The presentation in based on interesting experimental results of percolative systems. A weak temperature dependence of conductivity is observed in composite of 0.4 wt %. The coercivity of Fe-MWNT/PS composites varies non-monotonically as a function of MWNT loading.

1. GURUDAKSHITA
FACULTY INDUCTION PROGRAMME-2
Organized by
Human Resource Development Center
Guru Jambheshwar University of Science & Technology, Hisar
(Haryana)
Nov 18 – Dec 23, 2020
Presented by:
Dr. Ravi Bhatia
Assistant Professor
Department of Physics
Guru Jambheshwar University
of Science & Technology, Hisar (Haryana)
1
Novel Experimental Observations in
percolative systems

2. Plan of talk
Percolative system based on Multiwall Carbon
Nanotubes
 Synthesis and characterization
Charge transport near percolation threshold
Magnetic response

3. Charge transport in Percolative Systems
Electrical properties of polymer
composites is governed by
classical percolation theory
Conductivity of polymer
composite depends on
content of the conducting
filler material
Conductivity of the composite
sample increases abruptly as the
filler content just crosses a
particular value pc, called
percolation threshold
Electrical percolation in the CNT-
polymer composite depends on
 degree of dispersion
 aspect ratio
 waviness
 thickness of composite film
Variable Range Hopping (VRH)
Fluctuation Induced Tunneling
(FIT)
Conduction mechanisms

4. Percolation Threshold
pc is 16 wt %

5. Percolation Plot
Logσ

6. Motivation
Temperature (K)
H. M. Kim et al., Phys. Rev. B. 74, 054202 (2006).
0.4 wt%
30 wt%

7. Reduced Activation Energy
Plotted by our group by taking data from
H. M. Kim et al., Phys. Rev. B. 74, 054202 (2006).

8. SEM micrographs of MWCNTs
Length ~ 200 - 300 μm
A mixture of toluene and
ferrocene (100 mg/ mL)
was used as precursor
Reasonably good
Quality MWCNTs were
Obtained !
CVD grown MWCNTs !
(a)
(b) (c)
Our group developed quite
inexpensive
method for production of MWCNTs
Cost of the whole synthesis
set up less than 20000 INR
No carrier gas (inert gas) flow
required
High yield Growth of good quality MWCNTs by low cost approach

9. SEM micrographs of MWCNT-PS Composites
(Low magnification)
7 wt %5 wt %
1 wt % 3 wt %
Scale bar – 5 µm
(a)
15 wt %
(b)
15 wt %
R. Bhatia et al., Mater. Sci. and Eng. B 175, 189 (2010)

10. Temperature dependence of electrical
conductivity for various systems
near the percolation threshold
1. H. M. Kim et al., Phys. Rev. B. 74, 054202 (2006).
2. J. M. Benoit et al., Phys. Rev. B. 65, 241405 (2002).
3. P. Sheng et al, Phys. Rev. Lett. 40, 1197 (1978).
4. V. Augelli et al., J. Appl. Phys. 90, 1362 (2001).
5. M. Reghu et al., Phys. Rev. B 50, 13931 (1994).
R. Bhatia et al., Appl. Phys. Lett. 96, 242113 (2010)
Unusual metallic-like transport near the percolation threshold
Reduced activation energy (W)
vs. temperature
0.4 wt %

11. Sample Ref.
no.
pc (wt %) 300 K (S/cm)
at pc
300 K / 10 K Transport
model
MWCNT-PS - ~ 0.4 ~ 10-3 1.67 Power law
MWCNT-PMMA 1 ~ 0.4 ~ 10-3 11.8 VRH/ FIT
SWCNT-PMMA 2 ~ 0.33 ~ 10-6 ~ 104 VRH
PANI-PMMA 5 ~ 0.4 ~ 10-2 ~ 102 VRH
CB-PVC 3 ~ 15 ~ 10-2 ~ 102 FIT
Gold-PTFE 4 ~ 21 ~ 10-5 ~ 105 VRH
Parameters describing the charge transport in various
nanocomposite systems, near the percolation threshold pc
1. H. M. Kim et al., Phys. Rev. B. 74, 054202 (2006).
2. J. M. Benoit et al., Phys. Rev. B. 65, 241405 (2002).
3. P. Sheng et al, Phys. Rev. Lett. 40, 1197 (1978).
4. V. Augelli et al., J. Appl. Phys. 90, 1362 (2001).
5. M. Reghu et al., Phys. Rev. B 50, 13931 (1994).
R. Bhatia et al., Appl. Phys. Lett. 96, 242113 (2010)

12. The weak temperature dependence of electrical conductivity in MWCNT-PS
composite, near the percolation threshold (0.4 wt %), indicates metallic-like
behavior (power-law behavior).
Significance:
Fundamental research point of view:
This work signifies that even at the percolation threshold nanoscale connectivity
can be sustained at temperatures as low as 4.2 K which is hardly observed so far
in percolating media.
Application point of view:
The polymer/MWCNT composites with reasonable electrical conductivity can be
used in aeronautic industry, electromagnetic shielding applications and field
emission devices.
Importance of the work
R. Bhatia et al., Appl. Phys. Lett. 96, 242113 (2010)

13. Magnetic properties of Fe-MWCNTs and
polymer composites
Diamagnetic susceptibility
CNTs without catalyst
Anisotropic
Magnetic susceptibility of
tubes aligned parallel to
the field (χ∥) is found to be
much greater than that of
tubes perpendicular to the
field (χ⊥)
CNTs with catalyst
Encapsulation of magnetic
NPs within the CNT shell
constitutes a fantastic
magnetic system
Protected from oxidation
Prohibited from aggregation
Enhanced magnetic
coercivity
CNTs with catalyst dispersed
in polymer matrix
Dominances of particular
magnetic interactions as a
function of
(1) Inter-particle distance
(2) size and
(3) shape of magnetic NPs

14. (a)
TEM and HRTEM micrographs of MWCNTs
Diameter ~ 50 - 80 nm
Scale bar in inset-1 μm
10nm 10nm
(b) (c)
Fe nanorods get embedded within MWCNT at various lengths

15. (a) (b)
(c) (d)
(b)
(a)
(c)
MWNTs
7 wt %
1 wt %
Hysteresis loops at temperatures from 300 to 10 K
R. Bhatia et al., J. Phys. D: Appl. Phys. 44, 415001 (2011)
R. Bhatia et al., Mater. Sci. and Eng. B 175, 189 (2010)
Magnetic properties of Fe-MWCNTs and polymer composites

16. Non-monotonic Coercivity as a function of Fe-MWCNT wt %
R. Bhatia et al., J. Phys. D: Appl. Phys. 44, 415001 (2011)
 The coercivity of Fe-MWCNT/PS
composites varies non-monotonically
as a function of MWCNT loading. The
coercivity vs. MWCNT loading plot
shows a maximum for composite
of an intermediate Fe-MWNT loading
i.e. for 1 wt % composite
Significance:
Highly coercive and conductive polymer composite can be
fabricated with relatively small amount of Fe-filled MWCNTs.

17. Acknowledgments
Prof. REGHU MENON (IISc, Bangalore)
Dr. V. PRASAD (IISc, Bangalore)
Dr. JEAN GALIBERT (CNRS FRANCE)
Dr. I. SAMEERA (GJUST, Hisar)
Dr. C.S.S. SANGEETH (NIT, Calicut)
17

18. THANK YOU