Biomedical Engineering Reference
In-Depth Information
Figure 10.10
SEM images of Ag@Au core-shell nanocomposites.
Nanoparticles are dif erent from bulk materials and isolated molecules
because of their unique optical, electronic and chemical properties. As the
dimensions of the material are reduced the electronic properties change
drastically as the density of states and the spatial length scale of the elec-
tronic motion are reduced with decreasing size. h e optical, electronic,
magnetic, and physical properties of nanoparticles ot en deviate substan-
tially from their bulk counterparts as a result of their small size [71]. For
example, the melting temperature of crystalline gold nanoparticles is sig-
nii cantly lower than the melting temperature of bulk, crystalline gold [72].
When two particles are far apart or the distance between the surfaces
of two particles is larger than the combined thickness of two electric dou-
ble layers of two particles, there would be no overlap of dif usion double
layers, and thus there would be no interaction between two particles; but
when two particles move closer and the two electric double layers over-
lap, a repulsion force is developed. As the distance reduces, the repulsion
increases and reaches the maximum when the distance between two par-
ticle surfaces equals the distance between the repulsive barrier and the sur-
face as shown in Figure 10.11.
h e DLVO (Derjaguin, Landau, Venvey and Overbeek) theory has been
widely applied in practice to demonstrate the small particle stability in dif-
fusive medium [73]. h e DLVO theory describes the interaction between
two particles in dispersion as the potential combination of van der Waals
attraction and repulsion magnetic i eld, and van der Waals attraction
potential, electrostatic repulsion potential and the combination of the two
opposite potentials as a function of distance from the surface of a spherical
particle.
Steric stabilization, also called polymeric stabilization, is a method
that has been widely used in the stabilization of colloidal solution.
Polymeric stabilization of ers an additional advantage in the synthesis
