B. Gonzalo

Bio: B. Gonzalo is an academic researcher. The author has contributed to research in topics: Dielectric & Conductive polymer. The author has an hindex of 6, co-authored 7 publications receiving 112 citations.

Synthesis, characterization, and thermal properties of piezoelectric polyimides

Abstract: Three amorphous piezoelectric polyimides have been synthesized and characterized to analyze their utility for high-temperature applications. The studied polyimides have been prepared from 4,4'-oxydiphthalic anhydride and the diamines 2,4-di(3-aminophenoxy)benzonitrile (poly2-4), 2,6-bis(3-aminophenoxy)benzonitrile (poly2-6), and 1,3-bis-2-cyano-3-(3-aminophenoxy)phenoxybenzene (poly2CN). These polyimides differ in the position of the dipolar groups -CN in the aromatic ring (poly2-4 and poly2-6) and in the number of these groups in the repetitive unit (poly2-6 and poly2CN). The imidization degree has been studied by Fourier transform infrared (FTIR) and thermogravimetry-mass spectrometry (TG-MS) and thermal properties by differential scanning calorimetry (DSC) and thermogravimetry (TG). The piezoelectric behavior has been analyzed from remnant polarization measurements.

Improving the Processability of Conductive Polymers: The Case of Polyaniline

Abstract: Polyaniline (PANI) is one of the most widely used conductive polymers because of its ease of synthesis in addition to its good electrical properties. However, the difficulty in its processability limits its potential applications. In this work, conductive emeraldine salt (i.e., one of the different oxidation states of PANI) was synthesized by oxidative chemical polymerization. Different techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamical mechanical thermal analysis were used to characterize the synthesized PANI. The processability of PANI has been improved by processing it, both by compression and extrusion methods, with different thermoplastic matrices such as polycaprolactone and polybutylene terephthalate. The obtained compounds have not only better processability but also improved thermal and mechanical properties. However, their conductivity decreases with respect to PANI, to a greater extent, for the compounds synthesized by the extrusion method. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E180–E188, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21261

Shape memory effect for recovering surface damages on polymer substrates

Abstract: Self-repair properties based on shape-memory features of covalently crosslinked semi-crystalline polyalkenamers were demonstrated by thermal-activated recovery of performed surface marks (indented holes and scratches). Shape memory polymers were prepared by mixing a commercial polycyclooctene (PCO) with different percentages of peroxide, and then these mixtures were processed by compression moulding to obtain crosslinked sheets. With the aid of a hardness test pencil, holes and scratches in the surface of the materials were realized with different known forces (5, 10 and 15 N). The disappearance of surface defects was evaluated using both optical and contact surface profilometry, as well as optical microscopy under heating processes. This technique allowed evaluating shape recovery ratios of edgewise holes in PCO samples. In parallel, the analysis of maximum depth of indentations with temperature for edgewise samples by optical microscopy allows evaluating shape recovery. As a complementary tool for analysing thermal shape-recovery and surface resistance to indentation, thermal properties and hardness were investigated by DSC and Shore durometer test, respectively.

Electric modulus and polarization studies on piezoelectric polyimides

Abstract: The piezoelectric polymeric sensors and actuators are widely valued because of their low density, availability to obtain complex shapes, and easy processing among other characteristics. However, there are not many useful piezoelectric polymers. Aromatic polyimides are high-performance polymeric materials characterized by thermal stability, chemical resistance, and excellent mechanical properties. Besides, some of these polymers have been reported as candidates to present piezoelectric properties. Our research focuses in the electric characterization of three piezoelectric amorphous aromatic polyimides, containing CN groups in different number and positions. The piezoelectricity in amorphous polymers is mainly due to the orientation polarization of the molecular dipoles, which is induced by the application of an external electrical field to a temperature over their glass transition temperature (Tg). Polyimides are measured by thermally stimulated depolarization currents and dielectric spectroscopy and the analysis of the dielectric data has been performed using the electric modulus formalism to separate conductive and dipolar processes. These measurements have evidenced that the frozen-in polarization is mainly due to the dipole orientation of the dipolar CN groups, allowing us to understand in depth the mechanism of polarization that contributes to the piezoelectric properties. This will facilitate the obtention of materials with the best possible piezoelectric properties, comparable to those currently available but with higher mechanical and thermal performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Dielectric Properties of Piezoelectric Polyimides

Abstract: Polyimides are the most promising amorphous piezoelectric polymers not only because of their excellent thermal, mechanical and dielectric properties, but also and, mainly due to their high glass transition temperatures. Here we report on the synthesis of polyimides with one CN (poly2-6) and two CN groups (poly2CN) in the repetition unit, the latter being synthesised for the first time. The dielectric measurements show that remnant polarisation and piezoelectric coefficients values depend strongly on the number of pendant nitrile dipoles in the repetition unit, on the orientation of the backbone anhydride dipole as well as on the imidisation and the poling processes.

Piezoelectric Materials for Energy Harvesting and Sensing Applications: Roadmap for Future Smart Materials

Abstract: Piezoelectric materials are widely referred to as "smart" materials because they can transduce mechanical pressure acting on them to electrical signals and vice versa. They are extensively utilized in harvesting mechanical energy from vibrations, human motion, mechanical loads, etc., and converting them into electrical energy for low power devices. Piezoelectric transduction offers high scalability, simple device designs, and high-power densities compared to electro-magnetic/static and triboelectric transducers. This review aims to give a holistic overview of recent developments in piezoelectric nanostructured materials, polymers, polymer nanocomposites, and piezoelectric films for implementation in energy harvesting. The progress in fabrication techniques, morphology, piezoelectric properties, energy harvesting performance, and underpinning fundamental mechanisms for each class of materials, including polymer nanocomposites using conducting, non-conducting, and hybrid fillers are discussed. The emergent application horizon of piezoelectric energy harvesters particularly for wireless devices and self-powered sensors is highlighted, and the current challenges and future prospects are critically discussed.

Piezoelectric nanogenerators for personalized healthcare.

Abstract: The development of flexible piezoelectric nanogenerators has experienced rapid progress in the past decade and is serving as the technological foundation of future state-of-the-art personalized healthcare. Due to their highly efficient mechanical-to-electrical energy conversion, easy implementation, and self-powering nature, these devices permit a plethora of innovative healthcare applications in the space of active sensing, electrical stimulation therapy, as well as passive human biomechanical energy harvesting to third party power on-body devices. This article gives a comprehensive review of the piezoelectric nanogenerators for personalized healthcare. After a brief introduction to the fundamental physical science of the piezoelectric effect, material engineering strategies, device structural designs, and human-body centered energy harvesting, sensing, and therapeutics applications are also systematically discussed. In addition, the challenges and opportunities of utilizing piezoelectric nanogenerators for self-powered bioelectronics and personalized healthcare are outlined in detail.