Crystallization of a poly(ethylene-co-octene): I A precursor structure and two competing mechanisms

Observations of a sample of poly(ethylene-co-octene)in a polarizing optical microscope reveal peculiarities in its crystallization behavior. When cooled from the melt to a fixed crystallization temperature, at first a structure of diffuse appearance with variations on the length scale of micrometers forms rapidly. The transformation into the final semi-crystalline state then proceeds in two ways, by a continuous change of the inner structure of m-sized objects and by the growth of spherulites. Time dependent small angle and wide angle X-ray scattering experiments corroborate the occurrence of the two crystallization mechanisms. Atomic force microscopy indicates that the change of the inner structure of the preformed objects is due to an in-filling of crystallites.     

Crystallization kinetics and crystal morphology in thin poly(ethylene oxide) films

We present a detailed study of the kinetics of crystallization for thin films of poly(ethylene oxide) (PEO). Measurements of the growth rate have been carried out using optical-microscopy techniques on films of monodisperse PEO. Films with thicknesses from 13 nm to ~2 m were crystallized isothermally at temperatures ~20°C below the melting point. A remarkable non-monotonic slowing-down of the crystal growth is observed for films with thickness less than ~400 nm. The changes in the growth rate from bulk-like values is significant and corresponds to a factor of 40 decrease for the thinnest films studied. The morphologies of isothermally crystallized samples are studied using atomic-force microscopy. We find that a morphology, similar to diffusion-controlled growth (dendritic growth and densely branched growth), is observed for films with h < 150 nm. In addition, changes in the morphology occur for thicknesses consistent with changes in the growth rate as a function of film thickness.     

On the kinetics of the first order phase transitions

An attempt is made to analyse the kinetics of the first order structural phase transitions on the basis of the Landau-Ginzburg equation. Two simple solutions are proposed: One in the form of one-dimensional solitary wave which can be considered as a planar interface separating two phases and travelling along direction normal to the interface. Any direction of propagation is possible. The other solution has a form of a onedimensional kink-antikink couple which under supercooling conditions reveals properties of a critical nucleus. A short discussion of the free energy density form for one- and multidimensional order parameters, and of the symmetry of the quadratic gradient term is included.     

Crystallization of Lightly Sulfonated Poly(ethylene terephthalate) Ionomer. I. Isothermal Crystallization from the Melt

Thermal properties and overall rates of isothermal crystallization from the melt of a commercial ionic copolyester (K‐X/SPET) based on poly(ethylene terephthalate) (PET) were analyzed in detail over a composition range from pure PET to a copolymer containing 10.1 mol% of potassium‐neutralized sulfonated PET. For measurements, differential scanning calorimetry (DSC) was used. Copolyesters with the ionic group content of 4.4 mol% or more were unable to crystallize. The isothermal melt crystallization of the copolyesters was analyzed using both the Avrami and the modified Lauritzen‐Hoffman equations. It was found that both the overall rate constant, as well as the Avrami parameter for the primary crystallization stage, varied with the sulfonated unit percentage—but surface free energy and work of folding were practically independent of them. The observed changes in the thermal properties and the kinetic parameters of crystallization were attributed to the comonomer effects and the intermolecular aggregation of the ionic groups.     

Interfacial reactions: mixed order kinetics and segregation effects

We study A-B reaction kinetics at a fixed interface separating A and B bulks. Initially, the number of reactions R(t) approximately tn(infinity)(A)n(infinity)(B) is second order in the far-field densities n(infinity)(A), n(infinity)(B). First order kinetics, governed by diffusion from the dilute bulk, onset at long times: R(t) approximately x(t)n(infinity)(A), where x(t) approximately t(1/z) is the rms molecular displacement. Below a critical dimension, d0) leads to anomalous decay of interfacial densities. Numerical simulations for z = 2 support the theory.     

Characteristic variations in the effect of diluents on polymer crystallization and melting observed for a sample of poly(ethylene-co-octene)

Melting points in mixtures of a crystallizable polymer with a low-molar-mass diluent depend on both, the diluent fraction and the crystal thickness. A differentiation of the two factors can be achieved by temperature-dependent SAXS experiments. A corresponding study, complemented by DSC, dilatometry, microscopy and AFM-imaging, was carried out for mixtures of a poly(ethylene-co-octene) with n-C₁₆H₃₄, c-C₁₆H₃₂ and methyl-anthracene, respectively. All diluents lead for a constant crystal thickness to melting point depressions in agreement with Raoult's law. On the other hand, the effect of the diluents on the thickness of the crystals formed at a fixed crystallization temperature varies. While in the presence of the two alkanes thicker crystals form, no effect arises for the methyl-anthracene—as was previously found for the octene-co-units. We consider these observations as a further support for our view that polymer crystallization follows a multi-stage route which includes a passage through an intermediate mesomorphic phase. Under such conditions crystal thicknesses would only be affected if the diluent is still present in the mesomorphic phase and stay invariant if the diluent molecules are already rejected when this intermediate phase forms.     

Effect of Organoclay Platelets on Crystallization of PTT/EPDM-g-MA Blends: Nonisothermal Melt Crystallization Kinetics

PTT/EPDM-g-MA (80/20 w/w) nanocomposites were prepared by melt mixing of poly(trimethylene terephthalate) (PTT), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA), and organoclay. The blend nanocomposites show typical sea-island morphologies. The nonisothermal crystallization kinetics of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay were extensively studied by differential scanning calorimetry (DSC). The Avrami, Ozawa, and Mo methods were used to describe the nonisothermal crystallization process of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay. Avrami analysis results show that the crystallization rates of 80/20 (w/w) PTT/EPDM-g-MA blends with the clay were faster than those of pure PTT or PTT/EPDM-g-MA blends without clay, which indicates that the clay particles promote crystallization effectively, in agreement with the Mo analysis results. Ozawa analysis can describe the nonisothermal crystallization of pure PTT very well but was rather inapplicable to the 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay.     

Enthalpy determination of order in poly(vinyl chloride)

Enthalpy measurements by means of solution microcalorimetry were obtained on a PVC resin in the temperature range 37-110°C. Enthalpy measurements above T_g detect a heat of fusion of about 1.5 cal/g of polymer and thereby demonstrate the presence of a soluble ordered structure in PVC. Enthalpy measurements on samples quenched and slow-cooled from within the temperature interval 37-220°C confirm the value of 1.5 cal/g for the heat of fusion as well as demonstrate a broad melting range of 130-200°C.     

Radiation effects on poly(vinylidene fluoride)

Melt-crystallized poly(vinylidene fluoride)s (PVF₂) with different crystallization histories were irradiated with γ-rays within the range of irradiation doses 0–83 Mrad. The effects on the crystalline structure and mechanical properties have been measured, compared, and discussed. The degree of crystallinity of the samples was found to increase with radiation dose. The differential scanning calorimeter scans of the quenched samples indicate that there are two melting peaks, and that the area of the lower temperature peak increases while the area of higher temperature peak decreases with increasing dose. Yield stress and breaking stress for all samples are not significantly affected by irradiation but elongation at break is.     

Isothermal Melt Crystallization Kinetics for Poly(Trimethylene Terephthalate)/Poly(Butylene Terephthalate) Blends

The kinetics of isothermal melt crystallization of poly(trimethylene terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated using differential scanning calorimetry (DSC) over the crystallization temperature range of 184–192°C. Analysis of the data was carried out based on the Avrami equation. The values of the exponent found for all samples were between 2.0 and 3.0. The results indicated that the crystallization process tends to be two‐dimensional growth, which was consistent with the result of polarizing light microscopy (PLM). The activation energies were also determined by the Arrhenius equation for isothermal crystallization. The values of ΔE of PTT/PBT blends were greater than those for PTT and PBT. Lastly, using values of transport parameters common to many polymers (U*=6280 J/mol, T _∞=T _g – 30), together with experimentally determined values of T _m ⁰ and T _g, the nucleation parameter, K _g, for PTT, PBT, and PTT/PBT blends was estimated based on the Lauritzen–Hoffman theory.     

Crystallization kinetics of thin-film amorphous Cox(PZT)100 − x nanocomposites

Conductivity of thin-film heterogeneous Co_x(PZT)_{1 ? x} structures has been studied in a wide ranges of metallic phase concentrations and temperatures. The crystallization kinetics of amorphous samples of Co_x(PZT)_{100 ? x} nanocomposites has been investigated by analyzing the time dependences of their conductivity. The main parameters of the crystallization process have been determined.     

Correlation Between Solidification Behavior and Melt Crystallization Kinetics of Isotactic Polypropylene (iPP) during Injection Molding

The relationship between solidification behavior and crystallization kinetics, during the injection molding process of isotactic polypropylene (iPP) was investigated. It was found that the crystallization rate was in proportion to the cooling rate. The existence of a turning point (TP) in the dimensionless temperature (θ) vs. ln t curve, which is potentially applicable for the estimation of cooling time, was experimentally verified for iPP. The present study is expected to be useful for the optimization of the processing conditions during injection molding of crystalline polymers, and also supplies a good insight into further study of the “processing-structure-property” relationship of polymeric materials.     

Characterization of phenanthrenequinone-doped poly(methyl methacrylate) for holographic memory

The holographic recording characteristics of phenanthrenequinone- (PQ-) doped poly(methyl methacrylate) are investigated. The exposure sensitivity is characterized for single-hologram recording, and the M/# is measured for samples as thick as 3 mm. Optically induced birefringence is observed in this material.     

锌离子对聚乳酸结晶和热性能的影响

本文发现了Zn(II)离子掺杂可以加快聚乳酸的结晶过程. 测试了三种Zn(II)盐(ZnCl₂、ZnSt和ZnOAc),并与其它离子Mg(II)和Ca(II)进行对照. FT-IR以及变温拉曼光谱分析发现,经Zn(II)离子掺杂后,聚乳酸的结晶度和结晶速率均增加,差示扫描量热技术以及X射线衍射分析也进一步证实. 差示扫描量热技术测定PLA/ZnSt-0.4 wt%材料的结晶率达到22.46%,PLA/ZnOAc-0.4 wt%材料的结晶率达到24.83%.     

Dimensionality-induced effects on transport properties of poly(G)-poly(C)

We consider a ladder model of DNA for addressing the relation between the transport properties and electronic structure and the interbase coupling in poly(G)-poly(C). Based on the negative eigenvalue theorem and transfer matrix method, the density of states and current-voltage characteristics are evaluated, and an expression for the dependence of the band gap on intra- and inter-strand nucleobase couplings is proposed. There exists a semiconducting-metallic transition in poly(G)-poly(C) by modulating the interbase coupling, and the physical nature is traced back to dimensionality-induced effects. Our results provide possibility for interpreting a variety of transport behaviors observed in DNA molecules.     

Electron-beam irradiation effects on poly(ethylene-co-vinyl acetate) polymer

Poly(ethylene-co-vinyl acetate) (EVA) films were irradiated with a 1.2 MeV electron beam at varied doses over the range 0–270 kGy in order to investigate the modifications induced in its optical, electrical and thermal properties. It was observed that optical band gap and activation energy of EVA films decreased upon electron irradiation, whereas the transition dipole moment, oscillator strength and number of carbon atoms per cluster were found to increase upon irradiation. Further, the dielectric constant, the dielectric loss, and the ac conductivity of EVA films were found to increase with an increase in the dose of electron radiation. The result further showed that the thermal stability of EVA film samples increased upon electron irradiation.     

Singularrenormalization group transformations and first order phase transitions (I)

It is argued that standard position and momentum space renormalization group (RG) transformations are singular (i.e. lead to a singular hamiltonian after a finite number of RG steps) in large regions of the coupling constant space. It is shown in the d = 3, φ⁶ O(N)_N→∞ model that the momentum space RG transformation is singular in all those points of the coupling constant space, where metastable states exist. This region includes the full first order phase transition surface and its neighbourhood. Several other examples are discussed to illustrate that this phenomenon is generic and not a specific large N effect. Some earlier and recent anomalous Monte Carlo renormalization group results are consistent with this conclusion.