22
2 The Kinds of Ordinary Materials
Fig. 2.4 Fractional rate of
drop of autocorrelation as a
function of the square
scattering wave number, q 2 .
(From Wong & Wiltzius as in
Fig. 2.3)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.0
0.2
0.4
0.6
0.8
1.0
×10
9
q 2 (cm –2 )
Γ (sec
–1
)
Optical Effects
If the particles in a solution are comparable in size (or larger) to the wavelength
of the light illuminating them, they will become visible. For our eyes, this
means greater than or equal to about 4000 ångströms. The ‘Tyndall effect’ is the
observation of a bluish tinge to light scattering by a colloidal suspension of particles
whose size is comparable to the wavelength of the scattered light. As in Rayleigh
scattering, the intensity of the scattered light is greater for blue than red. However,
the effect is not as strong as in Rayleigh scattering, in that the particles are not
far smaller than the wavelength of the light, nor are they much larger than the
wavelength, which would be the realm of ‘Mie scattering’, for which the light of
all colors coherently produce no color in the reflected light, such as the light we see
from the surface of a droplet of water. The Tyndall effect can be used to estimate the
size of colloidal particles suspended in a clear liquid.
Blue eye color is due to the Tyndall effect, in that light is scattered from a turbid
translucent layer in the iris, without much melanin present to cause a brown color.
The blue shade to very fine smoke particles in air is also a Tyndall effect, as is the
blue ting to clouds of water droplets as the droplets evaporate.
2.2.3 Separating Materials
Any fluid mixture in an open system able to expel heat into the environment
will have a tendency to separate, by natural processes, into bulk amounts of the
embedded materials. Witness ore deposits in geologic material initially fluid at
relatively high temperature and then allowed to slowly cool, or the crystallization of
salts from a brine solution. Natural processes that can cause separation include:
2 The Kinds of Ordinary Materials
Fig. 2.4 Fractional rate of
drop of autocorrelation as a
function of the square
scattering wave number, q 2 .
(From Wong & Wiltzius as in
Fig. 2.3)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.0
0.2
0.4
0.6
0.8
1.0
×10
9
q 2 (cm –2 )
Γ (sec
–1
)
Optical Effects
If the particles in a solution are comparable in size (or larger) to the wavelength
of the light illuminating them, they will become visible. For our eyes, this
means greater than or equal to about 4000 ångströms. The ‘Tyndall effect’ is the
observation of a bluish tinge to light scattering by a colloidal suspension of particles
whose size is comparable to the wavelength of the scattered light. As in Rayleigh
scattering, the intensity of the scattered light is greater for blue than red. However,
the effect is not as strong as in Rayleigh scattering, in that the particles are not
far smaller than the wavelength of the light, nor are they much larger than the
wavelength, which would be the realm of ‘Mie scattering’, for which the light of
all colors coherently produce no color in the reflected light, such as the light we see
from the surface of a droplet of water. The Tyndall effect can be used to estimate the
size of colloidal particles suspended in a clear liquid.
Blue eye color is due to the Tyndall effect, in that light is scattered from a turbid
translucent layer in the iris, without much melanin present to cause a brown color.
The blue shade to very fine smoke particles in air is also a Tyndall effect, as is the
blue ting to clouds of water droplets as the droplets evaporate.
2.2.3 Separating Materials
Any fluid mixture in an open system able to expel heat into the environment
will have a tendency to separate, by natural processes, into bulk amounts of the
embedded materials. Witness ore deposits in geologic material initially fluid at
relatively high temperature and then allowed to slowly cool, or the crystallization of
salts from a brine solution. Natural processes that can cause separation include: