Maris Knite

Electric and elastic properties of conductive polymeric nanocomposites on macro- and nanoscales

Abstract In the past several years, the macroscopic electric and elastic properties of conductive polymeric composites have been studied from the viewpoint of such applications as thermistors and pressure sensors. In particular, we studied carbon black (CB) polymeric nanocomposites on macro- and nanoscales, using polyisoprene as the composite matrix. The filler component was an extra conductive carbon black (PRINTEX XE2, DEGUSSA) with a primary particle diameter of about 30 nm. A very strong reversible tensoresistive effect of electric resistance dependence on uniaxial tension deformation was observed in composites with the 10 carbon black mass parts added to 100 mass parts of polyisoprene. A conductive-type atomic force microscope (AFM) was used for the mapping of carbon black conductive network into an insulating matrix, while for studying the nanomechanical properties of composites, a tapping mode atomic force microscope was applied. A correlation between macroscopic and nanoscopic—both electric and elastic—properties was observed.

The effect of heating conditions on the properties of nano- and microstructured Ni–Zn ferrite

The structural, microstructural and morphological, as well as electric and dielectric, properties of nickel–zinc ferrite (Ni0.3Zn0.7Fe2O4) derived from sol–gel auto-combustion have been studied after sintering from 900 to 1300 °C. The effect of heating rate has not been previously investigated and is reported here. X-ray diffraction showed a pure cubic spinel after calcination. Atomic force microscopy revealed nanosized particles after calcination, but scanning electron microscopy showed nanosized grains after sintering at 900 °C. The heating rate has a marked effect on oxidation of Fe3+ to Fe2+, showing an additional approach to control charge carrier concentration in Ni–Zn ferrites (powder and monoliths). The heating rate also influences the average particle size and distribution. Grain size and resistivity of sintered pellets do not show significant change with heating rate, proving that resistivity is mainly dictated by the number of grain boundaries. The dielectric loss tangent curves at room temperature exhibit dielectric relaxation peaks attributed to the similarity in frequency of charge hopping between the localized charge states and external fields. The relaxation peak shifts to higher frequencies for ferrites with nanosized grains.

A straightforward and “green” solvothermal synthesis of Al doped zinc oxide plasmonic nanocrystals and piezoresistive elastomer nanocomposite

Plasmonic oxide nanocrystals hold great promise in a wide range of applications, for which the availability of scalable and “green” synthesis methods is prerequisite, whereas until recently an excellent response has been demonstrated only for samples prepared through intricate synthesis paths. We report here a simple ethanol solvothermal synthesis route of Al doped ZnO plasmonic nanocrystals (Zn1−xAlxO) at doping levels of x up to 0.15. The obtained Al doped ZnO samples consisted of nanoparticles and short nanorods with a diameter of around 10 nm at x = 0.15 doping level while reaching aspect ratio levels of 50 for lower doping levels. Detailed structural studies using powder X-ray diffraction Rietveld refinement, X-ray absorption and photoelectron spectroscopies show that all samples maintain the structure of the phase-pure zincite with the space group P63mc. The resulting powders exhibit strong infrared absorption while remaining largely transparent for visible light, enabling the preparation of transparent colloidal dispersions. Furthermore, as a test of applicability in a practical device, the nanocrystals were used to prepare transparent piezoresistive Zn0.925Al0.075O–polydimethylsiloxane composites. The prepared sensor material exhibits excellent repeatable and reproducible piezoresistive behaviour.

The investigation of sensing mechanism of ethanol vapour in polymer-nanostructured carbon composite

Polymer-nanostructured carbon composites (PNCC) using three different polymers as composite matrix materials (polyvinylacetate (PVAc), polyethylene glycol (PEG) and ethylene-vinylacetate copolymer (EVA)) have been developed. High structure carbon black Printex XE2 (Degussa AG) was used as a composites filler. Ethanol vapour sensor-effect of composites was determined as a change of electrical resistance as the composite was held in ethanol vapour for 30 seconds. Reversibility of electrical resistance of PNCC, response stability and repeatability have been measured and compared. The electrical resistance response of EVA-nanostructured carbon composite (EVA-NCC) to ethanol vapour as a function of vinylacetate content in the copolymer has been evaluated. Promising ethanol vapour sensor-effect has been observed for PEG-NCC followed by PVAc-NCC and EVA-NCC.

Mechanism of recording and erasing of optical information by laser radiation on SiO2-(Co + Si)-SiO2-Si multilayer structure

Abstract The optical properties of SiO2-(Co + Si)-SiO2-Si structures studied by treatment with Q-switched YAG:Nd and CO2 lasers are presented. The photo-thermo-chemical reaction of Co with Si has a threshold character. No change in optical properties of (Co + Si) mixture was observed up to 2 MW/cm2 intensities of CO2 laser radiation. A decrease of the reflection coefficient R (at λ = 663 nm) from 70% to 45% is observed as the intensity is increased up to 8 MW/cm2. When this multilayer structure is subject to Q-switched YAG:Nd laser radiation of an intensity from 14 MW/cm2 to 53 MW/cm2, the magnitude of the reflection coefficient returns to its initial value of 70%. It means that information recorded by the CO2 laser is erased. Calculations of the temperature field during irradiation with CO2 and YAG:Nd laser showed that the phase transition from mixture (Co + Si) to CoSi2 caused by CO2 laser irradiation results in recording of information, whereas the thermal impact caused by YAG:Nd laser irradiation results in amorphization of CoSi2 and erasing of information.

Investigation of mechanism of organic solvent vapours sensing effect in polyisoprene-high structure carbon black composite

A study of detecting organic vapour environments of nine different solvents by polyisoprene-high structured carbon composite (PHSCBC) sensors is reported. The electric resistance of the composite is found to be increased as soon as it contacts the vapour and to return to the initial value after being removied from the environment. To reveal the mechanism of the effect, simultaneous measurements of electrical resistance, elongation, and changes caused by sorption of organic solvent molecules in the bulk of PHSCBC samples were made in real time. From sorption experiments it has been found that the increase of electric resistance is generally dominated by absorption of solvent molecules in the matrix material, subsequently swelling it up and increasing the distance between conductor particles. The experiments prove that a remarkable and rapid change of the resistance could be explained by change of the tunnelling currents between adjacent carbon nano-particles.

CO2 laser-induced structure changes in lead zirconate titanate Pb(Zr0.58Ti0.42)O3 sol–gel films

Based on absorption spectra of lanthanum modified lead zirconate titanate Pb0.9La0.1(Zr0.65Ti0.35)O3 (PLZT10/65/35) ferroelectric ceramics an idea of local and selective treatment of lead zirconite titanate Pb(ZrXTi1−X)O3 (PZT) sol–gel film in the multi-layer structure by CO2 laser radiation was formulated. The possibility to obtain PZT perovskite film on the SiO2/Si substrate by irradiation with CO2 laser was shown experimentally. X-ray studies revealed the PZT perovskite structure ratio growth at the expenses of pirochlore structure with an increased power density of laser radiation.

Inversely polarised ferroelectric polymer contact electrodes for triboelectric-like generators from identical materials

Although it is known that triboelectric nanogenerators (TENGs) based on ferroelectric polymer films show better performance, the origin of this enhancement remains poorly understood. To date, it has been accepted that enhancement is observed due to shift of the “effective work function” of the ferroelectric polymer insulator, which in turn enhances electron transfer between the TENG electrodes. The present study reveals that this view is incorrect and, in reality, the enhancement is observed due to induction driven by piezoelectric charges. Furthermore a novel piezoelectric-electrostatic generator (PEEG) has been constructed from inversely polarised polyvinylidene films, which exhibits higher performance than TENGs for mechanical energy conversion to electricity.

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 properties 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.

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 sensors 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.