Carbon 43 (2005) 87–94
www.elsevier.com/locate/carbon
Composite graphitic nanolayers prepared by self-assemblybetween finely dispersed graphite oxide and a cationic polymer
Tamas Szabo a, Anna Szeri a, Imre Dekany a,b,*
a Department of Colloid Chemistry, University of Szeged, Aradi vertanuk tere 1, H-6720 Szeged, Hungaryb Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Aradi vertanuk tere 1, H-6720 Szeged, Hungary
Received 30 June 2004; accepted 23 August 2004
Available online 5 October 2004
Abstract
Chemical flaking of graphite has been performed by reacting natural graphite with a strong oxidizing agent, NaClO3/HNO3. The
formed hydrophilic, negatively charged graphite oxide (GO) colloids can be dispersed in water which allows the deposition of thin
GO/cationic polymer (poly(diallyldimethylammoniumchloride, PDDA) multilayer films on a glass substrate by wet-chemical self-
assembly. The feasibility of the charge-regulated layer-by-layer deposition is demonstrated by mutual charge titrations of the
film-forming species. Visible-light spectroscopy revealed progressive growth of the film thickness with the number of deposition
of steps, while XRD and AFM showed that partially exfoliated, highly anisometric (aspect ratio >50) graphite oxide platelet aggre-
gates were deposited with an average thickness of the stacked graphite oxide platelets of 10 carbon layers (7.4nm). Reduction of
multilayer assemblies of GO and PDDA on glass yielded a non-conductive turbostratic carbon nanofilm. The original, conductive
graphite-like structure was restored by reduction with N2H4 and annealing at 400 �C which, by gradual ordering of the carbon crys-
tallites, caused a significant decrease in the resistivity.
� 2004 Elsevier Ltd. All rights reserved.
Keywords: A. Graphite oxide, Carbon films; B. Graphitization; C. X-ray diffraction; D. Electrical (electronic) properties
1. Introduction
Graphite/polymer nanocomposites have long been
investigated and used as structural materials because
of their markedly superior mechanical [1] and thermal
properties [2] in comparison with conventional compos-
ites. The most important step of their preparation is thecleavage of coarse graphite crystals to finer, exfoliated
stacks of graphene sheets. A possible way for the flaking
of graphite along its cleavage planes is the chemical [3]
or electrochemical [4] oxidation, by which graphite can
be disaggregated to spherical particles with diameters
as low as 40nm [5]. The formed graphite oxide (GO) is
built of unoxidized aromatic islands of variable size that
0008-6223/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbon.2004.08.025
* Corresponding author. Tel.: +36 62 544210; fax: +36 62 544042.
E-mail address: [email protected] (I. Dekany).
are separated from each other by aliphatic six-mem-
bered rings containing double bonds, C–OH, COOH
and epoxide groups and their quantity depends on the
degree of oxidation [6,7].
Various graphite oxide/polymer [8–10] or expanded
graphite/polymer [11] composites have recently been pre-
pared and their outstanding physicochemical propertiesdemonstrated [12]. However, as pointed out by Kotov
et al. [13], availability of ultrathin films of graphite–poly-
mer composites is required for the construction of ad-
vanced electro-optical devices and sensors. For the
preparation of nanostructured graphite films we have
chosen wet-chemical layer-by-layer self-assembly that
we had successfully applied before for the deposition of
thin multilayer films of different charged colloidal parti-cles and polymers [14,15]. Although self-assembled GO/
polymer films have been fabricated previously [16,17],
88 T. Szabo et al. / Carbon 43 (2005) 87–94
their reduction was only performed by Kotov et al. [13].
They reported that reduction caused a change from an
insulating towards a conductive-like state, but restoration
of the graphite structure has not been proved. We show
here that during hydrazine reduction of a polymer/GO
film a turbostratic carbon film forms the conductivity ofwhich increases significantly when it is converted back
to a nanostructured graphitic film by heat treatment.
Fig. 1. Schematic representation of the layer-by-layer deposition of
S-(PDDA/GO)n films.
1 During the reduction step Zn2+ ions could react with unreduced
GO lamellae by ion-exchange. Besides, the high surface-area amor-
phous carbon film formed could also adsorb significant amounts of
Zn2+.
2. Experimental
2.1. Materials
The host graphite was a natural specimen provided
by Kropfmuhl AG, Germany. The fraction of 250–
500lm was used. Its ash content was less than
0.1wt.% as proved by a thermoanalytical measurement.
NaClO3, N2H4 (Aldrich), fuming HNO3 (Fluka) and
HCl (Reanal) were analytical grade chemicals. As a cat-
ionic polymer poly(diallyldimethylammoniumchloride)
(PDDA) was chosen and from the series of AldrichChemical products the one with medium molecular
weight (MW = 2 · 105�3 · 105) was used as a 20wt.%
aqueous solution. Aqueous dispersions were made by
distilled water filtered with a Millipore Milli-Q system.
2.2. Preparation of graphite oxide
Graphite oxide (denoted as GO) was prepared by thetraditional Brodie method [3]. 10 grams of graphite and
85g of NaClO3 were mixed in a round flask. 60mL of
fuming HNO3 was added from a dropping funnel in
210min with constant stirring. The mixture was then left
aging for a night�s period. Next day it was gradually
heated to 60 �C by a basket heater and kept at
60 ± 5 �C for 8h. The solid GO sample was washed with
1L of 3M HCl solution and at least with 7 · 1L distilledwater until it was chloride ion free (tested with AgNO3
solution). Finally, the suspension was filtered and dried.
2.3. Layer-by-layer deposition of polymer/graphite
oxide nanofilms
Multilayer GO films were prepared by the layer-by-
layer self-assembly process by means of a home madeautomated device, the dipping time and the rate of lift-
ing were controlled by a microprocessor. The deposition
steps and the simplified structure of the assemblies are
presented in Fig. 1.
Glass slides (Menzel Super Frost, Fischer Sci. Ltd.)
were used as substrates in all experiments. After a prelim-
inary cleaning procedure (cleaning with a detergent solu-
tion and soaking in concentrated H2SO4 saturated withK2Cr2O7 for 1h) the slide was immediately dipped into
a 1g/L PDDA solution for 20min, creating an adsorbed
monolayer of PDDA. The weakly adsorbed polymer
molecules were removed from the surface by rinsing withwater for about 1min. After drying, the glass slide was
immersed into a beaker containing freshly ultrasonicated
GO suspension (1g/L, pH = 4.03) which was prepared
by wet-grinding GO powder with water in an agate ball
mill for 4 · 30min (average particle size 62lm). Theimmersion time was chosen again to 20min to let the
adsorption process take place (other authors found
15min or even less to be sufficient for charge overcom-pensation [18,19] in case of different materials generally
used for self-assembly: azo dyes, polymers, etc.). Next,
the same rinsing followed as in the first dipping step.
We must note here that traces of weakly bound polymer
would dissolve from the glass surface and could have the
GO colloidal particles flocculated unless the rinsing pro-
cedure was precisely performed. The dipping/deposition
steps were continued to get further PDDA/GO bilayersdeposited. By this procedure we prepared thin films of
alternating PDDA and GO layers up to 25 bilayers (de-
noted as S-(PDDA/GO)25).
2.4. Reduction of PDDA/GO thin films to more
conductive carbon materials
Earlier bulk experiments indicated the possibility toreduce suspended GO by a nascent hydrogen generator
(Zn powder in HCl solution) or hydrazine [13,20]. The
former may seem to be more effective, yet, we chose to
reduce graphite oxide by N2H4 since its oxidation pro-
duces an inert gas (N2) while oxidation of Zn would
have lead to dissolved Zn2+ ions. 1
T. Szabo et al. / Carbon 43 (2005) 87–94 89
2.5. Characterization of the samples
Visible spectra of the composite films were taken on a
UVIKON 930 dual-beam spectrophotometer (Kontron
Instruments).
X-ray diffraction measurements were performed on aPhilips PW 1830 diffractometer operating with Cu anode
(40kV voltage, 30mA cathodic current). CuKb radia-
tion was absorbed by Ni filters. Basal distances (d002)
were calculated by the Bragg equation. Besides inter-
layer distance determination, crystallite size can be cal-
culated from X-ray line broadening using Scherrer�sequation [21]:
Lc ¼0:9k
bhkl cos hhklð1Þ
where k, h and b are the wavelength of X-rays, the
Bragg�s angle and the pure diffraction line broadening(in radians), respectively. The latter is defined here as
the observed diffraction peak breadth at half-maximum
intensity corrected for the instrumental line broadening
(determined by macrocrystalline K2Cr2O7). Lc is the
mean dimension of the crystallite perpendicular to the
diffracting plane (hk l). Lc-values can be determined by
Eq. (1) with ±5% precision in our experimental
conditions.Atomic force microscopy (AFM) images of the orig-
inal and the treated S-(PDDA/GO)25 films were ob-
tained with a Digital Instruments Nanoscope III
Multimode atomic force microscope operating in tap-
ping mode. 1cm · 1cm pieces of the slides were carefully
cut and fixed to the sample holder, and 1lm · 1lmareas were scanned by etched silicon tapping mode tips
(125lm length) that were purchased from VeecoGmbH.
Thermogravimetric analyses were carried out by a
MOM Q-1500 D Derivatograph in the temperature
range of 25–1000 �C at 5 �C/min heating rate. An inert
athmosphere was assured by N2 gas with �10cm3min�1
flow rate (STP).
Streaming potential measurements were done by
means of a PCD-02 Particle Charge Detector (MutekAnalytic GmbH, Munich, Germany). 2
2 A cylindrical test cell and a piston fitting into it (both made of
teflon) constitutes the heart of the PCD. Between them there is
concentric, narrow slit containing a solution or suspension. Some of
the dispersed charged colloids or macromolecules will adsorb on the
teflon surfaces by physical forces. Each of the adsorbed particles is
surrounded by a symmetrical charge cloud of counter-ions. In a typical
measurement, a synchron motor has the piston oscillated by �4Hzfrequency inducing thereby an intensive liquid stream that sweeps
away the counter-ions from the vicinity of the probe material. The
potential difference induced by the slipping of the counter-ion diffuse
layer from the surface is detected through two gold electrodes; it
corresponds to the so-called streaming potential.
Electrical resistivity of the thin films at ambient tem-
perature was measured by a Keithley 2400 Series Source
Meter with two-wire connections, applying a constant
voltage of 0.1V on two gold electrodes (fixed electrode
distance was 3mm). Five measurements were done at
different surface sites of the films and the values wereaveraged.
3. Results and discussion
3.1. Cyclic charge titration of the PDDA-GO system
Investigating the electrostatic interactions between theGO sheets and cationic polymers, a ‘‘cyclic charge titra-
tion’’ was performed. This term refers to the experiment
when known volumes of a 0.1g/L PDDA solution are
added to 10mL of 0.5g/L GO suspension (pH adjusted
to 9.8) with concomitant streaming potential measure-
ments. After the sign of the potential had reversed, the ti-
trant was changed to the original GO suspension and its
addition was continued until the next reversal, when thetitrant was changed again, and so on. The titration was
performed in a dynamic mode: portions of titrants were
added successively in 10min intervals. The titration curve
presented in Fig. 2a clearly indicates the feasibility of
PDDA to recharge GO surfaces and vice versa, thus,
indirectly indicating the applicability of these species
for the charge regulated self-assembly. This statement is
explained in terms of the streaming potential change (thathas the same sign as the surface charge density) over the
titration: The pure graphite oxide suspension consists of
highly negatively charged lamellae at pH = 9.8 [16,22], a
few of them adsorb on the teflon cell, so a high negative
streaming potential can be measured. Addition of PDDA
gradually decreases this value because the cationic chains
preferentially adsorb on the negative GO surfaces result-
ing in the rapid flocculation of the suspension. After aspecific amount of polyelectrolyte added, no streaming
potential can be measured, consequently, the net surface
charge of the heterocoagulated flocs is zero. Continued
titration overcompensates the original charge of graphite
oxide (high positive potential is detected). As we change
the titrant to the original GO suspension, the streaming
potential tends to decrease and even restoration of the
original charge of GO can be achieved. Subsequent alter-nate additions of the titrants cause charge reversal too,
though, the high starting potential value of GO cannot
be reached again.
In principle we would be able to determine the cation
exchange capacity (CEC) of GO at pH = 9.8 on the
basis of this experiment because the specific charge of
PDDA (meq charges/g polymer) can be calculated
from the molar weight of the monomer (1 monomerholds one positive charge in a very wide pH range)
that is 6.19meq/g. Assuming that the polyelectrolyte
Fig. 2. (a) Cyclic charge titration of the PDDA/GO system: (�) PDDA
solution (0.1g/L), (m) GO suspension (0.5g/L). (b) Equilibrium
titration of GO with PDDA.
Fig. 3. Absorption spectra of S-(PDDA/GO)n ultrathin film.
90 T. Szabo et al. / Carbon 43 (2005) 87–94
neutralizes all charges on GO, CEC values of 0.35; 0.33;
0.34 and 0.44mmol/g were calculated from the differentcycles of the titration curve. Thus, unfortunately, this
measurement cannot be applied for quantitative analyt-
ical purposes because the amount of titrants belonging
to the hypothetic equivalence points (where streaming
potential = 0mV) do not correlate with each other in a
systematic way. The main reason for this is the ‘‘dy-
namic’’ mode of the titration: in case of titration of lay-
ered materials like GO, the reaction is rather slow as thepolymer chains must penetrate into the interlayer space,
where they neutralize the charges. So, recording such a
‘‘titration curve’’ (streaming potential) in an equilibrium
method takes days. Equilibrium measurement was per-
formed by mixing graphite oxide suspensions with differ-
ent amounts of PDDA in plastic flasks (pH was set to
9.8) that were then shaken for a week and the streaming
potential was measured. The equilibrium data are shown
in Fig. 2b. Zero streaming potential was measured at
1.19mmol added PDDA/g GO. This value is three–four
times higher than those obtained in the dynamic mode,
showing that polymer uptake of graphite oxide films
(three–four times higher than in dynamic method) can-not be completed with deposition times as short as some
minutes or some hours. However, we must emphasize
again that the aim of these experiments was to demon-
strate the suitability of PDDA and GO for the ‘‘charge
regulated’’ electrostatic self-assembly method.
3.2. Spectrophotometric and XRD investigation of
S-(PDDA/GO)n nanofilms
Self-assembly of the ultrathin films was monitored by
absorption spectrophotometry in the visible range
(k = 350–800nm). This technique is often used to char-
acterize the consecutive build-up of oppositely charged
species. Numerous papers report on the growth of the
multilayer structure by a linear fashion for polymers,
semiconductor nanoparticles, aluminosilicate platelets,etc. [15,23,24]. Former publications dealing with poly-
mer/GO self-assembly found the same build-up ten-
dency [13,16,17]. Absorption spectra of S-(PDDA/
GO)n ultrathin films (n = number of bilayers) are shown
in Fig. 3. Since the glass slide substrates showed some
light absorption even in the visible range (Amax � 0.05),
subtraction of their spectra from that of the sandwich
layers were necessary to display the real optical featureof the assemblies. The shape of the film spectra coincides
with that of GO suspensions and no changes were ob-
served after deposition of the polymer, indicating that
only the graphite oxide bears the dominant light absorp-
tion and light scattering. Absorbances of the films at dif-
ferent wavelengths are plotted against the bilayer
5 10 15 20 25 302Θ °
Inte
nsit
y (a
.u.)
n=25
n=20
n=15
n=10
500
cps
GO powder
parent
graphite
Fig. 4. XRD patterns of graphite, graphite oxide and S-(PDDA/GO)nfilms.
T. Szabo et al. / Carbon 43 (2005) 87–94 91
number in the inset of Fig. 3. Absorbances at all fre-
quencies increased proportionally with increasing n,
however, true linear correlation was only observed at
NIR wavelengths (800nm). At visible wavelengths (400
and 600nm), a break point splits the linear growing ten-
dency at n = 11. After depositing 11 bilayers, a change inthe slope occurs. The same phenomenon was reported
by Dante et al. after deposition of 20 bilayers of PDDA
and an azo dye [25]. They claimed the slope decrease was
the result of progressive disordering of chromophoric
groups and not that of reduction of transferred mass.
In our system the reason must be that if n P 11 the
thickness is so high that the bonding forces between
the outermost layers are weakened compared to the onesclose to the glass substrate so the species prefer being
solvated in the liquid phase.
Absorbance increment due to the deposition of one
graphite oxide layer differs from that found in an earlier
study [13] applying almost the same conditions. As a
matter of fact, for an S-(PDDA/GO)7 film five times
higher absorption (A400 = 1) was measured than Kotov
and co-workers found (A400 = 0.2). This apparent con-tradiction can be partly explained by the different opti-
cal properties of the applied graphite oxides. It is
known that the colour of graphite oxide depends on
the stage of oxidation [26]: the higher the O:C ratio is,
the lighter colour the GO sample has. Since the graphite
used in Ref. [13] was oxidized three times, its specific
absorbance must be lower than that of the material we
prepared. On the other hand, centrifugation was omit-ted in this case, so greater lamellae were not removed
from the GO suspension. This indicates that smaller par-
ticles build more homogeneous, but significantly thinner
films by self-assembly.
X-ray diffraction is a powerful tool for the structure
analysis of layered materials like GO. Fig. 4 shows the
X-ray diffraction patterns of the starting materials and
the nanofilms, while Table 1 summarizes the XRDparameters.
The very intense and narrow peak at 2H = 26.28� cor-responds to the (002) planes of graphene layers
(d002 = 0.339nm). In the course of strong oxidation the
structure expands as oxygen-containing groups are
Table 1
XRD parameters and resistivities of the graphite oxide composite films
Sample 2H� d002 (nm)
Graphite powder 26.28 0.339
Graphite oxide powder 14.06 0.630
S-(PDDA/GO)10 11.54 0.767
S-(PDDA/GO)15 11.44 0.773
S-(PDDA/GO)20 11.24 0.787
S-(PDDA/GO)25 11.20 0.790
Red. (PDDA/GO)25 — —
Red. (PDDA/GO)25, 400 �C 25.86 0.345
incorporated between the carbon sheets: the d-spacing
is almost doubled (d002 = 0.630nm) The mean numberof GO sheets stacked along the c-axis (N) can be calcu-
lated in terms of the crystallite size and the basal spac-
ing: N = Lc/d002. Line broadening of the GO powder
diffractogram shows that Lc is nearly 22nm indicating
that parallel to layer expansion partial disaggregation
of the macrocrystalline graphite particles also occurred
(N = 35). XRD patterns of the nanofilms reveal swelling
of the GO layers to �0.77nm with concomitant linebroadening (position and breadth remained constant
after each bilayer numbers). This means that while air-
dry GO (d002 = 0.63nm) contains only few water mole-
cules (the thickness of a GO layer is 0.61nm [27]), GO
in the thin film is much more hydrated. However, since
the van der Waals diameter of H2O is 0.28nm [28], not a
monomolecular layer of water is built in the intergallery
space which would have increased d002 to 0.89nm. Thecrystallite sizes (0.76–0.78nm) and N-values (9–11) for
the GO incorporated in the nanofilms decreased signifi-
cantly which means that partial disaggregation took
place in the suspension and the self-assembly selected
these thinner platelets.
Lc (nm) N R (kX)
macroscopic — —
22 35 —
7.4 10 >2.11 · 105
7.3 9 >2.11 · 105
8.7 11 >2.11 · 105
8.5 11 >2.11 · 105
— — >2.11 · 105
6.5 19 6.6
Fig. 5. XRD pattern and absorbance (at 700nm) of the S-(PDDA/
GO)25 film as a function of reduction time.
-70
-60
-50
-40
-30
-20
-10
0
10
0 100 200 300 400 500 600 700 800T (˚C)
Mas
scha
nge
(wt%
)
DT
G,D
TA
sign
al (
a.u.
)
GO TG
GO DTG
reduced GO TG
GO DTA
Fig. 6. TG-DTA curves of pure and reduced graphite oxide under N2.
92 T. Szabo et al. / Carbon 43 (2005) 87–94
3.3. Reduction of S-(PDDA/GO)25 films
Reduction of (PDDA/GO)25 films with hydrazine was
performed at ambient temperature. It takes place in
maximally 24h [13]. So we soaked the multilayer films
on glass slides in 0.02M N2H4 and sped up the reaction
by using an elevated temperature (50 �C). XRD and
spectrophotometric measurements were done at differ-ent stages (times) of reduction (Fig. 5). The intensity
of graphite oxide reflection gradually decreased with
progressing reduction (the pattern of the starting film
was recorded with a smaller data collection time, that
is the reason for the low peak height), indicating the
destruction of the layered graphite oxide structure. After
one hour the GO was completely reduced. However, in-
stead of the sharp graphite (002) reflection near 26� 2H,only a broad halo developed that comes from the scat-
tering of the formed disordered, turbostratic carbon
[20]. A significant difference in the darkness of the par-
tially reduced films was observed visually that was sup-
ported by photometry (Fig. 5 inset). According to this
we reached an absorbance plateau (thus, completed
reaction) after 45min. This is not inconsistent with the
XRD measurement as this plateau is not caused bythe end of the reduction but the light absorption of
the black carbon film was so high that no further in-
crease of absorbance could be detected.
The pristine and reduced graphite oxide were sub-
jected to thermal analysis in N2 (Fig. 6). The GO has
a weight loss of 7–8% up to 200 �C (no DTA signal) that
is caused by the slow removal of physically adsorbed
water. A significant exothermic loss is followed thathas the maximum rate at 275 �C according to the
DTG and DTA curve. This is ascribed to the destruction
of different oxygen-containing (e.g. hydroxyl) groups
[28] by the deflagration of GO. The decomposition of
the strongly attached functional groups follows. We
think that loss at higher temperatures is due to carbon
combustion caused by the traces of oxygen gas in the
system (there is a broad exothermic hump up to
800 �C). There is a marked difference between the un-
treated and reduced GO samples. The reduced one doesnot have a water content (2% loss up to 200 �C) and it
has featureless DTG and DTA curves because hydro-
phobic carbon is formed. Also, the lack of functional
groups is evidenced by the minor weight loss up to
800 �C.Morphological changes of the nanofilm surface
brought by the reductive treatment is demonstrated in
the AFM images of Fig. 7. Scanning of the original(PDDA/GO)25 assembly visualized 25–35nm thick exfo-
liated slabs with micron-sized lateral dimensions stacked
upon each other. The aspect ratio of the anisometric
aggregates is at least 40 from the image assuming a
25nm thickness and 1000nm width, but it may be much
higher as the platelet was greater than the scanned sur-
face. Reduction has destroyed the layered graphite oxide
structure, mainly mounds of the formed turbostraticcarbon particles determine the topography which is con-
sistent with the lack of the sharp XRD reflection of well-
ordered graphite.
3.4. Postreduction treatment of S-(PDDA/carbon)25films
Formation of a conductive carbonaceous film hasprompted our effort to restore the original, more or-
dered graphitic arrangement of the layers. Heat treat-
ment of 1h in air was applied on the slides up to
400 �C (the glass substrate melts at higher temperatures).
There is a gradual shift of the scattering maximum to
higher angles (Fig. 8). The reduced (but not heated) film
Fig. 7. AFM images of freshly deposited (a) and reduced (b) S-
(PDDA/GO)25 film.
0
200
400
600
800
1000
1200
10 12 14 16 18 20 22 24 26 28 302Θ ˚
Inte
nsit
y (c
ps)
reduced
200˚C 400˚C
Fig. 8. Effect of heat treatment on the X-ray diffractogram of S-
(PDDA/GO)25.
T. Szabo et al. / Carbon 43 (2005) 87–94 93
has a broad peak near 2H = 22� that arises from carbon
layers stacked in an irregular fashion. Heating causes agradual ordering of the carbon (d002 = 0.37nm at
200 �C) and a significantly sharper peak appears at
400 �C, with d002 = 0.345nm which is typical for carbon
blacks, and close to the reflection of graphite. In conclu-
sion, three-dimensional ordering of adjacent graphene
layers was improved by the heat treatment that, in turn,
proved to improve the conductivity too. The electrical
resistivity of the reduced film showed an at least32000-fold increase upon heating (Table 1): while resis-
tivities of the (PDDA/GO) and the hydrazine-treated
nanofilms were higher than 211MX (that is the maxi-
mum measurable R), the annealed sample possessed a
resistivity of 6.6kX. Thus, we have managed to alter
the thin carbon/polymer composite from an insulator
to a conductor.
4. Conclusion
Crude graphite powder has been partly exfoliated
into thin platelet-like aggregates by a strong oxidation
process. Cyclic charge titrations of the as-prepared,
hydrophilic graphite oxide with poly(diallyldimethylam-
moniumchloride) showed that GO meets the require-ments of the layer-by-layer self-assembly method
which is the easiest, wet-chemical technique for thin film
deposition. X-ray diffractograms and AFM image of the
film consisting 25 bilayers of PDDA and GO showed
that self-assembly selects thin, anisometric graphite
oxide particule aggregates from its suspension. Reduc-
tion of the polyelectrolyte/GO composite and transfor-
mation of the formed turbostratic carbon to aconductive nanofilm was achieved by reduction with
hydrazine and subsequent heat treatment.
Acknowledgments
This work was supported by the Hungarian National
Scientific Fund OTKA (T034430). The authors thankProfessor Hanns-Peter Boehm for his valuable remarks
and for revising and improving the manuscript.
References
[1] Iroh JO, Bell JP, Scola DA, Wesson JP. Electrochemical process
for preparing continous graphite fiber thermoplastic composites.
Polymer 1994;35:1306–11.
94 T. Szabo et al. / Carbon 43 (2005) 87–94
[2] Xu J, Hu Y, Song L, Wang Q, Fan W, Liao G, et al. Thermal
analysis of poly (vinyl alcohol)/graphite oxide intercalated com-
posites. Polym Degrad Stabil 2001;73:29–31.
[3] Brodie BC. Sur le poids atomique du graphite. Ann Chim Phys
1860;59:466–72.
[4] Peckett JW, Trens P, Gougeon RD, Roppl A, Harris RK,
Hudson MJ. Electrochemically oxidised graphite. Characterisa-
tion and some ion exchange properties. Carbon 2000;38:
345–53.
[5] Weng WG, Chen GH, Wu DJ, Lin ZY, Yan WL. Preparation and
characterizations of nanoparticles from graphite via an electro-
chemically oxidizing method. Synth Met 2003;139:221–5.
[6] He H, Klinowski J, Forster M, Lerf A. A new structural model for
graphite oxide. Chem Phys Lett 1998;287:53–6.
[7] Hontoria-Lucas C, Lopez-Peinado AJ, Lopez-Gonzalez JD,
Rojas-Cervantes ML, Martın-Aranda RM. Study of oxygen-
containing groups in a series of graphite oxides: physical and
chemical characterization. Carbon 1995;33:1585–92.
[8] Matsuo Y, Tahara K, Sugie Y. Synthesis of poly (ethylene oxide)-
intercalated graphite oxide. Carbon 1996;34:672–4.
[9] Xiao P, Xiao M, Liu P, Gong K. Direct synthesis of a polyaniline–
intercalated graphite oxide nanocomposite. Carbon 2000;38:
626–8.
[10] Ding R, Hu Y, Gui Z, Zong R, Chen Z, Fan W. Preparation and
characterization of polystyrene/graphite oxide nanocomposite by
emulsion polymerization. Polym Degrad Stabil 2003;81:473–6.
[11] Zheng W, Wong S. Electrical conductivity and dielectric proper-
ties of PMMA/expanded graphite composites. Comput Sci Tech-
nol 2003;63:225–35.
[12] Higashika S, Kimura K, Matsuo Y, Sugie Y. Synthesis of
polyaniline-intercalated graphite oxide. Carbon 1999;37:354–6.
[13] Kotov NA, Dekany I, Fendler JH. Ultrathin graphite oxide–
polyelectrolyte composites prepared by self-assembly: transition
between conductive and non-conductive states. Adv Mater
1996;8:637–41.
[14] Szabo T, Nemeth J, Dekany I. Zinc oxide nanoparticles incorpo-
rated in ultrathin layer silicate films and their photocatalytic
properties. Coll Surf A 2003;230:23–35.
[15] Kotov NA, Dekany I, Fendler JH. Layer-by-layer self-assembly
of polyelectrolyte–semiconductor nanoparticle composite films.
J Phys Chem 1995;99:13065–9.
[16] Kovtyukhova NI, Ollivier PJ, Martin BR, Mallouk TE, Chizhik
SA, Buzaneva EV, et al. Layer-by-layer assembly of ultrathin
composite films from micron-sized graphite oxide sheets and
polycations. Chem Mater 1999;11:771–8.
[17] Cassagneau T, Guerin F, Fendler JH. Preparation and charac-
terization of ultrathin films layer-by-layer self-assembled from
graphite oxide nanoplatelets and polymers. Langmuir
2000;16:7318–24.
[18] Advincula RC, Fells E, Park M. Molecularly ordered low
molecular weight azobenzene dyes and polycation alternate
multilayer films: aggregation, layer order, and photoalignment.
Chem Mater 2001;13:2870–8.
[19] Shinbo K, Baba A, Kaneko F, Kato T, Kato K, Advincula RC,
et al. In situ investigations on the preparations of layer-by-layer
films containing azobenzene and applications for LC display
devices. Mater Sci Eng C 2002;22:319–25.
[20] Boehm HP, Clauss A, Fischer GO, Hofmann U. Das Adsorp-
tionsverhalten sehr dunner Kohlenstoff-Folien. Z anorg allgem
Chem 1962;316:119–27.
[21] Bartram F. Crystallite-size determination from line broadening
and spotty patterns. In: Kaelble EF, editor. Handbook of X-
rays. New York: Mc Graw-Hill; 1967. p. 17.1–17.
[22] Boehm HP, Clauss A, Fischer GO, Hofmann U. Dunnste
Kohlenstoff-Folien. Z Naturforsch 1962;17:150–3.
[23] Kim DW, Blumstein A, Kumar J, Samuelson LA, Kang B, Sung
C. Ordered multilayer nanocomposites prepared by electrostatic
layer-by-layer assembly between aluminosilicate nanoplatelets and
substituted ionic polyacetylenes. Chem Mater 2002;14:3925–9.
[24] Liu Y, Wang A, Clauss R. Molecular self-assembly of TiO2/
polymer nanocomposite films. J Phys Chem 1997;101:1385–8.
[25] Dante S, Advincula R, Frank CW, Stoeve P. Photoisomerization
of polyionic layer-by-layer films containing azobenzene. Langmuir
1999;15:193–201.
[26] Kinoshita K. Carbon, electrochemical and physicochemical
properties. New York: Wiley; 1988. p. 208.
[27] Dekany I, Kruger-Grasser R, Weiss A. Selective liquid sorption
properties of hydrophobized graphite oxide nanostructures. Coll
Polym Sci 1998;276:570–6.
[28] Liu Z, Wang ZM, Yang X, Ooi K. Intercalation of organic
ammonium ions into layered graphite oxide. Langmuir 2002;18:
4926–32.
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