The thermal properties of complex, nanophase-separated macromolecules as revealed by temperature-modulated calorimetry

Linear, flexible macromolecules are long recognized as phase structures limited to micrometer and nanometer dimensions with covalent bonds crossing the interfaces. This special, usually non-equilibrium structure leads to unique properties and a multitude of changes for different thermal and mechanical histories. Analyses that enable the study of these properties are temperature-modulated calorimetry and related techniques which allow the separation of equilibrium and non-equilibrium responses. Research on these topics is reviewed and combined to a model for the nanophases. The new approach to the complex nanophase systems yields a better understanding of the relationship between structure and thermodynamic properties. Special emphasis is placed on the size and surface effects on the glass and melting transitions, the development of rigid-amorphous phases, and the reversible melting within the globally metastable structure.     

Role of montmorillonite in flame retardancy of ethylene-vinyl acetate copolymer

The effects of non-treated (MMT), organophilic (OMM), and olefin/silicone polymer intercalated (IMM) montmorillonites on the thermal stability of ethylene-vinyl acetate copolymer (EVA) and on the flammability of magnesium hydroxide filled EVA were studied. The influence of various treatments on the delamination of montmorillonites in EVA was detected by rheological measurements and by Raman microscopy. The latter was a unique method for rapid detection of the dispersion also in highly filled EVA. Enhancement of thermo-oxidative stability of EVA and flame-retarded EVA could be observed by thermal analysis in the presence of variously treated montmorillonites. The flame-retardant efficiency of magnesium hydroxide was improved by simultaneous application of MMT and IMM. The increased performance of magnesium hydroxide was explained by the rheological effect of the IMM, catalytic effect of MMT and chemical interactions of montmorillonites with the metal hydroxide.     

聚苯基膦酸双酚A酯的合成与表征

聚苯基膦酸双酚Ａ酯的合成与表征唐旭东陈晓婷王玉忠杨科珂王波（四川联合大学化学系成都６１００６４）吴大诚（四川联合大学轻纺学院成都６１００６５）关键词聚膦酸酯，阻燃剂，熔融缩聚，热性能聚膦酸酯类化合物是一类重要的磷系阻燃剂［１～３］，与传统的非聚...     

Thermal effects and band spreading in capillary electro-separation

Summary Four Capillary Electroseparation methods are distinguished. All have an ultimate efficiency limited only by axial diffusion and are in principle capable of achieving 10⁶ plates in <1 hour.The main limitation to performance arises from Ohmic heating of the electrolyte. While forced convection at 10ms^–1 is recommended to keep tubes cool, the parabolic temperature profile within the electrolyte limits the tube bore which can be used. A simple limiting expression is derived: (d_c/m)³ (E/kV m^–1)³ (c/mol dm^–3) <3.3×10⁹.Values of constants underlined     

Structural and physical properties of Mg3−xZnxSb2 (x=0-1.34)

The Mg_3−xZn_xSb₂ phases with x=0-1.34 were prepared by direct reactions of the elements in tantalum tubes. According to the X-ray single crystal and powder diffraction, the Mg_3−xZn_xSb₂ phases crystallize in the same P3¯m1 space group as the parent Mg₃Sb₂ phase. The Mg_3−xZn_xSb₂ structure is different from the other substituted structures of Mg₃Sb₂, such as (Ca, Sr, Ba) Mg₂Sb₂ or Mg_5.23Sm_0.77Sb₄, in a way that in Mg_3−xZn_xSb₂ the Mg atoms on the tetrahedral sites are replaced, while in the other structures Mg on the octahedral sites is replaced. Thermoelectric performance for the two members of the series, Mg₃Sb₂ and Mg_2.36Zn_0.64Sb₂, was evaluated from low to room temperatures through resistivity, Seebeck coefficient and thermal conductivity measurements. In contrast to Mg₃Sb₂ which is a semiconductor, Mg_2.36Zn_0.64Sb₂ is metallic and exhibits an 18-times larger dimensionless figure-of-merit, ZT, at room temperature. However, thermoelectric performance of Mg_2.36Zn_0.64Sb₂ is still poor and it is mostly due to its large electrical resistivity.     

Modeling high-pressure densities at wide temperature range with volume scaling: Cyclohexane + n-hexadecane mixtures

High-pressure density data for cyclohexane + n-hexadecane mixtures at a wide temperature range was modeled with several classical equations of state (EOS) and correlative models. A modification for softening the co-volume and another for a volume scaling of the Peng–Robinson EOS (VS-PR) were proposed. The VS-PR model is able to correlate the pure component experimental data employing only five adjustable parameters, with root-mean-square deviation (RMSD) between calculated and experimental densities essentially within the experimental error. This result is superior to widely used approaches, i.e., a six parameter Tait model and six parameter volume translations (temperature and pressure dependent) for Peng–Robinson and Patel–Teja EOS. The VS-PR model also represents well the isobaric thermal expansion and the isothermal compressibility coefficients of the pure cyclohexane, a small naphthenic substance as well as a long chain n-alkane hydrocarbon, n-hexadecane. When modeling the mixture data, the use of VS-PR model of pure components along with the Redlich–Kister expansion, truncated at the first term, the density was correlated within a RMSD only 60% greater than the experimental error. The proposed model is able to accurately represent all the tested mixture data with a relatively small number of parameters.     

Poly(methyl methacrylate)/silica/titania ternary nanocomposites with greatly improved thermal and ultraviolet-shielding properties

Poly(methyl methacrylate) (PMMA)/silica/titania ternary nanocomposites with covalent bonding interaction between polymer and inorganic phases have been prepared using a novel non-hydrolytic sol-gel method. Transmission electron microscope (TEM) image of silica/titania binary inorganic component indicates a core-shell-like structure. Scanning electron microscope (SEM) images suggest that the well dispersed silica/titania particles in the hybrid are on the nanometer-scale. The transparencies of nanocomposites are maintained in visible region while the absorption band in ultraviolet (UV) region is red shifted with increasing inorganic content. The thermogravimetric analysis (TGA) results show that the thermal stability of PMMA copolymer increases dramatically with the addition of silica/titania moieties both in nitrogen and in air.     

Thermal and mechanical properties of UV irradiated collagen/chitosan thin films

The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend.     

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.     

Crystallization and second harmonic generation in thermally poled niobium borophosphate glasses

Crystallization of glasses with compositions (1−x)(0.95 NaPO₃+0.05 Na₂B₄O₇)+xNb₂O₅, x=0.4, 0.43, 0.45, 0.48 was investigated by differential scanning calorimetry and X-ray powder diffraction. Crystallization of two phases was observed in the glasses with x=0.43-0.48. First phase is a sodium niobate with the structure of tetragonal tungsten bronze () and second phase is Na₄Nb₈P₄O₃₂ (). The crystallization of sodium niobate is correlated with increasing of nonlinear optical efficiency reported for thermally poled glasses with x>0.4. The results of Raman spectroscopy show the formation of three-dimensional (3D) niobium oxide framework in the glasses with increase of niobium concentration. This framework is supposed to have tetragonal tungsten bronze structure and to be responsible for nonlinear optical properties of the glass. Second harmonic generation signals of as prepared and crystallized glass after thermal poling are compared. The nucleation and crystallization do not improve the NLO properties of the glasses under study.