Hybrid Tribo-Piezo-Electric Nanogenerator with Unprecedented Performance Based on Ferroelectric Composite Contacting Layers

This research was supported by the European Regional Development Fund within the project ‘‘Hybrid energy harvesting systems’’ 1.1.1.1./16/A/013.It was recently reported that more efficient triboelectric nanogenerator (TENG)-like devices can be prepared using inversely polarized ferroelectric films made of same material as the contacting layers. In the present work, a clear correlation between the piezoelectric response of inversely polarized ferroelectric PVDF/BaTiO3 nanocomposite films and the performance of the TENG-like device based on these films is demonstrated. This observation is explained by magnified electrostatic induction that is driven by piezoelectric charges and ferroelectric properties of these films. A double capacitor model is proposed that effectively portrays the interactions between ferroelectric layers during contact-separation and subsequent charge redistributions in the external circuit. The new understanding has allowed the result of 3-fold higher open circuit voltages (2.7 kV from 5 cm2) as compared to that of a state of the art TENG. Furthermore, findings uncover the potential for vast improvement in the field of nanogenerators for mechanical energy harvesting as a significantly better piezoelectric performance of flexible nanogenerators has been reported elsewhere.ERDF 1.1.1.1./16/A/013; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

The role of intermolecular forces in contact electrification on polymer surfaces and triboelectric nanogenerators

This research was supported by the European Regional Development Fund within the project ‘‘Hybrid energy harvesting systems’’ 1.1.1.1./16/A/013.The contact electrification of polymer interfaces provides an energy harvesting function to triboelectric (nano)generators (TEG). The electron transfer between contacted-separated surfaces has been considered as the main electrification mechanism for polymers in TEG. The electron transfer mechanism widely proposed in literature requires a contact between chemically different polymer materials, as well as subsequent increase of the specific contact area, which is commonly accomplished via nanostructuring. Herein, we showed that contact electrification could be controlled by intramolecular forces in the polymer bulk and adhesive forces at the contact interface, and the chemical contact between different polymers was not needed for contact electrification. The results also confirm the breaking of the covalent bond as a mechanism of the contact electrification of polymer insulators.ERDF 1.1.1.1./16/A/013; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Elastomēra / nanografīta kompozītu sensorelementu sistēmu pjezorezistīvās īpašības

Promocijas darba pētījums veltīts pjezorezistīvu poliizoprēna nanografīta kompozītu fizikālo īpašību izpētei un viscaur superelastīgu spiediena sensoru sistēmu izstrādei. Darbā salīdzināta dažādu oglekļa alotropisko veidu un koncentrāciju ietekme uz kompozītu pjezorezistīvo jutību. Noteikta ultraskaņas apstrādes ietekme uz termiski eksfoliēta grafīta daļiņu ģeometriskajiem izmēriem un izgatavotiem kompozītu sastāviem noteikta pildvielas ģeometrisko izmēru ietekme uz pjezorezistīvo efektu. Noteikti pjezorezistīvie efekti pie dažādām apkārtējās vides temperatūrām, kā arī noteikta elektriskās pretestības atkarība no temperatūras dažādu oglekļa alotropisko veidu poliizoprēna kompozītiem. Iegūtie rezultāti kvantitatīvi analizēti ar literatūrā pieejamiem matemātiskiem modeļiem, kā arī izstrādāts jauns matemātisks modelis, kas apraksta kompozītu elektriskās pretestības pieaugumu palielinoties temperatūrai, balstoties uz tuneļstrāvu samazināšanos un elektrovadošo kanālu trūkšanu matricas termiskās izplešanās rezultātā. Izgatavotas dažādu ģeometrisko izmēru viscaur superelatīgu spiediena spiediena sensoru sistēmas, kuros kā izejmateriāls izmantots AS „Baltijas Gumijas Fabrika” izgatavotie poliizoprēna nanooglekļa kompozīti. Kompozīta sastāvam, kas izmantots spiedienu sensoru sistēmās kā jutīgais elements noteikta slogošanas frekvences ietekme uz pjezorezistīvo jutību

Polymer/Nanographite Composites for Mechanical Impact Sensing

The purpose of this chapter is to give a review of the polymer/nanographite composite (PNGC) materials specially developed for applications in mechanical strain and pressure sensors that can be used for design of flexible sensing systems. Our recent achievements in design, processing and investigation of physical prop-erties of elastomer and nanostructured carbon composites as prospective materials for mentioned sensors are also presented. In the beginning theoretical principles of tunneling percolation theory and piezoresistivity have been described. We discuss the most suitable polymer matrices and electrically conductive nanographite fillers for sensitive PNGC. Preparation methods of mechanically sensitive PNGC have been considered. Different particularly produced and tested polymer/nanographite composites are overhauled and possible advantages and disadvantages of PNGC in different possible applications are analyzed

Improved Piezoresistive Sensitivity in Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites

In previous studies we have reported that piezoresistive effect in polyisoprene electrically conductive filler composites is highly dependent on filler concentrations, dispersion efficiency and filler geometry. In this study polyisoprene nanostructured carbon allotrope hybrid composites have been elaborated using various ratios and concentrations of multiwall carbon nanotubes (outer diameter 50-80nm, length 0,5-2 μm, surface area 40 m2/g) and electrically extra conductive high structure carbon blacks (average particle diameter 30nmm, surface area 950 m2/g). The piezoresistive effects of the hybrid composites have been tested under 1 and 10 atmospheres of external pressure in cyclic loading/unloading regime using Zwick/Roell Z2.5 universal material testing machine, coupled and synchronized with Agilent A34970A digital multimeter/multiplexer. It has been observed, that composite with certain filler concentrations and ratios has a significantly higher piezoresistive sensitivity compared to polyisoprene carbon nanotube composites or polyisoprene carbon black composites. Based on these results the impact of the synenergy of both carbon nanotubes and carbon black at different concentrations on the polyisoprene nanostructured carbon allotrope hybrid composites piezoresistive properties have been evaluated and improved piezoresistive sensitivity is discussed

Piezoresistivity and Electrical Resistance Relaxation of Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites

Polymer conductive filler composites are believed to be promising materials for flexible force sensor manufacture. Polyisoprene various carbon allotrope hybrid composites were made and their piezoresistive properties depending on the two filler concentrations and their ratio have been determined. Electrical resistance relaxations of hybrid composites at constant pressure in room temperature were determined as well. Experimental data of resistance relaxation was analyzed and fitted similarly to stress relaxation of polymers at constant pressure

Piezoresistivity and Electrical Resistance Relaxation of Polyisoprene Nanostructured Carbon Allotrope Hybrid Composites

Polymer conductive filler composites are believed to be promising materials for flexible force sensor manufacture. Polyisoprene/various carbon allotrope hybrid composites were made and their piezoresistive properties depending on the two type’s filler concentration and their ratio have been determined. Electrical resistance relaxations of hybrid composites at constant pressure in room temperature were determined as well. Experimental data of resistance relaxation was analysed and fitted similarly to stress relaxation of polymers at constant pressure

The Dependence of Piezoresistivity of Elastomer/Nanostructured Carbon Composites on Dynamic Mechanical Load Frequency

The aim of this article is to determine piezoresistive sensitivity of elastomer nanostructured carbon composites at dynamic loading tests and show the piezoresistive effect correlations to various frequencies of applied mechanical force in a manner that could provide a parameter of the highest detectible dynamic load frequency. This parameter is crucial when determining sensor’s usability in possible applications. There are only few articles on conductive polymer composite sensitivity in dynamic mechanical loading tests.With this article we are trying to estimate the values of dynamic loading frequencies in which sensor would be functional

Soft Piezoresistive Pressure Sensor Carpet Concept

Previous studies of polyisoprene – nanostructured carbon black composites (PNCBC) have proven that, depending on the carbon black concentration and dispersing methods, this material has got slighly higher or lower piezoresistive properties [1]. Since this material is hyperelastic it can be used to detect dynamic forces. Piezoresistive effect can be observed at relatively small pressures as well as large pressures. In this work we are trying to use PNCBC as a potential material for pressure sensor carpet application. Raw rubber composition with necessary vulcanization ingredients and variable electro conductive carbon black concentrations were made in Baltic Rubber factory. To determine electrical percolation behavior raw PNCBC was vulcanized with brass electrodes in a die, afterwards obtained results where treated with statistical percolation theory. Also piezoresistive effect was determined under 1 and 10 atmospheres of pressure. Based on this knowledge we produced a fully elastic pressure sensor system that consist from elements with various concentration of conductive filler. To make this possible each element was prevulcanized separately and afterwards vulcanized in to a one solid block. Prevulcanization conditions where determined experimentally at constant temperature and pressure while gradually increasing curing time until rubber element is able to retain its shape under small deformations. Afterwards piezoresistive properties for fully elastic pressure sensor system where determined under 1 (Figure 1) and 10 atmospheres of pressure

The Electrical Percolation Shift in Polyisoprene - Nanostructured Carbon Composite

Previous research approved polyisoprene – nanostructured carbon composite (PNCC) as a prospective material for use as a piezoresistive pressure sensing material in finger pressure range. The major advantage of this material would be hyperelastic flexibility compared with conventional ceramic piezoelectric pressure sensing elements as well outstanding sensitivity for small (<1 Bar) pressures. The PNCC is made when highly structured particles of good conductor (Printex XE2 carbon black) and necessary curing ingredients are dispersed into elastomer matrix (Thick Pale Creppe natural polyisoprene) and vulcanized afterwards. There electrical percolation of PNCC greatly depends on mixing method used. In our work we try to use ultrasound as an alternative way to disperse filler. The roll mixed, mechanically mixed in solution and ultrasound mixed in solution PNCC samples were made. The critical concentrations of electrical percolation were determined and critical indexes were calculated for all types of PNCCs using linear trendlines on log-log plots. The piezoresistive behavior of PNCCs was evaluated and compared