Conducting Polymer-Polyaniline Collect Multimeter w/ connecting wire 1 set DC power supply 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 1 2016/04/10 1
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
Conductivity Base on band theory According to band gap (E g ) between conduction band (CB) and valence band (VB) Conductor Semiconductor Insulator CB CB VB E g CB E g E g E g 1~3 ev 0 ev VB 價帶 VB E g E g > 3 ev (a) Conductor (b) Semiconductor (c) Insulator 3
Conducting Polymer Various conducting polymers and chemical structures Characterize with conjugated double bonds 4
Polyaniline Aniline as monomer; by oxidative polymerization n [O] N 2 Aniline Monomeric unit N N N N x A: Benzenoid B: Quinoid y n Polyaniline Degree of oxidation Color Leucoemeraldine, LE (Reduced form) Emeraldine base, EB (Alternating) Pernigraniline, PNB (Oxidized form) y = 0 (all benzenoid form) x > 0, y > 0 (benzenoid/quinoid) x = 0 (All quinoid form) White Green/Blue Purple 5
Conductivity of Polyaniline Structure and conductivity Conjugated double bond, i.e. repeated alternating single and double bonds Acid doping to increase conductivity.. N.. N...... N.. N Emeraldine base (EB) Blue, poor conductor n Cl N N Cl - Cl - N 3 N N + doping De-doping Emeraldine salt (ES) Green, conductor n 6
Synthesis of Polyaniline Chemical oxidative polymerization Aniline hydrogen chloride + ammonium persulfate 4n N 3 + Cl - + 5n (N 4 ) 2 S 2 O 8 N N N N + 2n Cl + 5n 2 SO 4 + 5n (N 4 ) 2 SO 4 + + n Cl - Cl - Electrochemical oxidative polymerization Aniline sulfuric acid as electrolyte Polymerize on ITO glass that connected to positive end of power supply n 電氧化聚合 Electrolysis N 2 2 SO 4(aq) 2 SO 4 SO 4 - N n 7
Step 1 Chemical Synthesis of PANI Synthesize emeraldine salt, ES Prepare filter paper strip Take 5 ml C 6 5 N 3+ Cl - Mix with 5 ml (N 4 ) 2 S 2 O 8 in 30 ml beaker ang paper strip in aniline soln Observe color change Polymerize for 5 min. Take paper strip out Record the color of polymer Dip into p 2.5 Cl(aq) Then wash with DI water Blow dry with hair dryer Fix paper strip onto microslide to test conductivity 8
Step 2-1 Electrochemical Synthesis 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 old ITO glass w/ binder clips Keep clips from touching soln to avoid contamination Electrolysis Take 7 ml C 6 5 N 3 SO 4 in 30 ml beaker Set up electrolytic cell Use microslide to separate two electrodes to avoid short circuit 9
Step 2-2 Electrochemical Synthesis (3) Adjust current (3) Adjust voltage (4) OUTPUT button (1) Connect electrodes correctly (2) Turn power on (3) Adjust voltage/current to 3 V (4) Press OUTPUT button (5) Electrolysis for 5 min. (6) Observe the color change (2) Power - + (1) Connect to ITO glass Polymerize 10
Step 2-3 Electrochemical Synthesis Dip ITO glass in p 2.5 Cl(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 11
Step 3 Conduction Test - + 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 12
Step 4 Resistance Test Multimeter Anode (black) to the COM slot Cathode (red) to the Ω slot Switch function mode to Ω Measure resistance Fix alligator clips onto PANI films Record the distance within two clips 13
Step 5 Electrochromic Test Reduce PANI film to observe the color change LE, all reduced benzenoid form; colorless EB, alternate benzenoid and quinoid; green/blue color PNB, all oxidized quinoid form; 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
Notice Put latex gloves on to avoid contacting with aniline that is toxic Microslide is easy broken that should be handled with care Connect ITO glass correctly After class Recycle ITO glass, microslide, 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 15