Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 744-756
Published Online July 2012 (
Preparation and Characterization of Electrically and
Thermally Conductive Polymeric Nanocomposites
Mousam Choudhury, Smita Mohanty, Sanjay K. Nayak*, Rakesh Aphale
Laboratory for Advanced Research in Polymeric Materials (LARPM), Central Institute of Plastics
Engineering & Technology, Bhubaneswar, India
Email: *
Received June 1, 2012; revised July 5, 2012; accepted July 22, 2012
The dielectric properties of composites and nanocomposites composed of epoxy resin as base matrix and AlN (Alumi-
num Nitride) as micro and nanofiller has been studied at variable loading of AlN. To improve the dispersion of the filler
within the polymer matrix, AlN was surface modified with silane coupling agent (SCA). The thermal conductivity be-
havior of epoxy/AlN composites and nanocomposites has been studied at variable percentage of filler and temperatures.
Test result indicated an increase of thermal conductivity of the composites at 20 wt% of AlN. Also, silane treated com-
posites exhibited improved electrical conductivity properties wherein the electrical insulation property decreased in
terms of di-electric strength and resistivity.
Keywords: Epoxy; Micro-AlN; Nano-AlN; Insulation; Electrical Properties; Resistivity
1. Introduction
Ceramic filler reinforced polymer composites have gen-
erated considerable interest in the recent years in the ar-
eas as of electronic packaging. Relative case of processi-
bility and excellent flexibility in these composites has
driven them as potential candidates for development of
devices for electric stress control and high storage capa-
bility and high permittivity material.
Epoxy, a versatile thermoset resin has been widely
utilized as a packaging and insulating material in elec-
tronic and electrical industries, due to its high resistivity,
low dielectric constant and excellent processibility. How-
ever, certain impediments like low thermal conductivity
and high CTE of these polymers have resulted in thermal
failure during its enduse application. Moreover, in addi-
tion to thermal and electrical properties, mechanical
properties of epoxy resin as a substrate and packaging
material also plays a vital role.
Several investigation pertaining to improving the
stiffness and strength in the electronic packaging materi-
als with the use of inorganic fillers like (Al2O3, SiO2,
ZnO and BeO) [1-6] have been suggested. Similar other
fillers such as silicon carbide SiC [3,7,8], nitride (AlN
and BN) [1-3,5,7-18] and carbon based materials are also
known to effectively resolve the problems of thermal
Aluminium nitride (AlN), an inorganic/ceramic filler
with high intrinsic thermal conductivity (319 W/mK) [19]
high electrical resistivity (>1014 ·cm) [20], low dielec-
tric constant (8.9 at 1 MHz) [20] and low cost has gener-
ated considerable research interest as a reinforcing agent
in the recent years. Various researches on polymer/AlN
composites with modified CTE, tensile strength and di-
electric constant have been performed and reported.
In the present study, AlN—epoxy composites prepared
using solvent casting technique has been investigated.
AlN particles at micro and nano levels have been used as
a reinforcing filler to evaluate its effect on thermal and
electrical conductive properties of the epoxy resin. Also
AlN has been modified using wet-reflux method and
silane based coupling agent has been used to improve the
compatibility with the matrix polymer. Various proper-
ties such as dielectric strength, volume and surface resis-
tivity, thermal conductivity of the composites and nano-
composites have been studied. Also, the morphology of
the composites has been investigated employing scan-
ning electron microscopic technique.
2. Experimental
2.1. Raw Materials
Aluminium Nitride (AlN) with an average diameter of
less than 4 µm was obtained from M/s Accer chemicals,
Mumbai. Nano size AlN of less than 100 nm was pro-
cured from Aldrich chemicals.
The epoxy resin used in the present study was liquid
*Corresponding author.
Copyright © 2012 SciRes. JMMCE
diglycidyl ether of Bisphenol-A type (Araldite LY556)
with an equivalent weight per epoxide group of 195
g/mol, has been supplied by M/s Marshal polymers, Kol-
kata, India. The hardener Triethylene tetramine (TETA,
HY951) was also obtained from M/s Marshal Polymers,
Kolkata, India.
γ-Aminopropyl-triethoxysilane (A1100) with a chemi-
cal formula C6H17NO3Si, having a density 1.027 g/cc was
purchased and used as a coupling agent, from M/s Sigma
Aldrich, India. All other reagents of AR grade have been
used as such without any further modification.
2.2. Surface Modification of AlN Particles
The surface modification of AlN Particles using γ-ami-
nopropyl-triethoxysilane coupling agent was carried out
using wet-reflux method. In wet reflux method the etha-
nol/water/AlN mixture was sonicated for 90 minutes with
addition of 10% silane by weight of AlN. The amount of
coupling agent used, was 10 wt% based on the weight of
the AlN powder.
Coupling agent/ethanol solution was slowly added to
90% ethanol and 10% water mixture by a dropping fun-
nel. Then the mixture was stirred continuously for 2 h
and AlN powder was added subsequently. The coupling
agent/ethanol/AlN powder mixture was stirred using an
electric mixer for 3 h at 80˚C. The resulting slurry was
centrifuged at 12000 rpm for 15 min and then washed
with ethanol. The surface modification of particles using
γ-aminopropyl-triethoxysilane is represented in the reac-
tion scheme (Figure 1).
2.3. Synthesis of Epoxy/AlN Micro and
Nanocomposites Using Casting Technique
Epoxy/AlN micro and nanocomposites were prepared us-
ing casting technique, initially; required quantity of AlN
powder was added to the epoxy resin and stirred. Then
the hardener TETA of desired amount was added to the
epoxy/AlN mixture and resulting mixture was stirred
vigorously to ensure homogenous dispersion of the AlN
within the epoxy matrix. Finally, the mixture was poured
onto stainless steel mold, pre-cured in an oven at 135˚C
for 3 h and then maintained for 12 h at ambient tempera-
ture. The post curing was carried out at 80˚C for 2 h,
100˚C for 1 h and 120˚C for 2 h respectively. Then the
mold were left in the oven and allowed to cool gradually
to room temperature. Similar procedure was also em-
ployed for preparation of epoxy/AlN nanocomposite. In
case of epoxy/AlN microcomposites both surface-treated
and untreated AlN have been fabricated. The composi-
tions in both surface-treated and untreated epoxy/AlN
composites are maintained the same as shown in the Ta-
ble 1. Various compositions prepared have been high-
lighted in the Table 1.
2.4. Characterization
2.4.1. Density Test of Composites and
The density test of the epoxy/AlN composites and nano-
composites was measured by the Archimedes principle
using alcohol as the medium. The theoretical densities in
the sample were calculated based on the density of AlN
of 3.26 g/cm3 and the measured density of the epoxy.
The volume percent of filler was determined from the
density of the neat epoxy and filler.
2.4.2. Dielectric Breakdown Strength
Dielectric breakdown strength was measured using OTS-
100 AF/2, alternating current dielectric strength tester
(Meggera OTS, UK) in accordance with ASTM D 149 -
2004. Specimen of 50 mm dia and 3 mm thickness were
placed between two 10 mm diameter copper ball elec-
trodes and the electrode system containing the measured
sample was immersed in the pure silicone oil to prevent
the surface flashover. The test voltage was applied across
two ball-typed electrodes and was increased until the
sample was punctured. Five breakdown tests were re-
peatedly performed on each specimen. All of the meas-
urements were performed under the same humidity and
2.4.3. Volume Resistivity
Volume resistivity in the samples was measured using
Ultra Megaohm Meter (SM-8220, TOA Electronics Ltd.,
Japan) in accordance with ASTM D 257. Square samples
of 100 mm × 100 mm × 8 mm were taken for measure-
ment of the resistivity in the samples.
2.4.4. Thermal Conductivity
The thermal conductivity (W/mK) was calculated by the
product of the thermal diffusivity (mm2/s), specific heat
(J/gK) and density (g/cm3), using Unitherm 2022 (Anter
Corpo, USA) thermal conductivity tester according to
Table 1. Composition of epoxy/AlN micro and nanocompo-
Specimen Composition Epoxy
Epoxy + Hardener + 0% AlN88 12 0
Epoxy + Hardener + 5% AlN83 12 5
Epoxy + Hardener + 10% AlN78 12 10
Epoxy + Hardener + 20% AlN68 12 20
Epoxy + Hardener + 30% AlN58 12 30
Epoxy + Hardener + 5% nAlN83 12 5
Epoxy + Hardener + 20% nAlN68 12 20
Copyright © 2012 SciRes. JMMCE
Copyright © 2012 SciRes. JMMCE
Figure 1. The schematic reactions of AlN particles and silane.
ASTM E 1530. Circular samples of 50 mm diameter and
3 mm thickness, flat on both the sides were taken for
measurement of thermal conductivity. The samples were
coated with a thin graphite layer on both front and back
sides to increase the emission/absorption behavior at
variable temperature conditions at 25˚C, 50˚C and 75˚C
2.4.5. Thermo Gravimetric Analysis (TGA)
The thermal stability in surface-treated and untreated
AlN particles along with the composite and nanocompo-
site samples have been studied employing TGA analysis
(TGA, Q50, TA Instruments, USA). All the samples
were scanned from 50˚C to 600˚C at a rate of 10˚C/min
under N2 atmosphere. Corresponding degradation tem-
peratures and percentage char have been reported.
2.4.6. Dynamic Mechanical Analysis (DMA)
DMA was carried out for composites and nanocompo-
sites using a dynamic mechanical thermal analyzer (Q
800, M/s TA Instruments, USA). The samples were
scanned in tension mode from 30˚C to 200˚C at a heating
rate of 10˚C/min and fixed frequency of 1 Hz. Corre-
sponding dynamic modulus, loss factor and Tg was de-
2.4.7. Scanning Electron Microscopy (SEM)
The dispersion characteristics of the epoxy/AlN compos-
ites and nanocomposites have been studied employing
scanning electron microscope (EVMA—15 Carl Zeiss,
UK). Prior to imaging a thin section of the fractured sur-
face of the sample was mounted on the aluminium stub
using a conductive silver paint and was coated with gold
prior to fractographic examination.
3. Results and Discussion
3.1. Modification of AlN Particles
The grafting percentage of the silane coupling agent was
determined by TGA measurements. For exact result, the
surface treated AlN nanoparticles were washed several
times to ensure complete removal of free silane coupling
agent or traces of any physically bonded silane mole-
As evident from Figure 2, the TGA thermogram of
untreated and treated AlN microparticles, the weight loss
in case of treated AlN particles were higher than that of
the untreated particles over the entire experimental range
at lower temperature region < 200˚C, the weight loss in
both the Unsurface-treated and treated AlN particles is
probably due to the removal of water molecules absorbed
on surface of AlN.
The significant weight loss in the surface-treated AlN
particles in the temperature range of 75˚C - 650˚C, is
probably related to the condensation of silanol groups
and the decomposition of grafted silane molecules [21].
This further confirms that the silane groups are success-
fully bonded onto the surface of the AlN particle.
3.2. Density of Composites
The interaction of the filler with the polymer matrix is a
complex phenomenon that is usually influenced by fac-
tors that includes free volume; molecular weight; which
in turn is influenced by its density. Figure 3 shows the
epoxy/surface-treated AlN composite showing higher
density as compared with epoxy/unsurface-treated AlN
composite which may be attributed towards the presence
of more volume fraction of voids and pores in epoxy/
unsurface-treated AlN composites.
The crosslink density of the composite sample is sen-
sitive towards its volume fraction of voids and pores. As
the grafting silanes on the surface of AlN particles en-
hanced the interaction between the matrix and the filler
(AlN); it further reduces the free spaces among the epoxy
molecules and increases the congestion or difficulty of
epoxy molecules to either rotate or move. This further
contributes to an increase in the density of the composites.
Figure 2. TGA Thermogram of untreated & treated AlN
Figure 3. Density of virgin epoxy and epoxy/surface treated
and unsurface-treated AlN composites.
Further, the density in the epoxy/AlN nanocomposites is
depicted in the Table 2.
3.3. Thermal Conductivity
The variation of thermal conductivity of epoxy/AlN com-
posites and nanocomposites is represented in Figures 4
and 5 and Table 3. Virgin epoxy shows a thermal con-
ductivity value of 0.142 W/mK at 25˚C which subse-
quently increases to 0.167 & 0.186 W/mK with the in-
crease in temperature up to 50˚C & 75˚C respectively.
The incorporation of micro as well as nano AlN to the
tune of 20 to 30 wt%, results in an increase in the thermal
Table 2. Density of epoxy/unsurface-treated and surface-
treated AlN nanocomposites.
Density (g/cm3)
Specimen Composition Epoxy/
Epoxy + Hardener + 5% nAlN1.231 1.242
Epoxy + Hardener + 20% nAlN1.362 1.382
conductivity in the virgin matrix. At low loading of un-
surface-treated AlN micro and nanoparticles of 5 wt%,
no significant increase in thermal conductivity of the
matrix polymer was observed at 25˚C and 50˚C. How-
ever, the conductivity increased with the increase in the
loading levels of AlN from 10 to 20 wt%, as there is a
consistent increase in the conductivity values of the ep-
oxy/AlN micro composites.
Further, surface treated epoxy/AlN micro composite
revealed higher conductivity values as compared with the
untreated samples. This behavior is probably due to the
fact that surface modification minimizes the defects in
the lattice structure of AlN, thus contributing to reduction
in interfacial phonon scattering and decreasing the inter-
face heat resistance while enhancing the conductivity.
The epoxy/AlN micro composite at 20% AlN loading
exhibits an optimum conductivity values, hence this
composition has been retained for nanocomposite sam-
ples. A comparison with minimal loading of 5 wt% in
epoxy/AlN has also been made with micro composite. It
is evident that at low loading levels of nAlN also, there
was no appreciable increase in the conductivity of the
matrix. However, at 30 wt% of nAlN (both surface
treated & untreated), there was a significant increase in
the conductivity of epoxy matrix when compared with
micro composite. This is probably due to the presence of
nanoscale platelets which creates an efficient pathway for
conduction. The epoxy/surface-treated nAlN, revealed
higher conductivity value, thus confirming efficient in-
terfacial adhesion between the filler & the matrix due to
reduction in agglomeration of AlN nanoparticles with
silane treatment. At higher loading of 30 wt% of AlN in
the microcomposite, there was a decrease in thermal
conductivity, which is possibly due to agglomeration of
AlN particles that results in the formation of micro
cracks at the interface in the composite [21]. In all the
cases, conductivity increases with the increase in tem-
perature which shows that there is an increase in interfa-
cial adhesion at higher temperature.
3.3.1. Relationship between Thermal Conductivity of
Epoxy Composites and AlN Fractions
It has been claimed that in case of nanofluids in which a
small quantity of small particles (some nanometers in
Copyright © 2012 SciRes. JMMCE
Figure 4. Thermal conductivity of epoxy/unsurface-treated
AlN and epoxy/surface-treated AlN microcomposites at dif-
ferent temperatures: (a) 25˚C; (b) 50˚C; and (c) 75˚C.
Figure 5. Thermal conductivity of epoxy/unsurface-treated
AlN and epoxy/surface-treated AlN nanocomposites at dif-
erent temperatures: (a) 25˚C; (b) 50˚C; and (c) 75˚C. f
Copyright © 2012 SciRes. JMMCE
Table 3. Variation of thermal conductivity of epoxy/AlN composites and nanocomposites.
Thermal Conductivity (W/mK)
Unsurface-Treated AlN Surface-Treated AlN
Specimen Composition
25˚C 50˚C 75˚C 25˚C 50˚C 75˚C
Epoxy + Hardener + 0% micro AlN 0.142 0.1670.186 0.142 0.167 0.186
Epoxy + Hardener + 5% micro AlN 0.142 0.1720.221 0.189 0.202 0.233
Epoxy + Hardener + 10% micro AlN 0.179 0.2010.221 0.179 0.209 0.229
Epoxy + Hardener + 20% micro AlN 0.192 0.2070.229 0.192 0.211 0.231
Epoxy + Hardener + 30% micro AlN 0.158 0.1970.281 0.202 0.229 0.253
Epoxy + Hardener + 5% nAlN 0.132 0.1830.195 0.150 0.191 0.210
Epoxy + Hardener + 20% nAlN 0.201 0.2370.267 0.225 0.257 0.280
size) present in a fluid matrix, gives very high thermal
conductivity. As thermal conductivity, k, is the property
of a material’s ability to conduct heat as it appears pri-
marily in Fourier’s Law for heat conduction, the conduc-
tivity of AlN is much greater than that of epoxy. The
addition of alluminium nitride filler to the epovy matrix
thereby results in increase in thermal conductivity of the
composite as in Figures 4 and 5. The thermal conductiv-
ity increases with increase in AlN fractions.
3.3.2. Use of Kanari Model for Prediction of Thermal
Properties of Polymer Composites
Kanari model is a revised Bruggeman’s equation and
presents a relationship between the thermal conductivity
of composites and the volume fractions of filler which is
a function of the shape of filler:
Figure 6. Thermal conductivity of the composite as a func-
tion of volume fraction of AlN.
Copyright © 2012 SciRes.
 (1) 1
treated micro composite at variable AlN loading. It is
evident that break down strength of virgin epoxy in-
creases marginally with the increase in AlN loading form
0 to 20 (wt%). At filler concentration of <10 wt%, the
break down strength of the untreated composite remains
almost the same as the virgin matrix polymer.
where Vf is the volume fraction of filler; km is the thermal
conductivity of matrix; kf is the thermal conductivity of
AlN as filler; kc is the thermal conductivity of composite;
km is the thermal conductivity of matrix and x is constant,
determined by sphericity of the filler. For alluminium
nitride, x is substituted as 2.5 in Equation (1). The re-
sullting model is given in Figure 6. Figure 6 clearly de-
picts the non-compliance of the experimental data curve
with Kanari model. It is clear that each curve shows a
small change in slope such as the thermal conductivity
increases gradually with an increase in volume fraction
of inorganic filler.
This behavior is probably because at lower concentra-
tion of filler, the number of AlN particles is less, the in-
terparticle distances are more and the volume fraction of
the loose polymer layer is large under the condition of
high electric stress, a large fraction of those polymer
layer allow the transfer of charge carrier between the
electrodes thereby loading to lower or marginally same
breakdown voltage as the epoxy. However at higher filler
content beyond 10 wt%. i.e. at 20 wt% of AlN loading,
the number of particles in the composite is larger with the
inter particle distance being smaller, hence the volume
3.4. Dielectric Break Down Strength
Figures 7 and 8 depicts the dielectric break down
strength of virgin epoxy and epoxy/AlN treated and un-
Figure 7. Dielectric break down strength of virgin epoxy
and epoxy/AlN surface-treated and untreated micro com-
posite at variable AlN loading.
Figure 8. Dielectric break down strength of virgin epoxy
and epoxy/surface-treated and untreated AlN nano compo-
site at variable AlN loading.
fraction of loose polymer layer reduces and the particles
themselves act as barriers to flow of current between the
electrodes. These factors contribute to hindrance in the
flow of current in the composite, resulting in higher
breakdown voltage. Similar facts may also be applicable
for epoxy/AlN nanocomposite at 5 and 20 wt% of nAlN
as described in Table 4.
Further, all the surface treated epoxy/AlN micro and
nanocomposite exhibited higher breakdown strength
which reveals effective compatibility of the surface-
treated AlN with the matrix beyond 20 wt% of AlN,
there was a reduction in the breakdown strength thus
Table 4. Dielectric strength of epoxy/(surface-treated and
untreated) AlN nanocomposites.
Dielectric Break Down Strength
Specimen Composition Epoxy/
Epoxy + Hardener + 5% nAlN12.25 13.61
Epoxy + Hardener + 20% nAlN13.88 14.32
revealing agglomeration of the AlN micro particles there-
by inducing voids and cracks within the matrix polymer
3.5. Volume Resistivity
The volume resistivity of virgin epoxy, epoxy/AlN micro
and nanocomposite at variable wt% of AlN is repre-
sented in Figure 9 and Table 5. Virgin epoxy shows a
resistivity value of 31.45 × 1014 ·cm which decreases
with the incorporation of AlN micro as well as nanopar-
ticles. It is evident that introduction of unsurface-treated
AlN micro particles to the tune of 5 to 10 wt% substan-
tially reduces the resistivity value to 0.26 - 0.43 ·cm,
which subsequently increases with higher filler loading.
This behavior indicates that at lower filler loading, the
fraction of extended loose polymer layers is high which
probably allows the existence of free ions and also their
unhindered transport through the bulk of the material
those results in an increase in the electrical conductivity
through the volume of the material [22]. However, with
the increase in AlN loading up to 20 wt%, immobilized
polymer chains act as ion traps which inhibit the ion mo-
bility thereby resulting in decrease in the overall conduc-
tivity values. Further, the epoxy/surface-treated AlN mi-
crocomposite exhibited higher resistivity values as com-
pared with the untreated samples at similar wt% of AlN
loading. This further reveals improved interfacial adhe-
sion at the interface which hinders the flow of electrons,
thus giving a less conductivity.
The volume resistivity of epoxy/AlN nanocomposite is
also displayed in the Table 5. As observed, the nano-
filled system (both surface-treated and untreated) display
lesser conductivity (higher resistivity) as compared with
the microcomposites at same loading. This decrease in
conductivity is primarily due to hindered conductive path
in the nanocomposite by the highly concentrated AlN
3.6. Dynamic Mechanical Analysis (DMA)
Figure 10 shows the storage modulus attained, as a func-
tion of the temperature for the various epoxy systems.
he figure clearly shows that the storage modulus of neat T
Copyright © 2012 SciRes. JMMCE
Table 5. Volume resistivity of virgin epoxy, epoxy/AlN micro and nanocomposite at variable wt% of AlN.
Volume Resistivity (·cm)
Specimen Composition
Epoxy/Unsurface-Treated AlNEpoxy/Surface-Treated AlN
Epoxy + Hardener + 0% micro AlN 31.45 × 1014 31.45 × 1014
Epoxy + Hardener + 5% micro AlN 0.260 × 1014 2.92 × 1014
Epoxy + Hardener + 10% micro AlN0.432 × 1014 7.06 × 1014
Epoxy + Hardener + 20% micro AlN5.14 × 1014 7.16 × 1014
Epoxy + Hardener + 30% micro AlN4.28 × 1014 4.33 × 1014
Epoxy + Hardener + 5% nAlN 6.84 × 1014 7.31 × 1014
Epoxy + Hardener + 20% nAlN 8.84 × 1014 10.5 × 1014
Figure 10. Storage modulus versus temperature of Virgin,
micro and nano composite.
epoxy, epoxy/micro AlN and epoxy/nAlN composites are
2172.13 MPa, 3565.57 MPa and 6295.08 MPa respec-
tively. In the glassy state the incorporation of micro alu-
minium nitride (AlN) yielded a 64.15% increase in stor-
age modulus as compared to virgin epoxy, which further
increased by 76.55% due to addition of nano AlN parti-
cles. In a rubbery state the modulus of virgin epoxy is
equal to the micro & nano composite. This behavior can
be explained in terms of possible physical interaction
between the micro/nano AlN with virgin epoxy matrix
through their enormous interfacial area. The modification
with nano AlN particle implies a greater value of storage
modulus (6295.08 MPa) which is due to the adhesion of
nano filler into the epoxy matrix resulting in the stiffness
and sufficient energy storage in the material.
(b) It can be definitely considered that the homogeneous
dispersion and the excellent interfacial coupling force in
a mixture state of the micro and nano particles limits the
Figure 9. Volume resistivity of virgin epoxy and (a) epoxy/
AlN micro; (b) epoxy/AlN nanocomposite.
opyright © 2012 SciRes.
mobility of the epoxy molecules and enhance the storage
modulus before Tg [23,24].
Loss modulus curves of the neat epoxy, epoxy/micro
AlN and epoxy/nAlN composites are shown in Figure 11.
In this the Tg value of micro composite is 137.90˚C
where as the Tg value of virgin and nano composite are
122.97˚C and 134.26˚C respectively.
The Tg of composite increased by 15 degree Celsius
from 122.97˚C (neat epoxy) to 137.90˚C (micro epoxy
composite). The shift of Tg for particulate-filled micro
composite reaches a higher temperature due to immobil-
ity of polymer molecules caused by local adsorption onto
the particles. The average interparticle distance decreases
with the incorporation of micro particles rather than
nanoparticles, resulting in the decrease in volume frac-
tion of loosely bound polymer. The peak height of the tan
delta and the area under tan delta curve of composite and
nano composite decreased substantially with the loading
of AlN particles. The peak value (131.27) of neat epoxy
is reduced to epoxy/micro AlN composite. Similarly the
peak value of tan delta is reduced considerably in epoxy/
AlN nano composite as compared to the neat epoxy. This
is probably due to the effect of increase in crystallinity,
the reduced fraction of epoxy composite and nano com-
posite and homogeneous dispersion of AlN nanoparticles
in epoxy matrix, results in a strong interaction on physi-
cal bonding between AlN particles micro, nano and vir-
gin epoxy matrix. It indicates that micro composite gave
excellent thermal property than virgin epoxy and nano
composite [26].
Loss modulus (E'') before and after Tg keep constant
with temperature but storage modulus (E') before and
after Tg varies with temperature this decrease in storage
modulus in the glassy and rubbery state may be due to
different coefficient of thermal expansion (CTE) of the
matrix and filler, inducing relaxation in the polymeric
phase and considering that the decrease of storage
modulus E' with temperature in glassy and rubbery state
is small [25]. The representation value E' & E'' in the
glassy state are taken at about 28˚C and the representa-
tion value of E' & E'' in the rubbery state are taken at
about 200˚C.
Tan delta curves of the micro, nano and neat epoxy
composite are shown in Figure 12. It is observed that
converse value that is tan delta represents a temperature
difference of 18.01˚C for micro composite and tempera-
ture difference of 11.39˚C for nano composite in com-
parison to virgin epoxy composite.
3.7. Morphological Analysis: Scanning Electron
Microscopy (SEM)
The micro structure of 20 wt% AlN loaded epoxy com-
posite and nanocomposites (both surface-treated & un-
treated) are shown in Figures 13 and 14. In case of both
Figure 11. Loss modulus versus temperature of Virgin, mi-
cro and nanocomposite.
Figure 12. Tan delta versus temperature of Virgin, micro
and nanocomposite.
surface-treated epoxy/AlN nano composite and micro
composites, silane coupling agent on the AlN surface is
found playing a significant role like an adhesion pro-
moter between filler particles and epoxy matrix. The
homogeneous dispersion of micro AlN in the epoxy ma-
trix as compared to the AlN nanoparticles is clearly ob-
served in Figures 13(b), 13(c), 14(a) and 14(b). Figure
13(a) indicates the SEM micrograph of virgin epoxy ma-
trix showing the fracture surface, which is further modi-
fied with the addition of AlN particles showing the en-
hancement of interaction within the layers of neat epoxy
matrix and the silane treated AlN micro composite and
nano composite.
Both the case of unsurface-treated epoxy/AlN micro
Copyright © 2012 SciRes. JMMCE
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(a) (b)
(c) (d)
Figure 13. SEM images of: (a) neat epoxy, (b), (c) epoxy with 20% surface-treated micro AlN and (d), (e) epoxy with 20%
unsurface-treated micro AlN.
(a) (b)
(c) (d)
Figure 14. SEM images of: (a), (b) epoxy with 20% surface-treated nano AlN and (c), (d) epoxy with 20% unsurface-treated
nano AlN.
composites and nano composites is illus trated in Figures
13(d), 13(e), 14(c) and 14(d), wherein the AlN particles
are agglomerated on the epoxy surface. These particles
are not properly embedded in to the matrix, resulting in
uneven flake like surface. The compatibility of the AlN
nanocomposite as compared with virgin epoxy matrix is
meager as compared to the microcomposite which is
clearly shown in the Figures 13(a)-(c), 14(a) and 14(b)
4. Conclusions
The following conclusions have been drawn from the
present study towards effective behavior of surface mo-
dification of nano and micro particles on the dynamic
mechanical strength, glass transition temperature, elec-
trical property and thermal conductivity and morphology
of epoxy/AlN composites.
The silane incorporation in composite yielded im-
proved electrical and thermal property when compared
with those loaded with unsurface-treated nanoparti-
The incorporation of silane in epoxy/AlN composite
and nanocomposite result in a better compatibility and
cross linking reveals to an increase in dielectric break
down strength, thermal conductivity and glass transi-
tion temperature when compared with the unsurface-
treated epoxy/AlN composite and nanocomposites.
The epoxy/AlN nanocomposites showed lower value
for volume resistivity when compared to virgin epoxy
at lower filler loading, due to better interfacial adhe-
sion, again. The conductivity falls to alower value.
At 20 wt% of nAlN both (surface-treated and un-
Copyright © 2012 SciRes. JMMCE
treated), there was a significant increase in the con-
ductivity of epoxy matrix when compared with com-
posite. This is due to the existence of nanoscale plate-
lets which forms the channel for conduction.
A significant change was noted in storage modulus of
the epoxy/AlN microcomposite up to the vicinity of
the Tg of the epoxy. The Tg of the epoxy was also
affected moderately by the addition of AlN nano par-
ticles. Since stiffness and strength appear to increase
with the incorporation of AlN micro and nano parti-
The result indicates the AlN nano and micro particles
dispersion is adequate which may induce some struc-
ture change in the epoxy matrix reflects on its viscoe-
lastic properties.
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