Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers - USP - Sao Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins.

Characterization of polyurethane resins by FTIR, TGA, and XRD

Polymers for additive manufacturing and 4D-printing: Materials, methodologies, and biomedical applications

A review of the corona charging of polymers is presented. After providing a brief account of the corona discharge process and of its application for charging materials, the paper focuses on the evolution of corona triodes that allow the sample surface potential to be monitored during the charging process. Particular emphasis is given to the main contributions arising from research, basically on Teflon FEP and ferroelectric polymers, in which a constant-current corona triode was used. Such a triode system has become a powerful tool in the study of charge transport and ferroelectric properties of polymers, because keeping the charging current constant facilitates matching of the experimental results to a number of theoretical models. >

Corona charging of polymers

Polymers with strong piezo-, pyro-, and ferroelectricity are attractive for a wide range of applications. In particular, semicrystalline ferroelectric polymers are suitable for a large variety of piezo- and pyroelectric transducers or sensors, while amorphous polymers containing chromophore molecules are particularly interesting for photonic devices. Recently, a new class of polymer materials has been added to this family: internally charged cellular space-charge polymer electrets (so-called “ferroelectrets”), whose piezoelectricity can be orders of magnitude higher than that of conventional ferroelectric polymers. Suitable patterning of these materials leads to improved or unusual macroscopic piezo-, pyro-, and ferroelectric or nonlinear optical properties that may be particularly useful for advanced transducer or waveguide applications. In the present paper, the piezo-, pyro-, and ferroelectricity of poled polymers is briefly introduced, an overview on the preparation of polymer electrets with patterned...

/pdf/patterned-piezo-pyro-and-ferroelectricity-of-poled-polymer-3eek133ae3.pdf

Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets

We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene (FEP) films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene (PTFE) template at 300 °C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d33 coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130 °C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer ...

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Cellular and porous polymers with internal bipolar space charge can exhibit large piezoelectric thickness coefficients and have therefore led to significant advances in the understanding and the application of piezoelectricity in polymer electrets. As possible alternatives to these cellular ferroelectrets, other potentially useful configurations of space-charge electrets, such as bi-layer or multi-layer stacks of at least one "soft" porous and one "hard" non-porous electret film have been suggested and investigated. Extending the concept of cellular or porous polymer electrets with microscopic voids, we propose and describe novel piezoelectret structures with regular arrays of millimeter-sized bubbles that are formed between fluoro-ethylene-propylene (Teflonreg-FEP) films via a vacuum-assisted thermal process. After internal charging by means of high impulse voltages, the bubble structures exhibit rather large piezoelectric activities in their thickness direction, with phenomenological quasi-static d33 coefficients of up to 500 pC/N (or pm/V) which quite strongly decrease with the amplitude of the applied force. The electromechanical behavior of the new piezoelectrets has been modeled in analogy to the operation of electret microphones

https://www.researchgate.net/profile/Luiz_Neto7/publication/3340734_Piezoelectrets_from_thermo-formed_bubble_structures_of_fluoropolymer-electret_films/links/54dbbf280cf28d3de65c78ed.pdf

Piezoelectrets from thermo-formed bubble structures of fluoropolymer-electret films

This paper shows that the dielectric anisotropy of conductivity in cells composed of nematic liquid crystal E7 (NLC-E7) is related to the fact that the diffusion constant (D) is greater in a cell with homeotropic alignment than in one with homogeneous alignment (D ∥ > D ⊥). This behaviour can be understood by the study of the dielectric properties of the NLC based on the ionic hopping behaviour and on the analysis of the electrical conductivity in relation to the voltage applied.

Ionic impurities in nematic liquid crystal displays

A novel method for producing electrets is proposed in which an electric discharge is induced by a negative impulse voltage in a small air gap. The dielectric foil to be charged is placed between two planar electrodes, being in contact with one of them and separated from the other by the air gap. The electric discharge in the gap causes electric charges to deposit onto the dielectric surface where they are trapped, thus forming the electret. Measurements carried out with Teflon FEP (fluoroethylene propylene) show a very uniform deposition, and that the sample surface potential increases linearly with increasing impulse peak voltage. In principle, this method compares with the corona discharge for the production of electrets with regard to high turnout and low cost. >

A novel method for electret production using impulse voltages

This study proposes a new method to obtain hydrophobicity classification (HC) in high voltage polymer insulators. In the method mentioned, the HC was analyzed by fractal dimension (fd) and its processing time was evaluated having as a goal the application in mobile devices. Texture images were created from spraying solutions produced of mixtures of isopropyl alcohol and distilled water in proportions, which ranged from 0 to 100% volume of alcohol (%AIA). Based on these solutions, the contact angles of the drops were measured and the textures were used as patterns for fractal dimension calculations.

https://www.scielo.br/pdf/mr/v11n4/06.pdf

Ruy Alberto Corrêa Altafim

Papers

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Piezoelectrets from thermo-formed bubble structures of fluoropolymer-electret films

Ionic impurities in nematic liquid crystal displays

A novel method for electret production using impulse voltages

Hydrophobicity classification of polymeric materials based on fractal dimension