PREPARATION OF NANOCOMPOSITES

1. PREPARATION OF
NANOCOMPOSIT
ES
CHINCHU KRISHNA
II MSc BPS
CBPST, KOCHI

2. A nanocomposite is as a multiphase solid material
where one of the phases has one, two or three
dimensions of less than 100 nanometers (nm),
OR
structures having nano-scale repeat distances
between the different phases that make up the
material.
NANOCOMPOSITES

3. Properties of Nanocomposites
 Tiny particels with very high aspect ratio, and hence
larger surface area.
 Larger surface area enables better adhesion with the
matrix/surface.
 Improvement in the mechanical performance of the
parent material.
 Better transparency due to small size(>wavelength of
light).

4. PREPARATION METHODS
 In situ polymerisation
 Melt mixing
 Solution mixing
 Precipitation
 Sol-gel process
 Electrospinning

5.  These methods enable the final
product with the following
characteristics :
 -Nano size particles
- Narrow particle size distribution
 - High surface area- Homogenous
 - Pure
 -Improved properties

6. SOL – GEL PROCESS
Sol–gel synthesis is a very viable alternative
method to produce nanocrystalline elemental,
alloy, and composite powders in an efficient
and cost-effective manner.
Sol-gel process involve the formation of sol
,followed by a formation of gel.
Sol is a colloidal suspension of solid particles in a
liquid phase
 Gel the interconnected network formed
between phases

7.  The sol-gel process is a wet-chemical technique that
is widely used to deposit nanocomposite films.
 In this process, sol (or solution) containing sources for
component materials, such as metal alkoxides and
metal chlorides precursors for metal oxides, metallic
nanoparticles for metals, tetraethoxysilane for silica
matrix, catalysers, stabilizers and other additives for
porosity generation, was prepared first.
 The sol then undergoes hydrolysis and
polycondensation reactions to evolve gradually
towards the formation of a gel-like network .
 The basic structure or morphology of the solid phase
can range anywhere from discrete colloidal particles
to continuous chain-like polymer networks.

8. The formation of the nanocomposite film from
the sol–gel precursor involves either dip coating
or spin coating on a substrate, decomposition
and pyrolysis of compounds, removal of water
and organics from the resulting network
followed by nucleation and growth of the
crystallites.
 The thermal decomposition behaviour of the
gel precursor plays an important role in
crystallites size and in film porosity.
Sol-gel is an excellent technique for preparing
high purity multicomponent films. Various types
of nanocomposite films have been prepared by
the sol-gel process and used as active materials
for gas sensors.

9. For example
OHHClOHHCSiOHC 252452 )( 
2SiO
OHHClOHHCSiOHC 252452 )( 
With diameter20-50nm
Nitration with NaOH
aerosol
Annealing with 600- 1000 C
Homogeneous mixture
Drying
Gel
Sol
Xerogel
Nitration with NH4OH
Drying in air
Glass of Nanoparticles
Drying with H in 1200 C and 1atm

10.  The preparation of a silica glass begins with an appropriate
alkoxide which is mixed with water and a mutual solvent
to form a solution.
 Hydrolysis leads to the formation of silanol groups (Si—OH).
 These species are only intermediates.
 Condensation reactions produce siloxane bonds (Si—O-Si).
 The silica gel formed by this process leads to a rigid,
interconnected threedimensional network consisting of
submicrometer pores and polymeric chains.

12.  During the drying process the solvent liquid is removed and
substantial shrinkage occurs.
 The resulting material is known as a xerogel. When solvent
removal occurs under hypercritical (supercritical)conditions,
the network does not shrink and a highly porous, lowdensity
material known as an aerogel is producd.
 Heat treatment of a xerogel at elevated temperature produce
viscous sintering
(shrinkage of the xerogel due to a small amount of viscous
flow) and effectively transforms the porous gel into a dense
glass.

13. During
formation
of gels,
sample
may
adhere to
wall and
cause
crack

14. Gel Drying
 Gel drying period, can get kinetic data from
weight loss
 Similar to ordinary drying process, classified as (a)
constant rate drying period; (b) reach a critical
point (prone to cracking); (c) first falling rate
period; (d) second falling rate period
 To prevent cracking during drying, control drying
rate (slow during certain period), some proposed
to add “drying control chemical additive
(DCCA) – objective: to lower capillary pressure, to
lower solvent pressure; or to use supercritical
evaporation method

15. A typical procedure for the preparation of PI/silica
hybrids via the sol-gel route,
 The polyamic acid (PAA) (PI precursor) is formed by a polyaddition
reaction of a di anhydride [e.g., pyromellitic anhydride (PMDA), 3,3′,4,4′-
biphenyltetracarboxylic dianhydride(BPDA), or 2,2-bis(3,4-dicarboxy-
phenyl)-hexafluoropropane dianhydride (6FDA)] with a diamine [e.g.,
4,4′-oxydianiline (ODA), or p-phenylene diamine (PPA)] in a common
solvent [e.g., dimethylacetamide (DMAc), or N-methyl pyrolidone (NMP)].
 The reaction and chemical structures of monomers are reported in fig.
Figure 1. Formation of polyamic acids, the precursor of
polyimides

16.  This method consisted of the silica
precursor [e.g., tetraethoxysilane(TEOS)
or tetramethoxysilane (TMOS) is added to
the PAA solution, and the hydrolysis and
polycondensation is carried out using an
appropriate catalyst.
 The PAA/silica solution is film cast by
drying the solvent, and then the film is
cured by successive heating treatments up
to 300°C.
 The heating induces the imidization
reaction to convert PAA to PI and the
crosslinking of the siloxane
component to form a silica

17. The prime requisite for obtaining
good quality in sol-gel process
 Variation of PH
 Temperature
 Time
 Concentration of Reagent
 Concentration of Catalyzor
 Phase transition Sol Gel
 Drying

18. One of the most interesting advantages of
the use of sol-gel method is its compatibility
with polymers and polymerization processes,
which allows the formation of nanoparticles
in the presence of organic molecules.

19. Advantages of Sol-Gel Processes
 Able to get uniform & small sized powder
 Can get at low temperature high density glass, without
high temperature re-crystallization
 Can get new compositions of glass
 New microstructure and composition
 Easy to do coating for films
 Can get objects or films with special porosity

20.  For improved adhesion
 Can get metal (inorganic) –
organic composites
 Can coat onto large area or
complex shape objects
 Can get fibers

21. ELECTROSPINNING
 Electrospinning is a unique technique for
producing polymer nanofibers with nanofillers.
It is a promising method for producing an
extremely light weight coating, where
nanoscale polymer fibers with a large specific
area are produced on a substrate from a
polymer melt, solution, or dispersion.
The nanoparticle functionalities are
incorporated into the fibers, as with fillers in
polymers that reinforce or increase the
electrical conductivity of the fibers.

22. Every polymer solution and dispersion has a
unique fiber-forming limit, above which a
continuous fiber network is obtained.
The solvent evaporates from the polymer
dispersion jet as it travels to the substrate in
electrospinning, and a polymer nanofiber or -
drop nanocomposite deposits on the substrate.
 A non-miscible third component can be used
to encapsulate the filler in emulsion drops
during travel. It must evaporate during the
travel from the electrode to the substrate.

23. The polymer solution and dispersion properties
influence the electrospun polymer/nanoparticle
fiber and network formation.
 Bead-like polymeric structures may appear.
The fiber diameter, the network structure, and
the filler distribution along the fibers can be
controlled by modifying the dispersion
properties, such as
 the molecular weight of the polymer,
 the interactions between the component
 concentration of the polymer and the filler in the
dispersion,

24. The processing parameters, such as
 the voltage between electrodes
 their distance
 the feeding rate.
 Filler particle agglomerates can disturb the flow
of a spinning dispersion and the formation of a
continuous jet.

25. Viscosity is one of the main factors influencing
composite formation in electrospinning
because it determines the formation of the
electrospun fiber and the network structure.
 It is relatively easy to change viscosity by
 1) changing the concentration of the filler and
polymer,
 2) changing the feeding order of the
components during the mixing,
 3) changing the pH of the solution,
 4) tailoring the interactions between the
components by functionalizing the components
in the solution.

26. Electrospraying is a process similar to
electrospinning but is used when the viscosity of
the liquid is sufficiently low.
The electric charge draws the liquid from the
capillary nozzle in the form of a fine jet, which
eventually disperses into droplets
 The droplets produced by electrospraying are
highly charged, usually close to one-half of the
Rayleigh limit, and can be smaller than 1 mm.
The size distribution of the droplets is usually
narrow,with low standard deviation.

27. Electrospraying can be used for the production
of small, nearly monodisperse particles when a
colloidal suspension of solid nanoparticles or a
solution of a material is sprayed .
In electrospraying the size of the droplets can be
controlled mainly by the liquid flow rate, and the
droplet charge by adjusting the voltage applied
to the nozzle.
The charged aerosol is selfdispersing, which
prevents the droplets from coagulation.

28. a) b)
Fig.ure 1. Schematic of the methods for the production of
nanocomposite mats: a) in a two-step process: electrospray deposition
after electrospinning; b) via simultaneous electrospinning and
electrospraying from two separate nozzles.

29.  Experiment
 Fibres were electrospun from a stainlesssteel capillary of
0.45 mm o.d. and 0.25 mm i.d. diameter, and 15 mm
length, placed horizontally.
 The fibres were collected on an aluminium drum of 60
mm diameter, covered with aluminium foil (10 mm thick),
rotating at a rotational speed of about 3000 r.p.m.
 The distance between the nozzle tip and the drum was
about 120 mm.
 In the simultaneous electrospraying process, a second
capillary nozzle of 0.7 mm o.d. and 0.5 mm i.d. diameter
was placed vertically above the drum.
 This nozzle served as a source of nanoparticles which
were deposited onto the fibres on the rotating drum. The
distance between the nozzle tip and the drum was 50
mm.
 In the two-step process: consecutive electrospraying
after electrospinning, the electrospun nozzle was
replaced with an electrospray nozzle.

30.  The electrospinning process was carried out at a 1 ml/h flow rate
of polymer solution for a time of 30 to 60 min.
 The particle colloidal suspension was electrosprayed at a flow rate
of 0.5 ml/h for a time of 30 - 60 min.
 The polymer solutions and particle suspensions were supplied to
the nozzles using two syringe pumps.
 In these experiments the voltage and distances were adjusted for
each configuration and particle suspension separately in order to
obtain a stable multijet mode.
 Although the viscosity of the polymer solutions was not measured
due to the large volume of solution required for such
measurements.
 The concentration of each polymer in a suitable solvent was
chosen experimentally in order to obtain a stable electrospun jet
that produced even, bead and pore free fibres.
 Before deposition, the particles were stirred for a time of 20 h in
methanol with an addition of surfactant in order to stabilise the

31. EXAMPLE :
 Polyurethane/ montmorillonite (PU/MMT) nanocomposites were
electrospun and the effect of MMT on the morphology and physical
properties of the PU/MMT nanofiber mats were investigated for the
first time.
 The average diameters of the PU/MMT nanofibers were ranged
from 150 to 410 nm.
 The conductivities of the PU/MMT solutions were linearly increased
with increasing the content of MMT, which caused a decrease in
the average diameters of the PU/MMT nanofibers.
 The electrospun PU and PU/MMT nanofibers were not microphase
separated.
 The exfoliated MMT layers were well distributed within the PU/MMT
nanofibers and oriented along the fiber axis.
 When the PU/O-MMT nanofibers were annealed, the exfoliated
MMT layers hindered the microphase separation of the PU.
 The electrospinning of PU/MMT nanocomposites resulted in PU
nanofiber mats with improved Young's modulus and tensile strength.

32. a
)
b
)
Figure 3. SEM images of PVC electrospun fi bres with deposited MgO nanoparticles
(particle concentration: 0.6 wt.%): a) Simultaneous electrospinning and
electrospraying process; b) Postspinning deposition.
a
)
b
)
Figure 4. SEM images of PVC electrospun fi bres with deposited Al2O3 nanoparticles (particle
concentration: 0.6 wt.%): a) Simultaneous electrospinning and electrospraying process; b) Postspinning
deposition.

33. CONCLUSION
The progress in nano composites is varied and covers many industries.
Nano Composites can be made with a variety of enhanced physical,
thermal and other unique properties.
They have properties that are superior to conventional micro scale
composites synthesized using simple and inexpensive techniques.
Materials are needed to meet a wide range of energy efficient applications
with light weight, high mechanical strength, unique color, electrical
properties and high reliability in extreme environments.
Applications could be diverse as biological implant materials, electronic
packages and automotive or aircraft components. Although some of the
properties will be common between the applications, others will be quite
different.
An electronic package polymer composite must be electrically insulating,
while an aircraft component may need to be electrically conductive to