1. Renaissance of the Plastic Age
Polymers for Electronics & Photonics
T.P.Radhakrishnan
School of Chemistry, University of Hyderabad Hyderabad , India
This file is available at

2. Materials and civilisation
(Before 5000 BC)
Stone age
( BC)
Copper age
( BC)
Bronze age
(800 BC - 40 AD)
Iron age
Plastic age ?

3. Types of materials Molecular materials Metals / Alloys Ceramics*
Ceramics
Polymers
Semiconductors
Composites
Biomaterials
Molecular materials
*Courtsey: W. D. Callister, Fundamentals of Materials Science and Engineering

4. Design of Molecular Materials
Elements / Compounds
Materials
Chemical /
Physical routes
Molecules
Crystals
Thin films / LB films
Polymers
Nanostructures
Chemical routes
Chemical / Physical routes

5. Molecular materials / Polymers

6. Natural polymers

7. Synthetic polymers Polytetrafluoroethylene Polyethylene (Teflon)
Phenol-formaldehyde
(Bakelite)
Polyethylene
Polytetrafluoroethylene
(Teflon)
Polyhexamethylene adipamide
(Nylon 6,6)
Polyethyleneterephthalate
(PET)
Polycarbonate

8. Discovery of conducting polymers
Lethby (College of London Hospital)
Oxidation of aniline in sulfuric acid
1970’s Shirakawa (Japan)
Acetylene gas
Ti(OBu)4 & Et3Al
Toluene
–78oC
Ti(OBu)4 & Et3Al
Hexadecane
150oC
silvery film
trans-polyacetylene
copper-coloured film
cis-polyacetylene

9. Polyacetylene (PA) Electrical conductivity (s)
cis PA – 10-9 S cm-1
trans PA 10-5 – 10-4 S cm-1
For comparison : s (copper) ~ 106 S cm-1
: s (teflon) ~ S cm-1

10. Doping leads to enhanced conductivity
s ~ 10-5 S cm-1
Semiconductor
+ e-
- e-
s ~ 104 S cm-1
Metal

11. Discoverers - Nobel Prize 2000
A. Heeger, A. McDiarmid, H. Shirakawa
(this photograph taken at the International Conference on Synthetic Metals, 2000, was kindly provided by Prof. Heeger)

12. Polyacetylene - electronic structure
-electronic energy levels and electron occupation
(a) ethylene
(b) allyl radical
(c) butadiene
(d) regular trans-PA
(e) dimerised trans-PA

13. How does a conducting polymer work ?
Oxidative doping of polyacetylene by iodine
Polaron
and its delocalisation

14. Excitations
Bipolaron
Neutral Soliton
Positive Soliton

15. Examples of conducting polymers

16. Electrical conductivities
Copper
Platinum
Bismuth
Graphite
10+6
10+4
10+2
100
10-2
10-4
10-6
10-8
10-10
10-12
10-14
10-16
10-18
S cm-1
Conducting
Polymers
Germanium
Silicon
Polyethylene
Diamond
Quartz

17. Synthesis of PANI Cathode Anode (ITO plate) Aniline + dil. HCl
Instead of electrochemical oxidation, chemical oxidation may be
carried out : Aniline + acid + oxidising agent ((NH4)2S2O8)

18. Voltage (~ V) applied

19. Result of electropolymerisation
The green coating on the ITO electrode is due to
the formation of emeraldine salt form of PANI

20. Polyaniline (PANI) Leucoemeraldine Colorless Emeraldine base Blue
(Insulator)
Emeraldine base
Blue
(Insulator)
Emeraldine salt
Green
(Conductor)
Purple
(Insulator)
Pernigraniline
Oxidation

21. Applications of conducting polymers
Polyaniline (PANI)
Transparent conducting electrodes
Electromagnetic shield
Corrosion inhibitor
‘Smart windows’ (electrochromism)
Polypyrrole (Ppy)
Radar-invisible screen coating
(microwave absorption)
Sensor (active layer)
Polythiophene (PT)
Field-effect transistor
Anti-static coating
Hole injecting electrode in OLED
Polyphenylenevinylene (PPV)
Active layer in OLED

22. Polypyrrole - conductivity switching

23. Enzyme Biosensor Using PPy
Glucose oxidase
-D-glucose + ½O2 + H2O  D-gluconic acid + H2O2
H2O2 + 2HCl + Ppy  2H2O + Ppy2+.2Cl-

24. PANI-PSS PSSn-(100 kDa) RT = 8.3x10-2 Scm-1 PSSn-(70 kDa)

25. Sensors Typical example : Ammonia sensing by PANI-PSSM film Resistance
change with
time
Ammonia in
Ammonia out

26. NH3 Constant Vacuum Two-way switch Digital Voltmeter
Current Source
Rotary Vacuum Pump
Two-way switch
Digital Voltmeter
NH3
Vacuum
FAN
10 V Battery

27. Resistance change at 150 sec. for different concentrations of ammonia

28. Electroluminescence - Electric field + Light Metal electrode
Organic thin film
Transparent
electrode (ITO)
Light
Electric field

29. Principle of EL
Cathode
Anode e-
HOMO
LUMO
HOMO
LUMO
Light h+

30. Polymers for Organic Light Emitting Diodes (OLED)
PPV
MEH-PPV
Commercial materials like Mn2+ in ZnS require 100V DC
PPV : requires V DC
runs even with AC
brightness ~40,000 cd/m2 ie. ~100 times brighter than a TV screen

31. Organic LED driven by organic transistor
Ca/Ag
MEH/PPV
Silica
Gold
P3HT
n+-Silicon
Aluminium G D S

32. Electrochromic devices
Polymer Undoped Doped
Polythiophene Red Blue
Polypyrrole Yellow-green Blue-black
Polyaniline Yellow Green/Blue
Viewing side
Li anode
Polymer electrolyte
Conducting polymer
ITO electrode V

33. On application of voltage
Viewing side
Li anode
Polymer electrolyte
Conducting polymer
ITO electrode V

34. Conjugated polymers for nonlinear optics
NLO materials interact with light
Polydiacetylene ( ) n
Light changes the material properties
Changes the properties of the light

35. Photonic Application of Conducting Polymers - Kerr gate
Polariser
Laser 1
Crossed
Polariser
No light
NLO (c(3))
polymer
Laser 2
Laser 1
Polariser
Crossed
Polariser

36. All organic transistor
Future Outlook
All organic transistor

37. Plastic solar cell based on MDMO-PPV/PCBM
(conducting polymer - fullerene composite)
on flexible ITO coated PET

38. Thank you