An elastomer is a polymer with the ability to reversibly deform under stress. The term, which was coined by Peter von Liebig in 1838, is derived from the Greek words ἔλασσεν (elasso), meaning to draw or stretch, and μέρος (meros), meaning part. Elastomers are amorphous polymers that can be vulcanized—that is, cross-linked into materials of improved strength, elasticity, and resistance to heat and chemicals. Vulcanization was first developed by Charles Goodyear in 1839.
Elastomers have long chains of atoms that are held together by weak Van der Waals forces. These intermolecular attractions are much weaker than the covalent bonds that hold together the atoms within each individual molecule. As a result, elastomers can be easily deformed when small amounts of force are applied. When the force is removed, they quickly return to their original shape due to the restoring force of the intermolecular attractions.
The elasticity of an elastomer results from its ability to store energy in its temporary deformation under load—that is, it behaves like a spring. The amount of energy stored per unit volume (and therefore the spring constant) increases with increasing cross-linking density; that is, as more chains become interconnected through vulcanization or other means of cross-linking.
The low modulus (springiness) of most elastomers makes them poor candidates for use as structural materials; however, their properties make them ideal for use as seals, gaskets, vibration isolation mounts, hoses, tires, conveyor belts and similar applications where flexibility and/or resilience are required. Some types of elastomeric materials display piezoelectricity or ferroelectricity—that is they generate an electric charge in response to applied mechanical stress or can be electrically polarized like a capacitor—and these properties can be exploited in sensors or actuators.