The experimental results concerning the characterization of a multiphase nanocomposite systems ba... more The experimental results concerning the characterization of a multiphase nanocomposite systems based on epoxy matrix, loaded with different amount of multi-walled carbon nanotubes (MWCNTs) and an optimized Hydrotalcite (HT) clay content (i.e. 0.6 wt%), duly identified by an our previous theoretical study based on Design of Experiment (DoE), are presented. Dynamic-mechanical analysis (DMA) reveal that even the introduction of higher HT loading (up to 1%wt) don’t affect significantly the mechanical properties of the nanocomposites while morphological investigations show an effective synergy between clay and carbon nanotubes that leads to peculiar micro/nanostructures that favor the creation of the electrical conductive network inside the insulating resin. An electrical characterization is carried out in terms of DC electrical conductivity, percolation threshold (EPT) and frequency response in the range 10Hz-1MHz. In particular, the measurements of the DC conductivity allow to obtain the typical “percolation...
In this paper we have tried to increase the electrical conductivity of CNFs by reducing the defec... more In this paper we have tried to increase the electrical conductivity of CNFs by reducing the defects on the nanofibers with the aim of increasing electrical conductivity of nanofilled/epoxy resins in such a way as to overcome some drawbacks related to the electrical insulation properties of epoxy resins used in the field of aeronautic materials. Heat treatment of carbon nanofibers has proven to be an effective method in removing defects from carbon nanofibers causing a strong increase in their structural perfection and thermal stability. Nanocomposites made of heat-treated CNFs dispersed inside an epoxy-amine mixture specifically designed for structural applications show significant increase in the electrical conductivity even at low concentration of nanofiller. Heat-treated CNF displays stiff structure and smooth surface which tend to lower the thickness of the unavoidable insulating epoxy layer formed around CNF which, in turn, plays a fundamental role in the electrical transport properties along the conducting clusters. The heat treatment of CNFs is very beneficial in terms of electrical conductivity but not in terms of mechanical properties which, in any case, were comparable to the properties of the unfilled resin
Functionalized Multi Wall Carbon Nanotubes, (MWCNT-COOH) were co-precipitated with Zinc and Alumi... more Functionalized Multi Wall Carbon Nanotubes, (MWCNT-COOH) were co-precipitated with Zinc and Aluminum nitrates, in conditions able to form a Hydrotalcite like solid, in which the positive charge of the inorganic lamellae is neutralized by the negative charge of the carboxylate linked to the nanotubes. This solid was characterized by TEM and showed a less entangled morphology of the CNT. It was successively incorporated into an epoxy resin, obtaining a good dispersion and a better electrical properties respect to the pristine MWCNT-COOH
In several applications for the aeronautic, automotive and electronic industries, there is an inc... more In several applications for the aeronautic, automotive and electronic industries, there is an increasing demand of structural nanocomposites exhibiting remarkable thermal and mechanical properties and, at the same time, tailored and controlled electromagnetic (EM) performances. Along this stream, an intense research activity has been carried out focused at producing new polymeric nanocomposites based on Carbon NanoTubes (CNTs). The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, has been investigated by sorption, mechanical and electrical properties
TIMES OF POLYMERS (TOP) AND COMPOSITES 2014: Proceedings of the 7th International Conference on Times of Polymers (TOP) and Composites, 2014
ABSTRACT A study concerning the temperature dependence of some electrical properties of multiphas... more ABSTRACT A study concerning the temperature dependence of some electrical properties of multiphase nanocomposite systems based on epoxy matrix, loaded with a 1% of multi-walled carbon nanotube (MWCNT) and different amounts of Hydrotalcite clay (HT), is presented. An extensive electrical characterization in DC was carried out highlighting that, consistently with the fluctuation-induced tunneling model, the electrical resistivity of the composites are characterized by a negative temperature coefficient (NTC) since it decreases monotonically with increasing temperature in the range 30-110°C. Furthermore, current-voltage (I-V) and temperature-voltage (T-V) characteristics with a perfect linear behavior are detected. The influence of different clay content on the electrical performance of the composites is also investigated. The interesting results open a new routes for such composites due their possible applications in the field of temperature sensor.
Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel met... more Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 • cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 • cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.
The degree of graphite exfoliation and edge-carboxylated layers can be controlled and balanced to... more The degree of graphite exfoliation and edge-carboxylated layers can be controlled and balanced to design lightweight materials characterized by both low electrical percolation thresholds (EPT) and improved mechanical properties. So far, this challenging task has been undoubtedly very hard to achieve. The results presented in this paper highlight the effect of exfoliation degree and the role of edge-carboxylated graphite layers to give self-assembled structures embedded in the polymeric matrix. Graphene layers inside the matrix may serve as building blocks of complex systems that could outperform the host matrix. Improvements in electrical percolation and mechanical performance have been obtained by a synergic effect due to finely balancing the degree of exfoliation and the chemistry of graphene edges which favors the interfacial interaction between polymer and carbon layers. In particular, for epoxy-based resins including two partially exfoliated graphite samples, differing essentially in the content of carboxylated groups, the percolation threshold reduces from 3 wt% down to 0.3 wt%, as the carboxylated group content increases up to 10 wt%. Edge-carboxylated nanosheets also increase the nanofiller/epoxy matrix interaction, determining a relevant reinforcement in the elastic modulus.
In this paper, a numerical model is presented in order to analyze the electrical characteristics ... more In this paper, a numerical model is presented in order to analyze the electrical characteristics of polymer composites filled by carbon nanotubes (CNTs) subject to tensile stress and investigate the possible usage of such materials as innovative sensors for small values of strain. The simulated mechano-electrical response of the nanocomposite is obtained through a multi-step approach which, through different modeling stages, provides a simple and effective tool for material analysis and design. In particular, at first, the morphological structures of the composites are numerically simulated by adopting a previously presented model based on a Monte Carlo procedure in which uniform distributions of the CNTs, approximated as of solid cylinders and ensuring some physical constraints, are dispersed inside a cubic volume representing the polymer matrix. Second, a geometrical analysis allows to obtain the percolation paths detected in the simulated structures. Suitable electrical networks composed by resistors and capacitors associated to the complex charge transport and polarization mechanisms occurring in the percolation paths are then identified. Finally, the variations of these circuit parameters, which are differently affected by the mechanical stresses applied to the composites, are considered to analyze the electromechanical characteristics of the composites and hence their performances as stress sensors. The proposed approach is used to investigate the impact on the electro-mechanical response of some physical properties of the base materials, such as the type of carbon nanotube, the height of energy barrier of polymer resin, as well as characteristics of the composite, i.e., the volume fraction of the filler. The tunneling effect between neighboring nanotubes is found to play a dominant role in determining the composite sensitivity to mechanical stresses. The simulation results are also compared with the experimental data obtained by performing stress tests on samples of a multi walled CNT filled composite based on poly (ε-caprolactone), a polymer which is of interest for its biocompatibility. Model simulations and measured data show generally satisfactory agreement, confirming the effectiveness of the proposed approach to account for the impact of the interactions between CNTs and the insulating resin on the electromechanical response of the composite.
in proceeding of Nanoscience and Nanotechnology 2011, INFN-Laboratori Nazionali di Frascati Italy... more in proceeding of Nanoscience and Nanotechnology 2011, INFN-Laboratori Nazionali di Frascati Italy 19-23 September 2011, 4 pp (poster presentation
A spherical excitable cell immersed in an electrolyte and subjected to an electric field is consi... more A spherical excitable cell immersed in an electrolyte and subjected to an electric field is considered to study its behavior for Electro-Chemotherapy Treatments (ECT). The total volume is discretized with a three-dimensional lattice to which an electrical network, modeling both the passive and linear behavior of the external electrolyte and of the cytosol than the complex behavior of the ionic fluxes through the cell membrane, is associated. The Electroporation Phenomenon (EP) is considered by modeling the electrically induced pores with a voltage controlled current source governed by the dynamic of the pore density, N, and the current in a single pore. The physiological Action Potential (AP) of a Normal Rat Kidney (NRK) cell is reproduced and the EP is analyzed by looking at the transmembrane voltage (TMV) of the cell exposed to a trapezoidal Pulsed Electric Field (PEF) with a duration of 100us, a rise/fall time of 4us and amplitude of 750V/cm.
This work proposes nanocomposites with carbon nanotubes characterized by self-sensing and self-he... more This work proposes nanocomposites with carbon nanotubes characterized by self-sensing and self-heating properties. Recently, a growing interest in these two properties has been found in many industrial sectors, especially in the aerospace and automotive fields. While the self-sensing function allows diagnosing the presence of micro-damage in the material thanks to the detection of residual resistance, the self-heating function is exploited to properly tune the heating performance in terms of the heating rate and final temperature values. An electrical percolation value of around 0.5% by weight of carbon nanotubes was found by electrical characterization. The AC conductivity of the nanocomposites, in the range of 100 Hz to 1 MHz, evidences that beyond a CNTs amount of 0.5% wt/wt, they are characterized by a purely resistive behavior. The self-sensing analysis displayed a gauge factor value of 4.1. The solid thermal stability up to 300 °C makes the material suitable as a heating eleme...
The experimental results concerning the characterization of a multiphase nanocomposite systems ba... more The experimental results concerning the characterization of a multiphase nanocomposite systems based on epoxy matrix, loaded with different amount of multi-walled carbon nanotubes (MWCNTs) and an optimized Hydrotalcite (HT) clay content (i.e. 0.6 wt%), duly identified by an our previous theoretical study based on Design of Experiment (DoE), are presented. Dynamic-mechanical analysis (DMA) reveal that even the introduction of higher HT loading (up to 1%wt) don’t affect significantly the mechanical properties of the nanocomposites while morphological investigations show an effective synergy between clay and carbon nanotubes that leads to peculiar micro/nanostructures that favor the creation of the electrical conductive network inside the insulating resin. An electrical characterization is carried out in terms of DC electrical conductivity, percolation threshold (EPT) and frequency response in the range 10Hz-1MHz. In particular, the measurements of the DC conductivity allow to obtain the typical “percolation...
In this paper we have tried to increase the electrical conductivity of CNFs by reducing the defec... more In this paper we have tried to increase the electrical conductivity of CNFs by reducing the defects on the nanofibers with the aim of increasing electrical conductivity of nanofilled/epoxy resins in such a way as to overcome some drawbacks related to the electrical insulation properties of epoxy resins used in the field of aeronautic materials. Heat treatment of carbon nanofibers has proven to be an effective method in removing defects from carbon nanofibers causing a strong increase in their structural perfection and thermal stability. Nanocomposites made of heat-treated CNFs dispersed inside an epoxy-amine mixture specifically designed for structural applications show significant increase in the electrical conductivity even at low concentration of nanofiller. Heat-treated CNF displays stiff structure and smooth surface which tend to lower the thickness of the unavoidable insulating epoxy layer formed around CNF which, in turn, plays a fundamental role in the electrical transport properties along the conducting clusters. The heat treatment of CNFs is very beneficial in terms of electrical conductivity but not in terms of mechanical properties which, in any case, were comparable to the properties of the unfilled resin
Functionalized Multi Wall Carbon Nanotubes, (MWCNT-COOH) were co-precipitated with Zinc and Alumi... more Functionalized Multi Wall Carbon Nanotubes, (MWCNT-COOH) were co-precipitated with Zinc and Aluminum nitrates, in conditions able to form a Hydrotalcite like solid, in which the positive charge of the inorganic lamellae is neutralized by the negative charge of the carboxylate linked to the nanotubes. This solid was characterized by TEM and showed a less entangled morphology of the CNT. It was successively incorporated into an epoxy resin, obtaining a good dispersion and a better electrical properties respect to the pristine MWCNT-COOH
In several applications for the aeronautic, automotive and electronic industries, there is an inc... more In several applications for the aeronautic, automotive and electronic industries, there is an increasing demand of structural nanocomposites exhibiting remarkable thermal and mechanical properties and, at the same time, tailored and controlled electromagnetic (EM) performances. Along this stream, an intense research activity has been carried out focused at producing new polymeric nanocomposites based on Carbon NanoTubes (CNTs). The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, has been investigated by sorption, mechanical and electrical properties
TIMES OF POLYMERS (TOP) AND COMPOSITES 2014: Proceedings of the 7th International Conference on Times of Polymers (TOP) and Composites, 2014
ABSTRACT A study concerning the temperature dependence of some electrical properties of multiphas... more ABSTRACT A study concerning the temperature dependence of some electrical properties of multiphase nanocomposite systems based on epoxy matrix, loaded with a 1% of multi-walled carbon nanotube (MWCNT) and different amounts of Hydrotalcite clay (HT), is presented. An extensive electrical characterization in DC was carried out highlighting that, consistently with the fluctuation-induced tunneling model, the electrical resistivity of the composites are characterized by a negative temperature coefficient (NTC) since it decreases monotonically with increasing temperature in the range 30-110°C. Furthermore, current-voltage (I-V) and temperature-voltage (T-V) characteristics with a perfect linear behavior are detected. The influence of different clay content on the electrical performance of the composites is also investigated. The interesting results open a new routes for such composites due their possible applications in the field of temperature sensor.
Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel met... more Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 • cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 • cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.
The degree of graphite exfoliation and edge-carboxylated layers can be controlled and balanced to... more The degree of graphite exfoliation and edge-carboxylated layers can be controlled and balanced to design lightweight materials characterized by both low electrical percolation thresholds (EPT) and improved mechanical properties. So far, this challenging task has been undoubtedly very hard to achieve. The results presented in this paper highlight the effect of exfoliation degree and the role of edge-carboxylated graphite layers to give self-assembled structures embedded in the polymeric matrix. Graphene layers inside the matrix may serve as building blocks of complex systems that could outperform the host matrix. Improvements in electrical percolation and mechanical performance have been obtained by a synergic effect due to finely balancing the degree of exfoliation and the chemistry of graphene edges which favors the interfacial interaction between polymer and carbon layers. In particular, for epoxy-based resins including two partially exfoliated graphite samples, differing essentially in the content of carboxylated groups, the percolation threshold reduces from 3 wt% down to 0.3 wt%, as the carboxylated group content increases up to 10 wt%. Edge-carboxylated nanosheets also increase the nanofiller/epoxy matrix interaction, determining a relevant reinforcement in the elastic modulus.
In this paper, a numerical model is presented in order to analyze the electrical characteristics ... more In this paper, a numerical model is presented in order to analyze the electrical characteristics of polymer composites filled by carbon nanotubes (CNTs) subject to tensile stress and investigate the possible usage of such materials as innovative sensors for small values of strain. The simulated mechano-electrical response of the nanocomposite is obtained through a multi-step approach which, through different modeling stages, provides a simple and effective tool for material analysis and design. In particular, at first, the morphological structures of the composites are numerically simulated by adopting a previously presented model based on a Monte Carlo procedure in which uniform distributions of the CNTs, approximated as of solid cylinders and ensuring some physical constraints, are dispersed inside a cubic volume representing the polymer matrix. Second, a geometrical analysis allows to obtain the percolation paths detected in the simulated structures. Suitable electrical networks composed by resistors and capacitors associated to the complex charge transport and polarization mechanisms occurring in the percolation paths are then identified. Finally, the variations of these circuit parameters, which are differently affected by the mechanical stresses applied to the composites, are considered to analyze the electromechanical characteristics of the composites and hence their performances as stress sensors. The proposed approach is used to investigate the impact on the electro-mechanical response of some physical properties of the base materials, such as the type of carbon nanotube, the height of energy barrier of polymer resin, as well as characteristics of the composite, i.e., the volume fraction of the filler. The tunneling effect between neighboring nanotubes is found to play a dominant role in determining the composite sensitivity to mechanical stresses. The simulation results are also compared with the experimental data obtained by performing stress tests on samples of a multi walled CNT filled composite based on poly (ε-caprolactone), a polymer which is of interest for its biocompatibility. Model simulations and measured data show generally satisfactory agreement, confirming the effectiveness of the proposed approach to account for the impact of the interactions between CNTs and the insulating resin on the electromechanical response of the composite.
in proceeding of Nanoscience and Nanotechnology 2011, INFN-Laboratori Nazionali di Frascati Italy... more in proceeding of Nanoscience and Nanotechnology 2011, INFN-Laboratori Nazionali di Frascati Italy 19-23 September 2011, 4 pp (poster presentation
A spherical excitable cell immersed in an electrolyte and subjected to an electric field is consi... more A spherical excitable cell immersed in an electrolyte and subjected to an electric field is considered to study its behavior for Electro-Chemotherapy Treatments (ECT). The total volume is discretized with a three-dimensional lattice to which an electrical network, modeling both the passive and linear behavior of the external electrolyte and of the cytosol than the complex behavior of the ionic fluxes through the cell membrane, is associated. The Electroporation Phenomenon (EP) is considered by modeling the electrically induced pores with a voltage controlled current source governed by the dynamic of the pore density, N, and the current in a single pore. The physiological Action Potential (AP) of a Normal Rat Kidney (NRK) cell is reproduced and the EP is analyzed by looking at the transmembrane voltage (TMV) of the cell exposed to a trapezoidal Pulsed Electric Field (PEF) with a duration of 100us, a rise/fall time of 4us and amplitude of 750V/cm.
This work proposes nanocomposites with carbon nanotubes characterized by self-sensing and self-he... more This work proposes nanocomposites with carbon nanotubes characterized by self-sensing and self-heating properties. Recently, a growing interest in these two properties has been found in many industrial sectors, especially in the aerospace and automotive fields. While the self-sensing function allows diagnosing the presence of micro-damage in the material thanks to the detection of residual resistance, the self-heating function is exploited to properly tune the heating performance in terms of the heating rate and final temperature values. An electrical percolation value of around 0.5% by weight of carbon nanotubes was found by electrical characterization. The AC conductivity of the nanocomposites, in the range of 100 Hz to 1 MHz, evidences that beyond a CNTs amount of 0.5% wt/wt, they are characterized by a purely resistive behavior. The self-sensing analysis displayed a gauge factor value of 4.1. The solid thermal stability up to 300 °C makes the material suitable as a heating eleme...
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