Page 144 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

130 Principles and Methods

Slits
Sample
I (θ, t)
detector
IO θ

Scattering volume

Incident radiation e
(X–rays, neutrons, light)
D
Figure 4.15 Illustration of the scattering principle upon which most scattering
techniques and apparatuses are based.

calibrated light scattering. Static scattering measures the value of I( , t)
averaged over a period of time t, typically as a function of u. Static
scattering measurements can be used to obtain structural information
such as size, shape, and agglomeration state. Dynamic scattering meas-
ures the instantaneous values of I(t) over time at a fixed angle, u. The
variability in scattering over time gives information on the diffusion
coefficient due to Brownian motion of the scattering nanoparticles in
suspension. Dynamic scattering is thus an indirect measurement of
particle size, shape, and interactions. The third type of information
given by scattering experiments is obtained by the calibration of the
measured intensity to obtain the quantitative average number of scat-
tered photons per unit solid angle [Thill et al., 2002]. This method
yields, with almost no approximations or model assumptions, physical
quantities such as the volume or specific surface averaged over the
whole sample. Different radiation sources used for scattering experi-
ments can yield complementary information on the sample. Light scat-
tering is associated with variations in dielectric properties (or refractive
index) [Berne and Pecora, 1976; Berne, 1996], X-rays are scattered by
electrons [Berne, 1996; Glatter and Kratky, 1982], and neutrons are
scattered by nuclei [Higgins and Benoit, 1994].

Static scattering experiment
Absolute scattered intensity. When a flux N 0 (counts/s) of photons or neu-
trons is incident on a sample (volume V and thickness e s ) then a part of
the flux N( u,
) is scattered in a direction u with a solid angle
:

Tse /V dds/d
sud
(8)
Nsu,
d 5 N 0 s