Differential scanning calorimetry

About: Differential scanning calorimetry is a(n) research topic. Over the lifetime, 50315 publication(s) have been published within this topic receiving 1152335 citation(s). The topic is also known as: DSC.

Structure and process relationship of electrospun bioabsorbable nanofiber membranes

Abstract: An electrospinning method was used to fabricate bioabsorbable amorphous poly( d , l -lactic acid) (PDLA) and semi-crystalline poly( l -lactic acid) (PLLA) nanofiber non-woven membranes for biomedical applications. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and synchrotron wide-angle X-ray diffraction/small angle X-ray scattering. SEM images showed that the fiber diameter and the nanostructured morphology depended on processing parameters such as solution viscosity (e.g. concentration and polymer molecular weight), applied electric field strength, solution feeding rate and ionic salt addition. The combination of different materials and processing parameters could be used to fabricate bead-free nanofiber non-woven membranes. Concentration and salt addition were found to have relatively larger effects on the fiber diameter than the other parameters. DSC and X-ray results indicated that the electrospun PLLA nanofibers were completely non-crystalline but had highly oriented chains and a lower glass transition temperature than the cast film.

Poly(ethylene oxide)-poly(propylene oxide )-poly (ethylene oxide) block copolymer surfactants in aqueous solutions and at interfaces: thermodynamics, structure, dynamics, and modeling

Abstract: The association properties of poly(ethylene oxide)-block-poly(propyleneoxide)-block-poly(ethylene oxide) (PEOPPOPEO) copolymers (commercially available as Poloxamers and Pluronics) in aqueous solutions, and the adsorption of these copolymers at interfaces are reviewed. At low temperatures and/or concentrations the PEOPPOPEO copolymers exist in solution as individual coils (unimers). Thermodynamically stable micelles are formed with increasing copolymer concentration and/or solution temperature, as revealed by surface tension, light scattering, and dye solubilization experiments. The unimer-to-micelle transition is not sharp, but spans a concentration decade or 10 K. The critical micellization concentration (CMC) and temperature (CMT) decrease with an increase in the copolymer PPO content or molecular weight. The dependence of CMC on temperature, together with differential scanning calorimetry experiments, indicates that the micellization process of PEOPPOPEO copolymers in water is endothermic and driven by a decrease in the polarity of ethylene oxide (EO) and propylene oxide (PO) segments as the temperature increases, and by the entropy gain in water when unimers aggregate to form micelles (hydrophobic effect). The free energy and enthalpy of micellization can be correlated to the total number of EO and PO segments in the copolymer and its molecular weight. The micelles have hydrodynamic radii of approximately 10 nm and aggregation numbers in the order of 50. The aggregation number is thought to be independent of the copolymer concentration and to increase with temperature. Phenomenological and mean-field lattice models for the formation of micelles can describe qualitatively the trends observed experimentally. In addition, the lattice models can provide information on the distribution of the EO and PO segments in the micelle. The PEOPPOPEO copolymers adsorb on both airwater and solidwater interfaces; the PPO block is located at the interface while the PEO block extends into the solution, when copolymers are adsorbed at hydrophobic interfaces. Gels are formed by certain PEOPPOPEO block copolymers at high concentrations, with the micelles remaining apparently intact in the form of a “crystal”. The gelation onset temperature and the thermal stability range of the gel increase with increasing PEO block length. A comparison of PEOPPO copolymers with PEOPBO and PEO PS block copolymers and CiEj surfactants is made, and selected applications of PEOPPOPEO block copolymer solutions (such as solubilization of organics, protection of microorganisms, and biomedical uses of micelles and gels) are presented.

Differential scanning calorimetry

Abstract: 1 Introduction.- 2 Types of Differential Scanning Calorimeters and Modes of Operation.- 3 Theoretical Fundamentals of Differential Scanning Calorimeters.- 4 Calibration of Differential Scanning Calorimeters.- 5 DSC Curves and Further Evaluation.- 6 Applications of Differential Scanning Calorimetry.- 7 Evaluation of the Performance of a Differential Scanning Calorimeter.- Appendix 1.- Appendix 2.- References.

Low temperature latent heat thermal energy storage: Heat storage materials

Abstract: Heat-of-fusion storage materials for low temperature latent heat storage in the temperature range 0–120°C are reviewed. Organic and inorganic heat storage materials classified as paraffins, fatty acids, inorganic salt hydrates and eutectic compounds are considered. The melting and freezing behaviour of the various substances is investigated using the techniques of Thermal Analysis and Differential Scanning Calorimetry. The importance of thermal cycling tests for establishing the long-term stability of the storage materials is discussed. Finally, some data pertaining to the corrosion compatibility of heat-of-fusion substances with conventional materials of construction is presented.

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.