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

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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

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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)

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Step 1 Chemical Synthesis of PANI

Synthesize emeraldine salt, ES

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• 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

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Step 2-1 Electrochemical Synthesis

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• 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

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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

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• 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

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Step 3 Conduction Test

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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

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Step 5 Electrochromic Test

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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

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Updated Form of Result Sheet

1. Print out and use

the updated form

in your report.

2. Document is

uploaded to CEIBA.