Environmental Engineering Reference
In-Depth Information
3.
Engineering behavior of large-scale construction problems, or bulk materials using
finite element methods where averaging constitutive laws are used to incorporate the
microstructure.
However, because of the unusual and sometimes complex character of interfaces and
associated phenomena, the development of fully satisfying theoretical models has been
slow. There exists a great deal of controversy in many areas related to interfaces [1].
Also, the classic thermodynamics has more or less neglected to interpret the interface
phenomena in modern science due to the appearance of computer simulation technique.
Note that many present controversies in theories and experiments in interface phenomena
are not bad, since it represents the fuel for continued fundamental and practical
research. However, for the practitioner who needs to apply the fruits of fundamental
research, such uncertainty can sometimes complicate attempts to solve practical
interfacial problems [1].
Nanoscience and nanotechnology are rapidly developed field in materials science and
engineering in recent years. As size of materials drops to nanometer size range,
interface/volume ratio increases and thus interface effect on materials properties becomes
evident. When the sample size, or grain size, or domain size becomes comparable with the
specific physical length scale such as the mean free path, the domain size in ferromagnets or
ferroelectrics, the coherence length of phonons, or the correlation length of a collective
ground state as in superconductivity, then the corresponding physical phenomenon will be
strongly affected [3].
The interface phenomena, which affect the materials behavior, are in nature produced
by different energetic states of molecules on the interface in comparison with those within
the materials. Since the molecular interactions on the interfaces differ from those on the
interior of phases, the excess specific Gibbs free energy or interface energy for molecules
of unit interface area exists, which is equal to the difference between the total Gibbs free
energy of interface molecules and that within the phases per unit area. The interfaces and
corresponding interface energies studied here are sometimes called as other ones. The
following is several examples of them. When the interface is composed of the same solids,
the interface is also called as grain boundary and the corresponding interface energy is
named as grain boundary energy. Usually solid-vapor interface energy and liquid-vapor
interface energy are considered to have the same size of solid-vacuum interface energy and
that of liquid-vacuum interface energy since their differences are often at least one order
smaller when the external pressure is ambient one although it is known that this difference
just leads to the absorption of vapor on interfaces. The solid-vapor interface energy is also
named as surface energy while the liquid-vapor interface energy is made as surface
tension [4].
Although surface tension of liquid can mean both surface energy and surface stress where
they have the same size and meaning, this identity fails for solids [5]. The former describes
the reversible work per unit area to form a new solid surface, whereas the latter denotes the
reversible work per unit area due to elastic deformation, which is equal to the derivative of γ
with respect to the strain tangential to the surface.
All above phenomena change as materials dimension and broken symmetry vary. The
dimensionality is dictated by the size in a certain direction of the object compared to an
appropriate length scale for the phenomena being discussed. If only one dimension of the
Search WWH ::
Custom Search