Abstract
A large volume of today’s research deals with nanophases of various types. The materials engineer,
chemist, or physicist, however, when dealing with applications of nanophases is often unaware of the
effect of the small size on structure and properties. The smallest nanophases reach the limit of phase definitions by approaching atomic dimensions. There, the required homogeneity of a phase is lost and undue
property fluctuations destroy the usefulness of thermodynamic functions. In fact, itwas not expected that
a definite nanophasewould exist belowthe size of a microphase.Aneffort ismadein this reviewto identify
macrophases, microphases, and nanophases. It is shown that nanophases should contain no bulk matter
as defined by macrophases and also found in microphases. The structure and properties of nanophases,
thus, must be different from macrophases and microphases. These changes may include different crystal
and amorphous structures, and phase transitions of higher or of lower temperature. The phase properties
are changing continuously when going from one surface to the opposite one. The discussion makes
use of results from structure determination, calorimetry, molecular motion evaluations, and molecular
dynamics simulations.