The piezoelectric and pyroelectric responses of ferroelectric Langmuir–Blodgett polymer films are less than the largest values measured with bulk films of the same composition. The films of the crystalline copolymer poly(vinylidene fluoride trifluoroethylene) fabricated by the Langmuir–Blodgett technique are 30 ML thick (15 nm) and are highly crystalline and oriented with polarization perpendicular to the film. Both piezoelectric and pyroelectric measurements show reversible ferroelectric switching. The films are suitable for use in pyroelectric infrared imaging and in piezoelectric acoustic transducers.

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Piezoelectric and pyroelectric properties of ferroelectric Langmuir-Blodgett polymer films

In this review the physical properties, mechanisms and models are reviewed which explain the high piezoelectricity of the ferroelectric polymers of the polyvinylidene fluoride (PVDF) family, the odd nylons, the vinylidene cyanide (VDCN) copolymers and polyurea. Because PVDF and its copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE) have been studied extensively in the last 25 years the main part of the review deals with these polymers. Additionally a short summary of the different piezoelectric applications of PVDF is presented. The odd nylons, the VDCN copolymers and the polyurea are compared with PVDF to show the different stabilization mechanisms of the remanent polarization and the different temperature behavior of the piezoelectricity. This review not only concentrates on the work done in the last few years but in order to describe the behavior of these polymers in detail, it is necessary to go back to the roots. Therefore many articles from the late seventies and early eighties are included.

Piezoelectric polymer electrets

The article presents the recent research development in controlling molecular and microstructures of thin ferroelectric polymer films for the application of non-volatile memory. A brief overview is given of the history of ferroelectric memory and device architectures based on ferroelectric polymers particularly emphasizing on the device elements such as metal/ferroelectric/metal type capacitor, metal-ferroelectric-insulator-semiconductor (MFIS) diodes and ferroelectric field effect transistor (FeFET) with ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers with trifluoroethylene (TrFE). Key material and process issues for optimizing the memory performance in each device architecture and thus realizing non-volatile ferroelectric polymer memory are in details discussed, including the control of crystal polymorphs, film thickness, various hetero-material interfaces between ferroelectric polymer and either metal or semiconductor, crystallization and crystal orientation. The current effort of micro and nanopatterning techniques is also addressed for high density and flexible memory arrays.

Control of thin ferroelectric polymer films for non-volatile memory applications

Substantial advances have recently been made in characterizing the structures and phase diagrams of Langmuir monolayers of alkyl-chain surfactants on water. These allow detailed comparisons to be made with the bulk phases formed by n-alkanes, in particular, the rotator phases. It is shown that the untilted Langmuir phases denoted CS, S, and LS, correspond to the herringbone-crystal, distorted rotator without long-range herringbone order (RI) and hexagonal rotator (RII), respectively. The quantitative behavior of the distortion and area/molecule in the Langmuir monolayers, their derivatives and jumps at the transitions are shown to correspond more closely to the behavior of n-alkane mixtures where the interlayer interaction is weakened than to that of the pure n-alkanes. It is shown that the tilted phases can be associated with the same three categories regarding distortion and herringbone order that characterize the untilted phases, if the distortion is measured perpendicular to the chain-axis. An “anomal...

Remarks Concerning the Relation between Rotator Phases of Bulk n-Alkanes and Those of Langmuir Monolayers of Alkyl-Chain Surfactants on Water

Ethanol is known to form two different kinds of glassy state, namely a structural glass and a glassy crystal, both showing the same glass transition temperature . The molecular dynamics in the different phases (supercooled liquid/plastic crystal) and during the corresponding phase transition is studied by dielectric spectroscopy in the frequency range (30 K-250 K). Extracting the time constant, width parameter and relaxation strength of the main relaxation (the -process), very similar dielectric loss is found in both phases, including also the high-frequency wing. Comparing the temperature dependence of the time constants , the plastic crystal exhibits a less fragile behaviour. Additionally, a secondary relaxation is detected, again essentially the same in the two glassy states. We conclude that the motional mechanisms probed in the plastic crystal and in the supercooled liquid state are very similar.

https://iopscience.iop.org/article/10.1088/0953-8984/10/37/005/pdf

Two glass transitions in ethanol: a comparative dielectric relaxation study of the supercooled liquid and the plastic crystal

Highly crystalline and uniaxial-oriented polytetrafluoroethylene films, nanostructured in one dimension, were used to produce a fully crystalline, thermoreversible morphology in the ferroelectric copolymer poly[vinylidenefluoride-trifluoroethylene]. The resulting state is built up of regularly stacked lamellar crystals of about 100 nm thickness and lateral dimensions of about 6 \ensuremath{\mu}m.

Surface-induced organization of linear molecules on nanostructured polytetrafluoroethylene: Crystalline state of poly[vinylidenefluoride-trifluoroethylene]

Frozen-in trans and gauche conformational disorder of symmetrical difluorotetra-chloroethane (DFTCE) produces the tendency of this plastic crystal to form an orientational glassy state on cooling below Tg=86 K. To throw light upon the freezing mechanism in DFTCE neutron diffraction and Brillouin scattering as well as infrared and dielectric measurements are employed. The overall picture of the results obtained can be characterized in terms of a classical glass-transition process with a relaxation frequency obeying the Vogel-Fulcher law. However, a more sophisticated picture of the freezing process is indicated by a quantitative analysis of the new Brillouin data, e.g. the temperature dependence of the sound velocity. The behaviour could be understood on the basis of a mode-coupling theory.

https://iopscience.iop.org/article/10.1088/0953-8984/6/35/006/pdf

Unconventional orientational glass transitions in symmetrical difluorotetrachloroethane

Within this work we present Brillouin and ultrasonic investigations performed on the liquid crystals p-methoxybenzylidene p-(n-butylaniline) (MBBA), p-azoxyanisol (PAA), 4-cyano-4-n-alkylbiphenyles (nCB), and 4-n-pentoxybenzylidene-4'-n-octoaniline (5O.8). Special attention has been paid to the evolution of a significant splitting of the two longitudinal polarized acoustic modes within the nematic phase. Angle-resolving Brillouin spectroscopy allowed the determination of the complete stiffness tensors and hence a discussion of the propagation of quasitransverse polarized acoustic modes in the nematic state of liquid crystals. We analyze the behavior of the eigenvectors of the relevant acoustic modes and discuss their significance for the propagation of quasishear modes. For 5O.8 we report an acoustic instability within its nematic state. We confirm the existence of a universal thermal relaxation mechanism of weak activation energy for the nematic state of classical liquid crystals. The observed hypersonic anisotropy is discussed in terms of that relaxation mechanism and is compared with that of glass-forming liquid crystals.

Second-order elasticity of liquid crystals within their nematic state at high frequencies

Phase-transition behavior of n-alkanes on nanostructured polytetrafluorethylene films : brillouin spectroscopic and calorimetric investigations on pen tacosane

Time domain Brillouin spectroscopy has been used as a definitive experimental approach to demonstrate the intrinsic nature of the thermal glass transition in Polyvinylacetate The transition from the equilibrium liquid to the ideal glassy state appears at the ultimate temperatureT
gs

R. Jiménez

Papers

Surface-induced organization of linear molecules on nanostructured polytetrafluoroethylene: Crystalline state of poly[vinylidenefluoride-trifluoroethylene]

Unconventional orientational glass transitions in symmetrical difluorotetrachloroethane

Second-order elasticity of liquid crystals within their nematic state at high frequencies

Phase-transition behavior of n-alkanes on nanostructured polytetrafluorethylene films : brillouin spectroscopic and calorimetric investigations on pen tacosane

On the existence of an intrinsic glass transition in a fragile liquid: polyvinylacetate