The term 'smart coatings', like 'nanotechnology' and many other fashionable technological terms, has no clear and recognised definition. The broadest possible scope is assumed by those seeking research funding or wishing to present papers at 'Smart Coatings' conferences! But for those of us who have no such bias, I would like to propose and work with a definition which seems logical, though still open to debate.
A smart coating is one which detects and responds actively to changes in its environment in a functional and predictable manner.
The changes it may respond to include temperature, atmospheric pressure and biological growth. This definition includes a number of coatings that were in use long before the term 'smart coatings' became fashionable, but excludes those whose appearance or properties change in a 'passive' way due to metamerism, the use of effect, luminescent or thermally reflective pigments or which merely(!) offer levels of performance that were undreamt of a decade ago, such as superhydrophobic and lotus-effect coatings.