Synthesis of Polyaniline - Step by Step Procedure

    Intrinsically conducting polymers (ICPs) are remarkable materials that exhibit electrical conductivities on par with metals, while maintaining the unique properties of polymers. Among conducting polymers, Polyaniline has gained a lot of interest due to its low cost and easy synthesis, multiple interchangeable electronic states, tunable conducting and optical properties, and high moisture stability. 

    The most common and easy method of synthesizing conducting polymers is "Chemical Oxidative Polymerization", in which the monomer is mixed with an oxidizing agent and a suitable acid to give products.

    Now let's prepare one of the most easily synthesized conducting polymers aka Polyaniline by this method. 

Synthesis of Polyaniline

Goal:

The appearance of a dark green-colored product, indicating the formation of the conducting state of Polyaniline (Emeraldine Salt).

Materials:

• Aniline: monomer, distilled before use for purification.
• Sulfuric acid (H₂SO₄): for doping and providing an acidic medium.
• Potassium persulfate (KPS): oxidizing agent.
• Sodium dodecyl sulfate (SDS): surfactant (optional).
• Distilled or deionized water.
• Other usual stuff for labwork, like beakers, funnels, flasks, filter papers, dropper, magnetic stirrer, analytical balance, etc.

Procedure:

A quick overview of the procedure is given here. You will find the detailed chemical calculations further down. 

The experiment was performed at room temperature ≈ 30 °C.

(You can adjust the concentrations or molarities slightly based on your preference or the literature you follow):

1). Prepare 0.2 M aniline solution in 100 mL of 0.8 M H₂SO₄ and pour it into a 250 or 500 mL beaker.

2). Stir the aniline solution for 15 minutes on a magnetic stirrer to ensure uniformity. The solution may appear clear or yellowish, depending on the purity of the aniline monomer.

3). Mix Sodium dodecyl sulfate (surfactant, 0.02 M) in the aniline solution and stir for 30 minutes. The solution will turn into a milky emulsion.

(The concentration of the surfactant should be equal to or greater than its critical micelle concentration (CMC). For SDS, the CMC is 8.5 mM/ 0.0085 M at 30 °C)

4). Prepare an equimolar amount of Potassium persulfate (oxidant, 0.2 M) in 100 mL of distilled water. 

(KPS is slightly soluble in room temperature water so use warm water)

5). Add the oxidant dropwise into the aniline solution while maintaining continuous stirring. The color will transition from milky white to dark green in a few minutes.

6). After the addition of oxidant, the contents are further stirred for 5 to 8 hours and then allowed to sit overnight for polymerization to complete.

7). After 24 hours from the start of oxidant addition, the green product is filtered and washed with plenty of distilled water and ethanol/ acetone.

8). The product is dried in air and then in an oven at 90 °C for 3 hours.

9). The dried product is crushed to a fine powder and stored in a clean, dry container. The final product should be weighed out to find the total amount produced.

Calculations:

Using the formula:

$Mass in grams = \frac{Molarity \times Molar mass \times Volume in mL}{1000}$

$\frac{}{}$

• 0.8 M Sulfuric acid (100 mL):

$Mass = \frac{0.8 \times 98.08 \times 100}{1000}$$=7.85g$

$$Density =1.84 g/mL

$Volume = \frac{m}{d}= \frac{7.85}{1.84} =4.26 mL$

Take 4.26 mL conc. H₂SO₄ and dilute it to 100 mL.

• 0.2 M Aniline (100 mL):

$Mass =\frac{0.2 \times 93.13 \times 100}{1000} =1.86g$

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$$Density =1.02 g/mL

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$Volume =\frac{1.86 g}{1.02 g/mL} =1.82 mL$

Take 1.82 mL of aniline and dilute it to 100 mL with 0.8 M H₂SO₄.

• 0.02 M SDS (100 mL):

$Mass =\frac{0.02 \times 288.38 \times 100}{1000} =0.58g$

Add the powder directly to the aniline solution.

• 0.2 M KPS (100 mL):

$Mass =\frac{0.2 \times 270.3 \times 100}{1000} =5.4g$

Take the amount and dissolve it in 100 mL of warm water.

Watch the video to practically see how polyaniline is synthesized: