【正文】 modes exhibit a VogelFulcherTammann(VFT) behaviour as for polyamide 11 [2224 ]:28the VFT parameters of each mode are reported in Table 2.The VFT。are presented in Fig. 1. This formalism allows a better resolution of high temperature modes that could be partially hidden by the MWS contribution.Six relaxation modes are pointed out on the 3D dielectric relaxation map. The low temperature g mode is attributed to the molecular mobility of aliphatic sequences of PA 6,9. It is now generally accepted in polyamides that the g relaxation involves a mobility of the 22methylene groups between amide linkages [16] . The β 2and β 1submodes are related to the mobility of watereamide plexes and free amide groups respectively [17] .Theɑ andɑ39。 formalism, the MWS peak is sometimes hidden by the conductivity rise.TSC analyses were carried out on a TSC/RMA analyser. For recording plex thermograms, the sample was polarized by an electrostatic field Ep= 1 1 during tp=2 min over a temperature range from the polarization temperature Tp = 90℃ down tothe freezing temperature T0=—16 0℃. Then the fi eld was turned off and the depolarization current was recorded with a constant heating rate (qh =+ 7℃.min 1), the equivalent frequency of the TSC spectrum was feq~102—103Hz. Elementary TSC thermograms were recorded with a poling window of 5℃. Then thefi eld was removed and the sample cooled down to a temperature Tcc = Tp — 30℃. The depolarization current was recorded with a constant heating rate qh .The series of elementary thermograms was recorded by shifting the poling window by 5℃ towards higher temperature.. Ferroelectric analysesFor ferroelectric measurements, fi lms were colddrawn at room temperature. In order 21to prevent voltage breakdown during the poling procedure, the samples were covered by Castor oil and measurements were made at low pressure (p= 2 10 4hPa). The samples were poled under triangular shape electric field at room temperature.Piezoelectric measurements were carried out using a PM 200 piezometer supplied by Piezotest, with a strength of N at 110 Hz in frequency. The piezoelectric coeffi cient d33 is measured in the same direction than the polarization fi eld.Pyroelectric measurements were performed by a Keithley femtoamperemeter. The samples were shortcircuited during 5 min at room temperature and cooled to 170℃. They were heated up to 100℃ with a constant heating rate qh to eliminate thermally stimulated currents. Then, they were cooled again to 170℃ and the pyrocurrent was recorded as a function of temperature. The pyroelectric coeffi cient p is proportional to the heating rate and to the sample surface as indicated by its definition:where i(T) is the current (A) as a function of temperature, S is the surface area (m2). Piezoelectric measurements were carried out af ter the pyroelectric tests to prevent any spontaneous poling effect (internal stresses).3. Results and discussion. Dielectric relaxation. Isothermal dielectric responseThe molecular dynamics of the dipolar entities of PA 6,9 in the high frequency range has been analyzed by dynamic dielectric spectroscopy. The dielectric modulus losses M39。2) (2)In the modulus formalism, Maxwelle Wagnere Sillars (MWS) polarization which usually occurs in heterogeneous systems like semicrystalline polymers [14,15]is observed as a mode. In the ε39。2+ε39。39。39。39。 is deduced from the real and theimaginary part of the dielectric permittivity ε39。 Paul Sabatier, 31062 Toulouse cedex 09, FranceARTICLE I NFOArticle history:Received 13 November 20 09Received in revised form7 July 2022Accepted 25 July 2022Available online 30 July 2022Keywords: Dielectric Relaxations Piezoelectric abstractABSTRACTTherm o Stim ulated Current (TSC) bined with Dyn amic Diel ectric Spec troscopy (DDS) have been applied to the investigation of dielectric relaxation modes of an evenodd Polyamide PA 6,9. The correlation between results obta ined by both meth ods allows us to describe precisely the molecu larmobility. At high temperature, the various dielectric relaxation phen omena are separated by applying t he dielectric modulus formalism. The parison between the activation enth alpy values obtained by DDS and TSC leads to the assignment of the socalled a mode to cooperative movements of 19polymeric sequences. Molecular mobility of PA 6,9 is pared with the one of PA 11. The piezoelectri cactivity of PA 6,9 is shown and analyzed.
2022 Elsev ier Ltd. All rights reserved.1. IntroductionPiezoelectric polymers have been the subject of a lot of work sincethe discovery of the piezoelectric behaviour of poly(vinylidene fluoride) PVDF by Kawai in 1969 [1].The understanding of the molecularorigin of the ferroelectricity of PVDF [24] initiates the developmentof its vinylidene fluoride etrifluoroethylene copolymers[5,6](P(VDFTrFE )) and v inyl id en e fluoride etrifluoroethylene echloro fluoroethylene terpolymers [7,8] (P(VDFTrFECFE)).Scheinbeim etal. [9].discovered the ferroelectric behaviour of odd numbered polyamidesand showed that the remanent polarization is linearly dependentupon the dipolar density of amide groups. More recently, a new class of evene odd polyamide PA 6,9 has been elaborated. Franco that the room temperature crystalline structure of PA 6,9 differs from the classic hydrogen bonded sheet structure of PA 6, a structural point of view, PA 6,9 might have analogies with oddeven polyamides but the corresponding studies are mostly concentrated on the crystalline structures and mechanical properties[11] . As far as we know, the dielectric and the ferroelectric behaviourof evene odd polyamides have not yet been shown. In this work,molecular mobility of dipolar entities of polyamide 6,9 has been characterized using a bination of thermo stimulated curren