Particle size analysis of nanoparticles and light scattering analysis and methods

1. Nanoparticles Characterization:
Measurement of the particles
size by the PCS technique
MSc. Priscyla D. Marcato
Dr. Nelson Durán

2. • If the particles or molecules are illuminated with a
laser, the intensity of the scattered light fluctuates at
a rate that is dependent upon the size of the particles
• Analysis of these intensity fluctuations yields the
velocity of the Brownian motion and hence the
particle size using the Stokes-Einstein relationship.
Principle of Measurement

3. Brownian Motion
Particles, emulsions and
molecules in suspension
undergo Brownian motion.
This is the motion induced by the
bombardment by solvent
molecules that themselves are
moving due to their thermal
energy
Temperature and viscosity must
be known

4. The velocity of the Brownian motion is defined by a
property known as the translational diffusion
coefficient (usually given the symbol, D).
Stokes-Einstein relationship

6. No spherical particles
Hydrodynamic diameter is calculated based on the
equivalent sphere with the same diffusion coefficient

7. Zetasizer Nano ZS
Malvern
He-Ne Laser
 = 633 nm

8. Brownian motion and scattering

9. Intensity of the scattered light
fluctuates

10. Intensity of the scattered light
fluctuates
Small particles- noisy
curve
Large particles- smooth
curve

11. Determining particle size
Determined autocorrelation function
Depend

12. Correlation function Correlograms

13. Correlogram from a
sample containing
large particles
Correlogram from a
sample containing
small particles

17. Low
concentration turbidity is linear with
concentration
High
concentration
Particles are so close together
that the scattered radiation is
re-scattered by other particles.

18. Optical
arrangement
in 173°
backscatter
detection

21. Information
Size by:
- Intensity I  d6
Rayleigh Scattering
(For nanoparticles less than d =λ/10 or around 60nm
the scattering will be equal in all
Directions-isotropic)

22. This particles will scatter 106 (one million) times
more light than the small particle (8 nm)
The contribution to the total light scattered by the
small particles will be extremely small
8 nm
80 nm

23. 8 80

24. - Volume  d3
 d1
- Number
V= 4r3
r = d/2
V= 4(d/2)3 = 4d3
8
By the Mie theory is possible convert intensity
distribution into volume

25. Two population of spherical nanoparticles :
5 nm and 50 nm
(in equal number)
Which of these distributions should I use?

26. d(intensity) > d(volume) > d(number)

30. Direct determination of the number-weighted
mean radius and polydispersity from dynamic
light-scattering data
Philipus et al., Applied Optics, 45, 2209 (2006)
We find that converting intensity-weighted
distributions is not always reliable, especially when
the polydispersity of the sample is large.

33. Zeta Potential