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Inkjet printed acrylic formulations based on UV-reduced graphene oxide nanocomposites

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Abstract

This work reports the formulation of waterbased graphene oxide/acrylic nanocomposite inks, and the structural and electrical characterization of test patterns obtained by inkjet direct printing through a commercial piezoelectric micro-fabrication device. Due to the presence of heavily oxygenated functional groups, graphene oxide is strongly hydrophilic and can be readily dispersed in water. Through a process driven by UV irradiation, graphene oxide contained in the inks was reduced to graphene during photo-curing of the polymeric matrix. Printed samples of the nanocomposite material showed a decrease of resistivity with respect to the polymeric matrix. The analysis of the influence of printed layer thickness on resistivity showed that thin layers were less resistive than thick layers. This was explained by the reduced UV penetration depth in thick layers due to shielding effect, resulting in a less effective photo-reduction of graphene oxide.
1 23
Journal of Materials Science
Full Set - Includes `Journal of Materials
Science Letters'
ISSN 0022-2461
Volume 48
Number 3
J Mater Sci (2013) 48:1249-1255
DOI 10.1007/s10853-012-6866-4
Inkjet printed acrylic formulations
based on UV-reduced graphene oxide
nanocomposites
R.Giardi, S.Porro, A.Chiolerio,
E.Celasco & M.Sangermano
1 23
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Inkjet printed acrylic formulations based on UV-reduced
graphene oxide nanocomposites
R. Giardi S. Porro A. Chiolerio
E. Celasco M. Sangermano
Received: 6 July 2012 / Accepted: 3 September 2012 / Published online: 13 September 2012
ÓSpringer Science+Business Media, LLC 2012
Abstract This work reports the formulation of water-
based graphene oxide/acrylic nanocomposite inks, and the
structural and electrical characterization of test patterns
obtained by inkjet direct printing through a commercial
piezoelectric micro-fabrication device. Due to the presence
of heavily oxygenated functional groups, graphene oxide is
strongly hydrophilic and can be readily dispersed in water.
Through a process driven by UV irradiation, graphene
oxide contained in the inks was reduced to graphene during
photo-curing of the polymeric matrix. Printed samples of
the nanocomposite material showed a decrease of resis-
tivity with respect to the polymeric matrix. The analysis of
the influence of printed layer thickness on resistivity
showed that thin layers were less resistive than thick layers.
This was explained by the reduced UV penetration depth in
thick layers due to shielding effect, resulting in a less
effective photo-reduction of graphene oxide.
Introduction
Nowadays we are witnessing an increasing request for
electronic devices production characterized by high
demanding properties such as low manufacturing cost,
long-time endurance, environmental sustainable production
methods, recycling, low energy consumption, and high
efficiency. Polymeric materials seem to be the most
promising candidates to meet all these challenges [1].
Inkjet printing is one of the most promising manufacturing
technique which can be used to deposit polymers on a
variety of substrates [2]. Several reviews dealing with new
applications of inkjet printing technology are now available
[3,4]. In the inkjet printing, low viscosity should be
maintained in the polymer precursor and fast polymeriza-
tion needs to be performed soon after the deposition. For
these reasons, the use of UV curing process seems to be
very interesting because it is performed at room tempera-
ture, allowing the ink polymerization even on thermal
sensitive substrates such as paper, and in addition is a fast
overall manufacturing process [5]. In order to decrease the
surface resistivity of the dielectric polymer network, it is
necessary to disperse conductive fillers in the precursor, to
reach a conductive network (referring to the percolation
theory, the so-called infinite cluster [6], which could ensure
the requested electrical properties).
Printable inks based on conductive fillers are subjected
to several constraints to meet specific conditions, to be
ejected through nozzles of micrometric size (e.g.,
20–80 lm). These include the optimization of rheological
properties, ink viscosity, surface tension, and solvent
evaporation rate [711].
Several materials have been tested for use as conductive
inks [12], reporting different drawbacks. For instance,
conductive polymers presented the disadvantage of rela-
tively low conductivity [13], while metal nanoparticles
(NPs) based inks need to be sintered at temperatures gen-
erally too high for application on most flexible substrates
[14,15]. Temperatures as high as 300 °C may be poten-
tially sustained by poly-imide as high cost flexible sub-
strate [16]. Other examples of inkjet printable conductive
materials are silver nanocomposite inks, which exploit UV
curing to create the NPs in situ during the exposure,
R. Giardi S. Porro (&)A. Chiolerio E. Celasco
Istituto Italiano di Tecnologia, Center for Space Human
Robotics, c.so Trento 21, 10129 Turin, Italy
e-mail: Samuele.Porro@iit.it
M. Sangermano
Politecnico di Torino, Dipartimento di Scienza Applicata
e Tecnologia, c.so Duca degli Abruzzi 24, 10129 Turin, Italy
123
J Mater Sci (2013) 48:1249–1255
DOI 10.1007/s10853-012-6866-4
Author's personal copy
starting from a precursor [17,18]. In this case, there is no
need to transfer heat to the system [19,20], and cheap
substrates (e.g., PP, PET, paper) may be used, even though
the ultimate resistivity reached by those nanocomposites is
suitable for resistor applications only [21] and not for
conductive tracks, unless thermal sintering is performed.
As an alternative, carbon-based materials can be good
candidates for conductive inks, due to their low cost and
good electrical conductivity without the need of tempera-
ture treatments. This has been demonstrated for carbon
nanotubes printed thin films [22], graphene bi- and tri-layer
used as protective coating against oxidation on copper
NPs-based inks [23], and in graphene/water suspensions
[24].
Because of its high specific surface area, good chemical
stability, electrical and thermal conductivity, and high
charge carrier mobility (20 m
2
V
-1
s
-1
)[25,26], graphene
is actually the most suitable candidate to be dispersed in
photo-curable formulations to obtain a UV-cured conduc-
tive ink. So far, the manufacturing of graphene-based
polymer composites required not only that graphene sheets
were produced on a sufficient scale, but also that they were
incorporated, and homogeneously distributed, into various
polymeric matrices as single layers. However, graphite,
although inexpensive and available in large quantity,
unfortunately does not readily exfoliate to yield individual
graphene sheets. A widely investigated alternative is the
use of graphite oxide, a layered material produced by the
oxidation of graphite [27,28]. In contrast to pristine
graphite, the graphene derived sheets in graphite oxide
(graphene oxide sheets, GO) are heavily oxygenated,
bearing hydroxyl and epoxide functional groups on their
basal planes, in addition to carbonyl and carboxyl groups
located at the sheet edges [29,30]. The presence of these
functional groups makes GO sheets strongly hydrophilic,
which allows them to readily swell and disperse in water
[31]. Previous studies have shown that a mild ultrasonic
treatment of graphite oxide in water results in its exfolia-
tion to form stable aqueous dispersions that consist almost
entirely of one-nm-thick sheets [32]. Due to their structure,
GO sheets are not electrically conductive. Therefore, an
additional step is needed to reduce the oxide to graphene.
This has been achieved using several methods, e.g., by
thermal [33], chemical [34,35], or photo-thermal [36,37]
treatments.
This work explores the possibility of introducing aque-
ous dispersion of GO into acrylic resin matrices, such as
poly(ethylene glycol) diacrylate (PEGDA), thus fabricating
a conductive printable ink which is environmentally
friendly. The reduction of GO was performed using UV
light irradiation, which allowed the simultaneous photo-
polymerization of the polymeric matrix [38] that acted as a
binder. Structural and electrical characterization showed
the efficiency of the reduction method and promising val-
ues of conductivity of printed test patterns.
Materials and methods
Material
Commercial reagents were used: GO (thickness
0.7–1.2 nm) was purchased from Cheap Tubes Inc. (USA)
and used without further purification, PEGDA with
M
w
=575 g mol
-2
was purchased from Sigma-Aldrich
and DAROCUR
Ò
1173 radical photoinitiator (PI) from
BASF. PEGDA was chosen as polymeric matrix due to its
non-toxicity and water solubility, to fabricate an environ-
mentally friendly ink.
Samples preparation
Spin-coated GO aqueous dispersions (GOx)
GO aqueous dispersions were prepared by mixing GO
powder and PI in 1 g of deionized water. The GO con-
centration in water was varied between 1 and 4 per hundred
parts of resin (phr), while the PI content was varied
between 1 and 8 phr. The relative GO/PI content was
varied between 1/0.25 and 1/8 weight ratio, to evaluate the
PI content effect on the GO reduction (samples will be
referred to as GOx).
The GO aqueous dispersions were spin-coated on 1 cm
2
portions of single crystalline p-doped silicon wafer, pre-
cleaned by ultrasonic bath in isopropyl alcohol, rinsed with
water, and dried with nitrogen. The coated formulations
were irradiated with UV light for 2 min, with a light
intensity of 60 mW/cm
2
. After UV irradiation, samples
were dried at 80 °C under vacuum for 2 h to remove
residual water.
Inkjet printed GO aqueous dispersions (GOi)
A printable GO/water dispersion was formulated by mixing
0.02 g of GO powder in 4.5 g of deionized water (samples
will be referred to as GOi). In this formulation, a lower
concentration of GO was used to reduce the viscosity to a
value compatible with the use of the inkjet nozzle. High-
speed Ultraturrax was used for 5 min to obtain a homo-
geneous dispersion. Two-step ultrasonic bath (30 min at
40 kHz ?30 min at 59 kHz) was then used to further
grind and disperse the GO agglomerates. Finally, the dis-
persion was centrifuged at 14,000 rpm for 5 min to allow
residual large and heavy particles to precipitate at the
bottom of the test tube. The upper portion of the centri-
fuged dispersion was inserted into an ink reservoir, thus
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discarding the large precipitated particles. This and the
subsequent formulation were tested in a MicroFab Inkjet
Printer with automatic 3D position control, using an 80 lm
piezoelectric nozzle vibrating at a frequency of 250 Hz, at
room temperature. A test pattern of the GOi formulation
(prepared to assess the system printability) was printed on a
Si substrate for structural characterization.
GO aqueous dispersion/PEGDA UV-curable formulations
(GOp)
The formulations were prepared by adding 0.5 g of PEG-
DA and 0.08 g of PI to 4.5 g of DI water in which 0.02 g of
GO was previously dispersed (samples referred to as GOp,
and corresponding to the GO/PI ratio of 1/4). This GO/
PEGDA/water ink (Fig. 1a) was tested by inkjet spotting
straight line patterns with variable resolution (85–190 dots-
per-inch, dpi) and repetition of passes on the same track
(from 1 to 5) on microscope slides (Fig. 1b). The printed
thin films were irradiated with UV light for 2 min.
As a reference for bulk nanocomposite material, 100 lm
thick films of the GOp were obtained by deposition on a
microscope slide glass using a wire-wound bar and sub-
sequently exposed to UV light for 2 min. As a reference for
electrical characterization, a PEGDA/PI thick film was
similarly prepared without adding GO.
Characterization
The structural analysis and morphology of thick and thin
printed films were characterized by optical and scanning
electron microscopy (SEM). X-ray photoelectron spec-
troscopy (XPS) was performed using a monochromatic
X-ray beam with an Al K-asource with energy of
1486.6 eV. Before performing XPS, the homogeneity of
the samples was verified using an in situ secondary X-ray
imaging. Current/voltage (I–V) measurements were per-
formed on thick and printed films using a standard two-
point micro-contact setup of a Keithley 2635A multimeter.
The electrical characterization was performed on all sam-
ples at room temperature, in the range -200 to ?200 V.
Resistivity was computed comparing GO/PEGDA thick
films with printed thin films of several thicknesses (varied
with dpi resolution and repetition of printing on the same
track, measured by profilometry). These measurements
were planned to assess the variation in resistivity due to
GO reduction to graphene by UV irradiation, and any
potential collateral effects produced by the high strain rate
to which inks are submitted to in the printing nozzle.
Figure 1c shows a typical setup of the measurement for
inkjet printed thin films.
Results and discussion
We have investigated conductive printable inks, based on
aqueous acrylic UV-curable formulations containing GO.
The oxide can be easily dispersed in water and it can be
reduced during UV irradiation, with the simultaneous build
up of the crosslinking network. The polymer network acts
as a binder during printing and the in situ reduced GO
decreases the resistivity of the acrylic polymer, forming a
conductive percolative network. The preparation of elec-
trically conductive acrylic resins containing reduced
graphene oxide was previously investigated [38], showing
the occurrence of a single-step procedure starting from a
Fig. 1 GO/PEGDA/water ink (a), InkJet nozzle printing GO/PEGDA/water ink (b), and the two-point micro-contact setup for I–V
measurements used for inkjet printed GOp thin films (c)
J Mater Sci (2013) 48:1249–1255 1251
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homogeneous aqueous dispersion of GO, which undergoes
reduction induced by the UV radiation during photopoly-
merization of the acrylic resin.
This method can be used for the preparation of aqueous
acrylic formulations of variable viscosity, which are suit-
able for the fabrication of inkjettable UV-curable inks.
XPS analysis of GO reduction by UV irradiation
of GOx samples
In order to confirm the effectiveness of GO reduction by
UV irradiation, XPS spectra of GOx samples deposited on
Si wafer were compared before and after irradiation.
The GO/PI weight ratio was varied from 1/0.25 to 1/8
(S1 =1/0.25; S2 =1/0.5; S3 =1/1; S4 =1/2; S5 =1/4;
S6 =1/8 wt ratio). Figure 2reports an example of the
variation of XPS C1 s peaks after 2 min of UV irradiation
of an aqueous dispersion containing 1 phr of GO and 4 phr
of PI with respect to water. After irradiation, it is possible
to observe a significant decrease in intensity of the peaks
associated with carbonyl groups, evidencing the photoin-
duced GO reduction [39]. This deconvolution evaluation
was performed on different aqueous GO dispersions vary-
ing both GO and PI content, to evaluate the best
performing GO/PI ratio. The area and height of XPS peaks
associated with carbon–carbon and carbon–oxygen bond-
ing (carbonyl and carboxyl groups) have been analyzed.
Figure 3summarizes the analysis of the ratios of heights
and areas of peaks associated with carbon–oxygen and
carbon–carbon groups, proving that all samples show a
decrease of oxygen bonded to carbon after UV irradiation.
The measurements prove the reduction of GO, with resto-
ration of the extended conjugated sp
2
structure. According
to these results, the sample with GO/PI ratio of 1/4 gave the
highest value of GO reduction.
Inkjet printed tracks of GOi and GOp formulations
Several test patterns of the GOp and GOi formulations
were inkjet printed on transparent substrates (microscope
glass slides). Figure 4shows an image of a glass substrate
with inkjet printed straight lines of the GOp formulation
with various thicknesses. The thickness of printed films
was varied either by increasing the spotting resolution
(variation of dpi) or repeating the same track in multiple
passes, up to five times. In particular, the repeated tracks
showed a good uniformity and coverage of the substrate
(inset in Fig. 4). The analysis of the microstructure of the
Fig. 2 XPS spectra of pristine
GO (a) and a GOx sample
irradiated for 2 min with UV
light (b), showing the best fits
(red) to experimental data
(black) and the deconvoluted
peaks (blue) used for fitting. The
spectrum in (b) refers to the
formulation containing a GO/PI
ratio of 1/4 (Color figure online)
Fig. 3 Analysis of XPS C1s
peak deconvolution: height
(a) and area (b) ratios of C=O to
C–C contributions plus height
(c) and area (d) ratios of O–
C=O to C–C contributions,
for samples with several
concentrations of GO and PI in
water after 2 min of UV
irradiation (the formulations
correspond to the GO/PI ratio
reported as following:
S1 =1/0.25; S2 =1/0.5;
S3 =1/1; S4 =1/2; S5 =1/4;
S6 =1/8 wt ratio). For
comparison, pristine GO before
UV irradiation is also reported
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printed tracks demonstrates that GO flakes distribute uni-
formly on the substrate and form a continuous layer with
each other, ensuring continuity of electrical signal (Fig. 5).
Electrical properties
The electrical response of printed thin films (GOp) was
compared with one of the thick films (GOp and PEGDA
reference) fabricated by wire-wound bar. Figure 6shows
the raw (not normalized to layer resolution/thickness) I–V
characteristics of those samples. The I–V response of the
thin inkjet printed track features an absolute current which
accidentally appears in the same range of the pure matrix
thick film. This effect obviously depends on the difference
in size and thickness of thick and thin printed films.
Remarkably, the GOp thick film shows a non-linear
response, strongly different from the other materials: since
the electrical response (at least in the DC regime) may be
interpreted in terms of superposition of different contri-
butions, we may expect the nonlinear effect to come from
either the PEGDA matrix or the reduced GO filler. None-
theless, neither the pure PEGDA matrix nor the inkjet
printed sample show such a nonlinear trend, allowing us to
conclude that in the thick wire-wound bar-fabricated
sample there should still exist a fraction of unreduced GO,
possibly due to the complete absorption of UV radiation in
a few micrometers at the top of the sample. This phe-
nomenon, leading to inhomogeneous samples in the
direction perpendicular to the film plane, was already
observed on different classes of materials featuring UV in
situ reduction processes [26,29]. These phenomena are
thought to be due to the shielding effect originating by the
filler (in our case, the GO flakes) which limits the light
penetration depth, and therefore hinders the UV-induced
GO reduction.
Figure 7shows the resistivity of thin printed layer
samples as a function of sample thickness, compared to
thick films of GOp and pure PEDGA. Each experimental
point in the plot is given by a computation based on linear
fits to average I–V curves (error bars shown in the plot).
The addition of GO to PEGDA, after reduction by UV
irradiation, results in a decrease of resistivity by over an
order of magnitude (GOp TF versus PEGDA TF). For what
concerns printed samples, two trends may be evidenced,
both concurring to a resistivity decrease. By increasing the
number of passes and thus the track thickness, a small
decrease of resistivity is obtained (green dashed arrow in
Fig. 7); this fact is normally due to an increased volume
Fig. 4 Image showing inkjet printed test tracks of the GOp ink on a
microscope glass, after UV irradiation. Tracks with different thick-
ness are shown, corresponding to variation of dpi resolution or several
repetition of the printing. The inset shows an optical microscope
magnification of a printed track with 125 dpi and 3 passes
Fig. 5 SEM image showing the microstructure of an inkjet printed
track of GOi suspension (water was evaporated before inserting the
sample into SEM chamber). The inset shows a low-resolution image
of the printed track
Fig. 6 Raw I–V characteristics of pure PEGDA and GOp thick films
(TF), and GOp inkjet printed thin film (IjP)
J Mater Sci (2013) 48:1249–1255 1253
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available for electrons’ drift. Furthermore, by decreasing
the amount of ink spotted on a single-pass track (i.e.,
reducing the dpi resolution) and thus reducing the line
thickness, a strong reduction of GO is obtained (blue solid
arrow in Fig. 7). Those samples show a decrease of resis-
tivity by two orders of magnitude with respect to the pure
matrix. This counter-intuitive fact may be explained con-
sidering that in a thin track a higher fraction of GO is
reached and reduced by UV light than in a thick track, thus
better contributing to electrical conduction [26,29].
The analysis of coefficients of dispersion as a function
of the film thickness (R
2
, not shown here), computed by
fitting I–V curves with a linear function, demonstrates that
all samples ideally follow the Ohm’s law (within 0.4 %).
Only the GOp thick film sample appears out of scale, if
compared to thin inkjet printed samples and to pure
PEGDA matrix (Ohm’s law likelihood around 1.5 %). This
confirms the nonlinear behavior of thick films and the
shielding effect previously described for Fig. 6.
Conclusions
A route to obtain inkjet printable, environmentally friendly
inks based on graphene/acrylic nanocomposites was pre-
sented. The excellent rheological characteristics of the
formulations warranted printability with good repeatability.
The concurrent UV-driven polymerization of PEGDA
matrix and reduction of graphene oxide filler was verified
by XPS analysis. Thin printed samples of the nanocom-
posite showed a decrease of resistivity by two orders of
magnitude with respect to the pure matrix. In particular, it
was observed that the resistivity of thin layers was much
lower than one of the thick layers. This effect is ascribed to
the formation of free radicals, which may have a role in the
reduction of graphene oxide, from the photo-initiator used
to start the polymerization of the matrix. This reaction is
proportional to the amount of incoming UV light, therefore
it is more effective in thin layers, where the light pene-
tration is higher than in thick layers.
Suggested applications for the so-prepared inks are
devoted to flexible and organic electronics: the realization
of an electrode on top of a stacked structure (e.g., an active
device such as a transistor or a photovoltaic cell) incor-
porating organic semiconductors requires either conductive
polymers or high vacuum processes. This is important
since metal nanoparticle-based inks require a sintering
thermal treatment which is not compatible with organic
materials. A conductive ink ready to be structured by an
additive process like inkjet printing and needing only a fast
post-deposition treatment like UV curing is very interesting
also from an industrial point of view.
Future activity will be devoted to the incorporation of
metal nanoparticles or carbon nanotubes, to increase the
percolation and reduce the ultimate resistivity.
Acknowledgements The support by A. Chiodoni in helping with
SEM characterization is gratefully acknowledged.
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... The C 1s spectrum could be deconvoluted into four peaks at 284.5, 286.5, 287.4, and 288.6 eV corresponding to C-C/C=C, C-O, C=O, and COOH functional groups, respectively [47,48]. Significantly higher intensities of peak components due to oxygen functionalities further corroborate the findings based on FTIR and NMR spectra of GO. ...
Article
Present work addresses the synthesis of different structural forms of polyaniline (PANI) and their nanocomposites with graphene as functional fillers to epoxy coating for minimizing mild steel corrosion. The π-π interactions between p-phenylenediamine functionalized graphene (fGO) and aromatic rings of in-situ grown covalently linked PANI on fGO facilitated the interfacial wrapping of graphene skeleton by PANI. The chemical, morphological, crystalline, and structural features of fGO-PANI nanocomposites are probed by FTIR, NMR, Raman, XPS, XRD, SEM, and HRTEM analyses. The emeraldine salt form of PANI (PANI-ES) exhibited significantly higher impedance and better corrosion inhibition properties than the emeraldine base (PANI-EB). Graphene skeleton in the fGO-PANI nanocomposite notably enhanced the anticorrosive properties of PANI with a multifold increase in total impedance. The 2D graphene skeleton in fGO-PANI nanocomposites provides excellent surface coverage as a structural barrier and increases the number of possible electron transfer pathways. Moreover, the oxidoreduction properties of PANI make the fGO-PANI-ES nanocomposite highly effective in increasing the impedance by multifolds. The corrosion protective mechanism of fGO-PANI-ES is discussed by emphasizing the role of graphene, different structural forms of PANI, and the dosing of graphene in fGO-PANI nanocomposites. The present work revealed fGO-PANI-ES as a promising material for new generation coatings to mitigate mild steel corrosion, particularly in a maritime environment.
... A wide range of polymeric binders have been used for printed electronics 28,29 . Common options include acrylic 30 , silicone 31 , styrene 32 , fluoroelastomer 33 and polyurethane materials 34 . The choice of the binder mainly depends on the properties of the filler and the intended application, which can require features such as selfhealing, water stability, heat stability or stretchability. ...
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Emerging technologies such as smart packaging are shifting the requirements on electronic components, notably regarding service life, which counts in days instead of years. As a result, standard materials are often not adapted due to economic, environmental or manufacturing considerations. For instance, the use of metal conductive tracks in disposable electronics is a waste of valuable resources and their accumulation in landfills is an environmental concern. In this work, we report a conductive ink made of carbon particles dispersed in a solution of shellac. This natural and water-insoluble resin works as a binder, favourably replacing petroleum-derived polymers. The carbon particles provide electrical conductivity and act as a rheology modifier, creating a printable shear-thinning gel. The ink’s conductivity and sheet resistance are 1000 S m−1 and 15 Ω sq−1, respectively, and remain stable towards moisture. We show that the ink is compatible with several industry-relevant patterning methods such as screen-printing and robocasting, and demonstrate a minimum feature size of 200 μm. As a proof-of-concept, a resistor and a capacitor are printed and used as deformation and proximity sensors, respectively.
... The O1s peak at 532.4 eV in the PGO spectrum is greatly weakened in comparison with that of GO, which is evidence that most of the oxygen-containing functional groups in GO were removed during the PPD grafting process to synthesize PGO, and the N1s peaks at approximately 399.0 eV confirm the presence of diamine. Furthermore, the C1s XPS spectrum of GO (Fig. 3b) contains three different peaks, at 285.1 eV, 287.1 eV, and 289.2 eV, corresponding to the C-C, C-O, and C=O groups, respectively [9,17]. As shown in Fig. 3c, the peaks corresponding to the oxygen-containing groups had significantly less intensity in the PPD-functionalized sample, particularly the peak of C-O (epoxy). ...
Article
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Wrinkled p-phenylenediamine (PPD)-functionalized graphene oxide (PGO) is synthesized, characterized, and subsequently incorporated in a ethanol-based polyvinyl butyral (PVB) film (ca. 10 μm thick). The anti-corrosive properties of the pure PVB and nanocomposite (PVB-PGO and PVB-GO) films are tested on steel and compared. Electrochemical impedance spectra reveal that the PGO-reinforced PVB nanocomposite film exhibits the slowest corrosion rate (4 × 10⁻⁴ mm a⁻¹ after a 20-day immersion) among the samples, and the results of 7-day saline spray bombardment tests show it is the most robust and durable. The PVB-PGO coating protects the steel substrate from visible corrosion. Incorporation of GO in the PVB matrix results in a reduction of the PVB film anti-corrosion properties. However, by functionalizing GO with PPD, highly dispersible wrinkled PGO flakes are obtained, thus leading to a uniform film that presents a highly tortuous path for impeding liquid and gas molecules. The PVB-PGO nanocomposite film exhibits high, stable capacitance without film delamination, cracking, or other visible damage. Readily accessible as a simple and environmentally friendly, this approach may present an advantageous strategy for creating protective coatings in marine and other applications. Graphical abstract PGO with wrinkle structure, as nanometer reinforcing materials in PVB coatings, improved the corrosion resistance of the coatings by extending the permeation path of the corrosive medium.
... Recently, nanoparticle-based inks of Ag [24], Au [25] and Cu [26] as well as carbon-based materials such as carbon nanotubes (CNTs) [27], graphene [28,29] and reduced graphene oxide (rGO) [30,31] are studied as electrode material for biosensing applications. These inks are either commercially purchased or prepared for printing onto suitable substrates. ...
Article
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Inkjet printing technology holds a great potential for fabrication of biosensor device. An optimized programmed printing makes the processing steps easier on a variety of substrates at low cost. The drop-on-demand piezoelectric mode of printing can construct a design pattern with low volume of material at specified position onto a suitable substrate. But to achieve this successfully, a formation of stable ink suspension remains the most challenging task. In recent times, nanoparticles are considered to pave a way for miniaturization of biosensing devices. Thus, we synthesized, characterized and investigated the stability of magnetic Fe3O4 nanoparticles stabilized by the polyamidoamine (PAMAM = N(CH2CH2C(O)NHCH2CH2NH2)(CH2CH2N(CH2CH2C(O)NHCH2CH2NH2)2)2) dendrimer (PAMAM@Fe3O4). A best stable ink dispersion of PAMAM@Fe3O4 nanoparticles was obtained in a solvent mixture of 70% ethylene glycol and 30% distilled water. The nanoparticle ink with surface tension of 57.47 mN/m and viscosity of 5.45 mPa/s formed a narrow and uniform printed pattern onto graphene paper. Further, as a model protein for future biosensing application, antibody against alpha-fetoprotein was conjugated onto the dendritic surface and printed onto graphene paper. The characterization of the printed pattern by TEM revealed spherical morphology, whereas SEM provided evidence of difference in printed line width and spacing of nanoparticles and antibody conjugated nanoparticles. As a proof-of-concept, the study demonstrated a printable ink dispersion based on PAMAM@Fe3O4 nanoparticles for future miniaturization of biosensing steps on a chip-based platform. Graphical Abstract
... In recent years, UV-curing has developed rapidly in many applications. The technology is now widely used in coating [62][63][64][65][66], electronic engineering [67], and printing industries [68]. ...
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Self-healing coatings or materials have received significant importance in paint, coating, and other industries, as well as in academia, because of their capability to extend materials service life, improving protection, and ensuring sustainability. This review article emphasizes significant advances accomplished in the preparation and properties of intrinsic self-healing materials exclusively based on hydrogen bonding interactions, with possible applications in coatings and adhesives. The main topic of discussion in this review article is the preparation, healing conditions, healing efficiency, and mechanical property recovery after healing. The last part of the review discusses the conclusions and outlook of self-healing materials.
... The sensor monitored human body temperature with a TRC value higher than 0.06%/ • C under optimal conditions (35-45 • C) [87]. Photocuring of 3D printed GO composites using UV light, is applied by Giardi et al. while developing components for flexible electronics [88]. This process reduces GO to graphene and its resistivity depends on the printed layer thickness. ...
Article
This review provides a comprehensive analysis of available peer-reviewed literature in which graphene and/or its derivatives are incorporated into a polymer matrix in order to enhance the final properties and functionalities of the three dimensional (3D) printed structure. Research in which graphene derivatives have been incorporated into plastic 3D printing technologies such as Fused deposition modeling (FDM), Stereolithography (SLA), Selective laser sintering, Inkjet 3D printing, Extrusion-based printing and Binder-jet printing is presented. For certain design requirements and applicability of the material, great care needs to be taken to select the appropriate printing method. Factors which play a key role in final performance of the printed parts are identified, including dispersion of graphene or its derivatives in matrix, interfacial interaction between graphene or its derivatives and matrix, printing orientation, nanofiller's aspect ratio, reduction of graphene oxide and ink viscosity. In fact, the multifunctional applications of the 3D printed structures based on graphene or graphitic filler composites open up the countless possibilities of current research. Although great progress has been made in exploring the mechanical, electrical, optical and thermal, characteristics of these materials, significant research and development need to be done to fully fetch their inherent potential. This article serves the purpose to researchers to improve latest research outcomes and explore new graphene–based nanocomposites for different applications.
Article
Stable composites of water-dispersed graphene oxide (GO) and UV-cured acrylic resin, poly (ethylene glycol) diacrylate (PEGDA), were prepared to make printed conductive patterns using a digital light processing (DLP) three-dimensional (3D) printing method. The targeted structures were successfully printed by DLP 3D printing and the electrically conductive properties were obtained by reducing the insulating GO in the composites to reduced GO by chemical and thermal reduction processes. Three basic reduction procedures, pre-thermal, pre-chemical, and post-thermal reduction, were performed to introduce a high conductivity into a printed structure and the lowest resistance was achieved by the pre-thermal reduction in our study. The stability of the printed structures was also evaluated by monitoring the change in resistance with time. The strategy pursued by photopolymerization gives the outstanding features of printed structures for extensive applications in the manufacturing of electronic and sensing devices.
Article
The invention of printing technologies has revolutionized the manner in which information is transmitted and reproduced. In the modern era, printing technologies , which are equipped with computerized control and design methods, have become considerably efficient and effective, facilitating A significant breakthrough in the manufacture of high-performance electrochemical energy storage systems. Through careful design and execution, the components of energy storage devices, particularly electrodes, can be formulated into functional inks, enabling the use of divers materials and devices in high-performance energy storage applications. This reviewfocuses on three major printing technologies: inkjet printing, screen printing, and 3D printing, introducing the principles of each printing technology, the design and preparation of various electrode inks, and their applications in supercapacitors. Finally, the challenges and scope for the future development of printing technologies forhigh-performance supercapacitors are presented.
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The combination of yttria-zirconia (3Y-ZrO2) and stereolithography (SLA) is essential for forming alternative bioceramics for complex, custom-designed dental implants. In addition, suitable bioceramic suspensions are preconditions for such fabrication using SLA technology. In this study, 3Y-ZrO2 and 3Y-ZrO2/graphene oxide (GO) powders dispersed in ultraviolet curable acrylic-based resins are developed. A sedimentation experiment is performed to evaluate various ratios of monomers and dispersants to ensure good stability and dispersion of the suspensions. The hydrophobic structures of KH560 are introduced on the surfaces of ceramic powders, representing better wettability performances with 40 vol% NPG2PODA and 60 vol% Di-TMPTA. Moreover, the effects of premixed solvents and solid contents on the rheological behaviors of suspensions are investigated to confirm shear thinning and pseudo plasticity, with the experimental results fitting the Krieger–Dougherty curves. Further, the cure depth and width of the ceramic suspensions are studied, the results of which show that the penetration depth and critical exposure of the 3Y-ZrO2 (3Y-ZrO2/GO) pastes are 17.2±0.50 μm and 4.80±0.62 mJ/cm² (11.8±1.20 μm and 22.80±9.34 mJ/cm²), respectively. The addition of GO results in a sharp increase in critical exposure, which intensifies the light scattering and hinders the curing of the ceramic paste. The research is expected to serve as a technical guide for the fabrication of ceramic suspensions for dental implants using SLA technology.
Article
Graphene (G) has been combined with carboxymethyl cellulose (C) for the development of environmentally friendly inks for printed electronics applications. Water based ink formulations have been developed for screen printing with graphene content up to 90 wt.%. The printed patters show a good distribution of the graphene within the cellulose matrix, allowing a good screen-printed pattern definition with line thickness of 200 μm. The electrical percolation threshold is found around 0.18 of volume fraction, corresponding to 1.9 wt.% of graphene in the ink composition. A maximum electrical conductivity of ρ= 1.8×10-2 Ω.m has been obtained for the G90:C10 ink composition, allowing the printing of suitable conductive patters for printed electronics. Further, the multifunctionality of the developed inks is demonstrated by the interesting thermoresistive and piezoresistive properties of the screen-printed G30:C70 and G65:C35 materials, respectively. The maximum thermoresistive sensitivity of S=-0.27 and piezoresistive Gauge Factor of 1< GF <5 demonstrate the suitability of the materials for temperature and deformation sensors, respectively, demonstrating the multifunctionality of the materials and their wide range of potential applications in the area of printed electronics.
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For the first time, stable aqueous dispersions of polymer-coated graphitic nanoplatelets can be prepared via an exfoliation/in-situ reduction of graphite oxide in the presence of poly(sodium 4-styrenesulfonate).
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Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. NMR spectra of GO derivatives confirm the assignment of the 70 ppm line to C−OH groups and allow us to propose a new structural model for GO. Thus we assign the 60 ppm line to epoxide groups (1,2-ethers) and not to 1,3-ethers, as suggested earlier, and the 130 ppm line to aromatic entities and conjugated double bonds. GO contains two kinds of regions:  aromatic regions with unoxidized benzene rings and regions with aliphatic six-membered rings. The relative size of the two regions depends on the degree of oxidation. The carbon grid is nearly flat; only the carbons attached to OH groups have a slightly distorted tetrahedral configuration, resulting in some wrinkling of the layers. The formation of phenol (or aromatic diol) groups during deoxygenation indicates that the epoxide and the C−OH groups are very close to one another. The distribution of functional groups in every oxidized aromatic ring need not be identical, and both the oxidized rings and aromatic entities are distributed randomly.
Book
Fractals and disordered systems have recently become the focus of intense interest in research. This book discusses in great detail the effects of disorder on mesoscopic scales (fractures, aggregates, colloids, surfaces and interfaces, glasses and polymers) and presents tools to describe them in mathematical language. A substantial part is devoted to the development of scaling theories based on fractal concepts. In 10 chapters written by leading experts in the field, the reader is introduced to basic concepts and techniques in disordered systems and is led to the forefront of current research. In each chapter, the connection between theory and experiment is emphasized, and a special chapter on "Fractals and Experiment" presents experimental studies of fractal systems. This second edition has been substantially revised and updates the literature in this important field. It is pedagogically written and so will be useful for students, teachers, and scientists who want to become familiar with this facinating subject.
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The inkjet printing of an aqueous suspension of carboxylic acid-functionalized single walled carbon nanotubes (SWCNT-COOH) and of a conductive ink combining SWCNT-COOH with the conductive polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT-PSS) was studied. A dimensionless study predicted the behavior of these two fluids in a given printing system. Observations at different scales were performed on the printed samples to visualize the arrangement of the carbon nanotube (CNT) network within the printed layer. An innovative way to localize CNTs within the printed patterns was developed by using a mapping technique of surface sample, based on a scanning electron microscope coupled with an energy dispersive X-ray spectroscope. The SWCNT-COOH aqueous suspension is subject to the halo (or “coffee ring”) effect, which is a well-known phenomenon in inkjet printing, whereas the SWCNT-COOH/PEDOT-PSS ink offers a more homogeneous CNT network. The CNT orientation has also been under investigation. For the SWCNT-COOH suspension, specific orientations of the CNTs were recorded, whereas for the SWCNT-COOH/PEDOT-PSS ink, a more homogeneous CNT distribution with a random orientation was obtained. This study proved also that the droplet ejection velocity can have an impact on the CNT distribution and consequently on the electrical performances of the ink.
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Aggregation and restacking of graphene nanosheets (GNS) can be efficiently inhibited by decorating the silver nanoparticles on the surface of GNS to form GNS/silver (GNS-Ag) composites, which can construct high transparent and electrically conductive thin films. Silver nanoparticles act as a useful nanospacer and conductor, which not only increase the interlayer distance but also improve the electrical conductivity between layers. A two-step reduction process using sodium borohydride and ethylene glycol was also demonstrated reducing graphene oxide to GNS efficiently. The GNS-Ag composite films showed a maximum sheet resistance of 93Ω□−1, while maintaining up to 78% light transmittance, which was two order of magnitude lower than that of GNS (8.2×103Ω□−1, 81%), and the value of DC conductivity to optical conductivity ratio was 13.5 instead of 0.25.
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As an emerging area in organic electronics, polymer memories have become an active research topic in recent years, because they are likely to be an alternative or supplementary technology to the conventional memory technology facing the problems and challenges in miniaturizing from microscale to nanoscale. This review provides a summary of the widely reported electrical switching phenomena in polymers and the corresponding polymer electronic memories. A general introduction to the current state of memory technology and some basic concepts of electronic memories is first presented, followed by a brief historical development and some key advances in polymer electronic memories. The subsequent sections give a comprehensive review of three categories of polymer electronic memories, classified by drawing the mechanistic analogy between the polymer switching element and one of the three primary circuit elements, viz., capacitor, transistor and resistor. Emphasis is placed on the relationships among material structures and properties, memory devices and operating mechanisms. Finally, the challenges facing the research and development in the field of polymer electronic memories are summarized.
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The reduction of graphite oxide (GO) thin films was evaluated at 220 °C using a combination of infrared (FTIR) and X-ray photoemission spectroscopies (XPS). The results were correlated with electrical resistance measurements. The chemical composition of GO was C8(OH)3O0.8 and reduced to C8(OH)0.5O0.3 after nearly 24 h of low-temperature processing, defined as 220 °C. The sheet resistance of dropcast GO thin films processed at 220 °C in air was 8 kΩ sq−1, similar to GO reduced at >800 °C in an inert atmosphere.
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Photographs of gray-scale OLEDs patterned on PEDOT-PSS surfaces by an ink-jet printer on plastic substrates. Summary: Due to its capability of dispensing very small volumes of different liquids in a controlled manner, ink-jet printing is well suited for combinatorial experiments. The multi-nozzle ink-jet delivery system is especially advantageous for parallel chemical synthesis of different materials. We have used ink-jet printing of an oxidizing agent to pattern a pre-coated conducting polymer, poly(3,4-ethylenedioxy)-thiophene-poly(styrene sulfonate) (PEDOT-PSS), yielding electrodes with predefined shapes and a controlled degree of sheet resistivity for use in gray-scale organic light-emitting devices (OLEDs). The electrical and optical properties of the PEDOT-PSS layer are modified via chemical interaction using the oxidizing agent. These experiments were performed using a desktop ink-jet printer in conjunction with common graphic software which employed color functions such as CMY (cyan, magenta and yellow), HSL (hue, saturation and luminosity) and RGB (red, green and blue).
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An approach to pattern a conducting polymer on various flexible substrates using vapor deposition polymerization-mediated inkjet printing method was demonstrated. Complex patterns of doped emeraldine salt polyaniline were obtained via chemical oxidation polymerization of vaporized aniline monomer on inkjet-printed oxidant patterns. The features of pattern were precisely controlled by inkjet printing with a micrometer-scale resolution. Fourier transformed infrared attenuated total reflection analysis was conducted in order to confirm the polymerization of aniline monomer and UV–visible spectroscopy analysis was used to investigate the oxidation state of obtained polyaniline. The minimum width of patterned line was ca. 80 μm. The sheet resistance of patterned polyaniline films was 3.8 × 103 Ω/□ for an average patterned film thickness of ca. 450 nm.