15 research outputs found
Thermal, dielectrical and mechanical response of α and ÎČ-poly(vinilydene fluoride)/Co-MgO nanocomposites
Nanocomposites of the self-forming core-shell Co-MgO nanoparticles, which were of approximately 100 nm in diameter, and poly(vinylidene fluoride) (PVDF) polymer have been prepared. When the polymer is crystallized in the α-phase, the introduction of the nanoparticles leads to nucleation of the γ-phase of PVDF, increasing also the melting temperature of the polymer. With the introduction of the Co-MgO particles, the dielectric constant of the material slightly increases and the storage modulus decreases with respect to the values obtained for the pure polymer
Vapor grown carbon nanofiber based cotton fabrics with negative thermoelectric power
Vapor grown carbon nanofiber (CNF)
based ink dispersions were used to dip-coat woven
cotton fabrics with different constructional parameters, and their thermoelectric (TE) properties studied
at room temperature. Unlike the positive thermoelectric power (TEP) observed in TE textile fabrics
produced with similar carbon-based nanostructures,
the CNF-based cotton fabrics showed negative TEP,
caused by the compensated semimetal character of the
CNFs and the highly graphitic nature of their outer
layers, which hinders the p-type doping with oxygen
groups onto them. A dependence of the electrical
conductivity (r) and TEP as a function of the woven
cotton fabric was also observed. The cotton fabric with
the largest linear density (tex) showed the best
performance with negative TEP values around
- 8 lV K-1
, a power factor of 1.65 9 10-3
lW m-1 K-2
, and a figure of merit of 1.14 9 10-6
.
Moreover, the possibility of a slight e- charge transfer
or n-doping from the cellulose onto the most external
CNF graphitic shells was also analysed by computer
modelling. This study presents n-type carbon-based
TE textile fabrics produced easily and without any
functionalization processes to prevent the inherent
doping with oxygen, which causes the typical p-type
character found in most carbon-based TE materialsFEDER funds through
COMPETE and by national funds through FCT â Foundation for
Science and Technology within the project POCI-01-0145-
FEDER-007136. E. M. F. Vieira is grateful for financial support
through FCT with CMEMS-UMinho Strategic Project UIDB/
04436/202
Mechanical, electrical and electro-mechanical properties of thermoplastic elastomer styreneâbutadieneâstyrene/multiwall carbon nanotubes composites
Composites of styrene-butadiene-styrene (SBS) block copolymer with multiwall carbon
nanotubes (MWCNT) were processed by solution casting in order to investigate the
influence of filler content, the different ratio of styrene/butadiene in the copolymer and
the architecture of the SBS matrix on the electrical, mechanical and electro-mechanical
properties of the composites. It was found that filler content and elastomer matrix
architecture influence the percolation threshold and consequently the overall composite
electrical conductivity. The mechanical properties are mainly affected by the styrene
and filler content. Hopping between nearest fillers is proposed as the main mechanism
for the composite conduction. The variation of the electrical resistivity is linear with the
deformation. This fact, together with the gauge factor values in the range of 2 to 18,
results in appropriate composites to be used as (large) deformation sensors.This work was funded by FEDER funds through the "Programa Operacional Factores de
Competitividade â COMPETE" and by national funds by FCT - Fundação para a
CiĂȘncia e a Tecnologia, through project references PTDC/CTM/69316/2006,
PTDC/CTM/73465/2006, PTDC/CTM-NAN/112574/2009, and NANO/NMed-
SD/0156/2007. PC, JS and VS also thank FCT for the SFRH/BD/64267/2009,
SFRH/BD/60623/2009 and SFRH/BPD/63148/2009 grants, respectively. The authors
also thank support from the COST Action MP1003 âEuropean Scientific Network for
Artificial Musclesâ and the COST action MP0902 âComposites of Inorganic Nanotubes
and Polymers (COINAPO)
Piezoresistive polypropylene-carbon nanofiber composites as mechanical transducers
Abstract: polymeric materials have been replacing other materials in various applications, from structural to electronic components. In particular, since the discovery of conducting polymers and the beginning of the manufacture of conducting composites with carbon fillers, their use in electronics is growing up. A group of electronic components with large potential for industrial applications such as structural monitoring, biomedical or robotics are sensors based on the piezoresistive effect, fabricated from conductive polymers and/or composites. The aim of this article is to characterize the piezoresistive effect of conductive polymer composites based on polypropylene filled with carbon nanofibers, and to demonstrate a way of fabricating strain gauges from these materials, using industrial techniques. With this purpose, some films were prepared by shear extrusion, which allows the composites to be produced industrially in a standard non-expensive process. Then, both the dependence of the electrical response on the preparation conditions and on the mechanical solicitations was measured. The obtained gauge factor values, up to 2.5, and piezoresistive coefficients up to 0.0019 mm2/N, prove the viability of these materials for fabricating strain-gauges, where their main advantages are the lower price and the ability to deal with much higher deformations, when compared to metal or semiconductor strain-gauges.We acknowledge the Foundation for Science and Technology through the 3 degrees Quadro Comunitario de Apoio, the POCTI and FEDER programs and the NANO/NMed-SD/0156/2007 project. The support of Applied Sciences Inc. for generously supplying the CNFs used. We would also like to thank Carla Leer and Patrick Lake for their assistance in the production of the CNF composites. J. G. Rocha thanks the FCT for the Grant SFRH/BSAB/1014/2010
Piezoresistive effect in spin-coated polyaniline thin films
Polymeric materials have been replacing other materials in various applications, from structural to electronic components. In particular, since the discovery of conducting polymers, the use of these materials is growing up in the manufacture of electronic components, such as organic light-emitting diodes, organic electrodes, energy storage devices and artificial muscles, among many others. On the other hand, examples of sensors of conductive polymers based on the piezoresistive effect with large potential for applications are not sufficiently investigated. This investigation reports on the piezoresistive effect of an intrinsically conductive polymer, polyaniline, which was prepared in the form of thin films by spin coating on polyethylene terephthalate substrates. The relationship between the electrical response and mechanical solicitations is presented for different preparation conditions. The values of the gauge factor ranges from 10 to 22 for different samples and demonstrates the viability of these materials as piezoresistive sensors.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade - COMPETE" and by national funds by FCT-Fundacao para a Ciencia e a Tecnologia, project references PTDC/CTM/69316/2006, PTDC/CTMNAN/112574/2009, and NANO/NMed-SD/0156/2007. J.N.P, A. F. and J. G. R. thank the FCT for Grants SFRH/BD/66930/2009, SFRH/BD/69796/2010 and SFRH/BSAB/1014/2010, respectively. The authors also than the support of the COST Action MP1003, 2010: The 'European Scientific Network for Artificial Muscles' (ESNAM)