zeta potential测试粒度

Intensity Fluctuations
Large Particles Intensity
Time Small Particles Intensity
Time
How A Correlator Works
G (τ ) = ∫ I (t ) I (t + τ )dt
0 ∞
Intensity
Delay Time
Hydrodynamic Diameter: Effect of Ionic Strength
1/K (Debye Length) is the thickness of the electrical double layer It is dependent upon the ionic strength of the medium Particle Diameter Hydrodynamic Diameter In high ionic strength media the double layer is suppressed Latex standards should be diluted in 10mM NaCl to suppress the double layer and hence give the correct result (ISO13321)
Screen
Brownian Motion And Scattered Light
Two beams interfere and ‘enhance each other’ resulting in an increased intensity in the scattered light
Screen
0.1000
0 0.1000
10.
1000. Time (us)
1.e+5
1.e+7
1.e+9
DATA INTERPRETATION: CORRELOGRAMS
Raw Correlation Data 0.8000
Very large particles High polydispersity Presence of very large particles/ aggregates present (noisy baseline)
0.9000
0.8000
0.7000
Correlation Coefficient
0.6000
0.5
ห้องสมุดไป่ตู้0.4000
0.3000
0.2000
0.1000
0 0.1000
10.
1000. Time (us)
1.e+5
1.e+7
1.e+9
DATA INTERPRETATION: CORRELOGRAMS
Raw Correlation Data 0.7000
Stokes-Einstein Equation
d(H) = kT 3πηD
where d(H) = hydrodynamic diameter k = Boltzmann’s constant T = absolute temperature η = viscosity D = diffusion coefficient
τ
0
t
δt 2δt 3δt 4δt
∞
Time
How A Correlator Works
• If the particles are large, the signal will be changing slowly and the correlation will persist for a long time • If the particles are small and moving rapidly then the correlation will disappear more rapidly
Typical Correlogram From Sample Containing Large Particles
Typical Correlogram From Sample Containing Small Particles
Combined Correlograms
Small Particles
Hydrodynamic Diameter
• The diameter which is measured in DLS is a value that refers to how a particle moves within a liquid • It is called the HYDRODYNAMIC DIAMETER • The diameter that is obtained is the diameter of a sphere that has the same translational diffusion coefficient as the particle
0.7000
0.6000
Correlation Coefficient
0.5
0.4000
0.3000
0.2000
0.1000
0 0.1000
10.
1000. Time (us)
1.e+5
1.e+7
1.e+9
The Cumulants Analysis
• ISO13321 states that a 3rd order fit of a polynomial should be used • Ln[G1] = a + bτ + cτ2 • The value of b = z-average diffusion coefficient • 2c/b2 = polydispersity index (the width of the distribution) • This method only gives a mean and a width and is only a good description for reasonably narrow monomodal samples • It is an INTENSITY mean size
Polydispersity Index
• 0 to 0.05 - Only normally encountered with latex standards or particles made to be monodisperse • 0.05 to 0.08 - Nearly monodisperse sample. DLS cannot normally extract a distribution within this range • 0.08 to 0.7 - This is a mid-range polydispersity, it is the range over which the distribution algorithm based on NNLS best operates over • Greater than 0.7 - Very polydisperse. Care should be taken in interpreting results as the sample may not be suitable for the technique, e.g. a sedimenting high size tail may be present
1/K
The Speckle Pattern
Sample Cell Laser Incident Beam Axis
Speckle Pattern
Screen
Brownian Motion And Scattered Light
Consider 2 stationary particles
Two beams interfere and ‘cancel each other out’ resulting in a decreased intensity in the scattered light
Very small particles Medium range polydispersity No large particles/ aggregates present (flat baseline)
0.6000
0.5 Correlation Coefficient
0.4000
0.3000
0.2000
Brownian Motion And Scattered Light
Consider many particles Screen
Many scattered beams interfere with one another resulting in a very complex intensity pattern of ‘speckles’
Intensity Fluctuations
• For a system of particles undergoing Brownian motion, a speckle pattern is observed where the position of each speckle is seen to be in constant motion • This is because the phase addition from the moving particles is constantly evolving and forming new patterns • The rate at which these intensity fluctuations occur will depend on the size of the particles
Optical Configuration Of The Nano
DLS and Brownian Motion
Dynamic Light Scattering or Photon Correlation Spectroscopy or Quasi-Elastic Light Scattering measures Brownian motion and relates it to size
Hydrodynamic Diameter: Effect of Ionic Strength
1/K (Debye Length) is the thickness of the electrical double layer It is dependent upon the ionic strength of the medium Particle Diameter Hydrodynamic Diameter 1/K In low ionic strength media (eg DI water) the double layer is extended A latex standard diluted in DI water will give the wrong result (too high)
Large Particles
DATA INTERPRETATION: CORRELOGRAMS
Raw Correlation Data
Large particles Medium range polydispersity Presence of very large particles/ aggregates (baseline not flat)
Brownian Motion
• Random movement of particles due to the bombardment by the solvent molecules that surround them
Brownian Motion
• Temperature must be accurately known because we need to know the viscosity • The temperature needs to be stable otherwise convection currents in the sample will cause non-random movements which will ruin correct size interpretation • The larger the particle the more slowly the Brownian motion will be • Higher the temperature the more rapid the Brownian motion will be • Velocity of the Brownian motion is defined by the translational diffusion coefficient (D)