Longitudinal piezoelectric strain measurements of poly(vinylidene fluoride) films

The longitudinal piezoelectric strain of poly(vinylidene fluoride) (PVF₂) films has been measured at room temperature using a high-sensitivity ac capacitance-type dilatometer. The dc bias field dependence of the piezoelectric strain coefficient d₃₃ has been determined. The polarization-related electrostrictive coefficient Q₃₃ obtained is several hundred times larger than the value in normal piezoelectric oxide crystals and is of opposite sign.     

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.     

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.     

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.     

NLO‐active maleimide copolymers with ­high glass transition temperatures

We synthesized some novel rigid NLO‐active maleimide copolymers bearing DR‐1 moieties ( PMPD , PHSD and PHND ). All copolymers exhibited high T_g's (190～197 °C), good solubilities for common solvents and excellent film‐forming properties. Dependence of film thickness on the d₃₃ value for the poled copolymer films induced by corona poling was investigated and it was demonstrated that in less than thickness of 0.3 µm decrease of the thickness gives rise to remarkable increase in the d₃₃ value. The poled copolymer films exhibited large d₃₃ values (270 × 10^?9 esu (film thickness 0.13 µm) for PMPD , 290 × 10^?9 esu (0.12 µm) for PHSD and 350 × 10^?9 esu (0.08 µm) for PHND ) as well as large r₃₃ values (51.0 pmV^?1 for PMPD and 60.4 pmV^?1 for PHND ) which are significantly large compared to the value of LiNbO₃ (31 pmV^?1) as a typical EO material. The d₃₃ values of the poled copolymers were kept constant even after standing 1000h at 80 °C, although a small decrease was observed at an initial stage. Further, the d₃₃ values did not change up to ca. 123 °C upon heating at the rate of 10 °C/min in all cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Electromechanical properties of poly(vinylidene fluoride‐trifluoroethylene) networks

Random copolymers of 65% vinylidene fluoride and 35% trifluoroethylene were reacted with an organic peroxide, in combination with a free‐radical trap, to yield networks of high crosslink density. Crystallization subsequent to the crosslinking yielded ferroelectric materials exhibiting large electrostrictive strains. The magnitude of the electromechanical response increased with an increasing degree of crosslinking, even though this reduced the crystallinity. For the most crosslinked sample, longitudinal (thickness) strains as high as 12% were induced at an electric field of 9 MV/m. This electrostrictive performance exceeded that obtained to date with any poly(vinylidene fluoride) material. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1975–1984, 2002     

Superdrawing of polytetrafluoroethylene virgin powder above the static melting temperature

A new two‐stage draw technique was successfully applied to the superdrawing of polytetrafluoroethylene (PTFE) virgin powder. A film, compression‐molded from powder below the melting temperature (T_m = 335 °C), was initially solid‐state coextruded to an extrusion draw ratio (EDR) of 6–20 at 325 °C, about 10 °C below the T_m. These extrudates from the first‐stage draw were further drawn by a second‐stage pin draw in the temperature (T_d) range of 300–370 °C that covers the static T_m. The maximum achievable total draw ratio was ～60 at a T_d = 300 °C and increased rapidly with increasing T_d, reaching a maximum of 100–160 at a temperature window between 340 and 360 °C, depending on the initial EDRs. At yet higher T_d's, the ductility was lost as a result of melting. The high ductility of the PTFE extrudates at such high temperatures was ascribed to the improvement of interfacial adhesion and bonding between the deformed powder particles upon the first‐stage extrusion combined with the rapid heating of only a portion of the extrudate followed by the elongation at a high rate. The highly drawn fibers were highly crystalline (χ_c ≤ 87%) and showed high chain orientation (f_c ≤ 0.997) and a large crystallite size along the chain axis (D₀₀₁₅ ≤ 160 nm). The molecular draw ratio, estimated from the entropic shrinkage above the T_m, was close to the macroscopic deformation ratio independently of the initial EDRs. These results indicate that the draw was highly efficient in terms of chain extension, orientation, and crystallization. Thus, the maximum tensile modulus and strength achieved in this work were 102 ± 5 and 1.4 ± 0.2 GPa, respectively, at 24 °C. These tensile properties are among the highest ever reported on oriented PTFE. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1995–2004, 2001     

Analysis of Low-k Organosilicon and Low-Density Silica Films Deposited in HMDSO Plasmas

Low-dielectric constant (low-k) films have been prepared by plasma-enhanced chemical vapor deposition from hexamethyldisiloxane (HMDSO). The films are analyzed by ellipsometry, infrared absorption spectroscopy while their electrical properties are deduced from C–V and I–V measurements performed on metal/insulator/silicon structures. First, it is shown that the carbon-containing silicon oxide films deposited in HMDSO and HMDSO/Ar plasmas have a dielectric constant equal to 3.0 ± 0.1 and are thermally stable at 400°C. The leakage current densities measured for an electric field of 1 MV/cm are less than 10^–9 A/cm² and the breakdown fields are in the range of 6–7 MV/cm. Then, a low-density silica film was obtained by exposing a film deposited in an HMDSO plasma to an O₂ plasma. The dielectric constant of this low-density silica film is 3.5 and its breakdown field is close to 6 MV/cm.     

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.     

Solid-state 13C-NMR studies of the aging of poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Solid state ¹³C-NMR was used to investigate the miscibility and subsequent separation of solution-cast blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) (PMMA) with aging for a range of compositions. It was found that one amorphous phase and intimate mixing of the polymer chains in this phase existed for all compositions of the blends, even after 2 months of aging at room temperature as determined by the proton spin lattice relaxation time T_1ρH in the rotating frame, and the time constant T_CH for transfer of magnetization. The T_1ρH is sensitive to the spatial homogeneity of the blend via spin diffusion and would indicate the presence of phases or domains in the amorphous component of the blend larger than approximately 19 Å. The T_CH is proportional to the inverse sixth power of the interatomic distances needed for transfer of magnetization from proton to carbon and would be sensitive to a separation of polymer chains in the amorphous phase with aging on the order of 4–5 Å. There was an increase of the T_1ρH and T_CH values with aging, indicating that a subtle separation between unlike chains in the amorphous phase was occurring although a single amorphous phase was present.     

Thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) modified with divinyl benzene and vinyltrimethoxysilane

The effect of butyl acrylate (BA), divinyl benzene (DVB) and vinyltrimethoxysilane (TMVS) on the thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) was investigated. Glass transition temperature (T_g), melting temperature (T_m) and specific heat capacity of the copolymers were investigated using Differential Scanning Calorimetry. Thermal stability of the copolymers which is associated with the degradation temperature (T_d) was studied by Thermogravimetric Analysis. Polyacrylates with T_g ranges between -19°Cand 19°C were obtained. With the incorporation of >7 wt% of DVB, the T_g of the copolymer increases from about ?17°C to ?10°C even though they have not undergone UV irradiation. Gel content results prove that crosslinking has occurred in the copolymers. With increasing amount of TMVS from 0 wt% to 7 wt%, the T_m of the copolymers prepared at acidic pH is about 40-60°C higher than that at the alkaline pH. However, the addition of TMVS gives no significant effect to the T_g and T_d of the copolymer films. The thermal stability of the copolymer has improved with increasing amount of BA and DVB, with DVB being more effective. The highest T_d of 425°C with 8% of DVB has been obtained. Consequently, a polyacrylate copolymer with a T_g of about ?13°C, a T_m of 170 °C and a T_d of about 424°C has been successfully synthesized. Hence, the soft polyacrylate with its relatively high T_m and T_d could serve as a superb material especially to be applied in the areas that require high melting temperature and good thermal stability.     

Spectroscopic studies on the effect of field strength upon the curie transition of a VDF/TrFE copolymer

Infrared spectroscopic studies of the effects of field strength upon the ferroelectric phase transition behavior of a VDF/TrFE (75/25) copolymer upon heating and cooling in an electric field have revealed new findings. The paraelectric phase in the absence of an electric field resembles the α phase of PVDF with a trace of short trans sequences distributed randomly along the chain axis. The paraelectric phase in a high electric field is very different from that in the absence of an electric field. The paraelectric phase under an electric field has much longer trans sequences. The Curie transition temperature upon heating is a first-order transition temperature (T^↑_c) and is dramatically elevated from 120 to 135°C under the field of more than 0.4 MV/cm. Upon cooling, the paraelectric phase in an electric field does not show a clear transition. The field-induced phase transition and the loss of dipole switchability observed below a cooling temperature of 120°C, and their dependence on time and filed strength when exposed to a cyclic bipolar electric field are discussed. © 1993 John Wiley & Sons, Inc.     

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     

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.     

To the Knowledge of Interpseudohalogens: A Contribution to Cyanogen Isocyanate (NC–NCO)

Cyanogen isocyanate (NC–NCO) has been prepared and studied using a combined experimental and theoretical approach. A crystalline film of the interpseudohalogen species was stabilized by vapor deposition on a cold substrate (T = –100 °C). From IR spectroscopy on the “free” molecule, trapped in a matrix of solid argon, the connectivity and geometry of this unstable interpseudohalogen was deduced and substantiated by theoretical calculations. With this information, the crystal structure of NCNCO in the solid state could be analysed using powder X‐ray diffraction [Pbca (No. 61), a = 7.63(1) Å, b = 6.50(2) Å, c = 6.03(6) Å; V = 299.5(1) ų]. The compound transforms into amorphous polymeric C₂N₂O at T > –68 °C. The results obtained were compared with recent findings and further discussed in the general context of C–N–(O) chemistry.     

Melting studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)

Blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) exhibit complex melting behavior when crystallized at low undercoolings. Three crystals comprised of two different PVF₂ forms grow. Hoffman-Weeks plots of the observed melting points T_m of these crystals versus crystallization temperatures are constructed. The lowest-melting-point species, the α form, shows a change in slope which is attributed to fewer head-to-head PVF₂ units trapped in the crystal at higher temperatures. Defect energies in the crystal due to these units are calculated to be from 6.3 to 10.3 kJ/mol. Estimating lamellar thicknesses from the slopes of the two regions gives much more reasonable values when the high-temperature data are used. Removal of kinetic effects that lower the observed T_m by extrapolating the data to obtain T permits the thermodynamic interaction energy density B between the two polymers to be obtained. The low-temperature α-form data give B = ?8.83 × 10⁶ J/m³. The high-temperature α-form data and the T of the γ-form crystals both show B to vary from ?5.40 × 10⁶ to ?2.96 × 10⁷ J/m³ as the blend composition goes from 40.1 vol % to pure PVF₂.     

The topochemistry of the catalytic systems on the surface of polymer supports

The method of spin labels based on stable iminoxyl radicals has been applied to the investigation of the topochemistry of polymer-supported polyethylene-grafting diallylamine (PE-gr-PDAA)and ofimmobilized catalytic systetms. The effective distances between fixed radicals are comparatively large (r? ～ 25-35Å for the case of functional groups of PE-gr-PDAA and r? ≥ 35Å for the case of fixed components of the catalytic systems). The demonstration of step-by-step penetration of the label into the functional cover (100-300 Å) has been made. Correlation times were calculated in the temperature range 290-440K. The dependence of log τ_c on 1/T shows two linear parts to the curve.The activation energies in the α region for PE-gr-PDAA and for the product of its interaction with TiCl₄. Ti(OC₄H₉)₄, and Al(C₂H₅)₂Cl are equal to 13, 14, 24, and 13 Kcal/mole, respectively. The method has been applied to the investigation of Ziegler-Natta immobilized catalytic systems. It has been noted that the labels are fixed not far from each other (r? ≤ 12Å) after the interaction of the catalytic components.     

Effects of POSS nanoparticles on glass transition temperatures of ultrathin poly(t‐butyl acrylate) films and bulk blends

As a model system, thin films of trisilanolphenyl‐POSS (TPP) and two different number average molar mass (5 and 23 kg mol^?1) poly(t‐butyl acrylate) (PtBA) were prepared as blends by Langmuir–Blodgett film deposition. Films were characterized by ellipsometry. For comparison, bulk blends are prepared by solution casting and the samples are characterized via differential scanning calorimetry. The increase in T_g as a function of TPP content for bulk high and low molar mass samples are in the order of ～10 °C. Whereas bulk T_g shows comparable increases for both molar masses (～10 °C), the increase in surface T_g for higher molar mass PtBA is greater than for low molar mass (～22 °C vs. ～10 °C). Nonetheless, the total enhancement of T_g is complete by the time 20 wt % TPP is added without further benefit at higher nanofiller loads. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 175–182     

ThSi2 Type Ytterbium Disilicide and its Analogues YbTxSi2–x (T = Cr,Fe, Co)

YbSi₂ and the derivatives YbT_xSi_2–x (T = Cr, Fe, Co) crystallizing in the α‐ThSi₂ structure type were obtained as single crystals from reactions run in liquid indium. All silicides were investigated by single‐crystal X‐ray diffraction, I4₁/amd space group and the lattice constants are: a = 3.9868(6) Å and c = 13.541(3) Å for YbSi₂, a = 4.0123(6) Å and c = 13.542(3) Å for YbCr_0.27Si_1.73, a = 4.0142(6) Å and c = 13.830(3) Å for YbCr_0.71Si_1.29, a = 4.0080(6) Å and c = 13.751(3) Å for YbFe_0.34Si_1.66, and a = 4.0036(6) Å, c = 13.707(3) Å for YbCo_0.21Si_1.79. YbSi₂ and YbT_xSi_2–x compounds are polar intermetallics with three‐dimensional Si and M (T+Si) polyanion sub‐networks, respectively, filled with ytterbium atoms. The degree of substitution of transition metal at the silicon site is signficant and leads to changes in the average bond lengths and bond angles substantially.