Electrothermochromic paper fabricated by depositing polypyrrole on one side

Paper with color changes caused by applied electric voltages was fabricated by combining the electric heating feature of conductive polypyrrole (PPy) and the temperature response color-changing feature of thermochromic ink. Highly conductive PPy was deposited selectively on the graphite-coated side of the paper via electrochemical polymerization. Thermochromic ink was coated on the reverse side with white color. The conductive coatings were tightly covered on the paper due to the hydrogen bonding between the pyrrole rings and the hydroxyl groups of cellulose. The obtained paper could be heated to about 45 °C and change its color significantly under an applied voltage of 4 V.