Conducting PolymersConducting Polymers - public.asu.eduntao1/Teaching/EEE598/Erica ppt...
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Transcript of Conducting PolymersConducting Polymers - public.asu.eduntao1/Teaching/EEE598/Erica ppt...
Conducting Polymers - AdvantagesCombination of properties
Metals Plastics
High conductivity LightnessHigh conductivity LightnessEase of processing (spin coating)Low costTailored synthesis
Conductivity of typical materials
-Semiconducting polymers comprise a wide range of conductivity
- The higher conductivities values are obtained when polymers are “charged“
Polymers
HH HH HH HH
CH2 CH2n
- Traditional plastic : Polyethylene“Always insulator”
CC
HH
CC
HH
CC
H
H
H
CC
H
H
H
C CH
H
H
H HH HH HH HHHH
Ethylene
- Conjugated polymer : Trans-polyacetylene CH CHn“insulator conducting”
HOW ?
C HCH CC
CC
CC
CC
CCH
H
H
H
H
H
H
H
H
HHOW ?
H H H H HAcetylene
+n
3 I2n
+ 2 I3-
2 +
Clue: alternate single-double bonds
Polyacetylene (PA)
PA i th i l t j t d l
Doped Polyacetylene (doped-PA)
•After exposure to iodide:•PA is the simplest conjugated polymer
• Conductivity at room temperature:- c-PA: 10-7 Sm-1
After exposure to iodide:
Conductivities are as high as 105 Sm-1
- t-PA: 10-3 Sm-1
compared to cooper 108 Sm-1
PA suffer a drastic increase of conductivity (108-1013)
moderate insulatorThe plastic becomes conductive
possibility of plastic wiresPA
+ 3 I2 + 2 I3-
2 +
PA doped-PA
+n
3 I2n
+ 2 I3
+n
3 I2n
+ 2 I3-
2 +
Nobel Prize in Chemistry 2000
“For the Discovery and Development of Conductive Polymers”
Hideki ShirakawaUniversity of TsukubaUniversity of Tsukuba
Alan HeegerUniversity of California
Alan MacDiarmidUniversity ofy
at Santa Barbaray
Pennsylvania
Other Conjugated Polymers Conducting Polymers
n Sn
N
Hn
Trans-polyacetylene (t-PA) Polythiophene (PT) Polypyrrole (PPY)
nn
Poly(p-phenylene) (PPP)
n
Poly(p-phenylenevinylene) (PPV)PEDOT (very conductive
NH NH N N
PEDOT (very conductive and stable)
ny 1-yPolyaniline (PAN)
π electrons from double bonds (sp2)
How the conjugated organic polymer is converted into a conducting polymer ?
It can not move pieces It can move pieces
A full orbital can not conduct electrons,
so to get a conjugated material to conduct, we must add or remove charges (doping process)
Two options:- Remove electrons from the HOMO (create holes)
Chemically (oxidizing/reducing agents) or electrochemically (applied potential)
Remove electrons from the HOMO (create holes)- Add electrons to LUMO
Doping process
p-doping Partial oxidation of polymer chain
Per functional unit: [P] + y A- [(Py+) A - ] + y e
-[P]x- + xy A- -[(Py+) Ay- ]-x + xy e
Per functional unit: -[P]- + y A- -[(Py+) Ay- ]- + y e
n-doping Partial reduction of polymer chain
Per functional unit: -[P]- + y e + y M+ -[(Py-) My+ ]-
-[P]x - + xy e + xy M+ -[(Py-) My+ ]x-
Doping process: involve ionic transportDoping process: involve ionic transport
can be described in terms of diffusion/reaction eqs. (e.g. Barttlet,Gardner)
Differences of the doping process withd i i l t l i d tdoping process in elemental semiconductors
• Significant doping levels (until 10 mole %)
• There is a charge transfer between the incorporated dopant atom and the polymer chainincorporated dopant atom and the polymer chain = the lattice is partially oxidized or reduced
What are the consequences of doping ?
Ionic transportCharge transport:
Polaron (+.)Bipolaron (++)Soliton (0,+, -)
A-
A-, A-p-doping
n-doping
+
A-
Let’s draw on the board a generic case !
R1 R1 R1A
Intra and inter chain charge transport R2 R2 R2
R1 R1 R1
Intra and inter chain charge transport R2 R2 R2R2 = neutral groupR2 = anionic group (A-)
Molecular versus Band Models
M. Lögdlund et al.E
1
2 3
4
56
7
8nE (eV)
Electronaffinity
n
HOMO
LUMOaffinity
Bandgap
Ionizationpotential
p-doping, example 1: p-doping, example 1: Generation of Polaron and Bipolaron defects in Conjugated PolymersCB
VBRadical-cation / Polaron (spin)
+
VB
+
Polaron
Dication / Bipolaron (spin less)
++
Bipolaron
Produced as far as is possible to produce quinoid resonance structures
CB
p-doping, example 2: Generation of Polaron and Bipolaron defects in Conjugated Polymers
Polypyrrole (PPy)
VBVB
Polaron0.5 eV
Bipolaron
H il d d l
Band structure of a conjugated polymer as a function of
p-doping levelSli htl d d
E
Undoped polymer Heavily-doped polymerCB
Slightly-dopedpolymer
LUMO (L)
CB CB CB
LL L
POL2POL2BIP2
HOMO (H)
VB VB VB
HH H
POL1 BIP1
VB
Neutral PolymerVB full, CB empty
VB VB
VBPolarongenerationvia fisrt
Bipolaron generationvia second Further oxidation
tVB full, CB empty via fisrt1e oxidation
via second1e oxidation generates
bipolaron bands
J. Cornil et al., Adv. Mater. 8, 447 (1996)
Conductivity dependence as a function of polymer length
C d tConductance
Length of polymer
Why ?What is the eq. associated to this trend ? And its meaning ?
CBSoliton structures in polyacetylene – Band structure
VB
. Neutral SolitonSpin 1/2
+Positive Soliton
Spin 0
..Negative Soliton
Spin 0
So far…• Conducting polymer features:
- conjugated structure (alternate doble-single bonds) free electrons from double bond of conjugated polymer (π electrons)- dopping process need it- mixed electronic and ionic conduction- conductivity dependent on charge transport carriers: polaronconductivity dependent on charge transport carriers: polaron, bipolaron, soliton.
Dig into more basic studiesDig into more basic studies…• Conducting polymer techniques used for characterization:
- EC (electroactivity)- Quartz Crystal Microbalance (QCM) and Probe Beam Deflection (PBD) (ionic movement towards and from the polymer)- UV-Vis-Near IR spectroscopy (absorption)- Fourier Transform Infrared Spectroscopy (FTIS) (chemical structure)- … many other surface characterization techniques based on X-Rays or optical detection
Applications- Energy storage (batteries) Easy to producee gy sto age (batte es)
-Electrochromic windows (intelligent windows)
Easy to produceUltra high capacitance
- Actuators (Artificial muscles)
Sensors (field effect transistors)
- Electrostatic coatings
- Sensors (field effect transistors)
Baytron P (Bayer) / Orgacon (AGFA)
S
nn
O O
SO3-
PEDOT PSS
- Electromagnetic shielding
Electrochromic windows (intelligent windows)
SS
SS
SS
ts) Bipolaron
ty (a
rb. u
nit
Neutral
Polaron
Inte
nsit Polaron
Energy (eV)600 800 1000 1200 1400 1600 1800 2000
Energy (nm)
J. Guay et al.Chem. Mater. 4, 1097 (1992)
Electrochromic windows, sensorsSee “electrochomic display”
& “polyaniline video” from youtube.com
Actuators (Artificial muscles) ionic movement swelling-shrinking
PPy
A-
A
PPy
Reduction:Anion release
Oxidation:Anion intake
A-
A solid state artificial muscle based on polypyrrole(PPy) andpoly(epichlorohydrin-co-ethylene oxide) [P(ECH-co-EO)]/LiClO4 (solid polymeric electrolyte) is developed
See “artificial muscles” from youtube.com
TF Otero, et.al
Conducting Polymer FET Sensors
1 cm
1 mmBSi3N4 window
Recognizingelement on the
junctiongold pads
5µm5µm
1µmpolymerGap smaller than 60 nm
Glucose NanosensorGlucose Oxidase
Conducting polymer
20-60
Oxidant by-product the increases p-doping level
Time response: ~ 200 ms20-60 nm
AGold nanoelectrode
Glucose, O2
H O
Sensitivity: 1nA/mM
Detection Limit: 1 µM
H2O2
PANIox(more conducting) Detection Limit: 1 µM
A>0
( g)
E. Forzani, H. Zhang, L. Nagahara, I. Amlani,R. Tsui, and N.J. Tao Nano Letters 4 ,9 2004
Time course of drain current at Eg = 35 mV vs SCE (Vsd = -20 mV) recorded on a PANI-PAA/PANI-bisulfite/GOx-PDAB nanojunction (20-60 nm) in 20 uL Mc Ilvaine buffer,
0.5 M Na2SO4 pH 5 upon 1 µL successive additions of 40 mM glucose.