.4Ca(NO3)2—0.6KNO3, and borosilicate crown glasses; Δh★ is equal, within experimental error, to the activation enthalpy for shear viscosity. Values of T′f from volume and enthalpy measurements obtained at the same cooling rate for the borosilicate crown glass are equal.

Preparation of ‘‘amorphous’’ Ni60Nb40 by mechanical alloying

Abstract: ‘‘Amorphous’’ Ni60Nb40 has been prepared by mechanical alloying of elemental nickel and niobium powders in a laboratory ball mill in controlled environments. X‐ray diffraction was used to follow the progress of the mechanical alloying which eventually produced ‘‘amorphous’’ diffraction patterns similar to those for liquid quenched amorphous Ni60Nb40. Crystallization behavior was measured by differential scanning calorimetry for the mechanically alloyed and liquid quenched material. The differences that were observed in this behavior, and in the products of crystallization, may be attributed to impurities (especially oxygen) introduced during mechanical alloying.

Determining Beta-Sheet Crystallinity in Fibrous Proteins by Thermal Analysis and Infrared Spectroscopy

Abstract: We report a study of self-assembled beta-pleated sheets in B. mori silk fibroin films using thermal analysis and infrared spectroscopy. B. mori silk fibroin may stand as an exemplar of fibrous proteins containing crystalline beta-sheets. Materials were prepared from concentrated solutions (2−5 wt % fibroin in water) and then dried to achieve a less ordered state without beta-sheets. Crystallization of beta-pleated sheets was effected either by heating the films above the glass transition temperature (Tg) and holding isothermally or by exposure to methanol. The fractions of secondary structural components including random coils, alpha-helices, beta-pleated sheets, turns, and side chains were evaluated using Fourier self-deconvolution (FSD) of the infrared absorbance spectra. The silk fibroin films were studied thermally using temperature-modulated differential scanning calorimetry (TMDSC) to obtain the reversing heat capacity. The increment of the reversing heat capacity ΔCp0(Tg) at the glass transition fo...