Pure and Applied Chemistry
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http://www.informaworld.com/smpp/title~content=t713597274
Ion Beam Modification of Polymethyl methacrylate
(PMMA) Polymer Matrix Filled with Organometallic
Complex
Anjum Qureshi a; N. L. Singh a; Sejal Shah a; F. Singh b; D. K. Avasthi b
a Department of Physics, M. S. University of Baroda, Vadodara, India
b Inter University Accelerator Center, New Delhi, India
Online Publication Date: 01 April 2008
To cite this Article: Qureshi, Anjum, Singh, N. L., Shah, Sejal, Singh, F. and
Avasthi, D. K. (2008) 'Ion Beam Modification of Polymethyl methacrylate (PMMA) Polymer Matrix Filled with
Organometallic Complex', Journal of Macromolecular Science, Part A, 45:4, 265 - 270
To link to this article: DOI: 10.1080/10601320701863668
URL: http://dx.doi.org/10.1080/10601320701863668
PLEASE SCROLL DOWN FOR ARTICLE
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This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction,
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The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or
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Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
Ion Beam Modification of Polymethyl methacrylate (PMMA)
Polymer Matrix Filled with Organometallic Complex
ANJUM QURESHI,1 N. L. SINGH,1 SEJAL SHAH,1 F. SINGH,2 and D. K. AVASTHI2
1Department of Physics, M. S. University of Baroda, Vadodara, India
2Inter University Accelerator Center, New Delhi, India
Received and accepted October, 2007
A Nickel Dimethylglyoxime (Ni-DMG) compound was dispersed in polymethyl methacrylate (PMMA) films at different concentrations.
PMMA was synthesized by a solution polymerization technique. These films were irradiated with 120 MeV Ni10þ ions at the fluences of 1 1011 and 1 1012 ions/cm2. The radiation induced changes in dielectric properties and average surface roughness were investigated by using an LCR meter in the frequency range 50 Hz to 10 MHz and atomic force microscopy (AFM), respectively. The electrical properties of irradiated films are found to increase with the fluence and also with the concentration of Ni-DMG. From the analysis of frequency, f, dependence of dielectric constant, 1, it has been found that the dielectric response in both pristine and irradiated samples obey the Universal law given by 1 a f n21. The dielectric constant/loss is observed to change significantly due to the irradiation. This suggests that ion beam irradiation promotes (i) the metal to polymer bonding (ii) convert the polymeric structure in to hydrogen depleted carbon network due to the emission of hydrogen gas and/or other volatile gases. Atomic force microscopy (AFM) shows that the average surface roughness and
surface morphology of irradiated films are observed to change.
Keywords: PMMA; composites; ion irradiation; AC electrical frequency response; AFM
1 Introduction
Polymer composites filled with metal fillers result in a
unique combination of thermal, mechanical and electrical
properties, which make them useful for various applications.
By introducing suitable fillers in polymers, composite
properties can be tailored to meet specific design
requirements such as low density, high strength, high stiffness,
high damping, chemical resistance, thermal shock
resistance, high thermal conducitvity, low coefficient of
themal expansion (CTE) and good electrical properties
such as dielectric constant. Composite materials of an
amorphous polymeric matrix and randomly dispersed
metal particles are considered as heterogeneous disordered
systems (1–3). The electrical performance of granular
materials, as these systems are sometimes referred to, is
directly related to the permittivity and conductivity of the
constituent phases, the size, shape and volume fraction of
the inclusions and can be experimentally investigated by
means of dielectric spectroscopy (DS) and dc conductivity
measurements (4–11). Other important factors could be
the adhesion between the host medium and the inclusions,
the method of processing and possible interactions
between the conductive and nonconductive phases
(12, 13). Polymers and polymer matrix composites are basically
electrical insulators, due to their low concentration of
free charge carriers. Thus, their electrical response is,
mainly, associated with relaxation phenomena occurring
under the influence of an AC field. The observed relaxation
processes are related to dipolar orientation effects or
space charge migration (3, 14). Molecular mobility and
interfacial polarization are regarded as the origin of dielectric
effects.
The high energy ion irradiation effects in polymers have
attracted considerable attention for applications of
polymers in radiation environment and also in the development
of new electronic devices (15, 16). The swift heavy
ions slow down in the matter and lose their energy
mainly via electronic excitations and ionizations. The
deposited energy may be converted into atomic motion
and finally leads to the structural and chemical modifications
within a cylindrical zone of several nanometers
in diameter (17, 18) and new structural arrangements
may emerge (19, 20). Ion beam irradiation has long been
Address correspondence to: N. L. Singh, Department of Physics,
M. S. University of Baroda, Vadodara 390002, India. Tel.: þ 91-
265-2783924; Fax: þ91-265-2795569;
E-mail: singhnl_msu@yahoo.com or anjumqur@gmail.com
Journal of Macromolecular Science w, Part A: Pure and Applied Chemistry (2008) 45, 265–270
Copyright # Taylor & Francis Group, LLC
ISSN: 1060-1325 print/1520-5738 online
DOI: 10.1080/10601320701863668
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
recognized as an effective method for modifying the
properties of diverse materials, including polymers and
polymer composites. Important properties of polymer
composites i.e. mechanical property, thermal stability,
chemical resistance, melt flow, process ability and
surface properties significantly improved by ion beam
irradiation (21–23). In this study, organometallic
complex was dispersed at different concentrations in
PMMA matrix and irradiated with 120MeV, Ni10þ ions
at the fluences of 1 1011 and 1 1012 ions/cm2. The
radiation induced changes in dielectric properties and
surface morphology were studied by means of LCR
meter and atomic force microscopy, respectively.
2 Experimental
Nickel dimethylglyoxime (Ni-DMG) compound was
formed by dissolving 0.4 mole nickel chloride in 200 ml
water and it was heated at 808C; a slight excess of the
alcoholic dimethylglyoxime (DMG) was added and then
dilute ammonia solution was added drop wise with continuous
stirring until precipitation took place. The precipitate
was then washed with cold water until free
from Cl2 and dried at 1108C for 1 h. PMMA was
prepared by solution polymerization method. In this
method, benzoyl peroxide (BPO; 0.8 g; an initiator for
polymerization) was dissolved in fresh inhibitor-free
MMA (80 ml methyl methacrylate) monomer, with
ethyl acetate as a solvent (80 ml) in a round bottom
flask; the solution was then refluxed for 5 h at 808C temperature
in the hot water bath. The resulting solution was
then precipitated out in another beaker containing
methanol (100 ml). The PMMA, precipitated out in
methanol, was dried at room temperature for 2 h. The
polymerized PMMA and Ni-DMG compound of 5%,
20%, and 40% were dissolved using toluene; acetone
(50:40) and Briz-35 surfactant (0.5 at % of the
polymer) the solutions were mixed and stirred thoroughly
for about an hour and then poured into a clean glass
trough. The solvent was evaporated at room temperature
(258C+18C) to get thin films (thickness 100 mm) of
dispersed PMMA with 5%, 20%, and 40% concentration
of Ni-DMG compound. The 1.5 1.5 cm2 size films
were cut and used for irradiation. All films were irradiated
with 120 MeV Ni10þ ions at the fluences of 1011,
and 1012 ions/cm2 from the Pelletron of the Inter University
Accelerator Center (IUAC), New Delhi, India. AC
electrical properties of all samples were measured in
the frequency range 50 Hz 2 10 MHz at room temperature
using a variable frequency LCR meter (General
Radio, USA; model-1689; model-1689/Hewlett Packard
4284A). Electrical contact on the sample was made by
applying an air drying type of silver paste, and then the
sample was mounted between the two electrodes
(diameter 8 mm) of sample holder. The conductivity of
the material was calculated using the relation
s ¼ 2pfCpDt/A (V.cm)21 and dielectric permittivity
1 ¼ Cp/Co.
Where Cp is the capacitance measured using an LCR
meter, f the frequency, D dielectric loss and Co ¼ 1oA/t, A
and t are the cross sectional area of the electrode and
thickness of the sample, respectively. 1o: permittivity of
vacuum ¼ 8.85 10212 F/m. The surface morphology of
pristine and irradiated surfaces was studied using an atomic
force microscope (AFM) in the contact mode (Digital
Nanoscope IIIa Instrument Inc.)
3 Results and Discussion
3.1 AC Electrical Frequency Response
AC electrical measurement was performed for pristine and
irradiated samples. Figure 1 (a, b, and c) shows the variation
of conductivity with log of frequency for the
pristine and irradiated samples at different Ni-DMG concentrations.
The conductivity was observed to increase in
pristine as well as irradiated samples. It was also
observed that conductivity increases with increasing concentration
of dispersed Ni-DMG compound (Figure 1a,
pristine) as well as those irradiated at the fluence of
1 1011 ions/cm2 (Figure 1b) and 1 1012 ions/cm2
(Figure 1c), respectively. The increase in conductivity
with different Ni-DMG concentrations for pristine
samples may be attributed to the conductive phase
formed by dispersed organometallic compound in
polymer matrix. It is known that electrical conductivity
of such composites depends on the type and concentration
of the dispersed compound (24, 25). As a result the conductivity
of dispersed films increases on increasing the concentration
of Ni-DMG compound in the polymer matrix.
It is also observed that after the irradiation the conductivity
increases with fluence (Figure 1). Irradiation is expected to
promote the metal to polymer bonding and convert the
polymeric structure in to a hydrogen depleted carbon
network. It is this carbon network that is believed to
make the polymers more conductive (26). Figure 2 (a, b,
and c) shows the plot of dielectric constant versus log frequency
for pristine and irradiated samples of pure PMMA
and different concentrations of Ni-DMG dispersed
PMMA films. When the fillers are dispersed in the insulating
polymer, the dielectric constant of composites investigated
increases with concentration of fillers. Such results
have been observed experimentally (27, 28).The partial
agglomerations also increase with increasing the filler concentration
as shown in Figure 4 (AFM). As evident from
Figure 2, the dielectric constant remains almost constant
up to 100 kHz. At these frequencies, the motion of the
free charge carriers is constant and so the dielectric
266 Qureshi et al.
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
Fig. 1. (a) AC conductivity versus log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) AC conductivity
vs. log frequency for irradiated (at the fluence of
1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) AC conductivity vs. log frequency for irradiated (at
the fluence of 1 1012 ions/cm2) pure and dispersed Ni-DMG
in PMMA films.
Fig. 2. (a) Plot of dielectric constant vs. log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) Plot of
dielectric constant vs. log frequency for irradiated (at the fluence
of 1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) Plot of dielectric constant vs. log frequency for irradiated
(at the fluence of 1 1012 ions/cm2) pure and dispersed
Ni-DMG in PMMA films.
Ion Beam Modification of Polymer Composite Films 267
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
constant presumably remains unchanged. It is also
observed that dielectric constant increases for irradiated
films with fluence. The increase in dielectric constant
may be attributed to the chain scission and as a result the
increase in the number of free radicals, unsaturation etc.
As frequency increases further (i.e., beyond 100 kHz),
the charge carriers migrate through the dielectric and get
trapped against a defect sites and induced an opposite
charge in its vicinity. At these frequencies, the polarization
of trapped and bound charges can not take place and hence
the dielectric constant decreases (29). The dielectric
constant decreases at higher frequencies (i.e., beyond
100 kHz) obeys the universal law (30) of dielectric
response given by 1 a f n21, where n is power law
exponent and varies from zero to one (0 , n , 1),
n ¼ 0.76 for pure PMMA, 0.63 for 5%, 20% and 40% Ni-
DMG dispersed pristine films were observed respectively.
The value of n ¼ 0.97 and 0.82 for pure PMMA; 0.80 and
0.74 for 5%; 0.69 and 0.74 for 20% and 0.69 and 0.74 for
40% dispersed Ni-DMG dispersed irradiated samples
were obtained at the fluences of 1 1011 ions/cm2
(Figure 2b) and 1 1012 ions/cm2 (Figure 2c), respectively.
The Figure 2 (a, b, and c) clearly shows that the frequency
dependence of dielectric constant, 1, obeys
Universal law. The observed nature of the fluence dependence
of dielectric constant in studied frequency range
can be explained by the prevailing influence of the
enhanced free carriers due to irradiation (31). Figure 3
(a, b, and c) shows the variation of dielectric loss with
log frequency for pristine and irradiated samples of pure
PMMA and Ni-DMG dispersed PMMA films at
the concentration of 5%, 20%, and 40%, respectively.
The dielectric loss decreases exponentially with the
increase of log frequency. It is noticed that dielectric loss
increases with the concentration of filler and also with
the fluence.
3.2 Morphology of the Composites
The surface morphology of pristine and irradiated films of
pure PMMA, and 40% Ni-DMG dispersed PMMA films
was measured by AFM on a 22 mm2 area as shown in
Figure 4. Each AFM image was analyzed in terms of
surface average roughness (Ra). The average roughness
values are 4.9 nm and 14 nm for unirradiated samples and
those of 2 nm and 4.6 nm for irradiated samples at the
fluence of 1 1012 ions/cm2. It was found that roughness
increases as Ni-DMG concentration increases. The increase
in roughness may be due to the increase of density and size
of metal particles on the surfaces of the PMMA films
(32, 33). It is also observed that after irradiation the roughness
of the surface decreases and the surface becomes significantly
smoother. This relative smoothness is probably due to defect
enhanced surface diffusion.
Fig. 3. a) Plot of dielectric loss vs. log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) Plot of dielectric
loss vs. log frequency for irradiated (at the fluence of
1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) Plot of dielectric loss vs. log frequency for irradiated
(at the fluence of 1 1012 ions/cm2).
268 Qureshi et al.
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
4 Conclusions
From this study, it is observed that dielectric property of
organometallic compound dispersed PMMA films is greatly
enhanced by ion beam irradiation. It may be attributed to (i)
metal to polymer bonding and (ii) conversion of the polymeric
structure to hydrogen depleted carbon network. Thus,
irradiation makes the polymer more conductive. Dielectric
loss and constant are observed to change significantly with
the fluence. This might be attributed to breakage of
chemical bonds and resulting in the increase of free
radicals, unsaturation, etc. It is also observed that dielectric
constant obeys Universal law of dielectric response. The
surface roughness increases as Ni-DMG concentration
increases but decreases on irradiation as observed from
AFM studies.
5 Acknowledgments
Authors are thankful to I˙nter University Accelerator Center
(I˙UAC), New Delhi for providing the irradiation facility
and IUC-DAFE Indore for providing the AFM facility. The
financial support given by IUAC, New Delhi is gratefully
acknowledged.
6 References
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Fig. 4. (a) AFM image of pure PMMA film (pristine); (b) AFM image of dispersed Ni-DMG (40%) in PMMA film (pristine); (c)
AFM image of pure PMMA film (irradiated at the fluence of 1012 ions/cm2); (d) AFM image of dispersed Ni-DMG (40%) in
PMMA film (irradiated at the fluence of 1 1012 ions/cm2).
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Publication details, including instructions for authors and subscription information:
http://www.informaworld.com/smpp/title~content=t713597274
Ion Beam Modification of Polymethyl methacrylate
(PMMA) Polymer Matrix Filled with Organometallic
Complex
Anjum Qureshi a; N. L. Singh a; Sejal Shah a; F. Singh b; D. K. Avasthi b
a Department of Physics, M. S. University of Baroda, Vadodara, India
b Inter University Accelerator Center, New Delhi, India
Online Publication Date: 01 April 2008
To cite this Article: Qureshi, Anjum, Singh, N. L., Shah, Sejal, Singh, F. and
Avasthi, D. K. (2008) 'Ion Beam Modification of Polymethyl methacrylate (PMMA) Polymer Matrix Filled with
Organometallic Complex', Journal of Macromolecular Science, Part A, 45:4, 265 - 270
To link to this article: DOI: 10.1080/10601320701863668
URL: http://dx.doi.org/10.1080/10601320701863668
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf
This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction,
re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly
forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or
arising out of the use of this material.
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
Ion Beam Modification of Polymethyl methacrylate (PMMA)
Polymer Matrix Filled with Organometallic Complex
ANJUM QURESHI,1 N. L. SINGH,1 SEJAL SHAH,1 F. SINGH,2 and D. K. AVASTHI2
1Department of Physics, M. S. University of Baroda, Vadodara, India
2Inter University Accelerator Center, New Delhi, India
Received and accepted October, 2007
A Nickel Dimethylglyoxime (Ni-DMG) compound was dispersed in polymethyl methacrylate (PMMA) films at different concentrations.
PMMA was synthesized by a solution polymerization technique. These films were irradiated with 120 MeV Ni10þ ions at the fluences of 1 1011 and 1 1012 ions/cm2. The radiation induced changes in dielectric properties and average surface roughness were investigated by using an LCR meter in the frequency range 50 Hz to 10 MHz and atomic force microscopy (AFM), respectively. The electrical properties of irradiated films are found to increase with the fluence and also with the concentration of Ni-DMG. From the analysis of frequency, f, dependence of dielectric constant, 1, it has been found that the dielectric response in both pristine and irradiated samples obey the Universal law given by 1 a f n21. The dielectric constant/loss is observed to change significantly due to the irradiation. This suggests that ion beam irradiation promotes (i) the metal to polymer bonding (ii) convert the polymeric structure in to hydrogen depleted carbon network due to the emission of hydrogen gas and/or other volatile gases. Atomic force microscopy (AFM) shows that the average surface roughness and
surface morphology of irradiated films are observed to change.
Keywords: PMMA; composites; ion irradiation; AC electrical frequency response; AFM
1 Introduction
Polymer composites filled with metal fillers result in a
unique combination of thermal, mechanical and electrical
properties, which make them useful for various applications.
By introducing suitable fillers in polymers, composite
properties can be tailored to meet specific design
requirements such as low density, high strength, high stiffness,
high damping, chemical resistance, thermal shock
resistance, high thermal conducitvity, low coefficient of
themal expansion (CTE) and good electrical properties
such as dielectric constant. Composite materials of an
amorphous polymeric matrix and randomly dispersed
metal particles are considered as heterogeneous disordered
systems (1–3). The electrical performance of granular
materials, as these systems are sometimes referred to, is
directly related to the permittivity and conductivity of the
constituent phases, the size, shape and volume fraction of
the inclusions and can be experimentally investigated by
means of dielectric spectroscopy (DS) and dc conductivity
measurements (4–11). Other important factors could be
the adhesion between the host medium and the inclusions,
the method of processing and possible interactions
between the conductive and nonconductive phases
(12, 13). Polymers and polymer matrix composites are basically
electrical insulators, due to their low concentration of
free charge carriers. Thus, their electrical response is,
mainly, associated with relaxation phenomena occurring
under the influence of an AC field. The observed relaxation
processes are related to dipolar orientation effects or
space charge migration (3, 14). Molecular mobility and
interfacial polarization are regarded as the origin of dielectric
effects.
The high energy ion irradiation effects in polymers have
attracted considerable attention for applications of
polymers in radiation environment and also in the development
of new electronic devices (15, 16). The swift heavy
ions slow down in the matter and lose their energy
mainly via electronic excitations and ionizations. The
deposited energy may be converted into atomic motion
and finally leads to the structural and chemical modifications
within a cylindrical zone of several nanometers
in diameter (17, 18) and new structural arrangements
may emerge (19, 20). Ion beam irradiation has long been
Address correspondence to: N. L. Singh, Department of Physics,
M. S. University of Baroda, Vadodara 390002, India. Tel.: þ 91-
265-2783924; Fax: þ91-265-2795569;
E-mail: singhnl_msu@yahoo.com or anjumqur@gmail.com
Journal of Macromolecular Science w, Part A: Pure and Applied Chemistry (2008) 45, 265–270
Copyright # Taylor & Francis Group, LLC
ISSN: 1060-1325 print/1520-5738 online
DOI: 10.1080/10601320701863668
Downloaded By: [Singh, N. L.] At: 08:25 26 February 2008
recognized as an effective method for modifying the
properties of diverse materials, including polymers and
polymer composites. Important properties of polymer
composites i.e. mechanical property, thermal stability,
chemical resistance, melt flow, process ability and
surface properties significantly improved by ion beam
irradiation (21–23). In this study, organometallic
complex was dispersed at different concentrations in
PMMA matrix and irradiated with 120MeV, Ni10þ ions
at the fluences of 1 1011 and 1 1012 ions/cm2. The
radiation induced changes in dielectric properties and
surface morphology were studied by means of LCR
meter and atomic force microscopy, respectively.
2 Experimental
Nickel dimethylglyoxime (Ni-DMG) compound was
formed by dissolving 0.4 mole nickel chloride in 200 ml
water and it was heated at 808C; a slight excess of the
alcoholic dimethylglyoxime (DMG) was added and then
dilute ammonia solution was added drop wise with continuous
stirring until precipitation took place. The precipitate
was then washed with cold water until free
from Cl2 and dried at 1108C for 1 h. PMMA was
prepared by solution polymerization method. In this
method, benzoyl peroxide (BPO; 0.8 g; an initiator for
polymerization) was dissolved in fresh inhibitor-free
MMA (80 ml methyl methacrylate) monomer, with
ethyl acetate as a solvent (80 ml) in a round bottom
flask; the solution was then refluxed for 5 h at 808C temperature
in the hot water bath. The resulting solution was
then precipitated out in another beaker containing
methanol (100 ml). The PMMA, precipitated out in
methanol, was dried at room temperature for 2 h. The
polymerized PMMA and Ni-DMG compound of 5%,
20%, and 40% were dissolved using toluene; acetone
(50:40) and Briz-35 surfactant (0.5 at % of the
polymer) the solutions were mixed and stirred thoroughly
for about an hour and then poured into a clean glass
trough. The solvent was evaporated at room temperature
(258C+18C) to get thin films (thickness 100 mm) of
dispersed PMMA with 5%, 20%, and 40% concentration
of Ni-DMG compound. The 1.5 1.5 cm2 size films
were cut and used for irradiation. All films were irradiated
with 120 MeV Ni10þ ions at the fluences of 1011,
and 1012 ions/cm2 from the Pelletron of the Inter University
Accelerator Center (IUAC), New Delhi, India. AC
electrical properties of all samples were measured in
the frequency range 50 Hz 2 10 MHz at room temperature
using a variable frequency LCR meter (General
Radio, USA; model-1689; model-1689/Hewlett Packard
4284A). Electrical contact on the sample was made by
applying an air drying type of silver paste, and then the
sample was mounted between the two electrodes
(diameter 8 mm) of sample holder. The conductivity of
the material was calculated using the relation
s ¼ 2pfCpDt/A (V.cm)21 and dielectric permittivity
1 ¼ Cp/Co.
Where Cp is the capacitance measured using an LCR
meter, f the frequency, D dielectric loss and Co ¼ 1oA/t, A
and t are the cross sectional area of the electrode and
thickness of the sample, respectively. 1o: permittivity of
vacuum ¼ 8.85 10212 F/m. The surface morphology of
pristine and irradiated surfaces was studied using an atomic
force microscope (AFM) in the contact mode (Digital
Nanoscope IIIa Instrument Inc.)
3 Results and Discussion
3.1 AC Electrical Frequency Response
AC electrical measurement was performed for pristine and
irradiated samples. Figure 1 (a, b, and c) shows the variation
of conductivity with log of frequency for the
pristine and irradiated samples at different Ni-DMG concentrations.
The conductivity was observed to increase in
pristine as well as irradiated samples. It was also
observed that conductivity increases with increasing concentration
of dispersed Ni-DMG compound (Figure 1a,
pristine) as well as those irradiated at the fluence of
1 1011 ions/cm2 (Figure 1b) and 1 1012 ions/cm2
(Figure 1c), respectively. The increase in conductivity
with different Ni-DMG concentrations for pristine
samples may be attributed to the conductive phase
formed by dispersed organometallic compound in
polymer matrix. It is known that electrical conductivity
of such composites depends on the type and concentration
of the dispersed compound (24, 25). As a result the conductivity
of dispersed films increases on increasing the concentration
of Ni-DMG compound in the polymer matrix.
It is also observed that after the irradiation the conductivity
increases with fluence (Figure 1). Irradiation is expected to
promote the metal to polymer bonding and convert the
polymeric structure in to a hydrogen depleted carbon
network. It is this carbon network that is believed to
make the polymers more conductive (26). Figure 2 (a, b,
and c) shows the plot of dielectric constant versus log frequency
for pristine and irradiated samples of pure PMMA
and different concentrations of Ni-DMG dispersed
PMMA films. When the fillers are dispersed in the insulating
polymer, the dielectric constant of composites investigated
increases with concentration of fillers. Such results
have been observed experimentally (27, 28).The partial
agglomerations also increase with increasing the filler concentration
as shown in Figure 4 (AFM). As evident from
Figure 2, the dielectric constant remains almost constant
up to 100 kHz. At these frequencies, the motion of the
free charge carriers is constant and so the dielectric
266 Qureshi et al.
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Fig. 1. (a) AC conductivity versus log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) AC conductivity
vs. log frequency for irradiated (at the fluence of
1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) AC conductivity vs. log frequency for irradiated (at
the fluence of 1 1012 ions/cm2) pure and dispersed Ni-DMG
in PMMA films.
Fig. 2. (a) Plot of dielectric constant vs. log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) Plot of
dielectric constant vs. log frequency for irradiated (at the fluence
of 1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) Plot of dielectric constant vs. log frequency for irradiated
(at the fluence of 1 1012 ions/cm2) pure and dispersed
Ni-DMG in PMMA films.
Ion Beam Modification of Polymer Composite Films 267
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constant presumably remains unchanged. It is also
observed that dielectric constant increases for irradiated
films with fluence. The increase in dielectric constant
may be attributed to the chain scission and as a result the
increase in the number of free radicals, unsaturation etc.
As frequency increases further (i.e., beyond 100 kHz),
the charge carriers migrate through the dielectric and get
trapped against a defect sites and induced an opposite
charge in its vicinity. At these frequencies, the polarization
of trapped and bound charges can not take place and hence
the dielectric constant decreases (29). The dielectric
constant decreases at higher frequencies (i.e., beyond
100 kHz) obeys the universal law (30) of dielectric
response given by 1 a f n21, where n is power law
exponent and varies from zero to one (0 , n , 1),
n ¼ 0.76 for pure PMMA, 0.63 for 5%, 20% and 40% Ni-
DMG dispersed pristine films were observed respectively.
The value of n ¼ 0.97 and 0.82 for pure PMMA; 0.80 and
0.74 for 5%; 0.69 and 0.74 for 20% and 0.69 and 0.74 for
40% dispersed Ni-DMG dispersed irradiated samples
were obtained at the fluences of 1 1011 ions/cm2
(Figure 2b) and 1 1012 ions/cm2 (Figure 2c), respectively.
The Figure 2 (a, b, and c) clearly shows that the frequency
dependence of dielectric constant, 1, obeys
Universal law. The observed nature of the fluence dependence
of dielectric constant in studied frequency range
can be explained by the prevailing influence of the
enhanced free carriers due to irradiation (31). Figure 3
(a, b, and c) shows the variation of dielectric loss with
log frequency for pristine and irradiated samples of pure
PMMA and Ni-DMG dispersed PMMA films at
the concentration of 5%, 20%, and 40%, respectively.
The dielectric loss decreases exponentially with the
increase of log frequency. It is noticed that dielectric loss
increases with the concentration of filler and also with
the fluence.
3.2 Morphology of the Composites
The surface morphology of pristine and irradiated films of
pure PMMA, and 40% Ni-DMG dispersed PMMA films
was measured by AFM on a 22 mm2 area as shown in
Figure 4. Each AFM image was analyzed in terms of
surface average roughness (Ra). The average roughness
values are 4.9 nm and 14 nm for unirradiated samples and
those of 2 nm and 4.6 nm for irradiated samples at the
fluence of 1 1012 ions/cm2. It was found that roughness
increases as Ni-DMG concentration increases. The increase
in roughness may be due to the increase of density and size
of metal particles on the surfaces of the PMMA films
(32, 33). It is also observed that after irradiation the roughness
of the surface decreases and the surface becomes significantly
smoother. This relative smoothness is probably due to defect
enhanced surface diffusion.
Fig. 3. a) Plot of dielectric loss vs. log frequency for pristine
pure and dispersed Ni-DMG in PMMA films; (b) Plot of dielectric
loss vs. log frequency for irradiated (at the fluence of
1 1011 ions/cm2) pure and dispersed Ni-DMG in PMMA
films; (c) Plot of dielectric loss vs. log frequency for irradiated
(at the fluence of 1 1012 ions/cm2).
268 Qureshi et al.
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4 Conclusions
From this study, it is observed that dielectric property of
organometallic compound dispersed PMMA films is greatly
enhanced by ion beam irradiation. It may be attributed to (i)
metal to polymer bonding and (ii) conversion of the polymeric
structure to hydrogen depleted carbon network. Thus,
irradiation makes the polymer more conductive. Dielectric
loss and constant are observed to change significantly with
the fluence. This might be attributed to breakage of
chemical bonds and resulting in the increase of free
radicals, unsaturation, etc. It is also observed that dielectric
constant obeys Universal law of dielectric response. The
surface roughness increases as Ni-DMG concentration
increases but decreases on irradiation as observed from
AFM studies.
5 Acknowledgments
Authors are thankful to I˙nter University Accelerator Center
(I˙UAC), New Delhi for providing the irradiation facility
and IUC-DAFE Indore for providing the AFM facility. The
financial support given by IUAC, New Delhi is gratefully
acknowledged.
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