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PZT-epoxy-multiwalled carbon nanotube (MWCNT) flexible thick film actuators .. between 6% and 10%, a nearly linear positive relationship exists. .. review of non-regenerative and regenerative power supply systems with. Although it's not making international headlines on a daily basis, Supplier Relationship Management (SRM) is one of the most influential. Therefore, the investigation of MWCNT toxicity has to be designed according to their specific However, the relationship between protein corona, functionalization and MWCNT biological effects is Supply and synthesis of carbon nanotubes.

Two forms of dielectric polarization were compared. Corona discharge polarization induced enhanced piezoelectric and dielectric properties by a factor of 10 in comparison to the parallel-plate contact method piezoelectric strain coefficient and dielectric constant were 0. Introduction Piezoelectric materials are used as sensors, actuators, and transducers for many applications such as quality assurance [ 12 ], process control [ 3 — 5 ], industrial and automotive systems [ 6 — 9 ], medical diagnostics [ 1011 ], aviation and structural health monitoring [ 12 — 15 ], biologically engineered scaffolds [ 16 ], and embedded passive devices in consumer electronics [ 17 — 19 ].

These challenges often restrict the use of these materials in advanced applications that require sensors that are electromechanically tuned to host structures, while maintaining high sensitivity and reliability over wide frequency ranges. Composites comprised of piezoelectric ceramic fillers embedded within a matrix material have been proposed for many applications such as hybrid energy systems [ 2425 ], battery separator materials [ 26 ], energy harvesting, energy conversion storage [ 6242527 ], and capacitors [ 3536 ].

Two-phase polymer matrix-based composites such as PZT-epoxy [ 37 ], comprised of piezoelectric particles embedded within a continuous polymer matrix, have attracted much attention due to their flexibility, ease of processing, and use in embedded passive devices. Integration of embedded passive components into printed circuit boards generally results in enhanced electrical performance of the device, improved reliability, reduction of device size, faster switching speed, and lower production costs [ 28 ].

Piezoelectric polymer composites are promising materials because of their excellent tailored properties [ 625 ]. These materials have many advantages including high electromechanical coupling factors [ 38 — 40 ], low acoustic impedance [ 4142 ], mechanical flexibility [ 4344 ], a wide broad bandwidth [ 4546 ], and low mechanical quality factor [ 2547 ]. The mechanical, electrical, and acoustic properties of these materials can also be tailored according to the nature of application as a function of composition of the composite material [ 48 — 51 ].

On the other hand, two-phase piezoelectric-epoxy composites suffer from poor electrical, dielectric, and piezoelectric properties due to the insulating nature and low dielectric constant of the epoxy matrix, which decreases the polarization of the piezoelectric phase [ 5253 ]. The nonuniform distribution of the ferroelectric phase in the polymer matrix can also cause clustering and agglomerations [ 654 ], which can contribute to the insulative nature of the composite.

The electrical properties of the matrix may be enhanced with the incorporation of electrically conductive inclusions [ 2855 ] such as carbon nanotubes CNTs [ 3256 ]. The mechanical and electrical properties of typical filler materials are presented in and compared to the properties of carbon nanotubes in Table 1. Many researchers have reported that the conductivity of the matrix component of the composite is enhanced by inclusion of electrically conductive fillers [ 5758 ].

However, less is known about interrelationship between the composite processing technique and the morphology and properties of the electrically conductive particles, which dictate the effective piezoelectric and dielectric properties of the composite material [ 632 ].

Furthermore, the inclusion of electrically conductive fillers leads to additional concerns such as the percolation of the conductive filler [ 405960 ], which is dictated by the distribution of the filler within the matrix and the aspect ratio of the filler as indicated by the variability in percolation values indicated in Table 2. Unique mechanical and electrical properties of carbon nanotubes as compared to other electrically conductive materials [ 3061 — 71 ].

Variation of percolation threshold with the variation in aspect ratio of the electrically conductive inclusion CNTs. In this work, the mechanisms that influence the piezoelectric and dielectric properties of three-phase composites PZT, epoxy, and MWCNTs are investigated as a function of the volume fraction of MWNTs with the aim at understanding the influence of polarization technique and percolation range on the aforementioned properties. The films were characterized in terms of their dielectric spectra, piezoelectric strain coefficients, dielectric lossand impedance spectra.

And the distribution of the fillers in the matrix, interfacial phase interactions, and preprocessing of MWCNTs and PZT were also studied with the aid of a scanning electron microscopy SEM and transmission electron microscopy TEM images to ascertain the degree of separation of particles, particle morphology, composite porosity, and agglomeration.

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The cold-setting resin was a two-part epoxy that consisted of a bisphenol-A-diglycidylether-based resin and a triethylenetetramine-based hardener. The piezoelectric, dielectric, and physical properties of the PZT and epoxy are presented in Table 3.

Overview of the piezoelectric, dielectric, and physical properties of PZT and epoxy. Composite Film Preparation An overview of the thick film fabrication process is provided in Figure 1. It is well known that the distribution of dielectric fillers and conductive fillers within an insulative matrix influences the macroscopic dielectric and piezoelectric characteristics of the thick composite films [ 32353731 ]. The PZT filler was preprocessed using the method described in [ 30 ] and then mixed with the bisphenol-A-diglycidyl ether part of the two-part epoxy and sonicated for four hours.

A study was performed to ascertain the appropriate sonication time for the surface treatment of the MWCNTs in ethanol proof, Sigma-Aldrich in the ultrasonicator procedure described in Section 2. Overview of the thick film fabrication process. The organic residues that were left behind by the gradual evaporation of the ethanol bound the different phases in the mixture during the desiccation step that occurred for four hours.

The binder component of the epoxy was then added to the mixture, and the solution then sonicated for an additional half hour. The stainless-steel substrate was 1.

The spin coat process included incremental increases by rpm, until a final speed of rpm was achieved. The piezoelectric strain coefficients, anddielectric and impedance spectra, and conductivity were determined as a function of polarization process, i. The parallel-plate contact polarization method was achieved by placing the film in between the top and the ground base plates in a dielectric medium silicone oil as shown in Figure 2 and applying an external electric field of 2.

The composite is heated to the glass transition temperature of the matrix phase, and an electric field is applied at the electrodes. The corona discharge polarization method is shown in Figure 3.

This process involves the application of an electric field via a needle that is held at a certain distance away from the composite material. A voltage is applied to the needle and the base ground plate, which is heated to its glass transition temperature of the epoxy. When the needle reaches the ionizing potential of the surrounding air, ionic species are generated and attracted towards the ground base plate.

When a sufficient surface charge density is reached, the ions flow towards the base plate through the thickness of the composite material leading to the polarization of the dielectric film. Parallel-plate contact polarization process where the film is submerged in a dielectric silicon oil and an external electric field is applied.

The corona discharge poling method is shown where the needle ionizes the volume of air surrounding it. The ions on the top surface of the composite material are attracted towards the ground base plate. The appropriate sonication time was determined by examining the average particle size and separation of particles with the aid of the SEM images.

The high-resolution TEM images give insight into the size, shape, and morphological structure of the MWCNTs after exposure to ethanol and sonication for specified amounts of time. Sample Characterization A piezometer was used to measure the dielectric constant, dielectric loss tangent, and the piezoelectric strain coefficients and at a frequency of Hz. Impedance spectroscopy and dielectric spectroscopy of the bulk and thick film composites are performed by using the HPA Impedance Analyzer at varying frequencies from Hz to 20 MHz.

Results and Discussion 3. MWCNTs that were produced by arc discharge cathode deposition were ultrasonicated in 40 ml of ethanol for time intervals equal to 30 minutes, 2 hours, 3 hours, 4 hours, and 8 hours.

Piezoelectric and Dielectric Characterization of MWCNT-Based Nanocomposite Flexible Films

MWCNTs that were treated for 30 minutes in ethanol and the associated piezoelectric composite films are shown in Figure 4. Current applications include electronics, batteries, solar cells, polymer composites, coatings, inks, adhesives, and biomedical devices WTEC, ; Milne et al. Adverse respiratory and systemic effects have been found in animal studies Lam et al. Early onset and persistent fibrosis Shvedova et al.

Acute pulmonary inflammation and interstitial fibrosis also have been observed in mice exposed to CNFs Murray et al. More alarming is the prospect of asbestos-like pathology, as reported for one type of multi-walled CNTs MWCNTs injected into the abdominal cavities of mice Poland et al. CNTs and CNFs can have vastly different properties, depending on synthesis parameters and post-production treatments. In particular, interest in surface area is based on toxicological studies on some types of insoluble nanoscale materials, wherein surface area was found to be better correlated with biological response than mass Lison et al.

Better correlation may relate to the greater surface reactivity Hsieh et al. CNTs have large surface areas because of their structure and physical form. This paper examines the relationship between the surface areas of commercially available CNT and CNF products and their physical and chemical properties.

To support some of the conclusions drawn, structural and elemental composition data on the materials were obtained by scanning electron microscopy SEM with energy-dispersive X-ray spectrometry EDS and transmission electron microscopy TEM with EDS.

Thermogravimetric analysis TGA was also performed to provide supplemental information.

Properties that Influence the Specific Surface Areas of Carbon Nanotubes and Nanofibers

The materials examined had a wide range of surface areas. Surface areas differed from product specifications, to varying degrees, and between products with similar dimensions and purity. The findings emphasize the multiple factors that can influence surface area and mark its utility for CNT characterization, a prerequisite to understanding their potential applications and toxicities. Nanostructured and Amorphous Materials Inc. Two raw CNF products and a processed, purified final product obtained from a major producer anonymous also were examined.

The raw CNF products were treated at high temperature in an inert gas to remove any associated organic compounds and catalyst residue. Sample mass was typically mg or more, with a minimum of mg. The free space was measured using UHP helium gas. As part of the quality assurance procedures, repeat analyses were performed and some samples were analyzed by two different laboratories.

Details and results of these procedures are provided as Supplementary material available at Annals of Occupational Hygiene online. Full details of the analysis and an in-depth discussion of the results will be given elsewhere.

A brief description is included here to provide supporting data for the conclusions drawn regarding the surface area results. A tungsten needle was used to transfer a small amount of the dispersed material to a beryllium substrate. The samples were imaged uncoated. Images were taken from three representative areas and spectra of the same areas were acquired.

A brief description is given here to provide supporting data for conclusions regarding the surface area results. Elemental analysis was performed with an Oxford INCAEDS system with an atmospheric thin window detector elements down to boronmapping capability, spectrum imaging, and drift collection software.

Except for one sample Sample 4samples were prepared by placing a small amount of material in a 1. Samples were sonicated in an ultrasonic bath for at least 5 min; several required a longer sonication period up to 15 min for dispersion. In a few instances, the suspension appeared too concentrated and was diluted to avoid overloading. No discernible settling of the material occurred prior to application of the suspensions. Distilled water was used for Sample 4 because it provided better dispersion of the material.

Thermogravimetric analysis TGA was performed on the samples to investigate their residual ash content.