Search results for "Enthalpy of fusion"
showing 9 items of 9 documents
Kristallisations- und schmelzverhalten von copolymeren aus 3,3-bis(chlormethyl)oxetan und ß-propiolacton
1974
Einkristalle von Copolymeren aus 3,3-Bis(chlormethyl)oxetan und s-Propiolacton wurden bezuglich Schmelzverhalten, Schmelzenthalpie, Dichte und Langperiode untersucht. Aus der Messung der Schmelzenthalpie und der Dichte berechnen sich Kristallisationsgrade von 50—60% in guter Ubereinstimmung mit einem Modell, welches den Ausschlus der aus s-Propiolacton (PL) entstandenen Grundbausteine von dem aus Sequenzen der 3,3-Bis(chlormethyl)oxetan (BCMO-)Einheiten aufgebauten Gitter verlangt. Im Vergleich zu reinem Poly-BCMO wird die Dicke der Copolymereinkristalle nur wenig durch Anderung der Kristallisationstemperatur beEinflust. Wegen des blockartigen Aufbaus der Copolymeren bestimmt die mittlere S…
Evaluation of entropies of fusion of polychlorinated naphthalenes by model congeners: A DSC study
2006
Abstract Thirteen congeners of polychlorinated naphthalenes (PCN) were synthesized and studied by differential scanning calorimetry (DSC). Melting points (Tm) were obtained for all thirteen, and enthalpies of fusion (ΔHf) were obtained for nine congeners. Melting points of other PCNs, except for five, were found in literature. In addition, experimental ΔHf values determined by DSC were found only for 1- and 2-mono-chloronaphthalenes in the literature. The missing or uncertain values of the eight melting points and 64 enthalpies of fusion were estimated by multiple linear regressions using a set of thirteen molecular descriptors as candidates for independent variables. The stepwise model of …
Comparison of two melting range analysis methods with lactitol monohydrate
2001
Abstract In pharmacopoeia, the melting point is determined by a standard method with a melting point instrument. The melting point can also be determined with differential scanning calorimetry (DSC). In this study, the standard method and DSC method are compared for determining the melting range of lactitol monohydrate. The effect of initial temperature, grinding, and drying on the melting range of different lactitol monohydrate samples was studied by a melting point instrument. The melting point and melting enthalpy of the stable form of lactitol monohydrate was identified by DSC. The statistical analysis of the results is based on a t-test. All studied variables had a small effect on the …
Structure and properties of polyethyleneterephthalate crystallized by annealing in the highly oriented state
1976
The structure of polyethyleneterephthalate bristles drawn about five times in the amorphous state and subsequently crystallized at temperatures between 100 and 260‡ C has been studied by means of small-angle X-ray scattering. In addition density, heat of fusion and wide-angle scattering behaviour were measured. For comparison, similar experiments were carried out with undrawn samples. The results showed that the degree of crystallinity of PET cannot be calculated from density data on the basis of a simple two-phase model, since the effective densitiesρc* andρa* of the crystalline and amorphous regions depend strongly on crystallization and drawing conditions. With rising crystallization tem…
Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ε -Caprolactone
2010
A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange a…
Influence of electronic and geometric properties on melting of sodium clusters
2004
Systematics of the melting transition for sodium clusters with 40-355 atoms has been studied with both ab initio and semiclassical molecular dynamics simulations. The melting temperatures obtained with an ab initio method for Na55 + and Na93 + correlate well with the experimental results. The semiclassically determined melting temperatures show similarities with the experimentally determined ones in the size region from 55 to 93 and near size 142, and the latent heat in the size region from 55 to 139, but not elsewhere in the size region studied. This indicates that the nonmonotonical melting behavior observed experimentally cannot be fully explained by geometrical effects. The semiclassica…
Environmentally Relevant Properties of All 209 Polychlorinated Biphenyl Congeners for Modeling Their Fate in Different Natural and Climatic Conditions
2009
The temperature dependence of physical properties and degradation lifetimes in the environment of all polychlorinated biphenyl (PCB) congeners (N = 209) were determined. For physical properties, the coefficients A and B in equations log(property) = A(property) − B(property)/T(K) were determined by thermodynamic and QSPR methods and compared with the results of independent methods in the literature. The coefficients Apl and Bpl for liquid state vapor pressure PL, As and Bs for solubility in water SW, Ah and Bh for volatility kH (or kH = PL/SW), and Aow and Bow for lipophilicity (KOW), stored in the database of the fate model program, allowed automatic temperature corrections for realistic fa…
Thermoanalytical studies on phases of D-mannitol
1993
Abstract D-mannitol exists in several polymorphic crystalline forms. The conditions of crystallization are not well-defined, and in some cases mixtures of the different forms are obtained. In the DSC study the different forms melted nearly at the same temperature (166±°C). The heat of fusion of the k form was lower than those of the other forms. With slow heating rate (2 ° C min ) the δ form changed to k between 140 and 165 °C. The crystallization of D-mannitol from the melt gave from one to seven peaks in the DSC between 95 and 126 °C depending on cooling rates and the amounts of sample.
Charge-Induced Deformation of the 4He Solid-Superfluid Interface
1984
The interface between solid and superfluid 4He has revealed unusual dynamic properties. Characteristic of this quantum system are the very high thermal conductivity of the superfluid phase, and an extremely small heat of fusion below temperatures of about 1 K. As a result, equilibrium at the solid-superfluid 4He interface is established quite rapidly, which gives rise, e.g., to melting — crystallization waves [1,2] — similar in appearance to surface waves on a free liquid surface — and to anomalous transmission of sound [3].