Real-time investigation of crystallization in poly(vinylidene fluoride)-based nano-composites probed by infrared spectroscopy

Via time-resolved Fourier transform infrared spectroscopy (FTIR), we examined the real-time investigation of the conformational changes of poly(vinylidene fluoride) (PVDF) chain segment during crystallization of neat PVDF and the corresponding nano-composites having intercalated structure. It was shown that in the following crystallization processes the crystal growth was virtually the same in both nano-composites and neat PVDF. We have examined an annealing at an infinitely long time at 200 °C (∼20 min) to erase the thermal history in the nano-composites. The dispersed titanate nano-filler particles exhibited strong contribution to enhance the heterogeneous nucleation for the formation of both γ- and β-phase crystals.     

Real-time investigation of crystallization in nylon 6-clay nano-composite probed by infrared spectroscopy

Via time-resolved FTIR, we examined the real-time investigation of the structural change in molecular chain of nylon 6 during crystallization of neat nylon 6 and the corresponding nano-composite (N6C3.7) having fully exfoliated structure. The neat nylon 6 predominantly formed α-phase in the crystallization temperature (T_c) range of 155-195 °C. For N6C3.7 crystallization at low T_c range of 150-168 °C, where the network structure formed by the dispersed clay particles still affected chain folding of nylon 6, the formation of the γ-phase was dominant. The crystallization took place so rapidly (less than 1 s) without induction time of crystallization. At high T_c range (=177-191 °C), the stable growth of the α-phase crystal coexisting with γ-phase occurred in N6C3.7 crystallization. The growth mechanism in the subsequent crystallization processes (amides IIIα and IIIγ) was virtually the same in both N6C3.7 and neat nylon 6.     

Thermal, spectroscopy, and morphological studies on polymorphic crystals in poly(heptamethylene terephthalate)

Polymorphism and its influential factors in poly(heptamethylene terephthalate) (PHepT) were probed using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and wide angle X-ray diffraction (WAXD). PHepT exhibits two crystal types (α and β) upon crystallization at various isothermal melt-crystallization temperatures (T_cs) by quenching from different T_maxs (maximum temperature above T_m for melting the original crystals). Melt-crystallized PHepT with either initial α- or β-crystal by quenching from T_max lower than 110 °C leads to higher fractions of α-crystal, but crystallization from T_max higher than 140 °C leads to higher fractions of β-crystal. In addition to T_max, polymorphism in PHepT is also influenced by crystallization temperature (T_c = 25-75 °C). When PHepT is melt-crystallized from a high T_max = 150 °C (completely isotropic melt), it shows solely β crystal for higher T_c, and solely the α-crystal for T_c < 25 °C; in-between T_c = 25 and 35 °C, mixed fractions of both α- and β-crystals. However, by contrast, when PHepT is melt-crystallized from a lower T_max = 110 °C, it shows α-crystal only at all T_cs, high or low.     

Impact of nanosilicates on poly(vinylidene fluoride) crystal polymorphism: Part 1. Melt-crystallization at high supercooling

Polymorphism of poly(vinylidene fluoride), PVDF, in the presence of Lucentite STN organically modified silicate (OMS) is investigated for PVDF nanocomposites melt-crystallized at high supercooling temperatures where neat PVDF crystallizes exclusively in the alpha crystalline phase. Nanocomposites were prepared from solution with 0-1.0 wt% OMS composition. Here we observed that clay addition promotes gamma phase formation in nanocomposites melt-crystallized at high supercooling (i.e., at low crystallization temperature), whereas previously we showed that even small amount of nanosilicates resulted in beta phase formation in cold-crystallized PVDF nanocomposites [1].Wide-angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) studies showed that α- and γ-phases co-existed in nanocomposites containing up to 0.1 wt% OMS, and the amount of α-crystals substantially diminished for higher OMS content. Formation of γ-crystal phase was confirmed with morphologic observation of spherulites of low-birefringence using polarizing optical and atomic force microscopies, and their crystalline structures were verified by FTIR and Raman microscopic spectroscopy. We also address in this work the ambiguities in assessing PVDF crystallographic phases, and correct the phase identification errors which have persisted up to this point in the literature based on melting point confusion. The crystal phase identification for PVDF nanocomposites is discussed and clarified, based on X-ray scattering, vibrational spectra, and thermal analysis. For reference, we provide a vibrational band list, indicating the close, or overlapping bands, of the three phases of PVDF: α, β and γ.     

High pressure crystallization of random propylene-ethylene copolymers: α-γ Phase diagram

Two random propylene copolymers with low ethylene content synthesized by Ziegler-Natta catalysts were used is this study to investigate the formation of γ-crystal phase during isothermal crystallization at high pressures. At atmospheric pressure these copolymers crystallize in a mixture of α- and γ-crystals. The content of the γ-phase in the copolymer crystals increased with increasing defect content, crystallization temperature and pressure. Wide-angle X-ray diffraction studies showed that crystallization of these copolymers at pressures above 88 MPa and temperature above 142 °C leads to formation of pure γ-phase. The equilibrium melting temperature of the γ-phase has been determined as a function of defect content and crystallization pressure. Temperature-pressure-composition α-γ phase diagram of isotactic polypropylene was constructed based on the Gibbs free energy approach. This diagram enabled the extrapolation of the equilibrium melting temperatures of both phases for defect free isotactic polypropylene. They were found to be 186.9°C for the α-phase and 189.9°C for the γ-phase.     

Confined crystallization phenomena in immiscible polymer blends with dispersed micro-and nanometer sized PA6 droplets part 4: polymorphous structure and (meta)-stability of PA6 crystals formed in different temperature regions

The genesis and stability of different PA6 crystalline polymorphs, dispersed as micro- and submicrometer sized droplets inside an amorphous polymer matrix, are discussed over a very broad temperature range. Different PA6 droplet sizes lead to different PA6 crystallization events in a 100 °C wide temperature window that extends down to 85 °C. Static WAXD and DSC experiments on micrometer sized PA6 droplets indicate the formation of a stable γ-crystal phase in the region between 175 and 130 °C. Sub-micrometer sized PA6 droplets only crystallize at 85 °C in the β-phase. Upon heating above the PA6 glass transition, these crystals progressively increase their perfection and ultimately transform into the α-phase around 170 °C.     

Microcrystallization of lactose during droplet drying and its effect on the property of the dried particle

Spray dried products with controlled crystallinity is desired to realize an improved quality and functionality of the final products. This study used the glass-filament single droplet drying technique to study lactose crystallization behaviour during convective drying. Single lactose droplets with different proportions of α- and β-isomers were subjected to air drying temperatures of 70 °C and 110 °C. Lactose particles dried at 70 °C with higher initial proportions of α-isomer showed the lowest dissolution rate. XRD analysis on the freshly dried particles showed that higher crystallinity was achieved with a higher air drying temperature and a higher initial α-isomer proportion. This observation was confirmed with the SEM observation of lactose particles that were both freshly dried and with a post-drying crystallization process. Dried lactose particles could have a two-layer morphology where the surface shell and the interior part possess different crystallinity, due to the different crystallization kinetics during drying. The results suggest that during drying there is a critical crystallization stage where both droplet temperature and moisture content are sufficiently high, constituting large T − T_g driving force. For rapid crystallization to occur. The findings provide experimental support for the solid-phase crystallization theory.     

Structure, phase transition and electric properties of poly(vinylidene fluoride-trifluoroethylene) copolymer studied with density functional theory

The geometry, energy, internal rotation, vibrational spectra, dipole moments and molecular polarizabilities of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) of α- and β-chain models were studied with density functional theory at B3PW91/6-31G(d) level and compared with those of the poly(vinylidene fluoride) (PVDF) homopolymer. The chain length and the trifluoroethylene (TrFE) concentration were examined to discuss the copolymer chain stabilities, chain conformations and electric properties. The asymmetrical internal-rotation potential energy curve shows that the angles for the g and g′ conformations in the α-chain (tg and tg′) models are 53° and −70°, respectively, and the β-chain (ttt) conformation is a slightly distorted all-trans plane with dihedral angle at 177°. The energy differences, E_β − E_α(g) and E_β − E_α(g′), between the β- and the α-conformation are 2.1 and 7.8 kJ/mol, respectively. These values are smaller than that in PVDF (8.4 kJ/mol), suggesting that the β-conformation in the copolymer will be more stable than in PVDF. The energy barriers for β → α(g) and β → α(g′) transitions are 16.2 and 5.8 kJ/mol, respectively. The former is almost twice of the energy barrier in PVDF by 8.2 kJ/mol and the latter is slightly smaller (by 2.4 kJ/mol) than that in PVDF. The respective energy barriers for α(g) → β and α(g′) → β transitions are 18.3 and 13.6 kJ/mol compared with the value 16.3 kJ/mol in PVDF. The asymmetrical energy barriers may be one of the reasons for the copolymers with 0.5-0.6 (mole fraction) VDF exhibiting complicated phase transition behavior. The conformation of α-chain P(VDF-TrFE) exhibits from a helical (containing higher TrFE) to a nearly beeline (containing lower TrFE). This behavior is different from that in the PVDF and the nearly beeline conformation might be responsible for the increasing crystallizability. The helical might also be associated with the complicated phase transition behavior and the larger lattice strain in the P(VDF-TrFE)s with higher TrFE concentration. The energy difference per monomer unit between the β- and α-chain decreases with increasing TrFE content. The ideal β-chain is curved with a radius of about 30 Å, which is similar to that in PVDF. The chain curvature and the TrFE content will affect the dipole moment contribution per monomer. The chain length and TrFE content will not significantly affect the mean polarizability. The calculations indicated that there are some additional characteristic vibrational modes that may be used in identification of the α- or β-phase P(VDF-TrFE)s with different TrFE contents.     

CO2 pressure effects on melting, crystallization, and morphology of poly(vinylidene fluoride)

Supercritical CO₂ fluids (SCF CO₂) assisting melting of poly(vinylidene fluoride) (PVDF) and the SCF CO₂ pressure affecting surface and bulk morphology, melting and crystallization of PVDF were investigated by means of SEM, AFM, FTIR, WAXD, DSC and SAXS. Three SCF CO₂ conditions at 84, 283, and 476 atm all at 140 °C for 30 min were studied. Morphological changes, induced by melting of PVDF under SCF CO₂ and recrystallization during depressurization of CO₂, were found. The level of the CO₂-assisted melting of PVDF was found to increase with increasing pressure. SEM and AFM images showed that the 84 atm of CO₂ assisted melting on the surface of PVDF film while both 283 and 476 atm of CO₂ gave rise to melting of the whole film. FTIR spectra and WAXD patterns found that the hot-pressed PVDF film exhibited predominant α-crystalline form, which is one of the reported four crystalline forms including α, β, γ, and δ forms, and did not transform to other crystalline form(s) upon the SCF CO₂ treatments although they lowered the bulk crystallinities of PVDF. SEM images showed that the SCF CO₂ treatments at 283 and 476 atm resulted in foam formations in PVDF, with smaller foam cells resulting from the lower pressure treatment. SAXS data found that the thickness of crystalline layer in the lamellar stacks increased while that of amorphous layers insignificantly changed after SCF CO₂ treatments at 283 and 476 atm, as compared with untreated PVDF. SAXS and DSC data suggested the presence of a bimodal distribution of crystal size of PVDF after SCF CO₂ treatments.     

Crystallization controlled by layered silicates in nylon 6–clay nano-composite

To understand the effect of the montmorillonite (MMT) particles on the crystallization kinetics and crystalline morphology of nylon 6 upon nano-composite formation, we have characterized the crystallization behaviors by using light scattering, wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and rheological measurement. The correlation between the nucleating effect and the growth mechanism of the different polymorphism (γ-phase) of nylon 6 in the nano-composite (N6C3.7) was probed. N6C3.7 exhibited γ-phase crystal due to the nucleating effect of the dispersed MMT particles into the nylon 6 matrix throughout the whole T_c range (=150–215 °C). The lamellar growth of the γ-phase crystal took place on both sides of the dispersed MMT particles. In comparison between the temperature dependence of the characteristic relaxation time and the crystallization time, the lamellar growth of the γ-phase crystal has been discussed. The stable growth of the γ-phase was strongly disturbed at low T_c range (=160–190 °C) due to the lack of time for crystallization.     

Structure and piezoelectric properties of poly(vinylidene fluoride) studied by density functional theory

The internal rotation, geometry, energy, vibrational spectra, dipole moments and molecular polarizabilities of poly(vinylidene fluoride) (PVDF) of α- and β-chain models were studied by density functional theory at B3PW91/6-31G(d) level. The effects of chain lengths and monomer inversion defects on the electric properties and vibrational spectra were examined. The results show that the tgtg′ conformation angle between g and g′ is about 55° and the ttt conformation is a slightly distorted all-trans alternating planar zigzag with ±175° repeating motif. The average distance between adjacent monomer units in the β-PVDF is 2.567 Å. The energy difference between the α- and β-chains is about 10 kJ/mol per monomer unit. The dipole moment will be affected by chain curvature (with a radius of about 30.0 Å for ideal β-chain) and by defect concentration other than localization. The chain lengths and defects will not significantly affect the mean polarizability. The calculations indicated that there are some additional characteristic vibrational modes that may help identification of the α- and β-phase PVDF.     

Analyses of crystal forms in syndiotactic polystyrene intercalated with layered nano-clays

A mixed polymorphic morphology of intercalated/exfoliated structure was observed in syndiotactic polystyrene (sPS)/clay nano-composites, which were successfully prepared by solution intercalation technique using 1,1,2,2-tetrachloroethane (TCE) as a solvent. Furthermore, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were used to examine the effect of montmorillonite clays (MMT, in pristine or organo-modified forms) in isothermally melt-crystallized sPS at several available crystallization temperatures (T_c) in a competitive environment of coexisting α- and β-crystals. A significant change in polymorphism of sPS was observed by the inclusion of different clays and the temperature regime of the α-crystal formation in sPS was found to increase considerably up to 250 °C by the presence of the organo-clay. Pristine clay (Na-MMT) was found to induce the β-crystal of sPS at all T_c's studied in this work. The overall thermodynamics of crystallization remained unchanged as the β-phases were found in major proportion at higher temperature of crystallization (∼260 °C), irrespective of the nature of the clays. The dispersibility of the clays in sPS matrix is assumed to play the pivotal role in modifying the crystalline structures, which was further corroborated by the polarized optical microscopy (POM). The spherulitic morphology clearly indicates differences in crystallites as affected by the nano-clays. Incorporation of organo-clay with nanoscale dispersibility through the intercalation of sPS molecules into the clay galleries was found to promote rapid formation of α-forms, which develops into spherulites of smaller dimension as compared to those of the β-forms. The alteration in melting behavior of sPS is attributed to the different crystallite structures that lead to formation of different kind of spherulites.     

Morphology, polymorphism behavior and molecular orientation of electrospun poly(vinylidene fluoride) fibers

The morphology, polymorphism behavior and molecular orientation of electrospun poly(vinylidene fluoride) (PVDF) fibers have been investigated. We found that electrospinning of PVDF from its N,N-dimethylformamide/acetone solutions led to the formation of β-phase. In contrast, only α- and γ-phase was detected in the spin-coated samples from the same solutions. In the aligned electrospun PVDF fibers obtained using a rotating disk collector, the β-phase crystallites had a preferred orientation along the fiber axis. The degree of orientation did not, however, vary significantly with the speed of the rotation disk collector, and the β-phase was also not significantly enhanced with the increase in the rotation speed or the decrease in the size of spinnerets. These facts indicated that the orientation was likely to be caused by Columbic force rather than the mechanical and shear forces exerted by the rotating disk collector and spinnerets. The Columbic force may induce local conformational change to straighter TTTT conformation, and hence promote the β-phase. The addition of 3 wt.% of tetrabutylammonium chloride (TBAC) into the polymer solutions effectively improved the morphology of the electrospun fibers, and led to almost pure β-phase in the fibers. With spin coating, PVDF-TBAC did not, however, show any strong β-phase diffraction peak. The synergistic β-enhancement effect of TBAC and electrospinning is possibly due to the fact that while TBAC could induce more trans conformers, electrospinning promotes parallel packing, and hence inter-chain registration.     

Crystallization, spherulite growth, and structure of blends of crystalline and amorphous poly(lactide)s

The effects of incorporated amorphous poly(dl-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(l-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (T_c) range of 90-150 °C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The small-angle X-ray scattering results revealed that for T_c of 130 °C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Low frequency ac conduction and dielectric relaxation behavior of solution grown and uniaxially stretched poly(vinylidene fluoride) films

The measurements of ac conductivity [σ_m(ω)], dielectric constant [?′(ω)] and loss [?″(ω)] have been performed on solution grown (thickness ∼85 μm) and uniaxially stretched (thickness ∼25, 45 and 80 μm) films of poly(vinylidene fluoride) (PVDF) in the frequency range 0.1 kHz-10 MHz and in the temperature range 77-400 K. The σ_m(ω) can be described by the relation σ(ω) = Aω^s, where s is close to unity and decreases with increase in temperature. Three relaxations, observed in the present investigation, have been designated as the α_c-, the α_a- and the β-relaxations appearing from high temperature side to the low temperature side. The α_c-relaxation could not be observed in the case of uniaxially stretched poly(vinylidene fluoride) films. The α_c- and α_a-relaxations are associated with the molecular motions in the crystalline regions and micro-Brownian motion in the amorphous regions of the main polymer chain, respectively, whereas the β-relaxation is attributed to the rotation of side group dipoles or to the local oscillations of the frozen main polymer chain.     

Pyroelectric performances of 1-3 ferroelectric composites based on barium titanate nanowires/polyvinylidene fluoride

Pyroelectric properties of 1–3 ceramic/polyvinylidene fluoride (PVDF) composites by using barium titanate nanowires (BTnws) and dopamine modified BTnws (DM-BTnws) as inclusions were firstly reported. 0–3 composites based on dopamine modified BT nanoparticles (DM-BTnps)/PVDF were also prepared for comparison. It was found that low contents of DM-BTnws in PVDF are beneficial for achieving high fraction of β-phase content based on the analysis results of X-ray diffraction (XRD), Fourier transform infrared (FTIR) and electric displacement-electric field (D-E) measurements. The enhancement of β-phase content in the DM-BTnws/composited film was believed to originate from strong hydrogen bonds interactions between poly-dopamine and PVDF molecules, which induced phase transition in PVDF from α-phase into β-phase. However, although DM-BTnws improved β-phase content and, accordingly, pyroelectric coefficient of the composites, they deteriorated dielectric performances of PVDF, reducing pyroelectric performances of the composites in terms of voltage and detectivity figures of merit.     

Microfibrillar composites based on polyamide/polyethylene blends. 1. Structure investigations in oriented and isotropic polyamide 6

The present paper discloses the structural changes caused by heating of polyamide 6 (PA6) samples with different thermal and mechanical histories in the 30-240 °C range. Wide and small-angle X-ray scattering (WAXS and SAXS) of synchrotron radiation, as well as solid-state nuclear magnetic resonance spectroscopy (NMR) measurements are performed. The NMR spectra show that in both isotropic and oriented samples there is a co-existence of α and γ-PA6 crystalline forms. Deconvolution of the WAXS patterns is performed to follow the temperature dependence of the unit cell parameters of the α and γ-forms and also of the equatorial (ECI) and total crystallinity indexes (CI), evaluating the contributions of the two crystalline phases. Estimates for the long spacing and for the average thicknesses of the crystalline (l_c) and amorphous (l_a) phases within the lamellae are calculated as a function of the heat treatment employing analysis of the linear correlation function calculated from the SAXS patterns. The X-ray results allowed the conclusion that upon heat treatment up to 160-200 °C, intensive transitions between the PA6 crystalline forms take place, whereby the content of the initial major crystalline phase decreases and that of the initial minor one increases reaching almost 1:1. Close to 200 °C a general trend toward increasing the content of the α-form is registered. The influence of annealing and quenching after melting on the PA6 crystalline structure is also studied.     

Isothermal crystallization of isotactic polypropylene blended with low molecular weight atactic polypropylene. Part I. Thermal properties and morphology development

The thermal properties and morphology development of isotactic polypropylene (iPP) homopolymer and blended with low molecules weigh atactic polypropylene (aPP) at different isothermal crystallization temperature were studied with differential scanning calorimeter and wide-angle X-ray scattering. The results of DSC show that aPP is local miscible with iPP in the amorphous region and presented a phase transition temperature at T_c=120 °C. However, below this transition temperature, imperfect α-form crystal were obtained and leading to two endotherms. While, above this transition temperature, more perfect α- and γ-form crystals were formed which only a single endotherm was observed. In addition, the results of WAXD indicate that the contents of the γ-form of iPP remarkably depend both on the aPP content and isothermal crystallization temperature. Pure iPP crystallized was characterized by the appearance of α- and γ-forms coexisting. Moreover, the highest intensity of second peak, i.e. the (0 0 8) of γ-form coexisting with (0 4 0) of α-form, and crystallinity were obtained for blended with 20% of aPP, the γ-form content almost disappeared for iPP/aPP blended with 50% aPP content. Therefore, detailed analysis of the WAXD patterns indicates that at small amount aPP lead to increasing the crystallinity of iPP blend, at larger amount aPP, while decreases crystallinity of iPP blends with increasing aPP content. On the other hand, the normalized crystallinity of iPP molecules increases with increasing aPP content. These results describe that the diluent aPP molecular promotes growth rate of iPP because the diluent aPP molecular increases the mobility of iPP and reduces the entanglement between iPP molecules during crystallization.     

Structure and electric properties of poly(vinylidene fluoride-tetrafluoroethylene) copolymer studied with density functional theory

The internal rotation, geometry, energy, vibrational spectra, dipole moments and molecular mean polarizabilities of poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TeFE)) of α- and β-chain models were studied with density functional theory at B3PW91/6-31G(d) level and compared with those of poly(vinylidene fluoride) homopolymer and P(VDF-TrFE) copolymer. The electric properties, chain conformation and stability of the copolymer influenced by the chain length and TeFE content were examined. Based on the internal rotation curves of P(VDF-TeFE) dimer models (H[CH₂CF₂-CF₂CF₂]H and H[CF₂CH₂-CF₂CF₂]H), the conformational angles, relative stabilities of α- and β-conformation, and the transition energy barriers of β → α and α → β were discussed. The results show that the β-conformation is more stable than the α-conformation thermodynamically and the β → α transition in P(VDF-TeFE) is more difficult than that in PVDF. Thus the copolymer should be in favor of preventing the piezoelectric phase from depolarization. The ideal β-chains are curved with a radius of about 30 Å, which is very close to those in both PVDF and P(VDF-TrFE). Similar to P(VDF-TrFE), the α-chain P(VDF-TeFE) containing 0.50 mole fraction of TeFE is also a helical structure. However, the α-chain with 0.33-0.20 mole fraction of TeFE are almost linear in structure, which might be responsible for enhancing crystallinity of the copolymer. The contribution of average dipole moment per monomer unit in the β-chain is affected by the chain curvature and TeFE content, and there is a weakly parabolic dependence on the VDF content. The chain length and TeFE content will not significantly affect the mean polarizability per monomer unit. The calculations show that there are some characteristic vibrational modes that may be used in the identification of the α- and β-phase P(VDF-TeFE) with different TeFE contents.