Conductivity evaluation of smart hydrogels composed of polyacrylamide-polyaniline

Electro active composite system as hydrogels was prepared from non-conducting polymer and conducting polymer combined together. This type of composite hydrogels has both properties of hydrogel and conducting polymer representing a new material. Polyacrylamide hydrogels was prepared by polymerizing acrylamide (5 mole/L) in an aqueous solution of (NH₄)₂S₂O₈(0.20 mole/L) containing a crosslinker N,N’ methylene bisacrylamide (0.2 mole/L) in a test tube at 40oc for 24 hours. After polymerization, the cross linked polymer was isolated from the tube in a long cylindrical shape which was cut into pieces in one cm in length. After getting it washed repeatedly to remove the soluble materials and then dried at room temperature for 48 hours. The hydrogel, so formed, was soaked in an aqueous solution of aniline hydrochloride (1 mole/L) solution to allow the monomer to diffuse inside the hydrogel networks. When 0.25 mole/L FeCL_3- an oxidant was added to the solution, the polyaniline was formed inside the porous structure of hydrogel. The resulting hybrid polymer was taken out from polymerizing mixture which was thoroughly washed and dried. The sample appeared deep dark green colour. The average surface resistance (Inverse representation of conductivity) of the sample was estimated about 103 Ohm. Another oxidant like Fe₂(SO₄)₃ gives almost the same results. The reproducibility of conductivity value is poor because it is very difficult to form uniform distribution of the conducting polymer throughout in the hydrogel networks.