Raman scattering in nonplanar poly(vinylidene fluoride)

The Raman scattering of nonplanar (form 2) poly(vinylidene fluoride) (PVF₂) is described. Unique Raman bands not observed in the infrared spectra are found at 2973, 1437, 1327, 1198, and 1059 cm^?1. Band assignments are discussed by comparing infrared and Raman spectra of form 2 PVF₂.     

Raman scattering in uniaxially oriented samples of planar zigzag poly(vinylidiene fluoride)

Band assignments of phase-I PVF₂ have been Revised by using additional data obtained by laser Raman spectra of oriented samples. A set of least-squares refined force constants was obtained which reproduce the experimental data to an average error in frequencies of 1.3 cm^?1. In order to determine the effect of electrical polarization on the spectra, a Gaussian distribution of the dipole axis was assumed. The calculation shows that polarizations of less than 60% will not significantly affect the Raman spectra.     

Far-infrared spectra of piezoelectric polyvinylidene fluoride

Poly(vinylidene fluoride) (PVF₂) is currently used to form piezoelectric films. The PVF₂ molecule can exist in more than one stable conformation and it has electrically polar groups making the polymer amenable to the electrification processes involved in the formation of the piezoelectric film. The two crystalline forms of PVF₂ are distinguishable by far-infrared spectroscopy. Polarized far-infrared spectra (1000-50 cm^?1) of uniaxially oriented PVF₂ show changes in the strong perpendicular dichroism in a number of absorptions before and after being made piezoelectric. The dichroism is attributed to a structural rearrangement from a staggered trans-gauche-trans-gauché conformation to a planar zig zag conformation. In the latter conformation the permanent dipoles are oriented approximately at right angles to the surfaces of the film and result in an electrically polarized film.     

Melting and crystallization behavior of poly(vinylidene fluoride) produced isothermally in the intercrystalline spaces of poly(ethylene terephthalate) from its blends

The melting of isothermally crystallized poly(vinylidene fluoride) (PVF₂), produced in the intercrystalline spaces of poly(ethylene terephthalate) (PET) from its blends, showed a unique behavior: the melting temperature decreased with the increasing crystallinity of PVF₂ (i.e., with increasing crystallization time) for PVF₂ volume fractions of 0.64 and 0.51. The melting temperature of already crystallized PET also decreased as the PVF₂ crystallization progressed and the isothermal crystallization temperature of PVF₂ increased. Separate reasons were proposed to account for these behaviors. The equilibrium melting temperatures of PVF₂ in the blends, measured by the Hoffman–Weeks extrapolation procedure, were used to calculate the polymer–polymer interaction parameter (χ₂₁); only the noncrystallized portion of PET contributing to the mixed amorphous phase was considered. The χ₂₁value (−1.75) was lower than χ₁₂ (−0.14), calculated from the melting temperature depression of PET. However, when they were normalized to the unit volumes of the respective components, the two values were found to be the same. The crystallization rate of PVF₂ decreased with an increasing volume fraction of PET in the blend. The Avrami exponent increased for the volume fraction of PVF₂ (0.77) and then progressively decreased with an increasing volume fraction of PET. A gradual change in the nature of the regime transition from regime II/regime I to regime III/regime II with increasing PET concentration was observed. The value of the chain-extension factor of PVF₂ significantly increased with an increase in the PET concentration in the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2215–2227, 2004     

Interdiffusion of PMMA and PVF2, studied by solid-state NMR

A previously published new solid-state nuclear magnetic resonance (NMR) method is applied to the interdiffusion of poly(methacrylate) (PMMA) and poly(vinylidene fluoride) (PVF₂) above their T_g. Via a variation of the cross-polarization technique magnetization is transferred from protons to fluorines. When this magnetization is made to disappear at the fluorine sites, only those protons that are distant from fluorines greater than the distance over which cross-polarization functions will retain their magnetization. In this way we detect the fraction of PMMA near (ca. 20 Å) PVF₂. Starting from sheets of PMMA and PVF₂, which are then heated at 190°C for a variable time, and applying the above technique, we can determine the fractions of PMMA and PVF₂ that have diffused within a distance of a few Å of each other. The intrinsic diffusion coefficients of PMMA and PVF₂ determined from such experiments compare well with literature data. Initial attempts to fit the experimental data suggest that the concentration dependence of the diffusion coefficients cannot be neglected. © 1994 John Wiley & Sons, Inc.     

Recent advances in ferroelectric polymers

In the Polymer Electroprocessing Laboratory at Rutgers University, we have discovered that the odd-numbered nylons constitute the second known class of ferroelectric polymers^1–3, and that polarized films exhibit piezoelectric properties similar to poly(vinylidene fluoride) (PVF₂) and copolymers of PVF₂ and trifluoroethylene (PVF₂/PVF₃). A study of a series of these polymers including nylon 11, nylon 9, nylon 7 and nylon 5 showed that the remanent polarization produced in quenched, cold-drawn films was a linear function of polymer dipole density⁴. The highest remanent polarization produced was that of nylon 5, the value attained (P₁=125mC/m²) being approximately 2.5 times that of PVF₂. We also discovered that (unlike PVF₂ or PVF₂/PVF₃) the remanent polarization could be stabilized to elevated temperatures (close to the polymer melting point). For nylon 5, the remanent polarization and piezoelectric response was stable to over 250°C⁵. We showed that the hydrogen-bonded sheet structure in nylon 11 for quenched cold-drawn films was parallel to the plane of the film, and that after application of high electric fields the hydrogen-bonded sheet structure was rotated 90° to an orientation perpendicular to the plane of the film³. A detailed X-ray diffraction study of the effects of humidity and electroprocessing on the switching behavior of nylon 5, nylon 7 and nylon 11 films was carried out⁵. The piezoelectric and pyroelectric response⁶ of these films was also determined. The different switching mechanisms observed and the measured piezoelectric and pyroelectric properties will be presented and discussed.     

A synchrotron SAXS study of miscible blends of semicrystalline poly(vinylidenefluoride) and semicrystalline poly(1,4‐butylene adipate). II. Crystallization,morphology, and PBA inclusion in PVF2 spherulites

The incorporation of poly(1,4‐butylene adipate) (PBA) and its crystallization behavior within poly(vinylidenefluoride) (PVF₂) spherulites in miscible PVF₂/PBA blends have been further studied with small‐angle X‐ray synchrotron scattering (SAXS). The incorporation of PBA into the PVF₂ interlamellar region was found to be dependent on the PVF₂ crystallization conditions. In our previous work, where the blends were crystallized by a one‐step quenching process directly from 190 (a single‐phase region) to 20 °C (a three‐phase region), the transition from PBA inclusion in the PVF₂ interlamellar region to interlamellar exclusion occurred at a PBA weight fraction of ∼ 0.5. In this case, where the blends were first quenched from 190 (a single‐phase region) to 130 °C (a two‐phase region) and then further quenched to 20 °C (a three‐phase region), the transition occurred at a PBA weight fraction of less than 0.3. That is, when a blend is crystallized under different conditions, different amounts of the PBA component are incorporated into the PVF₂ interlamellar phase. The thickness of the PVF₂ interlamellar phase, in turn, may affect the PBA crystalline structure in the interlamellar region. Time‐resolved SAXS was used to probe the crystallization dynamics of both PVF₂ and PBA components in a blend containing 60 wt % PBA. The blend was quenched from the single‐phase region at 190 to 130 °C to crystallize the PVF₂ component and was then further quenched to 20 °C to crystallize the PBA component. This study, together with our earlier results, shows that the time dependence of the PVF₂ crystallization rate and crystalline lamellar thickness is a function of the PBA content in the blend. The glass‐transition temperature of the blend and the PBA diffusion process are the two dominant factors that control the PVF₂ crystallization dynamics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2296–2308, 2000     

Multiscale Porosity from Thermoreversible Poly(vinylidene fluoride) Gels in Diethyl Azelate

Poly(vinylidene fluoride) (PVF₂) produces thermoreversible gels in a series of diesters. The polymer-solvent complexation occurred for intermittent number of carbon atoms n ⩾ 2 and the enthalpy of complexation increased with increasing n. The gels were dried by replacing the diesters with low boiling solvent like cyclohexane (bp. 80 °C) and methylcyclohexane (bp. 99 °C). The porosity of the dried gels was measured using Poremaster-60. For PVF₂-DEAZ gel meso and macro porosity have been observed. The former pore dimensions have been attributed for polymer-solvent complexation while the macroporosity has been attributed for caging of solvent between the PVF₂ fibrils The porosity measured from nitrogen adsorption isotherms using BJH method indicate presence of minimum pore diameter of 3.8 nm for the 10% dried gel of PVF₂.     

Importance of the metal–polymer interface for the piezoelectricity of polyvinylidene fluoride

The piezoelectric effect in films of polyvinylidene fluoride (PVF₂) is investigated using optical and ultrasonic detection techniques. From the analysis of the vibrational resonance frequencies of a freely suspended film we conclude that the polarization induced in PVF₂ is inhomogeneous across the volume of the sample. Poling the foils in a sandwich configuration or using blocking electrodes, we can clearly demonstrate that the piezoelectric effect in PVF₂ originates from the positive metal electrode. Monitoring the time dependence of the piezoelectric effect during the poling process, a fast and slow component are observed. Using a blocking electrode, however, the same dynamical poling behavior is found only if the contacting metal electrode is positive. In view of these observations, which clearly demonstrate the importance of the metal–polymer interface for the strong piezoelectricity of PVF₂, the existing theoretical models, based on the bulk properties of the polymer, are critically reviewed.     

Multiporous Materials From Thermoreversible Poly(vinyledene fluoride) Gels

Poly(vinylidene fluoride)(PVF₂) produces thermoreversible gels with alkyl diesters of general formula (CH₂)_n (COOEt)₂ as well as with camphor, a naturally occurring ketone. These gels containing polymer-solvent intercalates yield multiporous materials when subjected to controlled solvent removal techniques. The micro and meso pores are attributed to polymer-solvent complexation while the macro pores are formed as a result of removal of the solvent trapped in the fibrillar network. PVF₂ –diethyl azelate (DEAZ, n = 6) and PVF₂ -camphor gels produce porous polymer network when dried by cyclohexane leaching. FESEM images exhibit porous network structures with fibrillar morphology. Mercury intrusion porosimetry (MIP) shows presence of pores having diameter in the range 4 nm–400µm for both the systems. The BJH pore size distribution curves for both systems confirm the presence of mesoporosity. The HK pore size distribution plots indicate that micropores are also created and it also puts evidence of single molecule solvent intercalation between the PVF₂ strands. The hysteresis between the extrusion and the intrusion curves indicates the presence of channel type/ink-bottle type structure in these systems.     

Brillouin scattering of oriented films of poly(vinylidene fluoride) and poly(vinylidene fluoride) -poly( methyl methacrylate) blends

Temperature dependent Brillouin scattering studies of PVF₂ films stretched to various stretch ratios have been carried out. Elastic constants for unstretched and stretched films have been obtained as functions of temperature. The elastic constant C₃₃ of the stretched films has a greater temperature dependence than that of unstretched films. To elucidate the effect of the surrounding amorphous matrix on the Brillouin spectrum of semicrystalline PVF₂ film, we carried out Brillouin scattering studies of films made from blends of PVF₂ and PMMA.     

Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films

The ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF₂) bilaminate films, prepared by a co-melt-pressing method, is presented. The bilaminate films exhibit typical ferroelectric D-E hysteresis behavior with a remanent polarization, P_r, of about 75 mC/m², which is higher than the value of 52 mC/m² observed for PVF₂ or nylon 11 films measured under the same conditions. The coercive field, E_c, of the bilaminate films is ～ 78 MV/m, which is higher than that of either PVF₂ or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d₃₁, and the piezoelectric stress coefficient, e₃₁, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d₃₁, of 41 pC/N at room temperature, which is significantly higher than the PVF₂ films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d₃₁ of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF₂ (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e₃₁, of the bilaminate films shows a value of 109 mC/m² at room temperature, almost twice that of the PVF₂ films (59 mC/m²) and about 18 times that of the nylon 11 films (6.2 mC/m²). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, d_h, of the bilaminate films also shows an enhancement with respect to the individual components, PVF₂ and nylon 11. ©1995 John Wiley & Sons, Inc.     

Structure and energy studies of Β-diketonates. 4. vibrational characteristics of Y(DPM)3 and Y(DPM)2

The vibrational problem for the Y(DPM)₃ and Y(DPM)₂ molecular forms that are present in the overheated vapor of yttrium tris-dipivaloylmethanate is solved. For this purpose, the experimental Raman spectra of Y(DPM)₃ solutions are interpreted. The force field of the Y(DPM)₂ radical is estimated on the basis of the force constants determined for Y(DPM)₃. Rms vibrational amplitudes and corrections for perpendicular displacements to the internuclear distances of the two molecular forms needed for interpreting electron diffraction data are calculated. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 3, pp. 470–479, May–June, 1997.     

Electrical field-effect of polyvinylidenefluoride (PVF2)

Summary By means of modified field-effect measurements the properties of space charge distribution in polymers at the polymer-metal interface have been investigated. In general, these properties are due to excess charge and/or dipole orientation. The superposition of both effects is investigated in PVF₂ (phase-II) in order to show whether the conformational PVF₂ properties in the crystalline or in the noncrystalline regions control the space charge distribution. In the temperature region 60 °C <T < 90 °C and for times greater than 60 sec the space charge properties are significant influenced by additional dipole relaxations which result from the beginning chain mobility within the crystallites of PVF₂. In the time interval 1 sec <t < 60 sec charge carrier injection at the PVF₂-gold contact can be described by the Richardson-Schottky theory. Based on this theory, a plot of reduced current versus reduced field is presented displaying all experimental data obtained at various temperatures and field-strength on a single curve. No clear distinction can be given in this case between bulk-limited and electrode-limited processes.With 6 figures     

EFFECT OF TACTICITY OF PMMA ON CRYSTALLINE STRUCTURE OF POLY VINYLIDENE FLUORIDE

Fourier transform infrared spectroscopy (FTIR) has been used to study the effect of tacticityof PMMA on β phase formation of poly vinylidene fluoride (PVF_2) during quenching process.For pure PVF_2, quenching at lower temperature results in the formation of β phase crystallites.The critical quenching temperature for β phase formation is about 30℃. Adding a given amountof PMMA (30%) results in the increase of the critical quenching temperature. For the blends ofPVF_2 with atactic PMMA (a-PMMA), the critical quenching temperature is about 45℃, whilefor the blends with syndiotactic PMMA (s-PMMA), attains to about 70℃.     

Raman spectral studies of uranyl sulphate and its urea complex structural isomers

Using Raman spectroscopy, the authors have studied two forms of the dioxouranium(VI) sulphate complexes of the urea molecule, the bis(urea)dioxouranium(VI) sulphates α- and β-UO₂SO₄·2CO(NH₂)₂. Raman spectra were recorded using λ = 488 and 647.1 nm laser excitation lines. For λ = 448 nm, the crystals exhibit strong, structured luminescence, with peaks separated by 857 cm⁻¹ (α-form) and 853 cm⁻¹ (β-form). For λ = 647.1 nm, very intense Raman spectra are obtained which are similar but slightly different and can be used to distinguish each form. A comparison with the urea and uranyl sulphate hydrate (USH) spectra has clarified the Raman band assignment of the two parent α- and β forms. Contributions of the urea donor ligand and the sulphate have been identified. Charge transfer to uranium and the uranium—oxygen force constant in the uranyl ion have been evaluated. The results agree with previous X-ray structural investigations.     

Molecular design of multicomponent polymer systems. X. Emulsifying effect of poly(styrene-b-methyl methacrylate) in poly(vinylidene fluoride)/noryl blends

The emulsifying activity of block copolymers is investigated in blends of incompatible engineering polymers such as polyvinyldene fluoride (PVF₂) and Noryl (high impact polystyrene-poly-2,6-dimethyl-1,4-phenylene oxide mixture). When the blends are modified by a poly(styrene-b-methyl methacrylate) copolymer, (PS-PMMA) each block of which being selectively miscible with Noryl and PVF₂ respectively, Phase dispersion, interfacial adhesion and ultimate mechanical properties are significantly improved; major effect is observed upon addition of 12 percent copolymer, resulting in intermingled and firmly adherent phases and a rough additivity of both tensile strength and elongation at break. All these features clearly demonstrate the important emulsifying effect of PS-PMMA in these very attractive PVF₂/Noryl blends.     

FTIR-ATR studies of drawing and poling in polymer bilaminate films

A large increase in the remnant polarization of drawn and poled poly(vinylidene fluoride) (PVF₂)/nylon 11 bilaminates compared with the individual films observed in other studies provides the motivation for the examination of dipole orientation in variously treated single and bilaminate films with FTIR-ATR spectroscopy. Four ATR spectra are collected from each surface using two sample orientations and two light polarizations for each incident light angle. The incident light angle is varied to obtain information about the change in structure with depth. Computer simulations of the experimental optics using anisotropic optical constants aides in the interpretation of experimental results. As the result of simple one-way drawing in PVF₂ and nylon 11, anisotropy in dipole orientation is observed in the plane transverse to the draw direction. In both single and bilaminate films, the average direction of the amide plane in nylon 11 and the CF₂ dipoles in PVF₂ resides in the plane of the film, perpendicular to the subsequent poling field direction as a result of one-way drawing. The transverse plane orientation is depth dependent in nylon 11 in both single and bilaminate films and is attributed to a surface-induced effect. Poling fields of 1.6 MV/cm produce large differences between the surfaces of single films and the bilaminates. At the interior interface of the drawn and poled bilaminates, the PVF₂ and nylon 11 dipoles important in polarization appear to be random. The structural implications of this as well as other observations from the spectra are interpreted in terms of the large remnant bulk polarization in the poled bilaminate. © 1994 John Wiley & Sons, Inc.     

Conversion of colloidal aggregates into polymer networks on aging

After long-term aging, surfactant-mediated colloidal aggregates of sulfonated polyaniline (S-PANI) and poly(vinylidene fluoride) (PVF₂) converted into three-dimensional polymer networks, whereas colloidal crystals prepared from pure PVF₂ remained unaltered. A model, where the surfactant tails anchored from the colloidal particles interdigitate with time resulting in coalescence of the particles to form the network morphology, has been proposed. X-ray photoelectron spectroscopy (XPS) revealed higher relative abundances of carbon atoms on the surface of the polymer networks than those of the colloidal aggregates, which adequately supports the proposed model.     

Characteristic ratio of the mean-square end-to-end distance of poly(vinylidene fluoride) with microstructural defects

The segment length distribution of isoregic head-to-head and tail-to-tail sequences in poly-(vinylidene fluoride) (PVF₂)

1 System. name: poly(1,1-difluoroethylene).

chains is calculated from ¹⁹F NMR literature data. It is found that the average length of inverse segments is very close to one unit; therefore almost all head-to-head defects are immediately repaired by an adjacent tail-to-tail addition. The role of microstructure on the characteristic ratio of the end-to-end distance is then investigated. Results obtained by two different methods indicate that, in agreement with previous Monte Carlo calculations, defects play a minor role for the conformational characteristics of PVF₂. However, a slight contraction of about 4% is expected for very defective chains.