Abstract

The field of smart materials is extremely large and probably includes representatives from all types of materials. The term, “smart material”, has some confusion attached to it as to what it actually means. A critical defining element for a material to qualify as “smart” is for it to have the ability to respond to a stimulus in a useful way, in an engineering sense, this response being both timely and in a controlled manner. Otherwise, all materials could be considered to be smart since all materials respond to external stimuli in same way. The discriminating factor is whether this response can be harnessed for some useful purpose. Stimuli may include mechanical deformation, stress and pressure, temperature, chemicals, incident radiation, electric and magnetic fields, electric current and charges, and other stimuli. Material responses to these types of stimuli include the rearrangement of atomic and molecular structures, the creation and motion of crystallographic defects or other local conformations, absorption of and emission of photons, chemical reactions, generation of charge and voltage, and other effects. Smart materials are most often reversible in nature with the stimulus and response being interchangeable actions.

This article includes examples of materials with piezoelectric, ferroelectric, shape memory, electrostrictive, magnetostrictive, electrorheological, magnetorheological, photo responsive, and sensitive and chemically and biochemically responsive properties. Some particular classes of materials are also considered including, conducting polymers, electroactive polymers, semiconductor films, metal oxides, nanotechnology (including carbon nanotubes), and smart catalysts.