6.
Materials Characterization Lab
www.mri.psu.edu/mcl
Instruments at MRL
Malvern Mastersizer S  Wet and Dry Laser Diffraction
(0.05 to 900 µm)
7.
Materials Characterization Lab
www.mri.psu.edu/mcl
Dynamic Light Scattering (DLS)
Quasi Elastic Light Scattering (QELS)
Photon Correlation Spectroscopy (PCS)
relies on measuring the Brownian motion of small
particles and relating this to the hydrodynamic
diameter, dh of the particle system by means of
the StokesEinstein equation:
d h = kT/3πηD
where k is Boltzmann's Constant,
T is the absolute temperature,
η is the viscosity of the medium and
D is the diffusion coefficient.
9.
Materials Characterization Lab
www.mri.psu.edu/mcl
Brownian Motion
Particles move or diffuse as a consequence
of thermally driven solvent collisions.
Translational
diffusion is not the
same as linear
diffusion.
10.
Materials Characterization Lab
www.mri.psu.edu/mcl
The diffusion coefficient (D) is calculated by fitting the correlation
curve to an exponential function G(t), with D being proportional to the
lifetime of the exponential decay
where I is the scattering intensity, to is the initial time, t is the delay
time, A is the amplitude or intercept of the correlation function, B is the
baseline, D is the diffusion coefficient, and q is the scattering vector.
11.
Materials Characterization Lab
www.mri.psu.edu/mcl
Classical vs. Backscatter
12.
Materials Characterization Lab
www.mri.psu.edu/mcl
Backscatter Benefits
Increased scattering volume and variable cell position
Dilute low MW Concentrated high
samples MW samples
• Enhanced Sensitivity • Higher Concentrations
• Larger Size Range • Better Reproducibility
13.
Materials Characterization Lab
www.mri.psu.edu/mcl
Typical Analysis Algorithms
• Cumulants
– Assumes a single exponential decay, i.e. one particle size
– Gives only the Z average size and polydispersity index
– Recommended by International Standards Organization
G(t) = B + A e2q2D
• Multimodal
– Fits the curve to the optimal number of exponentials
G(t) = B + ΣA e2q2D
14.
Materials Characterization Lab
www.mri.psu.edu/mcl
Ideal Samples
Cumulant & multimodal distribution results are consistent
15.
Materials Characterization Lab
www.mri.psu.edu/mcl
Typical Samples
Cumulant & multimodal distribution results are NOT consistent
16.
Materials Characterization Lab
www.mri.psu.edu/mcl
Hydrodynamic radius
By definition, the DLS measured radius is the radius of
a hypothetical hard sphere that diffuses with the same
speed as the particle under examination. In practice,
particles are solvated. As such, the radius calculated
from the diffusional properties of the particle is
indicative of the size of the dynamic hydrated/solvated
particle.
17.
Materials Characterization Lab
www.mri.psu.edu/mcl
High Concentration  Issues
• Multiple Scattering  light scattered from diffusing
particles is rescattered by other particles => size
reduction.
• Excluded Volume  the presence of other particles blocks
or hinders free particle diffusion => size increase.
• Aggregation Equilibrium  concentration dependent
aggregation of primary particles => increase distribution,
polydispersity and average size.
• Electrostatic Interactions  overlapping electric fields
lead to interactions that can influence the translational
diffusion => change in size.
18.
Materials Characterization Lab
www.mri.psu.edu/mcl
High Concentration  Solutions
• Use the bulk, rather than the solvent,
viscosity.
• Use salt.
• Dispersion:
Chemical dispersion: Dispersants.
Mechanical dispersion: Sonication:
Excess thermal and mechanical agitation increases the
Possibility of collisions between particles causing agglomeration,
Rule:
Use absolute minimum mechanical agitation and in
short periodic bursts.
20.
Materials Characterization Lab
www.mri.psu.edu/mcl
Sedimentation
uSt= (r s  r f)g D²
h 18
f
b
Rate dependent on
fd
density
Underestimates
size
fg
Limited dynamic
Liquid
range
Slow
24.
Materials Characterization Lab
www.mri.psu.edu/mcl
Hosokawa Micron Air Jet Sieve
Sieve Analysis
Solids only
Large particles
38 µm min
Inexpensive
Limited accuracy,
resolution,
precision
25.
Materials Characterization Lab
www.mri.psu.edu/mcl
Technique and Dynamic Range
Sieve
Microscope
Sedimentation
Electro zone
PCS
Acoustic
Image Analysis
Diffraction
.001 .01 .1 1µm 10 100 1000
26.
Materials Characterization Lab
www.mri.psu.edu/mcl
Zeta Potential
Slipping plane
The liquid layer surrounding the
Particle with
particle exists as two parts; an
negative
inner region (Stern layer) where
surface
the ions are strongly bound and
charge
an outer (diffuse) region where they
are less firmly associated.
Stern layer
Within this diffuse layer is a notional
boundary within which the particle
Diffuse layer
100
{
acts as a single entity.

Surface potential
Stern potential
mV Zeta potential
The potential at this boundary is the
ZETA POTENTIAL
0
Distance from particle surface
27.
Materials Characterization Lab
www.mri.psu.edu/mcl
Why Is Zeta Potential Important
Particles do not interact electrostatically according
to the magnitude of their surface charge, but
according to the zeta potential at the slipping plane.
The magnitude of the zeta potential gives an
•
indication of the stability of the system
 If all the particles have a large negative or
positive zeta potential they will repel each other
and there is dispersion stability.
 If the particles have low zeta potential values
then there is no force to prevent the particles
coming together and there is dispersion
instability (aggregation).
28.
Materials Characterization Lab
www.mri.psu.edu/mcl
Instruments at MRL
Brookhaven ZetaPALS Zeta Potential and
Particle Size Analyzer
31.
Materials Characterization Lab
www.mri.psu.edu/mcl
Acoustic Attenuation
Acoustic wave out
Acoustic wave in
Is
I0 f
Frequency
f
Frequency
Suspension
DL
⎛ ⎞
I
1
α= lo g ⎜ ⎟
0
Attenuation
∆L ⎝ S⎠
I
• The double layer is disturbed by an ultrasonic wave. The
displacement of the ionic cloud with respect to the surface
creates a dipole moment. The sum of these dipole moments
over many particles creates an electrical field which is sensed
by a receiving antenna immersed in the sample.
38.
Materials Characterization Lab
www.mri.psu.edu/mcl
New Instruments
ASAP 2020 Accelerated Surface Area and Porosimetery Analyzer.
Unique Capability
• Two Independent
vacuum systems.
• Oilfree “dry” vacuum
pump.
• Intelligent degas
system.
• New longduration
cryogen system.
• Automated selection of
gas
• Ability to connect to a
mass spec.
39.
Materials Characterization Lab
www.mri.psu.edu/mcl
ASAP 2020 Chemisorption Option
Uses the static
volumetric technique to
determine the percent
metal dispersion, active
metal surface area,
size of active particles,
and surface acidity of
catalyst materials.
41.
Materials Characterization Lab
www.mri.psu.edu/mcl
Source Material
• Instrument Manuals.
• Several books on specific materials.
• journals.
• Conferences
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