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NEW METHODS FOR THE SYNTHESIS OF METAL/POLYMER
NANOCOMPOSITES
Luigi Nicolais
Institute of Composite and Biomedical Materials.
National Research Council. Piazzale V. Tecchio,
80 - 80125 - Napoli. Italy.
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Self-assembled organic monolayers
3D-Superstructures
Fullerenes and endohedrals
Molecular machines
Eterofullerenes
Polyfullerenes
TECHNOLOGY
Cluster compounds
Metal and semiconductor clusters
Special carbon structures
Nano-rods and nano-wires
Multi-walled nanotubes
Carbon nanotubes
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Biological Evolution
Nature has optimised the microstructure of the
tissues to fulfil the specific tissue function,
using a slowly but efficiently process of Trial
and Error (survival of the fittest)
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COMPOSITE IMPLANT TECHNOLOGY
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Natural Joints
Long bone
Vertebrae
Coupling through soft connective tissue

• Cartilage
• Ligaments
• Disc
• Synovial Fluids

disc
Temporo-Mandibular
Tooth-alveolar bone
MAIN
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Tissue Reconstruction Scheme
Partially Degradable and Biodegradable Scaffolds
synthesis
in vivo implantation Bone Ligament/Tendon Interve
rtebral Disc Cartilage Vitreous
BIOACTIVE MATERIALS
in vitro culture
cell seeding
or
Osteoblasts Chondrocytes Fibroblasts Etc.
in vitro tissue growing through bioreactors
MAIN
TISSUE ENGINEERING
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Tissue Engineering Approach
MAIN
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Cell Proliferate on Polymer Scaffolds

CaCo2 undergo spontaneous enterocytic
differentiation 20 days of culture showing
microvilli on the apical side, tight junctions
and enzymatic activities of brush border
hydrolases
MAIN
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MATERIALS FOR ADVANCED FUNCTIONAL APPLICATIONS
Available techniques for nanostructure handling
Self-Assembly
STM-Manipulation
Dielectrophoresis
Nanostructures
Nanocomposites
Characteristics
Characteristics
Polymer-embedding
Unique physic-chemical properties
Plastics functionalization
Unstable (aggregation, oxidation, etc.)
Nanostructure stabilization
Difficult handeling.
Easy handling, processing, and use.
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METAL CLUSTERS AND CLUSTER COMPOUNDS
Clusters nano-scale metallic crystal fragments
Atomic metal cluster formation
Naked atomic metal clusters
Metal cluster compound
Alkyl group
Sulphur atom
Surface Au atoms
HR-TEM image of a metal cluster
Structure of metal-organic interface
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THE ORIGIN OF NOVEL PROPERTIES
Quantum-size effects
Confinement
Surface effects.
3D-Periodic Table of Elements
Metal clusters behave just like atoms
Electron energies in a litium cluster
Electron states in a litium cluster
Examples of quantum-dot structures
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SURFACE EFFECTS
High percentage of surface atoms
Full-Shell Magic Number Clusters
Number of shells
4
5
3
2
1
Number of atoms in cluster
M309
M55
M13
M147
M561
Percentage of surface atoms
92
63
52
45
76
Different nature of surface atoms
B
B
A
C
A
C
0
10
5
20
SEM-micrograph of 3D self-organized poly(methyl
methacrylate) particles
The percentage of different atoms changes with
size decreasing.
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PROPERTIES OF MESOSCOPIC METALS
New magnetic properties
New catalytic properties
- Super-paramagnetism
- Super-catalytic effect
- Size-dependent ferromagnetism
New chemical properties
- New reaction schemes
- Stoichiometric heterogeneous reactions
- reactive noble metals, etc.
New transport properties
New optical properties
- Plasmon absorption
- Photo-luminescence, thermo-luminescence, etc.
New thermodynamic properties
Emission spectrum of Ag clusters irradiated at
254nm.
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SURFACE-PLASMON FILTERS
Color filters or UV-absorbers with
Intensive coloration at very low filling
factors
Light fastness
Plasmon resonance mechanism
High transparency
Possibility to fabricate ultra-thin color
filters
Color can be modified using alloyed clusters with
different compositions (e.g., Pd/Ag, Au/Ag)
1/l f1/l1 (1-f1)/l2
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HYDROGEN STORAGE SYSTEMS
Metal hydrides
Absorption/desorption curve
Metals reversibly absorb hydrogen producing
hydrides 2 Me H2 ? 2 MeH
H2(gas)
Metal cluster
Advantages
H
H
Fast absorption/desorption kinetic
H
Large amount of stored hydrogen
Dimensional stability
Reduction of decrepitation.
Unsatured polymer matrix (e.g., conductive
polymer)
Porous structure required for the nanocomposites.
Absorption mechanism
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MAGNETO-OPTICAL DEVICES
The Verdets constant of polymers can be
significantly increased by filling with
ferromagnetic nanoparticles (e.g., Fe, Co,
Ni). Nano-scale particles are required for
transparency.
Optical modulator
Applications
Optical insulators
Optical modulators
Optical shutters.
Optical insulator
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MICROWAVE ABSORBERS
Polymers do not absorb microwaves but filling
with metallic powders makes them high-absorbing
materials.
Microwave absorption mechanisms
Interfacial polarization
Magnetic loss (really effective)
HC
Single domine
Multi-domine
Pist n/r ? ?HdB (J/m3)
Super-para magnetic
Diameter
Applications
Antiradar varnishes
Hot-melts
Transparent EMI/RFI shielding materials
Microwave devices
Mechatronics
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TRANSPARENT DIFFUSION BARRIER AND OXYGEN
SCAVENGER SYSTEMS
Active iron
O2 N2 CO2
?
?
Polymer matrix
?
?
?
?
?
?
Electrolytes
N2 CO2
Nano-structured active diffusion barrier
Oxygen removal systems for food packaging
Chemical reaction involved at metal-polymer
interface
4Fe 3O2 ? 2 Fe2O3
The presence of an electrolyte (e.g., NaCl-)
significantly increases the oxygen scavenger
activity because a corrosion mechanism becomes
involved.
Tortuosity represents an additional barrier effect
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ULTRA HIGH/LOW REFRACTIVE INDEX MATERIALS
Optical plastics n ? 1.5-1.7
n2 2.8
Refractive index
n1 1.4
0
1
Metal
Non-linear behaviour of gelatin/Os nanocomposite
refractive index.
n ? f nplastic (1-f) nmetal
Applications
Plastic planar waveguides
Plastic optical fibers
Plastic lenses, prisms, etc.
Plastic optical fibers
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POLARIZATION-DEPENDENT COLOR FILTERS
Drawn bar
Extruded bar
Draw die
The cold-drawing technology
Plasmon absorption dependence on the polarization
direction
100nm
100nm
Pearl-necklace like microstructure produced by
cold-drawing
Dicroic devices made by nanocomposite
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SURFACE-PLASMON SENSORS
Vsp
Vsp
1,0
lmax f(d,n)
0,8
0,6
Absorbance
0,4
0,2
T
T
Tg
Tf
0,0
400
600
800
Polymer expansion above Tg and melting point
Wavelength (nm)
Optical fiber
- Fluid absorption
n
n
- Thermal expansion
Quartz window
d
d
Nanocomposite
Sample
Applications
- Liquid and gas sensors
- Thermo-chromic materials
- Bio-sensors
- Immuno-assay devices
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FURTHER APPLICATIONS
Non-linear optical devices
Not-opaque ionizing radiation shielding
(X-rays, a-, b, g-rays, cosmic rays, etc.)
Dielectrics for electrical super-capacitors
Antistatic films
Photo-thermal converters
Electro-optical devices
Component of phthalocyanine-based solar cells
Heterogeneous catalysts with selectivity
defined by the polymer nature
High-density recording media.
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NANOCOMPOSITE PREPARATIVE APPROACHES
Active metal preparation (chemical synthesis or
ball-milling)
Metal precursor synthesis
Surface passivation and isolation-purification of
the nano-sized powder
Polymer-precursor blending
Precursor decomposition (thermolysis, photolysis,
chemical reduction, etc.)
Polymer embedding process
Ex-situ synthesis
In-situ synthesis
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NANOFILLER PREPARATION the bottom-up vs. the
top-down approaches
Regular nano-sized powders
Bottom-up
Top-down
Irregural sub-micronic powders
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PREPARATION OF SUB-MICRONIC POWDERS BY
BALL-MILLING
Traditional Stirred Ball Milling
Milling
Cold welding
Bulk
Fine Powder
Owing to cold welding, mesoscopic metals are
difficult to be obtained by ball-milling.
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SOFT-CHEMISTRY TECHNIQUES FOR METAL CLUSTER
SYNTHESIS
Metal clusters are obtained by precipitation from
oversaturated metal solutions produced by the
action of a mild reductant on a metal salt.
Reduction
n e-
5 mm
Men
Me
Nucleation-growth
Me
m Me
Mem
Mem1
Mono-metallic clusters
Noble metals Au, Ag, Pd, Pt, Os, Ir, Ru, Rh, Re,
Hg
1 mm
Easy reducible metals Cu, Pb, Cd, Sn, Sb, W
Light transition metals Co, Ni, Fe
SEM image of Co particle obtained using different
Co(OH)2/ethylen glycol ratios.
Poly-metallic clusters
Alloys, multi-layered clusters, ecc.
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GOLD/POLYSTYRENE NANOCOMPOSITE PREPARATION
Colloidal gold solutions can be simply obtained
by alcoholic reduction of a gold salt in presence
of poly(vinylpyrrolidone) (PVP) as protective
agent.
Ligand-Exchange Reaction
-SR
-SR
RS-
m R-SH
-SR
RS-
RS-
PVP-embedded Au clusters
Thio-aurites
L.Nicolais et al. J. Mater. Chem. 13(2003)1038
Au clusters obtained by the exchange process
Au clusters embedded in polystyrene
Scheme of the synthesis process
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IN SITU SYNTHESIS OF NANOCOMPOSITES
Metal mercaptide synthesis
Alcoholic thiol solution
R-S- Me2 ? Me(SR)2 ?
or alternatively
Alcoholic salt solution
Me 2 R-SH Me(SR)2 H2?
L.Nicolais et al., Eur. Physc. J. B 31(2003)545
Mercaptide
SEM-picture of Co(SC12H25)2 film.
Metal mercaptide thermolysis
Me(SR)2 ? Me R-S-S-R
Co(SC12H25)2
The R nature is selected on the basis of the
polymer processing temperature.
Co
Characteristics of the mercaptide precursor
Decomposition temperatures (120-230C)
compatible with thermal stability of most
technopolymers
High-solubility in polymers
A large number of metal mercaptides gives metal
as thermolysis product
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METAL CLUSTER FORMATION
The LaMer model
I. Generation of metal atoms
Metal concentration
Me(SR)2 ? Me R-S-S-R
II. Atomic clustering
Nucleation concentration
Me Me Me2
Me2 Me Me3
..
..
Saturation
I
II
III
Men-1 Me Men
Time
III. Cluster growth
Men Me Men1
L.Nicolais et al., J. Mater. Chem. 13(2003)1-5
Cluster
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LARGE-SCALE METAL/POLYMER NANOCOMPOSITE PRODUCTION
The in-situ synthesis allows large-scale
nanocomposite production by many traditional
techniques already used for thermoplastic polymer
processing.
Metal precursor
.
.
.
.
.
Posible metal/polymer nano-composite artifacts.
.
.
.
.
Metal/polymer nano-composite
Microstructure of a Co/PS nanocomposite produced
by extrusion
Extruder and brabender machines
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CONCLUSIONS
The novel properties of nano-sized metals can
be used for plastic functionalization
A number of advanced functional devices can be
made by metal/polymer nanocomposites
Both ex-situ and in-situ metal cluster
formation techniques are being developed for
nanocomposite preparation
In situ synthesis allows large-scale production
of metal/polymer nanocomposites by the same
tecniques used for plastic processing.