Environmental Engineering Reference
In-Depth Information
Fig. 13.3 Schematic
showing the optical path of
the laser
Fig. 13.4 Monitoring of
the nanoparticle movements
in NTA equipment
Mounted on a mount, a CCD camera, operating at 30 frames per second, is used
to capture a video with a field of view approximately 100
m. Particles in
the scattering volume are seen moving rapidly under Brownian motion.
The NTA programmer simultaneously identifies and tracks the center of each
particle on a frame-by-frame basis throughout the length of the video (typically
900 frames or 30 s). Figure
13.4
shows an enlarged image of two such particles and
the trajectory they have taken over several frames as tracked by the NTA image
analysis programmer.
The average distance each particle moves in
x
and
y
in the image is automatically
calculated. From this value, the particle diffusion coefficient,
D
, can be obtained
and, knowing the sample temperature
T
, and solvent viscosity
μ
m
80
μ
the particle
hydrodynamic diameter
d
identified. That 3 dimensional Brownian movement is
tracked only in 2 dimensions (
x
and
y
) is accommodated by use of the following
ʷ
