Termokromism

Termokromizm is the property of certain materials to change color in response to a change in temperature. The color change can be reversible or, less commonly, irreversible, and is typically due to alterations in the material’s electronic structure, molecular configuration, or optical path.

The underlying mechanisms include several distinct processes. In organic thermochromic systems, color changes often arise from temperature-driven shifts between two molecular forms of a dye or a leuco dye in a colorless and colored state, typically managed by a developer or matrix that stabilizes one form at a given temperature. In liquid crystal thermochromic materials, temperature affects the arrangement and pitch of liquid crystal phases, altering the wavelengths of light that are reflected and producing visible color changes. In inorganic systems, materials such as vanadium dioxide (VO2) exhibit a metal–insulator transition near a characteristic temperature, which changes the material’s optical properties, including color and infrared transmittance.

Thermochromic materials are commonly categorized as organic thermochromic pigments (including leuco dye systems and polymer matrices), liquid crystal thermochromic materials, and inorganic thermochromic materials. Applications cover temperature indicators and visual sensors on packaging, novelty items like mood rings, smart textiles, and some switchable coatings or smart windows. Advantages include simple actuation by temperature alone and relatively low cost, while limitations involve restricted and sometimes narrow operating temperature ranges, potential fading with ultraviolet exposure, and stability concerns depending on the specific chemistry and encapsulation.