Novel processing to produce polymer/ceramic nanocomposites by atomic layer deposition

Article abstract of DOI:10.1111/j.1551-2916.2006.01359.x

An innovative process to uniformly incorporate dispersed nanoscale ceramic inclusions within a polymer matrix was demonstrated. Micron-sized high density polyethylene particles were coated with ultrathin alumina films by atomic layer deposition in a fluidized bed reactor at 77°C. The deposition of alumina on the polymer particle surface was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Conformai coatings of alumina were confirmed by transmission electron microscopy and focused ion beam cross-sectional scanning electron microscopy. The results of inductively coupled plasma atomic emission spectroscopy suggested that there was a nucleation period. The results of scanning electron microscopy, particle size distribution, and surface area of the uncoated and nanocoated particles showed that there was no aggregation of particles during the coating process. The coated polymer particles were extruded by a heated extruder at controlled temperatures. The successful dispersion of the crushed alumina shells in the polymer matrix following extrusion was confirmed using cross-sectional transmission electron microscopy. The dispersion of alumina flakes can be controlled by varying the polymer particle size.

Full text of DOI:10.1111/j.1551-2916.2006.01359.x

J. Am. Ceram. Soc., 90 [1] 57–63 (2007)
DOI: 10.1111/j.1551-2916.2006.01359.x
r 2006 The American Ceramic Society
ournal
J
Novel Processing to Produce Polymer/Ceramic Nanocomposites by
Atomic Layer Deposition
Xinhua Liang, Luis F. Hakim,* Guo-Dong Zhan,* Jarod A. McCormick, Steven M. George,
and Alan W. Weimer*,w
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309
Joseph A. Spencer II and Karen J. Buechler
ALD NanoSolutions, Broomfield, Colorado 80020
John Blackson and Charles J. Wood
Dow Chemical Company, Midland, Michigan 48667
John R. Dorgan
Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 80401
An innovative process to uniformly incorporate dispersed nano-
scale ceramic inclusions within a polymer matrix was demon-
strated. Micron-sized high density polyethylene particles were
coated with ultrathin alumina films by atomic layer deposition in
a fluidized bed reactor at 771C. The deposition of alumina on the
polymer particle surface was confirmed by Fourier transform
infrared spectroscopy and X-ray photoelectron spectroscopy.
Conformal coatings of alumina were confirmed by transmission
electron microscopy and focused ion beam cross-sectional scan-
ning electron microscopy. The results of inductively coupled
plasma atomic emission spectroscopy suggested that there was a
nucleation period. The results of scanning electron microscopy,
particle size distribution, and surface area of the uncoated and
nanocoated particles showed that there was no aggregation of
particles during the coating process. The coated polymer parti-
cles were extruded by a heated extruder at controlled tempera-
tures. The successful dispersion of the crushed alumina shells in
the polymer matrix following extrusion was confirmed using
cross-sectional transmission electron microscopy. The dispersion
of alumina flakes can be controlled by varying the polymer par-
ticle size.
are often not enough for end use.4 Confinement of polymer
and mineral pedigrees is one of the effective ways to improve
material performance.5
Work has primarily been done with nanoscopic montmorillo-
nite clay.6–8 Two widely adopted approaches to forming poly-
mer/inorganic nanocomposites are high shear mixing of the
preformed polymer with the ceramics (compounding)8–10 and
in situ polymerization of monomer that has been premixed with
the ceramics. Both approaches are feasible at the bench scale,
but ceramics are not homogeneously dispersed in the polymer
matrix at a nanoscopic level7 and there are voids between
ceramics and polymer. Commercialization will also require a
low-cost continuous process. Previous studies show that the
combined effects of aspect ratio and dispersion of clay particles
ultimately control the mechanical properties of the nanocom-
posite, with dispersion playing a major role.5,6 Relatively few
compounding studies have appeared in the literature as a route
toward polymer/ceramic nanocomposites.
There is therefore a need to chemically bond ceramics and
polymer and disperse ceramics homogeneously throughout the
polymer matrix. A novel process to promote intimate mixing is
to coat polymer particles with ultrathin, uniform ceramic films.
The coated polymer particles can be extruded into pellets or
films. During the high shear/high stress extrusion process, the
shell on the polymer particle surface will crack and the shell
remnants will be dispersed homogeneously throughout the pol-
ymer matrix. By means of this novel technique, the mechanical
and barrier properties of this kind of polymer/ceramic nano-
composite may be further improved and new advanced features
may appear.
There are many problems in depositing inorganic films on
polymer surfaces by conventional methods. Chemical vapor
deposition (CVD) and plasma-enhanced CVD (PE-CVD) pro-
cessing have been reported for polymer surface coating.11–15
However, typical CVD processes generally operate at tempera-
tures (B3001–5001C) much higher than the softening and
melting temperatures of the polymers (B1251–2501C). CVD
techniques are not able to effectively control the use of precursor
gases or to inherently control the location and the thickness of
the ceramic film. In addition, both CVD and PE–CVD will leave
defects and pinholes in the deposited inorganic films.12–15 Atom-
ic layer deposition (ALD) provides unparalleled advantages
over other techniques to deposit inorganic films on polymer
surfaces.
I. Introduction
OLYMERIC materials are widely used in packaging applica-
tions. Biomedical uses of plastic materials have been wide-
P
spread and the combination of ceramics and certain polymers is
the choice for medical devices.1–3 The automobile industry also
has embraced plastics to improve efficiency and improve manu-
facturing methods. However, the strength and some other prop-
erties, such as thermal stability, permeability to gases and
organic solvents, and flame retardance of the pure polymer
R. Riedel—contributing editor
Manuscript No. 21954. Received June 28, 2006; approved August 21, 2006.
Supported by the National Science Foundation, under Grant 0400292, U.S. Depart-
ment of Energy, under STTR Grant DE-FG02-03ER86157, and the GAANN Program in
Functional Materials, U.S. Department of Education. Support from Department of Energy
does not constitute an endorsement by Department of Energy of the views expressed in the
article.
*Member, American Ceramic Society.
wAuthor to whom correspondence should be addressed. e-mail: alan.weimer@
colorado.edu
57

58
Journal of the American Ceramic Society—Liang et al.
ALD is a surface controlled layer-by-layer process, which II. Experimental Procedure
Vol. 90, No. 1
deposits low impurity content, pin hole-free, conformal, and
ultrathin flexible films.16–19 The film thickness is inherently con-
trolled by self-limiting sequential surface chemical reactions, so
precursors are used efficiently. ALD has been successfully dem-
onstrated using a fluidized bed reactor (FBR).20–23 A FBR has
the main advantages of excellent gas/particle contact and ther-
mal efficiency, and its control is easy due to stable operating
conditions.
Al2O3 is non-flammable and has a melting point of 20501C.
The chemical and thermal stability of Al2O3 allows its applica-
tion as a good diffusion barrier.24 From a toxicological view-
point, Al2O3 is non-toxic, but the montmorillonite clay can lead
to toxic byproducts as the product ages, which may mean that
many clay-based nanocomposites will never be suitable for food
packaging applications. Therefore, Al2O3 is a good alternative
to montmorillonite clay. High density polyethylene (HDPE) is a
widely used polymer and a good candidate for experimentation.
Polyethylene and Al2O3 are also biocompatible. Combining
these two materials could make a stronger polymer with many
potential applications. For example, along with the typical ar-
throplasty applications for polyethylene, successful biocompat-
ibility has recently been observed for an Al2O3/polyethylene
blood pump.3
Al2O3 films have been deposited on several substrates, using re-
peated exposures of trimethylaluminum (TMA) and H2O in an
ABAByysequence.18–23,25–27 Al2O3 ALD is derived from the
following binary CVD reaction:
2AlðCH3Þ3 þ 3H2O ! Al2O3 þ 6 CH4
(1)
This binary reaction can be divided into two half-reactions:
ðAÞ AlOHꢀ þ AlðCH3Þ3 ! ½AlOAlðCH3Þ2ꢁꢀ þ CH4
ðBÞ AlðCH3Þꢀ þ H2O ! AlOHꢀ þ CH4
(2)
(3)
where à indicate the surface species.17–19 In each half-reaction, a
gas-phase precursor reacts with a surface functional group and
forms CH4 as a by-product. The surface reaction continues until
all the available surface functional groups have reacted.
The experimental ALD-FBR is shown in Fig. 1. The reactor
itself was composed of a 3.5 cm inside diameter stainless steel
tube with a 10 mm pore size porous metal disc as the gas
distributor. A 316 L porous metal filter element (1.9 cm
ID ꢂ 15.24 cm long; 0.5 mm pore size) was used at the inside
top of the reactor column to prevent particles from leaving the
system. The reactor was encased by a clamshell-type furnace and
bolted to a platform that rested on four large springs. The re-
actor was maintained at low pressure by a vacuum pump
(Model 2063, Alcatel, Paris, France), and the dosing header
could also be pumped down directly using a smaller separate
pump (Model 2008A, Alcatel). A vibration system (Model
The main objective of this research is to develop a new cost-
effective efficient process to fabricate uniform polymer/ceramic
nanocomposites. In this paper, the successful deposition of ultra
thin Al2O3 films on micron-sized HDPE particles by ALD at the
temperature of 771C is reported, and the successful dispersion of
Al2O3 flakes in the polymer matrix following the extrusion pro-
cess is demonstrated.
1
To pump 1
2
3
4
9
5
5
N supply
2
1
7
7
6
To pump 2
8
8
Fig. 1. Schematic diagram of atomic layer deposition–fluidized bed reactor (ALD-FBR): (1) pressure transducers, (2) metal filter, (3) reaction column,
(4) distributor plate, (5) vibro-motors, (6) spring supports, (7) pneumatic valves, (8) reactant containers, (9) mass flow controller.

January 2007
Polymer/Ceramic Nanocomposites by Atomic Layer Deposition
59
CD36210, Martin Engineering, Marine City, MI) was utilized to
overcome some of the interparticle forces and improve the qual-
ity of fluidization. High purity N2 gas was used as the purge gas
to remove the unreacted precursor and any CH4 formed during
the reaction. The purge gas flow was fed in through the dis-
tributor of the reactor and its flow rate was controlled by a
MKSs mass flow controller (Model 1179, MKS, Boulder, CO).
Piezoelectric transducers (Model 902, MKS) were located below
the distributor plate and at the outlet of the reactor column to
measure the pressure drop across the bed of the particles. All
valves used to provide the transient dosing were automatically
controlled through LabViews from National Instruments (Aus-
tin,TX). Pressure measurements were recorded to monitor the
progress of each dosing cycle.
of concentration and morphologies of nanoscale ceramic flakes
were formed. The structure information of the nanocomposite
films was confirmed by cross-sectional TEM.
III. Results and Discussion
(1) Test for Composition of Al2O3 Films on HDPE Particles
The composition of HDPE particles (16 mm) before and after
coating was characterized by ex situ FTIR spectroscopy. As
shown in Fig. 2, the FTIR spectrum of the reference alumina
sample shows the Al2O3 bulk vibrational mode at the frequency
of 1100–500 cmꢃ1 and the vibration of the OH group at the
frequency of 3700–3000 cmꢃ1 25
No above-mentioned Al2O3
.
and OH group features are observed for uncoated HDPE par-
ticles. An Al2O3 vibrational mode and a broad OH group fea-
ture appear for coated particles after 25 and 50 cycles. This is a
direct confirmation of the composition of the Al2O3 films on the
polymer surface. For HDPE samples, the features at 3000–2800,
1460, and 720 cmꢃ1 are attributed to C–H stretching, deform-
ation, and rocking modes of CH2 groups.25
Two different sizes of HDPE particles (Lyondell Chemical,
Houston, TX) were used. One had an average size of 16 mm, and
the other had an average size of 60 mm. The density of both
primary particles was 952 kg/m3. The peak melting point was
1341C. For a typical run, about 20 g of HDPE particles were
loaded into the reactor. The feeding lines were kept at about
701C to avoid excessive absorption of H2O on the internal walls
of the system that could promote CVD reactions. The minimum
pressure inside the reactor was about 10 Pa and the minimum
fluidization superficial gas velocity was determined by measur-
ing the pressure drop across the bed versus the N2 superficial gas
velocity. Precursors, TMA (Sigma Aldrich, St. Louis, MO) and
deionized H2O, were fed separately through the distributor of
the reactor using the driving force of their vapor pressures. The
flow rate of TMA and H2O was adjusted using needle valves to
ensure that a precursor pressure was high enough for particle
fluidization. The reaction temperature was 771C, which was
lower than the softening/melting point of the HDPE particles.
Before the reaction, the particles were dried at 771C under a
continuous N2 flow for 3 h. During each coating cycle, the pre-
cursors were fed for enough time so that saturation of all active
sites occurred for every dose. A typical coating cycle occurred
with the following sequence: dose TMA, purge N2, evacuate;
dose H2O, purge N2, evacuate. In this manner, there is no over-
lap between the two reactants, and no CVD reactions occur.
A Fourier transform infrared (FTIR) spectrometer (Model
750 Magna-IR, Thermo Nicolet, Waltham, MA) was used to
analyze the composition of the HDPE particles before and after
coating. The particles were milled with FTIR grade potassium
bromide (Sigma Aldrich) to form a very fine powder. This pow-
der was then compressed into a thin pellet using a hydraulic
press and polished stainless steel die. An X-ray photoelectron
spectroscopy (XPS) system (Model PHI 5600, Physical Elec-
tronics, Chanhassen, MN) with a high-energy resolution ana-
lyzer was used for this study. Aluminum concentration on
HDPE particles was analyzed by inductively coupled plasma
atomic emission spectroscopy (ICP-AES; Model ARL 34101,
Thermo Electron, Waltham, MA). Analysis by ICP-AES was
achieved by placing the coated HDPE particles in a strong base
solution (NaOH) to dissolve the Al2O3 films from the HDPE
particles. The HDPE particle itself will not dissolve at normal
laboratory conditions. The conformality of the Al2O3 coatings
on the HDPE particles was evaluated by transmission electron
microscope (TEM; Model CM 10, Philips, Eindhoven, the
Netherlands). The morphology of the HDPE particles before
and after coating was investigated by scanning electron micro-
scope (SEM; Model JSM-6400, JEOL, Tokyo, Japan). The size
distribution of HDPE particles was performed using an Aero-
sizers particle size analyzer (Model 3225, TSI, Shoreview, MN).
Surface area analysis was performed using a physisorption ana-
lyzer (Model Autosorbs-1, Quantachrome, Boynton Beach,
FL).
XPS measurements were also performed on uncoated and
Al2O3 coated HDPE particles (16 mm) after 50 cycles. The anal-
ysis was performed using an aluminum source, pass energy of
187.85 eV, and an energy step of 0.2 eV. In Fig. 3, the spectrum
for the uncoated HDPE particles shows a photoelectron peak at
284.7 eV (C, 1s). In contrast, the carbon spectrum for coated
HDPE particles reveals much weaker photoelectron intensity at
284.7 eV. This reduction of carbon signal is expected if the
Al2O3 film conformally covers the entire polymer particle. The
carbon XPS signal cannot be completely attenuated as some of
it corresponds to surface carbon. Photoelectrons from the
Al2O3-coated HDPE particles are observed at 118.7 eV (Al,
2s), 73.9 eV (Al, 2p) and 530.7 eV (O, 1s). It is clearly evident
that there is only a single peak centered at 73.9 eV, which cor-
responds to Al–O bonds of Al2O3. The absence of a shoulder
region around 72.5 eV, which corresponds to Al–Al bonds,
clearly confirms that the aluminum metal is not present in our
films.28,29 So, the XPS results corroborate the FTIR results and
verify the composition of deposited Al2O3 films on the HDPE
particles.
(2) Uniformity of Al2O3 Films on HDPE Particles
In order to study the uniformity of Al2O3 films on HDPE par-
ticles, TEM analysis was performed at 100 kV on the coated
particles (16 mm) after 50 cycles. The TEM image in Fig. 4 shows
that an Al2O3 film was successfully coated on the particle sur-
face. The contrast between the film and the particle substrate is
given by the difference in density between Al2O3 and HDPE.
The thickness of the Al2O3 films is about 2374 nm, which
4.0
Alumina
Al O feature
2
3
After 50 cycles
After 25 cycles
Uncoated
3.0
2.0
1.0
0.0
The coated particles were extruded by a bench-sized, heated
extruder (Bonnot, Uniontown, OH) at controlled temperatures.
16 and 60 mm HDPE particles were extruded at 1351 and 1751C,
respectively. To extrude a ribbon of polymer, the ribbon die was
attached downstream of the heated barrel of the extruder.
HDPE/Al2O3 nanocomposite films comprising various levels
4000 3500 3000 2500
2000 1500 1000
500
−1
Wavenumbers(cm
)
Fig. 2. Fourier transform infrared spectra of uncoated high density
polyethylene particles, Al2O3-coated HDPE particles, and reference
Al2O3 powders.

60
Journal of the American Ceramic Society—Liang et al.
Vol. 90, No. 1
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Epoxy resin
Al O growth
2
3
Reduced C signal
for coated particles
(b)
(a)
1000
800
600
400
200
0
HDPE particle
Binding energy (eV)
Fig. 3. X-ray photoelectron spectroscopy spectra of (a) uncoated and
(b) Al2O3-coated high density polyethylene particles (16 mm) after 50
cycles.
200 nm
Fig. 5. Focused ion beam cross-sectional scanning electron micrograph
of Al2O3-coated high density polyethylene (HDPE) particle (60 mm) after
100 cycles.
represents a growth rate of about 0.5 nm per coating cycle at this
experimental condition. The Al2O3 films appear to be very uni-
form and smooth.
Focused ion beam (FIB) cross-sectional SEM imaging allows
precise observation at the edge interface of the polymer and
Al2O3 film. The FIB cross-sectional SEM image of HDPE par-
ticles (60 mm) after 100 cycles is shown in Fig. 5. Al2O3 islands
began to grow below the polymer surface and the film merged
into a linear layer as it grew. Approximately 3577 nm thick
Al2O3 films were coated on the polymer surface. This thickness
represents a growth rate of about 0.4 nm per coating cycle at this
experimental condition. The SEM image also shows that the
Al2O3 films appear to be very uniform and smooth.
The Al2O3 film growth rate was much higher than the 0.11–
0.13 nm per cycle of an ALD process reported in the literature.19
Recent FTIR measurements of Al2O3 ALD on low density
polyethylene (LDPE) indicated the presence of hydrogen-bond-
ed H2O molecules on the Al2O3 surface.25 This higher growth
rate may be explained by the presence of hydrogen-bonded
H2O. This H2O can react with TMA to deposit additional Al2O3
by CVD.25 Another reason is the increase in the surface cover-
age of reactants at lower temperatures.30,31 Though the reaction
kinetics is slower at lower temperatures, the growth rate is de-
termined by the higher surface coverage.30,31 Also, it is import-
ant to mention that the growth rate of films may vary with the
size and geometry of the substrate.22 For particles with a high
ratio of curvature, more active sites on the surface are exposed
to the gas phase reactants. The different initial surfaces may
partly explain the discrepancy between Al2O3 growth rates on
the HDPE particles and on some other substrates.
(3) Nucleation and Linear Growth of Al2O3 Films After
Nucleation
The concentration of aluminum on HDPE particles was ana-
lyzed by ICP-AES. ICP-AES provides the concentration in parts
per million (ppm) by mass of aluminum in relation to the HDPE
particles. The ICP-AES aluminum concentration versus number
of coating cycles is shown in Fig. 6. The average diameter of the
particles was 16 mm. The lower growth rate of Al2O3 before 25
cycles shows that there is a delay before film growth starts,
which verifies that a nucleation period is needed for the depos-
ition of Al2O3 on an HDPE particle surface.32 From this plot,
the nucleation period is 10 cycles at this experimental condition.
The Al2O3 ALD is conventionally thought to begin with na-
tive hydroxyl groups on the surface. HDPE, however, is one
kind of saturated hydrocarbon, which lacks typical chemical
functional groups such as hydroxyl species that are necessary to
initiate the growth of an inorganic film. So, the fundamental
concept of Al2O3 ALD cannot take place on the HDPE particle
surface. The nucleation of Al2O3 ALD on HDPE requires a
mechanism that does not involve the direct reaction between
TMA and HDPE. Consequently, an alternative mechanism is
needed to explain the Al2O3 ALD on HDPE.
HDPE has a porous surface, which is due to the interstitial
space between individual molecules as HDPE does not have the
regular lattice-type structure found in metals. Both HDPE and
TMA are nonpolar, so it is expected that TMA has a reasonable
solubility in the HDPE particles, and TMA can adsorb onto the
surface of the polymer and subsequently diffuse into the near-
surface regions of the polymer.25,32 During the ALD reaction,
5
1.2×10
5
1.0×10
4
8.0×10
4
6.0×10
Nucleation period
4
4.0×10
4
2.0×10
0
0
20
40
60
80
Coating cycles
Fig. 4. Transmission electron micrograph of Al2O3-coated high density
polyethylene particle (16 mm) after 50 cycles.
Fig. 6. Aluminum concentration on high density polyethylene particles
versus coating cycles.

January 2007
Polymer/Ceramic Nanocomposites by Atomic Layer Deposition
61
TMA will be first exposed to the HDPE particles and diffuse
into the bulk of the polymer matrix; therefore, the incoming
H2O will react efficiently with TMA molecules at or near the
surface of the polymer particles and Al2O3 clusters will be
formed. The pores on the particle surface will become smaller
and will gradually close with progressive coating cycles. After
several coating cycles, the Al2O3 clusters will eventually merge to
create a continuous adhesion layer on the polymer particle sur-
face. This phenomenon can be observed in Fig. 5. Al2O3 clusters
with hydroxyl groups will provide a ‘‘foothold’’ for the depos-
ition of Al2O3 films on the polymer. As shown in Fig. 6, the
concentration of aluminum is almost directly proportional to
the number of coating cycles after 25 cycles, which indicates a
constant growth rate and a linear dependence between the film
thickness and number of growth cycles after a nucleation period.
The model of the predicted growth mechanism is illustrated in
Fig. 7.
(4) Effect of Coating on Particle Size Distribution and
Surface Area
Fine particles will aggregate during fluidization because of in-
terparticle forces, such as Van der Waals forces.20 SEM was
used to analyze the morphology of the HDPE particles (16 mm)
before and after coating. SEM analysis was performed at 15 kV.
Figure 8 shows that no aggregates were coated; rather, particles
were coated individually.
This is also confirmed by the results of particle size distribu-
tion (PSD) of HDPE particles (16 mm) before and after coating.
The PSD curves for uncoated particles and Al2O3-coated par-
ticles after 50 cycles are shown in Fig. 9. As shown in the plot,
the size of particles remains fairly unchanged after the coating
process, meaning that no aggregates were being coated. If ag-
gregates of particles were coated and glued together, the size
distribution of particles after coating would drastically shift to
the right.
Fig. 8. Scanning electron microscopy of (a) uncoated and (b) Al2O3-
coated high density polyethylene particles (16 mm) after 75 cycles.
In addition to PSD analysis, Brunauer–Emmett–Teller (BET)
measurements indicated that the surface area of Al2O3 coated
HDPE particles (16 mm) after 50 cycles was 0.7270.02 m2/g,
which was very close to that of uncoated HDPE particles
(0.7070.03 m2/g). A drastic decrease in surface area, which
did not occur, would have indicated necking of particles.20 This
result also indicated that the individual particles were coated as
opposed to necking multiple particles together in the FBR.
sized inclusions of Al2O3 throughout the samples. The brightest
spots are areas in the films where the rough microtoming pene-
trated the films. In Fig. 10(a), the smaller image on the top left
corner represents one of the Al2O3 flakes at higher magnifica-
tion, which indicates that Al2O3 flakes were formed of much
smaller Al2O3 particles. The desired loading percent of Al2O3
can be controlled by adjusting starting polymer particle size. In
the case of HDPE particles with the size of 16 mm, as shown in
Fig. 10(b), more Al2O3 flakes were dispersed in the matrix, and
the Al2O3 flakes were dispersed more homogeneously. Hence,
the dispersion of Al2O3 flakes can be controlled by varying the
polymer particle size.
(5) Structure Information of Nanocomposite Films
The 16 mm Al2O3-coated HDPE particles after 75 cycles and the
60 mm Al2O3-coated HDPE particles after 100 cycles were ex-
truded to crush Al2O3 shell coatings. Remnants of the crushed
shell coatings were then dispersed throughout the polymer. The
extruded nanocomposite films were cut using a microtome to
achieve a thickness of approximately 100 nm for TEM analysis.
The cross-sectional TEM images of the nanocomposite films are
shown in Fig. 10. These two images show a scattering of nano-
IV. Conclusions
This work represents the first successful attempt to fabricate
polymer/ceramic nanocomposites by extruding nanocoated
1.2
Uncoated
~ TMA
~ Al O
~ TMA
~ Al O
1.0
After 50 cycles
2
3
2
3
0.8
0.6
0.4
0.2
0.0
HDPE polymer
HDPE polymer
(b)
(d)
(a)
(c)
~ TMA
~ Al O
~ TMA
~ Al O
2
3
2
3
0
20
40
60
Size (µm)
HDPE polymer
HDPE polymer
Fig. 9. Particle size distribution of uncoated and Al2O3-coated high
density polyethylene particles (16 mm) after 50 cycles.
Fig. 7. Proposed Al2O3 growth mechanism.

62
Journal of the American Ceramic Society—Liang et al.
Vol. 90, No. 1
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Nanocomposites,’’ Chem. Mater, 12 [7] 1866–73 (2000).
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G. A. D. Briggs, T. Miyamoto, M. Kano, Y. Tsukahara, and M. Yanaka, ‘‘Gas
Permeation in Silicon-Oxide/Polymer (SiOx/PET) Barrier Films: Role of the Oxide
Lattice, Nano-Defects, and Macro-Defects,’’ J. Membr. Sci., 208 [1–2] 75–88
(2002).
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Wertheimer, ‘‘A Study of Defects in Ultra-Thin Transparent Coatings on Poly-
mers,’’ Surf. Coat. Technol., 119, 1204–10 (1999).
14A. S. D. Sobrinho, G. Czeremuszkin, M. Latreche, and M. R. Wertheimer,
‘‘Defect-Permeation Correlation for Ultrathin Transparent Barrier Coatings on
Polymers,’’ J. Vac. Sci. Technol., A, 18 [1] 149–57 (2000).
15G. L. Graff, R. E. Williford, and P. E. Burrows, ‘‘Mechanisms of Vapor
Permeation Through Multilayer Barrier Films: Lag Time Versus Equilibrium
Permeation,’’ J. Appl. Phys., 96 [4] 1840–9 (2004).
Fig. 10. Cross-sectional transmission electron micrograph of (a) high
density polyethylene/Al2O3 nanocomposite extruded from 60 mm Al2O3-
coated HDPE particles after 100 cycles and (b) HDPE/Al2O3 nanocom-
posite extruded from 16 mm Al2O3-coated HDPE particles after 75 cycles.
16T. Suntola, ‘‘Atomic Layer Epitaxy,’’ Thin Solid Films, 216 [1] 84–9
(1992).
17S. M. George, A. W. Ott, and J. W. Klaus, ‘‘Surface Chemistry for Atomic
Layer Growth,’’ J. Phys. Chem., 100 [31] 13121–31 (1996).
18A. C. Dillon, A. W. Ott, J. D. Way, and S. M. George, ‘‘Surface Chemistry of
Al2O3 Deposition Using Al(CH3)3 and H2O in a Binary Reaction Sequence,’’ Surf.
Sci., 322 [1–3] 230–42 (1995).
polymer particles. Micron-sized HDPE particles were coated with
an ultrathin Al2O3 film in a fluidized bed reactor by atomic layer
deposition at a large scale. The FTIR and XPS revealed that
Al2O3 films were deposited on the polymer particle surface. TEM
and FIB cross-sectional SEM revealed ultrathin and conformal
Al2O3 coatings. A nucleation mechanism for Al2O3 atomic layer
deposition on the polymer surface was confirmed. The results of
ICP-AES suggested a nucleation period of 10 coating cycles, after
which, a linear dependence between the film thickness and num-
ber of growth cycles was verified. The results of SEM, particle size
distribution, and surface area of the uncoated and nanocoated
particles showed that the particles were not coated as agglomer-
ates during the coating process, rather as individual particles.
Al2O3-coated HDPE particles were successfully extruded into
HDPE/Al2O3 nanocomposite films by a heated extruder at con-
trolled temperatures. Cross-sectional TEM indicated that nano-
scale Al2O3 flakes were successfully dispersed in the polymer
matrix. The dispersion of Al2O3 flakes can be controlled by
varying the polymer particle size. The process, firmly depositing
nearly perfect nanometer thick ceramic films on polymer particle
surfaces by atomic layer deposition and then extruding the coat-
ed polymer particles into final products, will provide unparal-
leled opportunities to produce quality nanocomposites with
improved mechanical properties and reduced permeability in a
continuous high throughput process at low cost.
19A. W. Ott, J. W. Klaus, J. M. Johnson, and S. M. George, ‘‘Al2O3 Thin Film
Growth on Si(100) Using Binary Reaction Sequence Chemistry,’’ Thin Solid Films,
292 [1–2] 135–44 (1997).
20J. R. Wank, S. M. George, and A. W. Weimer, ‘‘Nanocoating Individual
Cohesive Boron Nitride Particles in a Fluidized Bed by ALD,’’ Powder Technol.,
142 [1] 59–69 (2004).
21J. R. Wank, S. M. George, and A. W. Weimer, ‘‘Coating Fine Nickel Particles
with Al2O3 Utilizing an Atomic Layer Deposition–Fluidized Bed Reactor (ALD-
FBR),’’ J. Am. Ceram. Soc., 87 [4] 762–5 (2004).
22L. F. Hakim, S. M. George, and A. W. Weimer, ‘‘Conformal Nanocoating of
Zirconia Nanoparticles by Atomic Layer Deposition in a Fluidized Bed Reactor,’’
Nanotechnology, 16 [7] S375–81 (2005).
23L. F. Hakim, J. Blackson, S. M. George, and A. W. Weimer, ‘‘Nanocoating
Individual Silica Nanoparticles by Atomic Layer Deposition in a Fluidized Bed
Reactor,’’ Chem. Vapor Depos., 11 [10] 420–5 (2005).
24G. D. Wilk, R. M. Wallace, and J. M. Anthony, ‘‘High-kappa Gate Dielec-
trics: Current Status and Materials Properties Considerations,’’ J. Appl. Phys., 89
[10] 5243–75 (2001).
25J. D. Ferguson, A. W. Weimer, and S. M. George, ‘‘Atomic Layer
Deposition of Al2O3 Films on Polyethylene Particles,’’ Chem. Mater., 16 [26]
5602–9 (2004).
26N. Kawakami, Y. Yokota, T. Tachibana, K. Hayashi, and K. Kobashi,
‘‘Atomic Layer Deposition of Al2O3 Thin Films on Diamond,’’ Diam. Relat.
Mater., 14 [11–12] 2015–8 (2005).
27A. Paranjpe, S. Gopinath, T. Omstead, and R. Bubber, ‘‘Atomic Layer De-
position of AlOx for Thin Film Head Gap Applications,’’ J. Electrochem. Soc., 148
[9] G465–71 (2001).
28Y.-C. Jung, H. Miura, K. Ohtani, and M. Ishida, ‘‘High-Quality Silicon/In-
sulator Heteroepitaxial Structures Formed by Molecular Beam Epitaxy Using
Al2O3 and Si,’’ J. Cryst. Growth, 196 [1] 88–96 (1999).
Acknowledgement
29W. S. Yang, Y. K. Kim, S.-Y. Yang, J. H. Choi, H. S. Park, S. I. Lee,
and J.-B. Yoo, ‘‘Effect of SiO2 Intermediate Layer on Al2O3/SiO2/n1-Poly
The authors thank Lyondell Chemical for providing the HDPE particles.

January 2007
Polymer/Ceramic Nanocomposites by Atomic Layer Deposition
63
Si Interface Deposited Using Atomic Layer Deposition (ALD) for Deep
Submicron Device Applications,’’ Surf. Coat. Technol., 131 [1–3] 79–83
(2000).
31J. W. Klaus, O. Sneh, and S. M. George, ‘‘Growth of SiO2 at Room Tem-
perature with the Use of Catalyzed Sequential Half–Reactions,’’ Science, 278
[5345] 1934–6 (1997).
30M. D. Groner, F. H. Fabreguette, J. W. Elam, and S. M. George, ‘‘Low-
Temperature Al2O3 Atomic Layer Deposition,’’ Chem. Mater., 16 [4] 639–45
(2004).
32C. A. Wilson, R. K. Grubbs, and S. M. George, ‘‘Nucleation and Growth
During Al2O3 Atomic Layer Deposition on Polymers,’’ Chem. Mater., 17 [23]
5625–34 (2005).
&