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1
Conducting Polymer -Polyaniline
Collect Multimeter w/ connecting wire 1 set
Connecting wire w/ two alligator clips 1
30 mL beaker 3
50 mL beaker 3
Timer (from TA) 1
Binder clip 2
Conducting glass (ITO glass) 1
Microscope slide 2
Filter paper strip (2 cm x 4 cm ) 1
Copper wire 2
LED
Prepare
Glass rod
Tweezer
Wash bottle
DC power supply w/ connecting wire (underneath lab bench)
2020/04/11 revised
Objective and Techniques
Video: www.youtube.com/user/ntuchemistrylab
Objective – Synthesize polyaniline (PANI)
• Chemical synthesis
• Electrochemical synthesis
– Examine its performance
• Conduction test
• Electrochromic properties
Techniques – DC power supply
– Multimeter
2
3 3
Conductivity
Base on band theory
According to band gap (Eg) between conduction band (CB) and valence band (VB) – Conductor
– Semiconductor
– Insulator
Eg
Eg
(a) Conductor (b) Semiconductor (c) Insulator
價帶
CB
CB
VB VB
CB Eg
0 eV VB
Eg
1~3 eV
Eg
> 3 eV Eg
Conducting Polymer
Various conducting polymers and chemical structures
Characterize with conjugated double bonds and multi-
paralleled p orbitals
4
5 5
Polyaniline
Oxidative polymerization of aniline
A: Benzenoid B: Quinoid
Polyaniline Degree of oxidation Color
Leucoemeraldine, LE (Reduced form)
y = 0 (all benzenoid form)
White
Emeraldine base, EB (Alternating)
x > 0, y > 0 (benzenoid/quinoid)
Green/Blue
Pernigraniline, PNB (Oxidized form)
x = 0 (All quinoid form)
Purple
HN
HN N N
x y n
Aniline
monomer
NH2n
[O]
Monomeric unit
6
Conductivity of Polyaniline
Structure and conductivity – Conjugated double bond, i.e. repeated alternating single
and double bonds
– Acid doping to raise conductivity
HN
NH
N
N
n
HN
NH
NH
HN
n
HCl
NH3
Cl-Cl-
.. ..
..
..
.. ..
Emeraldine base (EB)
Blue, poor conductor
Emeraldine salt (ES)
Green, conductor H+ doping
De-doping
7 7
Synthesis of Polyaniline
Chemical oxidative polymerization
Aniline hydrogen chloride + ammonium persulfate
Electrochemical oxidative polymerization
– Aniline sulfuric acid as electrolyte
– Polymerize on ITO glass that connected to positive end of
power supply
4n NH3+Cl-
HNHN NH
HN
nCl- Cl-
+ 2n HCl + 5n H2SO4 + 5n (NH4)2SO4+ +
+ 5n (NH4)2S2O8
H2SO4(aq)
n NH
HSO4-
n
電氧化聚合NH2
Electrolysis
H2SO4(aq)
8
Step 1 Chemical Synthesis of PANI
Synthesize emeraldine salt, ES
8
• Prepare filter paper
strip
• Take 5 mL
C6H5NH3+Cl-
• Mix with 5 mL
(NH4)2S2O8 in 30
mL beaker
• Hang paper strip in
aniline soln
• Observe color change
• Polymerize for 5 min.
• Take paper strip out
• Record the color of polymer
• Dip into pH 2.5 HCl(aq)
• Then wash with DI water
• Blow dry with hair dryer
• Fix paper strip onto
microslide to test conductivity
9
Step 2-1 Electrochemical Synthesis
9
• Immerse ITO glass in
alcohol to clean up
• Wash with DI water
• Wipe dry with paper towels
• Use tweezers to avoid
being contaminated by
hands
• Connect ITO glass to
positive end (red)
• Cu wire to negative end
(black) of power supply
• Take 7 mL C6H5NH3HSO4
in 30 mL beaker
• Set up electrolytic cell
• Use microslide to separate
two electrodes to avoid
short circuit
Electrolysis
• Hold ITO glass w/ binder clips
• Keep clips from touching soln
to avoid contamination
10
Polymerize
Step 2-2 Electrochemical Synthesis
Voltage
adjust
knob
Current
adjust
knob
+ -
Connect to
Cu wire
Connect to
ITO glass
(1) Set all knob/button at zero before
connecting to Cu wire and ITO glass,
(2) Power on, press OUTPUT button
(light on)
(3) Adjust voltage/current knobs to 3 V
(4) Press OUTPUT button again (light off)
(5) Connect Cu wire/ITO glass correctly
(6) Press OUTPUT button (light on) to
electrolyze for 5 min
(7) Observe the color change
Power on
button
OUTPUT
button
11
• Immerse ITO glass in pH 2.5
HCl(aq) to wash clean
• Then rinse with DI water
• Blow dry with hair dryer
• Apply transparent tape to PANI
surface firmly, then peel off
• Fix the polymer tape on microslide to
test conductivity
Step 2-3 Electrochemical Synthesis
12
Step 3 Conduction Test
12
LED emission conduction test
1. Connect synthesized PANI film with LED to DC power
supply
2. Turn on power supply and adjust voltage to observe the
emission of LED
+ -
Note:
Connect LED to DC current
directly to test function well by
applying voltage under 2 V.
13 13
Multimeter • Anode (black) to the COM slot
• Cathode (red) to the Ω slot
• Switch function mode to “Ω”
• Examine resistance from
maximum scale, i.e. 20M, to
lower scale, such as 2000K
• If LCD shows “1”, it means over
scale
Measure resistance • Fix alligator clips onto PANI films
• Record the resistance and
distance within two clips
Step 4 Resistance Test
Reduce PANI film to observe the color change
LE (all reduced benzenoid form) appears colorless
EB (alternate benzenoid and quinoid) appears green/blue
PNB (all oxidized quinoid form) appears purple
• Take 7 mL of 20% NaCl in 30 mL beaker
• Connect ITO glass to negative end (black) of
power supply
Cu wire to positive end (red)
• Apply 1.5 V voltage to reduce PANI on ITO glass
• Observe and record the color change
14
Step 5 Electrochromic Test
14
15
Notice
Put latex gloves on to avoid contacting with toxic aniline
Microslide is easy broken that should be handled with care
Connect ITO glass correctly
Check the alligator clips’ and LED’s function to avoid open
circuit
Connect alligator clips onto ITO glass directly
After class
– Recycle ITO glass, microslide, Cu wire, and chemical waste
– Wash binder/alligator clips with water and wipe dry to avoid
rusting
– Turn off multimeter and DC power supply; return the
connecting wires
Condensed Report
16
Updated Form of Result Sheet
1. Print out and use
the updated form
in your report.
2. Document is
uploaded to CEIBA.
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