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

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

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

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

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

Zetasizer Nano ZS Malvern He-Ne Laser = 633 nm

Brownian motion and scattering

Intensity of the scattered light fluctuates

Small particles- noisy curve Large particles- smooth curve

Determining particle size Determined autocorrelation function Depend

Correlation function Correlograms

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

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

Optical arrangement in 173° backscatter detection

Information Size by: - Intensity I  d 6 Rayleigh Scattering (For nanoparticles less than d =λ/10 or around 60nm the scattering will be equal in all Directions-isotropic)

This particles will scatter 10 6 (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

8 80

- Volume  d 3  d 1 - Number V= 4  r 3 r = d/2 V= 4  (d/2)3 = 4  d 3 8 By the Mie theory is possible convert intensity distribution into volume

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

d(intensity) > d(volume) > d(number)

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.

Zeta Potential