Nanoparticles by chemical synthesis,
processing to materials and innovative
applications
Helmut Schmidt*
Institut fu¨r Neue Materialien, Im Stadtwald, Gebaeude 43, 66123 Saarbruecken, Germany
Nanoparticles have been fabricated by using
chemical synthesis routes under specific condi-
tions. During a precipitation process from liquid
phases, surface controlling agents (SCAs) have
been added during or shortly after the formation
of precipitates. These interfere with the nucleat-
ing and growing particle to avoid agglomeration
and to control size. Nanoparticles from many
systems have been fabricated. If the SCAs are
bifunctional, the surfaces chemistry could be
tailored and the zeta potential of these particles
was tailored also. SiO2 particles have been used
for gene targeting using this approach. In other
investigations, FeOx nanoparticles have been
surface modified by amino groupings together
with a sonochemical route to obtain very stable
coatings. These particles have been used for in
vitro tumor cell penetration and hyperthermal
treatment. Boehmite nanoparticles were used to
serve as condensation catalysts to prepare very
hard transparent coatings for polycarbonate
and an overcoat with polymerizable nanoparti-
cles was used to produce anti-reflective and
ultrahard coatings. In systems with incorporated
fluoro silanes, leading to low surface free energy
coatings, nanoparticles were used to tailor the
fluorine depth profile in self-aligning transpar-
ent easy-to-clean coatings by influencing the
critical micelle concentration. The examples
show the usefulness of the chemical nanoparticle
approach for nanocomposite fabrication and the
high potential of these materials for medical and
industrial application. Copyright # 2001 John
Wiley & Sons, Ltd.
Keywords: nanoparticles; colloids; nanocompo-
sites; wet coating
1 INTRODUCTION
Nanostructured materials have been of interest
since the early 1980s and are mainly based on
papers where metallic nanoparticles have been
prepared by various gas-phase or vacuum methods,
and then are densified to nanostructured solids.1­5
These materials showed very interesting properties
that have been attributed to the high volume
fraction of interfacial structures that are different
from the crystalline structures of the core. The
investigations have been extended to ceramics,
where Niihara,6
in particular, has carried out many
investigations on ceramic nanocomposites, and
very interesting properties with respect to tough-
ness and strength have been reported. However,
despite the high very interesting potential of
ceramic nanostructured materials, with a few
exceptions, no broad industrial breakthrough has
taken place so far, despite the fact that many
companies have tried to commercialize these
concepts.
On the other hand, nanostructured powders
obtained by a flame pyrolysis process have been
commercial products for a long time, e.g. SiO2
or TiO2 (Aerosil1
, Cab-o-sil1
). Nanoparticles,
through colloidal chemistry in liquid environments,
play a role in many processes in nature, in industrial
processes (e.g. the fabrication of water glass), and
also in biology.7
Typical colloids are representative
of nanoparticles stabilized in solution in order to
prevent aggregation. The stabilization, in general,
takes place by the absorption of electric charges on
the surface, leading to a repulsion of the nanopar-
ticles as long as a critical distance is maintained.
This phenomenon was investigated by Stern at the
beginning of the 20th century.8
The utilization of
the colloidal route leads to interesting concepts for
the preparation of new nanostructured materials.
For this reason, many investigations have been
carried out on the so-called colloidal processing of
ceramics through sol­gel routes. Bowen and co-
workers at MIT developed routes for colloidal
APPLIED ORGANOMETALLIC CHEMISTRY
Appl. Organometal. Chem. 2001; 15: 331­343
DOI: 10.1002/aoc.169
Copyright # 2001 John Wiley & Sons, Ltd.
* Correspondence to: H. Schmidt, Institut fu¨r Neue Materialien, Im
Stadtwald, Gebaeude 43, 66123 Saarbruecken, Germany.
E-mail: schmidt@inm-gmbh.de
 Based on work presented at the 1st Workshop of COST 523:
Nanomaterials, held 20 ­22 October 1999, at Frascati, Italy.
processing of ceramics by centrifugation or pres-
sure filtration,9
but it was very difficult to obtain
sufficient green density through these routes. The
reason for this is that during the up-concentration of
the colloids, according to Stern's model, after the
particle distance becomes smaller than the critical
distance, the repulsion changes into attraction; this
leads to the formation of strong bonds between the
colloidal particles and a random network formation
that is characterized by a high porosity takes place.
This leads to low green densities with a bimodal
pore size distribution; the result is a two-step
sintering process with the closure of the small pores
and the enlargement of the large pores, and the
benefit of the small particles vanishes through this
effect.10
For this reason, the high expectations
attributed to colloidal routes for making ceramics
could not be fulfilled and colloidal processing
became rather unattractive in the past.
Nanoparticles and nanocomposites prepared by
precipitation or in situ formation in a given matrix
through the sol­gel processes have been investi-
gated for more than 10 years.11­81
This is an
interesting route for the fabrication of nanocompo-
sites by chemistry. In all these investigations, very
similar principles using alkoxides as a basis are
used. The idea of z-potential tailoring or surface
modification for compatibilization or specific
reactivity is only discussed in a very few papers.
Almost no data about processing and product
development are given. In order to obtain a
sufficient dispersion the particle surface has to be
compatibilized to the matrix, and surface modifica-
tion of the nanoparticles becomes an indispensable
means for the development of appropriate proces-
sing routes, or, as in the case that reactive
monomers are introduced into a given polymer,
nucleation and growth have to be controlled.
Another area of nanocomposites with polymer
matrices is clay-based systems.82­84
In the present paper, various aspects of nano-
particles and nanoparticle fabrication are discussed.
The main objective of this paper, however, is to
show how basic results of sol­gel and colloidal
chemistry can be used for industrial product
development. The sol­gel process, praised as a
route for the fabrication of novel materials with a
tremendous application potential now for more than
two decades, has not fulfilled the expectations by
far. Only in Japan, where many product-developing
industries have their own chemistry departments or
can share developments of in-house chemical
companies, is the situation quite different, and
many products are on the market.85
For this reason,
several examples for the preparation of materials
are chosen, and it is shown, how by appropriate
processing technologies industrial applications
have been developed starting from very basic
results. The preparation of nanocomposites by
chemistry will be summarized and a short overview
of some developments for materials for industrial
applications will be given. In these systems, an
intercalation process is required to delaminate the
stacks, which seems to be possible for many
polymers. The concentration seems to be limited
to about 15 vol.% due to the platelike shape of the
clay.
2. GENERAL CONSIDERATIONS
FOR COLLOIDAL ROUTES TO
NANOPARTICLES
The concept of fabricating nanoparticles by a
simple precipitation process seems to be intriguing.
But to overcome the problem of aggregation or
growth to micrometer-sized particles, and to obtain
processable particles, new concepts had to be
developed. The inorganic colloidal route is a
special case of a precipitation process with nuclea-
tion and growth to amorphous or crystalline
Figure 1 Scheme of the formation of agglomerates from
colloidal sols (sol­gel transition).
Figure 2 General scheme of a chemical route to nanoparticles
(after Refs 96 and 99).
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
332 Helmut Schmidt
particles. If the concentration of the feed is low and
the pH value of the solution is in a range that
surface charges are generated, colloidal particles
with diameters in the lower nanometer range are
accessible. This has been shown by Matijevich and
Her for many systems in very diluted solutions.86­88
The basics of these processes are also discussed in
the book by Scherer and Brinker.89
The utilization
of the colloidal state-of-the-art for the production of
nanostructured materials, however, was not a
matter of detailed investigations in the field of
sol­gel chemistry. However, recent investigations
including microwave and hydrothermal processing
have been used for nanoparticle systems.4
One of
the serious problems is the strong aggregation
during processing from sols to gels. This is shown
in Fig. 1, where the formation of low-density
aggregates is demonstrated. The intriguing per-
spective, however, is that through simple precipita-
tion processes a wide variety of composition is
available, ranging from simple oxides to chalco-
genides or even metals.90­95
For these reasons, a precipitation route under a
growth-controlling condition has been devel-
oped.96­98
This process is based on the hypothesis
that molecules able to interact with the particle
surface are influencing nucleation and growth
through the interfacial free energy. It could be
shown that the growth reaction follows rather
simple rules.99
It also could be shown that by use
of surface-controlling agents, very uniform particle
sizes in the nanometer range could be obtained.
Various types of component can be used as growth
and size-controlling agents, e.g. complex-forming
agents as b-diketones, which are very useful for
oxides, other complex ligands, like amines or
chelating agents, which have shown their useful-
ness for metals,100
or sulfides in the case of
chalcogenides like CdS2.101,102
It is postulated that
these components control the surface free energy
during the nucleation and growth process in a way
that very uniform particle size distributions are
obtained. This can be explained by assuming that an
optimal coverage of the surface with the surface
modifier exists that is specific for a given system
(leading to a free energy minimum), and that an
exchange of ions or molecules between the particle
can take place. In this case, as shown in Ref. 97.,
the particle size can be tailored by the feed-to-
ligand (surface-controlling agent, SCA) ratio. In
only a few papers, however, was an attempt made to
fabricate materials based on nanoparticles.100,101
Based on these considerations, a generalizable
process has been developed for the fabrication of
nanoparticles that is shown schematically in Fig. 2
and described in detail.96
In this process, liquid
precursors are used, which, as a rule, react with
water in the presence of H
or OH
and a specific
SCA to the corresponding precipitates. For multi-
component systems, diphasic systems, e.g. micro-
emulsions, are preferred.98
After precipitation,
separation processes like centrifugation or filtration
follow, after changing the zeta-potential to obtain
weak and reversible aggregation. After precipita-
tion, a composition like Y­ZrO2 is only poorly
crystallized. By employing the hydro- or solvo-
thermal process described in detail in the experi-
mental part in Ref. 103, fully crystallized nano-
particles of about 10 nm in diameter are obtained.
Similar results have been obtained by Komarneni
and coworkers.104,105
The surface modifiers fulfill
several requirements: they not only control nuclea-
tion and growth, they also prevent the agglomera-
tion and they provide a desired surface chemistry
for further processing. This is shown schematically
in Fig. 3 (bifunctional molecule or SCA approach).
As shown by Sanchez et al.106
or Naß and
Schmidt,107
b-diketones are suitable for surface
modification, but no data with respect to materials
synthesis are given. The surface chemistry em-
ployed is basically not different from the well-
known chemistry taking place on all types of solid
surface with reactive molecules. However, there is
a quantitative difference, since solid surfaces, in
general (with the exception of highly porous
adsorbents), only show the geometric surface,
which is distinctively below 1 m2
g1
. Nanoparti-
cles in the range of 10 nm in diameter, however,
show specific surface areas of several hundred
square meters per gram. This means the contribu-
tion of the surface modifiers to the chemistry of the
nanoparticles is several orders of magnitude larger
than on common solid surfaces. This also means
that the surface modifiers influence the chemical
nature of the nanoparticles remarkably, but, if small
molecules are used, they do not contribute very
much to the volume or the weight of these particles.
As is well known from Ref. 1, nanoparticles are
characterized by a large volume fraction of
`disordered' shell; the additional surface modifica-
tion leads to a three-phased system, consisting of a
well-ordered core, a less ordered shell and an
organic thin cover layer. As shown in section 3.1,
the coatings made from these particles show very
interesting properties with respect to densification.
The `construction principle' of this type of new
material is shown in Fig. 4. The assumption is made
that the organic layer is able to reduce the particle
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 333
to particle interaction and to allow a `gliding' of
one particle on the others surface. It is expected that
a denser packing than with uncoated particles is
obtained. Gels or layers prepared from unmodified
sols, in general, are porous due to the brittleness of
the structure. In addition to the surface chemistry,
the surface modifiers also may be used to tailor the
surface charge of the particles. In this case, the
modifiers have to be ionic, e.g. by use of amino
groupings. The surface charges are, for example,
measured by acoustophoretic measurement, which
is a very fast analytical method monitoring the
surface charge. Since the surface charge, in general,
is dependent on pH, the zeta potential (indicating
the quantity of surface charges), as a rule, is
measured as a function of the pH. The effect of
amino grouping modification of SiO2 on the zeta
potential is shown in Fig. 5. As one can see clearly,
the zeta potential is shifted considerably to positive
values, and, what is remarkable, at neutral pH a
high positive value is still maintained. This
principle has been used to fabricate SiO2 nanopar-
ticles for the binding of nucleic acid plasmids for
transfecting them into living cells.108,109
The
stabilization at pH 7 is of importance for the
processing of sols, for example in industrial coating
technologies where especially the use of acids to
stabilize sols leads to corrosion problems of
equipment. Using this approach, neutral sols have
been prepared from SiO2 and SiO2­Au sols110
for
dip coating purposes on glass. During firing at 450
to 500 °C, gold complexes made from Au3
and g-
aminopropyltriethoxysilane form gold nanoparti-
cles to produce the well-known gold ruby color.
Nanoparticles show the potential of introducing
specific properties into a given matrix. Table 1
shows a survey over basic properties and their
potential for application. It becomes clear that, for
Figure 3 Scheme of surface modifying and tailoring of
surface chemistry of nanoparticles (SCA concept).
Figure 4 Structural model of a Nanomer1
-type of inorganic­
organic nanocomposite.
Table 1 Some examples for properties and applications of nanostructured materials
Basic properties Physical effect Application
Small size low light scattering optical composites with transparent matrix
Small size high specific surface area low sintering ceramics, catalysts
electron/hole formation photocatalytic activity/TiO2 NLO in
semiconductors
Quantum effects plasmon resonance NLO in metal colloids, colors
Small size reinforcement high interface volume fraction polymer matrix nanocomposites (hard,
transparent, abrasion resistant, functional)
Size effect ferromagnetic  superparamagnetic properties magneto-fluids, energy and separation systems
Small size high excess energy low sintering ceramics, ceramic coatings,
ceramic additives
Small size transfectability into living cells gene targeting, transport vehicles into cells
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
334 Helmut Schmidt
the utilization of this potential, many developments
towards materials and processes are required.
By a combination of the solid-state properties of
the nanoparticles with properties obtained by the
surface modification and a polymeric glass-like or
ceramic matrix, an interesting material-tailoring
concept for nanostructured materials has been
developed. As one can see from Table 1, there are
many possibilities for the development of interest-
ing applications based on nanoparticles. This, of
course, is only a small section, but this indicates the
wide range of possibilities.
3. EXAMPLES FOR PRODUCT
DEVELOPMENTS
3.1 Development and processing
of magnetic nanoparticles
Iron oxides, such as magnetite or maghemite, are
ferromagnetic if multidomain structures are pre-
sent. By employing an external magnetic field, the
domains become aligned and, by influencing each
other, they also maintain a permanent magnetic
field when the external magnetic field is switched
off. Fe2O3 particles of this type of microstructure
show a strong hysteresis and are used for many
applications, like magnetic recording. The coupled
spins in the domains, however, have to fight against
the Brownian movement, and in single domain
systems, if the domain size gets below 10 to 6 nm,
Brownian movement at room temperature destroys
the spin coupling. This means that, after switching
off the external magnetic field, the magnetism
disappears and no hysteresis is to be found (super-
paramagnetism). Particle sizes distinctively above
10 nm show a multidomain structure with a
permanent magnetism. This leads to an attraction
of the particles and to aggregation. These aggre-
gates, however, are too large for some interesting
applications, for example for the transport of such
particles into living cells. For this reason, single-
domain particles with surface properties to keep
them stable at pH 7 have been developed.
Well-crystallized iron oxide particles can be
easily obtained by precipitation.111­114
However, in
general, these particles are strongly agglomerated,
and it is extremely difficult to obtain completely
redispersed distributions in the primary particle size
between 6 and 10 nm with a single-domain
structure. Fe2O3 shows a zeta potential with a point
of zero charge close to neutral; this means that these
particles flocculate or aggregate at neutral and
cannot be used in a biological environment. In Ref.
115, a process is described where FeOx particles
have been precipitated in presence of aminosilanes.
This leads to amino-grouping-coated FeOx parti-
cles. Owing to the weak bonding of SiOH
groupings to the surface of =FeOH, the stability
of the suspension is only maintained at low pH
values. To use such suspensions under neutral
conditions, a hydrolytically stable coating with a
zeta potential at pH 7 high enough to avoid
flocculation or agglomeration has to be established.
To obtain an amino grouping modification more
stable than described in Ref. 115, a sonochemical
process, the details of which are described else-
where, has been developed; this is shown in Fig. 6,
according to Refs 116 and 117. In this process, a
precipitation step has led to weak agglomerates.
After precipitation, amino silanes and ethylene
glycol have been added and the system is treated
with ultrasound. As one can see from Fig. 7, during
this treatment, the average particle size is reduced
remarkably and, at the same time, the particles are
coated by the amino silane. The self-condensation
Figure 5 Effect of amino groupings as surface modifier on
the zeta-potential curve of colloidal SiO2 (after Ref. 108).
Figure 6 Scheme of the precipitation and redispersion
process under sonochemical conditions.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 335
of the amino silane is carried out under conditions
where ultrasonic energy is used to enhance the
condensation, which leads to a very stable coating.
Without ultrasonic treatment, a simple reaction of
the iron nanoparticles with the amino silane does
not lead to a chemically stable coating. The
ultrasonic treatment leads to a stability between
pH 1 and pH 11 over a long period without change
of the zeta potential curve (testing period 12 h).
Through the amino silane treatment, the zeta
potential of the system is shifted to higher pH
values, so that at pH 7 a zeta potential of about
40 mV exists, as shown in Fig. 8; it is results in very
stable colloids at pH 7. This is attributed to a core­
shell structure that includes the formation of a
silicate-type of network, which is the only ex-
plaination for the strongly increased stability
compared with the `simple' surface modification.
A structural model is shown in Fig. 9. As shown
elsewhere,67
these particles do not show any
hysteresis and are completely superparamagnetic.
The positive zeta potential (40 mV) of the
particles is very important to obtain bonding to
the surface of proteins and for a high stability under
physiological conditions. These particles have been
shown to be preferentially consumed by tumor cells
very fast, and about 3 to 4 billion particles per cell
are consumed but are not digested.118
Even
daughter cells produced by the tumor cells show
the magnetic load. This means that the particles
affect neither the cell division, nor the metabolism.
By employing alternating magnetic fields, energy
can be introduced into the cells and they can be
destroyed by overheating (hyperthermal treatment).
This opens up interesting perspectives for cancer
treatment in the future.96,119
In other investigations,
iron oxide nanoparticles that have been surface-
tailored for certain polymer matrices have been
used for the fabrication of polymer matrix nano-
composites that are easily able to take up energy by
heating, and those are presently being developed
for many applications.120
The use of sonochemistry
seems to open up new preparation routes in
multifunctional nanoparticle synthesis, and more
investigations are necessary.
3.2 Nanocomposite hard coatings
The materials basis for nanocomposite hard coat-
ings is broadly used for plastic surfaces. Inorganic­
organic composites based on organoalkoxysilanes
and other alkoxides have demonstrated their
usefulness for hard coatings on eye-glass lenses.121
It has been shown that the addition of nanoparticles,
especially in combination with epoxy silanes,
which act as an inorganic as well as an organic
Figure 7 Reduction of particle size by ultrasonic treatment.
Figure 8 Change of the zeta-potential by the amino coating;
(a) untreated, after precipitation; (b) after modification and
ultrasonic treatment.
Figure 9 Structural model of a core­shell FeOx nanoparticle
with silicate-type bonds between the surface modifier.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
336 Helmut Schmidt
crosslinking agent, leads to a substantial increase of
the abrasion resistance of such systems without
losing any transparency.122,123
For the application of these systems on poly-
carbonate as a transparent scratch-resistant coating,
a very specific processing route has been devel-
oped. In general, the abrasion resistance of
transparent coatings is measured by the decay of
transmission by the scattered light after an abrasion
treatment by the taber abrader test (two alumina-
filled rubber wheels with 500 g load are abraded on
a 10 Â 10 cm2
plate). The haze is determined after
500 or 1000 revolutions. For example, the haze
value for float glass is about 1.5% after 1000 cycles,
for UV-curable hard coatings for polycarbonate on
automotive headlights it is about 15%, and for
uncoated polycarbonate it is over 30% after 100
cycles. In order to obtain very high scratch-
resistance values, a combination of several steps
has been carried out, which is shown in Fig. 10
(after Refs 124 and 125). For the synthesis, a
commercially available nanoparticulate boehmite
surface modified with acetic acid (1) is dispersed in
aqueous HCl. Here the `boehmite acetate' is
hydrolyzed to boehmite, which is followed by an
increase of viscosity.126
By addition of the
epoxysilane (2), a hydrolysis and condensation
reaction on the boehmite surface takes place,
leading to partially coated boehmite. The addition
of Al(OR)3 together with butoxyethanol leads to an
Al(OH)2­butoxyethanolate, which is a stable inter-
mediate and does not undergo further condensation
without solvent removal and heat treatment. By
addition of ethanol, the viscosity of the liquid is
adjusted to 20­100 mPa s for carrying out dip and
spin-on coating processes (5). At this point, as
shown by NMR, the epoxy grouping is still
unreacted. By heat treatment of these coatings
above 90 °C, the epoxy ring reacts to form a
polymeric chain (6),126
and by evaporation of
butoxyethanol the additional formation of AlOOH
from Al(OH)2­butoxyethanolate takes place. Com-
paring this process with the boehmite-free system,
far higher abrasion-resistance values and almost no
epoxy polymerization are observed. The difference
in abrasion resistance is shown in (7) in Fig. 10. For
the development of a practical product, several
problems had to be solved: the optimization was
carried out by statistical approaches. UV-protection
has been obtained through addition of UV-absor-
bers (Tinuvin) and CeO2 nanoparticles. The process
has been scaled up to batches of several hundred
Figure 10 Scheme of the preparation of a scratch-resistant boehmite nanocomposite coating and the effect of boehmite on the
abrasion resistance.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 337
kilograms. The abrasion resistance of 2% haze
meets specifications of automotive applications,
and this system is being used as a basis for the
development of plastic automotive glazing.
The sand-trippling shows lower haze numbers on
these coatings, similar to those of float glass, and
distinctively lower numbers than conventionally
available polycarbonate coatings. This is shown in
Fig. 11. This type of coating has been used as a
basic layer for the development of interference
layers by employing so-called polymerizable nano-
particles. The process is shown schematically in
Fig. 12.127
The coating materials are prepared
through a sol­gel synthesis of SiO2 nanoparticles,
which are reacted with methacryloxysilanes and by
a sol­gel synthesis of TiO2 nanoparticles, which are
coated with epoxy silanes, since with epoxy silanes
colored complexes are formed. After the addition of
a photoinitiator for the polymerization of the
methacrylates and the polyaddition of the epoxides,
a dip-coating process is carried out to form layer
thicknesses in the range 150­300 nm. For optical
purposes, interference layers according to the
refractive index ($1.90 for TiO2 and 1.45 for
SiO2) of the films have been developed. The
refractive index of TiO2 is surprisingly high for
only having undergone a photopolymerization
process. This is due to the high green density of
>90%, completely unusual for `gels'. This, how-
ever, shows clearly the effect of the formation of
the surface modification of nanoparticles, leading to
rather dense Nanomer1
structures; see Fig. 4. After
photopolymerization, abrasion resistant surfaces
with abrasion numbers down to about 1.5% haze
at 120 or 130 °C curing temperature are obtained.
This technique has been used for the fabrication of
antireflective layers on plastic by dip- and spin-
coating. For eye glass lenses, a so-called wet
process antireflective coating has been developed
that allows the fabrication of hard and antireflective
coatings on plastic lenses with one and the same
technique. Otherwise, hard coatings have to be
employed by wet coatings and antireflection coat-
ings by vacuum techniques.
3.3 Nanoparticles for
hydrophobicsuperhydrophobic
surfaces
As shown in Refs128 and129, nanocomposites have
been developed for the fabrication of low surface
free energy coatings. In these investigations, it
could be demonstrated that it is possible to obtain
self-aligning coatings. With nanoparticles incorpo-
rated into the matrix, high abrasion resistance can
be obtained. To promote good adhesion to different
substrates, like metals, ceramics and plastics,
adhesion promoters have been added. The self-
aligning process up-concentrates the perfluorinated
side chains of the silane at the surface, as proved by
ESCA profiling and time-of-flight mass spectro-
scopy measurements. The results can be interpreted
by a thermodynamically driven process of the
system to minimize the interfacial or surface free
energy. In the case of the fluorine-containing
compounds, the free energy minimum of the
fluorinated side chains can be achieved at the
atmospheric side rather than at the polar interface to
the substrate. This means that during the drying of
Figure 11 Comparison of the nanocomposite coating on
polycarbonate with glass and conventionally available coatings
(data with permission of Bayer AG).
Figure 12 Overview of the fabrication and application over
the boehmite nanocomposite for the fabrication of abrasion-
resistant overcoatings on hard coatings (a) or multilayer
coatings for abrasion-resistant coatings on polycarbonate (b).
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
338 Helmut Schmidt
mixtures, e.g. made from TEOS/MTOS epoxy or
methacryloxy silanes optionally, perfluorinated
silanes, e.g. (RO)3Si(CH2)2(CF2)8CF3(FTS), and/
or in combination with other alkoxides for the
fabrication of inorganic networks, a diffusion
process of the fluorinated silanes to the surface
takes place. The scheme of the process is shown in
Fig. 13.
Owing to the immiscibility of polar and fluori-
nated compounds, a maximum concentration of
fluorinated silanes in the liquid mixture in the
miscible regime exists. This can be determined by
measuring the surface tension of the mixture as a
function of the fluorine content. If the point of
immiscibility is reached (critical micelle concen-
tration, CMC), the surface tension reaches its
minimum. The CMC of methacryloxy or epoxy
silane based systems with TEOS, as a rule, ranges
from 0.5 to 2 mol% of FTS.130
For this reason, it
was of interest to investigate how far the addition of
nanoparticles influences the CMC. For this reason,
an FTS-containing system was prepared by reacting
a nanoscale boehmite suspension in EtOH, with an
FTS-containing alcoholic solution in 0.1 M HCl.131
The total content of the boehmite was 10 wt% of the
FTS 0.05 mol l1
. It could be shown that the surface
tension increases with time (Fig. 14). This can be
explained by a bonding of the FTS to the AlOOH
nanoparticles and a subsequent compatibilization of
the FTS to the system, as shown in Fig. 15 in a
structural model. If the surface tension is measured
as a function of the FTS content of these systems
with and without boehmite, the CMC is determined
from the surface tension versus the FTS content plot
by locating the intersection of the corresponding
straight lines, as shown in Fig. 17132
(CMC2 mol
l1
of FTS). However, it is very difficult to
determine the variation of the CMC in the case of
boehmite addition, because the curve cannot be
divided into two clear sections. However, it clearly
can be seen that it takes much higher concentrations
of FTS to obtain surface tensions as low as without
boehmite. This clearly points out that the CMC
must be much higher in the case of boehmite-free
systems, which again can be explained by the
model depicted in Fig. 15.
These results have been used to develop gradient
coatings for various applications. Owing to the
Figure 13 Self-aligning process for the preparation of low
surface free energy coatings.
Figure 14 Increase of the surface tension as a function of
time in a system containing 10 wt% boehmite ($20 nm) and
0.05 mol l1
of FTS.
Figure 15 Reaction of FTS for the formation of FTS-covered
boehmite nanoparticles.
Figure 16 Surface tension of a system containing 1.8 wt% of
boehmite (20 nm) as a function of the FTS content (epoxy
silane/TEOS/FTS composition according to Ref. 130).
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 339
thermodynamically driven gradient formation, the
adhesion of films obtained by simple wet coating
techniques could be solved for any type of substrate.
Owing to the content of nanoparticles, the coatings
are highly transparent. For applications, it is of
importance to know about the the fluorine concen-
tration as a function of the distance to the surface.
For these reasons, investigations133
with different
FTS concentrations under different reaction condi-
tions have been carried out. The matrix system used
for these experiments consists of methyl triethoxy-
silane (MTEOS), tetraethylorthosilicate (TEOS)
and FTS. The FTS content was varied between 1
and 12 mol%. The fluorine profile was determined
by ESCA analysis after repeated argon ion sputter-
ing. Important results of the investigations are
shown. Fig. 17 shows ESCA profiles of different
systems. HCl-catalyzed systems with 1% FTS (a)
without nanoparticles show high fluorine concen-
trations at the very top of the film of several
nanometers only, and show a strong decay down to
about 4% at 20 nm depth. The SiO2 nanoparticle-
containing system with 1 mol% FTS system with 28
mol% of SiO2 (b) shows a distinctively lower
surface concentration but a higher concentration at a
depth of 20 nm. This indicates that the SiO2 acts as a
CMC-increasing agent in a similar way to boehmite.
The NaOH-catalyzed system (d) shows a remark-
ably higher concentration at 20 nm, which is
attributed to the fact that NaOH is superior to HCl
as a condensation catalyst (c), immobilizing FTS by
forming larger fluorine-containing entities and
reducing their diffusion rate. The addition of
Zr(OR)4 alkoxides, which immediately forms n-
ZrO2, leads to the highest average profiles. This can
be explained by the ZrO2 acting as a condensation
catalyst123
as well as an immobilizer for FTS at the
same time. To find out how thick the fluorine-
enriched layer is, an SNMS analysis of the NaOH
system has been carried out. Fig. 18 shows the
profile, which demonstrates the layer is about 1 m
thick. These investigations show that nanoparticles
can be used for profile tailoring of gradient layers
very advantageously. The contact angles of these
layers with water vary between 90 and 110 °. Owing
to the low surface free energy, the adherence of dirt
and soil is reduced drastically, and coatings with
these properties can be considered as so-called
easy-to-clean (ETC) coatings. Based on these
results, many applications have been developed so
far, e.g. on sanitary ware (Wondergliss1
), for glass
windows, for stainless steel surfaces or for mold
release applications.
Meanwhile, a concept has been realized by
additional incorporation of larger particles (80­
100 mm). Coatings have been fabricated, and
surface roughnesses of about 150­200 nm have
been obtained. These (also self-aligning) systems
show contact angles of about 140­160 ° with water
and 100 to 110 ° with oil. The principle is shown in
Fig. 19.134
These rough surfaces lead to the so-
called superhydrophobicity, a principle that is used
by many plants, like plums, cabbage or the lotus
plant, in order to get rid of moisture. This principle
Figure 17 ESCA profiles of various FTS-containing coatings.
Figure 18 SNMS profile of the NaOH-catalyzed MTEOS/
TEOS/FTS system.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
340 Helmut Schmidt
at present is being developed further for specific
application.
4. DISCUSSION
For the transfer of basic results into industrial
applications, a specific approach has to be realized.
Besides the fulfilling of all specific requirements
defined by the customer, which, in general, can be
carried out under laboratory conditions, in most
cases a technology development has to be carried
out, since the majority of the industrial appliers of
materials are neither familiar with chemical
processing and synthesis of materials nor able to
develop the appropriate application technologies;
but of course, they are highly interested in novel
products. For this reason, a well-organized `vertical
interdisciplinarity' is linking together chemists,
physicists, engineers and production technologists
to develop customer-oriented new technologies
beginning at the materials basis. Using this
approach, in combination with the appropriate
technological equipment, is an indispensable pre-
requirement to process nanomaterials to products
close to the market as described above.
5. OUTLOOK
There is a huge potential for nanostructured
materials produced through chemistry in the future.
The large potential is mainly based on the needs of
the end users. In order to exploit these potentials,
developments close to the markets starting from
basic research are necessary. If this becomes more
common, nanostructured materials will obtain a
large and widespread significance in industry.
REFERENCES
1. Gleiter H. Nanocrystalline Materials, Prog. Mater. Sci.
1989; 33: 223­315.
2. Gleiter H. Mater. Sci. Forum 1995; 189­190: 67­80.
3. Gleiter H. Nanostruct. Mater. 1995; 6(1­4): 3­14.
4. Siegel RW. Nanomater.: Synth. Prop. Appl. 1996; 201­218.
5. Siegel RW. Adv. Top. Mater. Sci. Eng. 1991; 273­288.
6. Niihara K. Seramikkusu 1992; 27(4): 293­299.
7. Sto¨ber W, Fink A, Bohn E. Colloid Interface Sci. 1968; 26:
62­69.
8. Stern O. Z. Elektrochem. 1924; 30: 508.
9. Oguir Y, Riman RE, Bowen HK. J. Mater. Sci. 1988;
23(8): 2897­2904.
10. Hausner H, Roosen A. Adv. Ceram. Mater. 1988; 3(2):
131­137.
11. Sanchez C, Lebeau BP. Appl. Opt. 1996; 5(5): 689­699.
12. Koch T, Mennig M, Schmidt H. CIMTEC 1998.
13. Mark JE, Jiang CY. Macromolecules 1984; 17(12): 2613­
2616.
14. Wen J, Mark JE. Rubber Chem. Technol. 1994; 67(5):
806­819.
15. Garrido L, Mark JE, Sun CC, Ackerman JL, Chang C.
Macromolecules 1991; 24(14): 4067­4072.
16. Krug H, Mu¨ller P, Oliveira PW, Schmidt H. DE 19719948,
1998.
17. Lange F. International Symposium on Molecular Level
Designing of Ceramics. Team of the NEDO International
Joint Research Program: Nagoya (eds), 1991; 14.
18. Gan F. J. Sol­Gel Sci. Technol. 1998; 13(1­3): 559­563.
19. Sanchez C, Ribot F, Lebeau B. J. Mater. Chem. 1999;
9(1): 35­44.
20. Saravanamuttu K, Andrews MP, Najafi SI. SPIE 1998;
3417: 19­24.
21. Andrews MP, Saravanamuttu K, Touam T, Sara R, Du
XM, Najafi SI. SPIE 1998; 3282: 50­58.
22. Lal M, Joshi M, Kumar DN, Friend CS, Winiarz J, Asefa
T, Kim K, Prasad PN. Mater. Res. Soc. Symp. Proc. 1998;
519: 217­225.
23. Wong HP, Dave BC, Leroux F, Harreld J, Dunn B, Nazar
LF. J. Mater Chem. 1998; 8(4): 1019­1027.
24. Cordoncillo E, Viana B, Escribano P, Sanchez C. J. Mater.
Chem. 1998; 8(3): 507­509.
25. Blanc D, Peyrot P, Sanchez C, Gonnet C. Opt. Eng.
(Bellingham, Wash.) 1998; 37(4): 1203­1207.
26. Friend CS, Lal M, Biswas A, Winiarz J, Zhang L, Prasad
PN. SPIE 1998; 3469: 100­107.
27. Etienne P, Coudray P, Moreau Y, Porque J. J. Sol­Gel Sci.
Technol. 1998; 13(1­3): 523­527.
28. Chen Y, Chan HLW, Choy CL. ISAF '96, Proceedings of
the IEEE International Symposium on Applied Ferro-
electrics, 10th Annual Meeting, Hong Kong, 1996; 619­
622.
Figure 19 Scheme of the principle fluorine-containing super-
hydrophobic systems by a self-micropatterning process using
nanoparticles as a patterning tool.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 341
29. Hirano S, Yogo T, Kikuta K, Yamada S. Ceram. Trans.
1996; 68: 131­140.
30. Zhang Q, Chan HLW, Zhou Q, Choy CL. Chin. Sci. Bull.
1998; 43(2): 111­114.
31. Chen Y, Chan HLW, Choy CL. Thin Solid Films 1998;
323(1­2): 270­274.
32. Chen Y, Chan HLW, Choy CL. J. Korean Phys. Soc. 1998;
32 (Suppl.): 1072­1075.
33. Chen Y, Chan HLW, Choy CL. J. Am. Ceram. Soc. 1998;
81(5): 1231­1236.
34. Zhang Q, Chan HLW, Choy CL. Composites, Part A 1998;
30(2): 163­167.
35. Zhang Q, Chan LW, Zhou Q, Choy CL. Mater. Res.
Innovations 1999; 2(5): 283­288.
36. Chan HLW, Lau ST, Kwok KW, Zhang Q, Zhou QF, Choy
CL. Sens. Actuators A 1999; 75(3): 252­256.
37. Mark JE. International SAMPE Technical Conference
(Diversity into the Next Century). 1995; 27: 539­548.
38. Sarwar MI, Ahmad Z. Advanced Materials--97, [Pro-
ceedings International Symposium], 5th, Khan MA (ed.).
Dr A. Q. Khan Research Laboratories Kahuta: Rawalpin-
di, Pak, Islamabad, 1997; 73­77.
39. Motomatsu M, Takahashi T, Nie H-Y, Mizutani W,
Tokumoto H. Polymer 1997; 38(1): 177­182.
40. Gerard JF, Kaddami H, Pascault JP. Extended Abstracts--
EUROFILLERS 97, International Conference Filled
Polym. Fillers, 2nd Lyon, 1997; 407­410.
41. Reynaud E, Gauthier C, Perez J. Rev. Metall./Cah. Inf.
Tech. 1999; 96(2): 169­176.
42. Mauritz KA, Stefanithis ID, Davis SV, Scheetz RW, Pope
RK, Wilkes GL, Huang H-H. J. Appl. Polym. Sci. 1995;
55(1): 181­190.
43. Shao PL, Mauritz KA, Moore RB. Polym. Mater. Sci. Eng.
1995; 73: 427­428.
44. Shao PL, Mauritz KA, Moore RB. Chem. Mater. 1995;
7(1): 192­200.
45. Deng Q, Cable KM, Moore RB, Mauritz KA. J. Polym.
Sci. Part B: Polym. Phys. 1996; 34(11): 1917­1923.
46. Young SK, Deng Q, Mauritz KA. Polym. Mater. Sci. Eng.
1996; 74: 309­310.
47. Harmer MA, Farneth WE, Sun Q. J. Am. Chem. Soc. 1996;
118(33): 7708­7715.
48. Robertson MAF, Mauritz KA. J. Polym. Sci. Part B:
Polym. Phys. 1998; 36(4): 595­606.
49. Honma I, Hirakawa S, Yamada K, Bae JM. Solid State
Ionics 1999; 118(1­2): 29­36.
50. Dahmouche K, Santilli CV, Pulcinelli SH, Craievich AF.
J. Phys. Chem. B 1999; 103(24): 4937­4942.
51. Hu Z, Slaterbeck AF, Seliskar CJ, Ridgway TH,
Heinemann WR. Langmuir 1999; 15(3): 767­773.
52. Nunes SP, Schultz J, Peinemann K-V. J. Mater. Sci. Lett.
1996; 15(13): 1139­1141.
53. Hu Q, Marand E, Dhingra S, Fritsch D, Wen J, Wilkes G.
J. Membr. Sci. 1997; 135(1): 65­79.
54. Malla PB, Komarneni S. Mater. Res. Soc. Symp. Proc.
1993; 286: 323­334.
55. Okada A, Usuki. Mater. Sci. Eng. C 1995; 3(2): 109­115.
56. Gray DH, Hu S, Juang E, Gin DL. Adv. Mater. 1997; 9(9):
731­736.
57. Olivera-Pastor, Maireles-Torres P, Rodriguez-Castellon E,
Jimenez-Lopez A, Cassagneau T, Jones DJ, Roziere J.
Chem. Mater. 1996; 8(8): 1758­1769.
58. Ukrainczyk L, Bellman RA, Smith KA, Boyd JE. Mater.
Res. Soc. Symp. Proc. 1997; 457: 519­524.
59. Ukrainczyk L, Bellman RA, Anderson AB. J. Phys. Chem.
B 1997; 101(4): 531­539.
60. Chakravorty D. In New Materials, Joshi SK (ed.). Narosa:
New Delhi, India, 1992; 170­194.
61. Nakamura O, Saito Y, Nakamura H, Asai T, Ado K,
Haruta M, Kobayashi T, Tsubota S, Sakurai H et al. Osaka
Kogyo Gijutsu Shikensho Hokoku 1992; 386: 1­180.
62. Roy R. Mater. Res. Soc. Symp. Proc. 1993; 286: 241­250.
63. Roy R. Trans. Mater. Res. Soc. Jpn. B 1994; 19: 719­728.
64. Lantelme B, Dumon M, Mai C, Pascault JP. J. Non-Cryst.
Solids 1996; 194(1­2): 63­71.
65. Robertson MAF, Mauritz KA. Polym. Prepr. (Am. Chem.
Soc. Div. Polym. Chem.) 1996; 37(2): 248­249.
66. Courtois C, Rabih A, O'Sullivan D, Leriche A, Thierry B.
Key Eng. Mater. 1997; 132­136: 1010­1013.
67. Matejka L, Plestil J. Macromolecules Symposium, Inter-
national Symposium on Polycondensation, Related Pro-
cesses and Materials, 1996, Prague, Czech Republic,
1997; 191­196.
68. Tutorskii IA, Tkachenko TE, Malyavskii NI. Proizvod.
Ispol'z. Elastomerov 1997; 8: 6­10.
69. Ulibarri TA, Derzon DK, Wang LC. Annual Technical
Conference ­Society of Plastics Engineers, 55th, 1997; 2:
1925­1930.
70. Mohseni M, James PF, Wright PV. J. Sol­Gel Sci.
Technol. 1998; 13(1­3): 495­497.
71. Hay J, Raval H, Porter D. Chem. Commun. (Cambridge)
1999; (1): 81­82.
72. Yano S, Iwata K, Kurita K. Mater. Sci. Eng. C 1998; 6(2­
3): 75­90.
73. Senna M. Electrical Phenomena at Interfaces, Surfactant
Science Series, 76. Yokohama, Japan, 1998; 503­517.
74. Kang J, Park SH, Kwon HY, Park DG, Kim SS, Kweon H-
J, Nam SS. Bull. Korean Chem. Soc. 1998; 19(5): 503­
506.
75. Ahmad Z, Sarwar MI, Krug H, Schmidt H. Int. J. Polym.
Mater. 1998; 39(1­2): 127­140.
76. Asif KM, Sarwar MI, Rafiq S, Ahmad Z. Polym. Bull.
(Berlin) 1998; 40(4­5): 583­590.
77. Sharp KG. Mater. Res. Soc. Symp. Proc. 1998; 123­135.
78. Lebeau B, Sanchez C. Curr. Opin. Solid State Mater. Sci.
1999; 4(1): 11­23.
79. Saravanamuttu K, Du XM, Najafi SI, Andrews MP. Can.
J. Chem. 1998; 76(11): 1717­1729.
80. Sanchez C, Lafuma A, Rozes L, Nakatani K, Delaire JA,
Cordoncillo E, Viana B, Escribano P. Organic­Inorganic
Hybrid Materials for Photonics, SPIF 1998; 3469: 192­
200.
81. Tagaya H, Nagaoka T, Kuwahara T, Karasu M, Kadokawa
J-I, Chiba K. Micropor. Mesopor. Mater. 1998; 21(4­6):
395­402.
82. Messersmith PB, Giannelis EP. Chem. Mater. 1994; 6(10):
1719­1725.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
342 Helmut Schmidt
83. Reichert P, Kressler J, Thomann R, Muehlhaupt R,
Steppelmann G. Acta Polym. 1998; 49(2­3): 116­123.
84. Heckmann W, Ramsteiner F, Mehler C. Morphology of
polyamide nanocomposites by transmission electron
microscopy (TEM) and electron spectroscopic imaging
(ESI), oral presentation at Fall 2000 ACS National
Meeting, Washington, DC, 20­24/08/2000.
85. Sakka Y, Sodeyama K. American Ceramic Society 1998;
83.
86. Matijevic E. Langmuir 1994; 10(1): 8­16.
87. Matijevic E. NATO ASI Ser., 1996; 12: 1­2.
88. Matijevic E, Her YS. NATO ASI Ser., 1996; 18: 189­202.
89. Scherer GW, Brinker C. Sol­Gel Science: the Physics and
Chemistry of Sol­Gel Processing, Jeffrey (ed.). Academic
Press: San Diego, 1990.
90. Henglein A. Chem. Rev. 1989; 1861­1873.
91. Henglein A, Fojtik A. Ber. Bunsenges. Phys. Chem. 1987;
91(4): 441­446.
92. Henglein A, Gutierrez M. Ber. Bunsenges. Phys. Chem.
1983; 87: 852­885.
93. Schmid G. Bull. Pol. Acad. Sci. Chem. 1998; 46(3): 229­
235.
94. Schmid G, Peschel S. New J. Chem. 1998; 22(7): 669­675.
95. Schmid G, Klein N, Morun B, Lehnert A, Malm S, Olle J.
Pure Appl. Chem. 1990; 62(6): 1175­1177.
96. Schmidt H, Nonninger R. Proceedings of Fine, Ultrafine
and Nano Powders '98, New York, 1998.
97. Schmidt HK. Kona Powder and Particle 1996; 14: 92­
103.
98. Schmidt HK, Nass R, Burgard D, Nonninger R. Mater.
Res. Soc. Symp. Proc. 1998; 520: 21­31.
99. Schmidt H. Mater. Funct. Des. Proc. Eur. Conf. Adv.
Mater. Proce. Appl., 5th, 1997.
100. Mennig M, Schmitt M, Becker U, Jung G, Schmidt H.
SPIE 1994; 2288: 120­129.
101. Spanhel L, Arpac E, Schmidt H. J. Non-Cryst. Solids
1992; 147: 657­662.
102. Henglein A, Fojtik A, Weller H. Ber. Bunsenges. Phys.
Chem. 1987; 91(4): 441­446.
103. Burgard D, Naß R, Schmidt H. DE 19515820 A1, 1996.
104. Roy R, Komarneni S. Report (AD), 1993; 121.
105. Komarneni S, Menon VC et al. Ceram. Trans. 1996; 62:
37­46.
106. Sanchez C, Livage J, Henry M, Babonneau F. J. Non-
Cryst. Solids 1998; 100: 65.
107. Naß R, Schmidt H. Powder Processing Science. Deutsche
Keramische Gesellschaft: Ko¨ln, 1989; 69.
108. Schiestel T, Schirra H, Gerwann J, Lesniak C, Kalaghi-
Nafchi A, Sameti M, Borchard G, Haltner E, Lehr CM,
Schmidt H. Mater. Res. Soc. Proc. 1998; 65­71.
109. Kneuer C, Sameti M, Haltner EG, Schiestel T, Schirra H,
Schmidt H, Lehr CM. Int. J. Pharm. in press.
110. Mennig M. Personal communication, to be published later.
111. Pileni MP, Feltin N, Moumen N. Sci. Clin. Appl. Magn.
Carriers. Proceedings of International Conference 1st
1997; 117­133.
112. Feltin N, Pileni MP. Langmuir 1997; 13(15): 3927­3933.
113. Monroe LD, Erickson DD, Wilson DM, Wood TE. US
5611829, 1995.
114. Erickson DD, Monroe LD, Wood TE, Wilson DM. US
5645619, 1996.
115. Sieber W. WO 96/02060, 1996.
116. Schmidt H, Lesniak Chr, Schiestel T. F. Part. Sci. Tech.
1996; 23­642.
117. Lesniak Chr, Schiestel T, Naß R, Schmidt H. Mater. Res.
Soc. Proc. 1997; 122­134.
118. Jordan A, Scholz R, Wust P, Schirra H, Schiestel T,
Schmidt H, Felix R. J. Magn. Magn. Mater. 1999; 194(1­
3): 185­189.
119. Lesniak C, Schiestel T, Schmidt H, Jordan A. E 19726282
A1, 1997.
120. Nonninger R. In preparation.
121. Schmidt H, Seiferling B, Philipp G, Deichmann K. Proc.
Ultrastruc. Proc. Ceram. Glas. Comp. John Wiley & Sons:
San Diego, 1988; 651­660.
122. Kasemann R, Geiter E, Schmidt H, Arpac E, Wagner G,
Gerhard V. DE 4338361 A1, 1995.
123. Schmidt H, Kasemann R, Burkhart T, Wagner G, Arpac E,
Geiter E. ACS Symp. Proc. Ser. 585; 331­347.
124. Kasemann R, Schmidt H, Wintrich E. Mater. Res. Soc.
Proc. 1994; 346: 915­921.
125. Braune B, Geiter E, Krug H, Mu¨ller P, Schmidt H. DE
19630100 A1, 1996.
126. Geiter E. Dissertation.
127. Mennig M, Oliveira PW, Frantzen A, Schmidt H.
Proceedings of 2nd ICCG, 1998.
128. Schmidt H, Kasemann R. DE 4118184, 1991.
129. Schmidt H, Bru¨ck S, Kasemann R. Bol. Soc. Esp. Cer. C
1992; 31: 75­80.
130. Sepeur S. Masters Thesis, University of the Saarland,
1994.
131. Kra¨mer P. Master Thesis, University of the Saarland,
1997.
132. Sepeur S. Personal communication, to be published.
133. Schmidt H, Schmitjes O. Personal communication, to be
published.
134. Schmidt H et al. Personal communication, patent pending,
to be published later.
Copyright # 2001 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2001; 15: 331­343
Chemical synthesis of nanoparticles 343