Thermal behavior of vinylidene chloride—methyl acrylate copolymers

The thermal behavior of random copolymers of vinylidene chloride-methyl acrylate (VDC-MA) was monitored with differential scanning calorimetry. The effects of composition, annealing, and heating rate on the copolymer melting process were studied. Increasing levels of comonomer decreased the crystalline melting point and percent crystallinity of the copolymers. A combination of information obtained from heating rate and small-angle x-ray scattering studies led to a model of the melting behavior of PVDC and its copolymers. Apparently a simultaneous melting/recrystallization phenomenon occurs in these materials during heating.     

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N,N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.     

Structure and morphology of vinylidene chloride—methyl acrylate copolymers

The structure and morphology of vinylidene chloridemethyl acrylate copolymers were studied using small-angle and wide-angle x-ray scattering. Long period increased with comonomer concentration for compressionmolded films crystallized at the same temperature. An increase in the “a” dimension of the unit cell was noted for the “as polymerized” powder as comonomer content increased. Sequence distribution information obtained from the instantaneous copolymer composition equation agreed well with the observed powder data. No such trend was observed for melt-crystallized films, possibly because of a greater restriction on crystallization and a lower level of crystallinity within these samples.     

Structural and property changes in poly (vinylidene fluoride–trifluoroethylene) 70/30 mol % copolymer induced by proton irradiation

Poly(vinylidene fluoride–trifluoroethylene) 70/30 mol% copolymer has been irradiated with 3 MeV protons at doses ranging from 43 to 200 Mrad. The effects of irradiation on the polarization hysteresis, dielectric properties, lattice spacing, phase transition behavior and electric-field-induced strain have been studied. The irradiated copolymer exhibits the characteristic behavior of a relaxor ferroelectric, including frequency dispersion of the dielectric constant, which follows the Vogel–Fulcher rule. These results indicate that the proton irradiation breaks up the coherent polarization domains in the copolymer into nano-sized regions, thereby converting the copolymer to a relaxor ferroelectric. X-ray diffraction measurements show that the nano-sized regions are in the non-polar phase. Since the lattice spacing of the non-polar phase is substantially different from that of the polar phase, the local phase transformation between these two phases induced by an external electric field gives rise to a large lattice strain and hence a giant electrostrictive response. PACS 77     

Enhanced β Crystalline Phase in Poly(vinylidene fluoride) via the Incorporation of Graphene Oxide Sheets assisted by Supercritical CO2 Treatment

Graphene oxide (GO) sheets were pre-modified with a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF), using a simple supercritical carbon dioxide (SC CO₂) method, and then the PVDF-decorated GO was added into a PVDF matrix by solution blending. Transmission electron microscopy (TEM) revealed that the decorating degree of PVDF on the surface of the GO increased significantly with increasing of SC CO₂ pressure and PVDF concentration. The mechanism of the polymer adsorption on the GO sheets through favorable interaction between the GO and PVDF chains was identified via Fourier transform infrared spectroscopy (FTIR). Further, the crystallization behavior of PVDF/GO composites was investigated by differential scanning calorimetry (DSC), FTIR and polarized optical microscopy (POM). Interestingly, the composite with PVDF-decorated GO as the filler showed higher β-phase content compared to the composite with pristine GO as the filler. The study showed that the supercritical fluid-induced epitaxial crystallization process has significant potential for fabricating functional GO-based nanocomposties containing piezoelectric or conducting materials.     

Laser optogalvanic investigations of the Neon 6302 (A) transition

The optogalvanic effect of neon, in the presence of CO gas, has been specifically investigated for the 630.2 nm transition. Our theoretical model, based on rate equations, predicts well the observed signals as a sum of exponential functions.     

Crystalline Phase Formation of Poly(vinylidene fluoride) from Tetrahydrofuran/N,N‐dimethylformamide Mixed Solutions

The present work focused on the effect of the interactions between poly(vinylidene fluoride) (PVDF) chains and solvent molecules on the structure and crystallization behavior of PVDF in films obtained by solution casting. In a single solvent system, the film cast from the good solvent of N,N‐dimethylformamide (DMF), showed dominantly β‐phase crystals with the highest PVDF crystallinity (50.6%) and the largest spherulite size, about 4 μm, at the top surface. The samples deposited from good swelling agents, such as tetrahydrofuran (THF) and methyl ethyl ketone (MEK), exhibited mainly the original α phase with some amount of β‐phase crystals; the crystallization behavior and the morphology of the surface were similar to the original PVDF resin, because of the only partially dissolved PVDF chains in these two solvents. In a mixed solvent system (THF/DMF), the β phase formation linearly increased as the DMF component increased, determined by Fourier transform infrared spectroscopy (FTIR) techniques, owing to increased interactions between PVDF chains and DMF molecules. The film surface consisted of β spherulites with average size of about 3 μm, which were smaller than those grown from pure DMF, because of the increased crystallization rate in the mixed solvent.     

Comparison of the thermal stability of the α, β and γ phases in poly(vinylidene fluoride) based on in situ thermal Fourier transform infrared spectroscopy

The electroactive β phase of poly(vinylidene fluoride) (PVDF) is induced due to the aging time of PVDF solutions. The feasibility of the combination of the three crystalline polymorphs (α, β and γ) is demonstrated where their relative proportion within the PVDF film can be tailored by the simple monitoring of the preparation conditions. To identify all these phases, Fourier transform infrared (FT-IR) spectroscopy is carried out and it is spotlighted that the vibrational bands at 510 and 841 cm^?1 are not sufficient to state the formation of the β phase. The main aim of this work is devoted to develop a better understanding on the thermal stability of these several phases of PVDF, which has a longstanding ambiguity persisting in this area. It has been found that the in situ thermal FT-IR spectroscopy is one of the best alternatives to understand this important issue. It is ascertained that the β phase is the least thermally stable phase among α, β and γ phases, whereas the γ phase is the most thermally stable phase.     

Role of copper ions in dielectric and structural investigations of lead– borate glasses

Glasses in the system 0.1CuO-(x-0.1)PbO-(1-x)B₂O₃ (0.3≤ x ≤ 0.7) were synthesized by using the melt quench technique. A number of studies such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), fourier-transform infrared (FTIR) and Raman spectroscopy, electron paramagnetic resonance (EPR) and dielectric properties (viz., dielectric constant ??, dielectric loss and ac conductivity σ_ac) are employed to characterize the glasses. The amorphous nature of the glasses was confirmed using XRD while the glass transition temperature (T_g) of glass samples have been estimated from DSC investigation and found that the T_g decreases with increasing PbO content. Raman and FTIR spectroscopy reveals that when increasing lead ions, the tetrahedral [BO₄] units are gradually replaced by trigonal [BO₃] units. The EPR study leads to determine the local site of Cu²⁺ ions and its transformation with the Pb content in the studied glasses.     

Effects of Molecular Weight on Thermal Degradation of Poly(α-methyl styrene) in Nitrogen

The effects of molecular weight on the thermal degradation behavior of poly(α-methyl styrene) (PAMS) was investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and thermogravimetric analysis (TGA). The Py-GC/MS analysis results showed that the degradation of PAMS with different molecular weights in nitrogen produced only the monomer, alpha-methylstyrene. The TGA results showed a pronounced reduction in the decomposition temperature with increasing molecular weight. The degradation kinetic parameters, calculated by the Kissinger and the Coats–Redfern methods, further revealed that the activation energy and the pre-exponential factor decreased with increasing molecular weight. Most importantly, the degradation order of the PAMS in nitrogen remained around 1, independent of the molecular weight, suggesting the maintenance of the depolymerization mechanism. All the above results provided an insight into the effects of molecular weight on the thermal degradation behavior of PAMS.     

Influence of Thermal Treatment on the Thermal Behavior of Poly‐L‐lactide

The influences of thermal treatment on cold crystallization and the thermal behavior of poly‐L‐lactide (PLLA) were investigated by DSC and polarizing microscopy. Both the cooling and heating rates had effects on cold crystallization. Double peaks were observed for the samples on subsequently heating at 10°C min^?1 after cooling between 5 and 20°C min^?1. The degrees of crystallinity dramatically increased with decreasing cooling rate, and the size of PLLA spherulites increased with a decrease in the cooling rate. Double cold crystallization peaks were also observed during heating traces at higher rates for this material after fast cooling (20°C min^?1) from the melt. The competition between the crystallization from the nuclei formed during cooling, and that from spontaneous nucleation might be responsible for the appearance of double peaks.     

Effect of Dichloromethane on Transport,Thermal, and Thermal‐Mechanic Properties of Amorphous Glass Poly(Ether Imide) Films

Abstract

In this work the interaction effect of dichloromethane on amorphous glassy poly(ether imide) (PEI) films was analyzed from the correlation between transport, thermal, and mechanical properties. The resulting sorption curves were anomalous two‐stage in the solvent activity range 0–0.34 and pseudo‐Fickian for the solvent activity range 0.40–0.50. From a generalized diffusion equation to describe the combination of Fickian and Case II mechanisms we found that the velocity of solvent penetration (v) was higher than the diffusion coefficient (D) for all solvent activities studied. It was observed from the cluster function and the mean size cluster that solvent–solvent interactions may occur at higher solvent activities. Thermal differential scanning calorimetry (DSC) and thermal gravimetric analysis [(TGA) and thermal mechanical (DMTA)] characterization showed that the solvent clusters may act as an antiplasticizer, increasing the elastic modulus of the PEI matrix by 1.9 times. Therefore, a shifting of the β transition was observed at higher temperatures around the glass transition.     

Thermal Behavior of Polyamide‐12 and Poly (Styrene‐Co‐Acrylonitrile) Blend

In this work, an unusual morphology of a mixture of polyamide‐12 (PA‐12) with a series of poly (styrene‐co‐acrylonitrile) (SAN) was obtained by solution casting and fast solvent evaporation. The prepared film was transparent although it contained many crystals. These crystals apparently prevented phase separation despite the instability of the PA‐12 and SAN mixtures below 180°C. In isothermal experiments, once the crystals were melted, phase separation began and the scattered intensity fit the Cahn–Hilliard theory. When the AN content in the SAN copolymer was less than 5%, the phase separation took place when only part of the crystals were melted at 180°C. However, due to the constraint of unmelted crystals, the growth rate of phase separation at this temperature was much slower.     

Low-temperature optical spectra and zero-phonon transition of color centers in γ-rayed lithium fluoride crystals

The zero-phonon lines on R_2, R~ , N_1 and R′_2 centers and some new narrow lines have been observed in bivalent-metal-doped and air-grown LiF crystals irradiated by γ-ray in the temperature range of 9.5—130K. The spectral properties and thermostabilities of the lines are investigated systematically at different temperatures.     

Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)_n–(PO)_m–(EO)_n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO₁₄–EO₂₄–PO₁₄ (17R4) was added to the Pluronics EO₂₀–PO₇₀–EO₂₀ (P123), EO₁₀₀–PO₆₅–EO₁₀₀ (F127), and EO₁₃₃–PO₅₀–EO₁₃₃ (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.     

A Comparison of the Effects of Calcium Glutarate and Pimelate on the Formation of β Crystalline Form in Isotactic Poly(propylene)

The effect of calcium glutarate (Cagt) and calcium pimelate (Capt) on the formation of β crystalline form in isotactic poly(propylene) in the crystallization temperature range of 110–130°C has been investigated. The content of β phase crystals increase with the addition of calcium glutarate. K (relative content of β crystalline form in the iPP sample) attains its maximum value for iPP doped with 0.3 wt.% Cagt isothermally crystallized at 110°C (26.71%) or 120°C (30.27%), and for iPP doped with 0.2 wt.% Cagt isothermally crystallized at 130°C (31.97%), respectively. Compared with the K values of iPP doped with 0.1 wt.% Capt (78.33–94.76%), the β nucleation ability of Cagt is inferior to that of Capt. The spherulite size of iPP doped with Capt is smaller than that of iPP doped with Cagt. The difference in the β nucleation ability between Cagt and Capt is explained by the difference between their crystal structure parameters and those of β‐iPP.     

Polymer–Polymer and Single Polymer Composites Involving Nanofibrillar Poly(vinylidene Fluoride): Manufacturing and Mechanical Properties

Nanofibrillar polymer–polymer composites (NFCs) and single polymer composites (SPCs) were produced using linear low density polyethylene (LLDPE) and poly(vinylidene fluoride) (PVDF). The NFCs were fabricated by means of a microfibrillar composite concept comprising melt blending, cold drawing, and compression molding retaining the highly oriented PVDF reinforcing nanofibrils (diameter of approximately 250 nm) dispersed without any agglomeration in the isotropic LLDPE matrix. The SPC films were prepared by partial surface premelting of neat PVDF nanofibrils (diameter of about 130 nm) using hot compaction at 148°C (about 20°C below the complete melting of PVDF), thus preserving the PVDF nanofibrillar identity. Tensile testing of NFCs based on LLDPE and PVDF showed an increase in the tensile modulus by 135% and in the tensile strength at break by 211%, as compared to those of an isotropic LLDPE film. Furthermore, the PVDF SPCs showed an enhancement of tensile modulus of 30% and strength at break of 305% when compared to those of an isotropic PVDF film.     

O(5) symmetry in IBA-1 — the O(6)—U(5) transition region

All IBA-1 hamiltonians whose eigenstates are combinations of states with numbers of d-bosons differing by an even number have O(5) symmetry. Consequences of this symmetry are presented for the O(6)—U(5) transition region for energy levels and electromagnetic transitions. We draw the distinction between evidence for O(6) character of nuclei and that for O(5) symmetry only.     

Diode laser spectroscopy of the ν1 and ν3 bands of thiazyl fluoride (FSN)

The ν₁ (FS stretch) and ν₃ (SN stretch) bands of FSN have been measured with Dopplerlimited resolution using a diode laser spectrometer. An accurate set of band constants were determined for ν₁ from a simultaneous fit to 265 infrared data and 73 ground state rotational transitions. The ν₃ band was found to be perturbed as the result of a Coriolis-type interaction between the states (0, 0, 1) and (1, 2, 0). Further difficulties with ν₃ were produced by the presence of many strong absorption lines from an SO₂ impurity. A limited set of effective band constants were determined for this band. Some general aspects of Q-branch absorption line patterns are briefly discussed.     

Cure Behavior and Thermal Properties of Poly (Amide-Amidic Acid) Modified Diglycidyl Ether of Bisphenol-A/4,4′-Diaminodiphenylsulfone

Poly (amide-amidic acid) (PAA) was selected to modify diglycidyl ether of bisphenol-A (DGEBA)/4,4′-diaminodiphenylsulfone (DDS). The cure behavior was studied by means of nonisothermal differential scanning calorimeter (DSC) analysis, indicating that PAA played a role of catalyst during the process of the curing reaction. Results of Fourier transform infrared spectroscopy (FT-IR) analysis showed that the PAA acted as a co-curing agent when the PAA content was 3.2–38.4 phr and also as a modifier when the PAA content was 12.8–38.4 phr. The glass transition temperature (T_g ) decreased with the increase of PAA content. The thermal stability improved when the PAA content was 3.2–6.4 phr because of the catalytic effect of PAA. The flexural strength improved for the varying PAA content studied in this work, with the highest flexural strength being obtained when the PAA content was 6.4 phr. The fracture surface morphology was observed using scanning electron microscopy (SEM); the morphologies varied with changing content of PAA.