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Transcript
786
Suspended Nanomaterials
Nanomaterials & Colloids: How small?
~1 nm
nm (10-9m)
 Atoms
~5 um
~1 cm
~50 um
um (10-6m)
mm (10-3m)
macroscopic 
cm (10-2m)
Emulsions
Suspensions
Foams
Tang et. al. Colloids & Surfaces 2015
Biomaterials, Polymers, Liquid Crystals
Complex Fluids ~ Soft Materials
– Solids dispersed in liquid
– Liquid dispersed in liquid
– Gas dispersed in liquid
– Polymers, surfactants
SUSPENSION
EMULSION
FOAM
Mesoscopic length scales determine macroscopic phenomena
Some History…
• 1905: Einstein’s “Miraculous Year”
4 landmark papers
– E=mc2
– Theory of relativity
– Photoelectric effect
(quanta of light)
– Described Brownian motion
based on Kinetic theory of heat
• Nobel Prize in 1921
Some History…
• Pierre de Gennes (1932-2007)
“Founding father of soft matter physics”
– Nobel Prize in 1991
“for methods developed for studying order
phenomena in simple systems can be generalized to
more complex forms of matter, in particular to liquid
crystals and polymers”
Characterizing Different Length Scales
• Microscopy
– Optical
– Electron
• Scattering
– Neutrons
– X-rays
– Light
Characterization by Waves
• Light is an Electromagnetic field
• Characterized by wavelength, frequency,
phase
• Interaction with materials
– Absorption
– Reflection
– Flourescence/luminescence
– Scattering
– Transmission
We all experience light scattering…
…from small particles… in nature:
Why is the sky blue…? And the sunset red…?
Mie vs. Rayleigh Scattering
• Mie
– Particle size larger than wavelength of light
– Multiple photon scattering
• Rayleigh
– Particle size smaller than wavelength of light
– Single photon scattering
– Atmospheric particles are comparable to
– Shorter wavelengths (blue) scattered more
strongly than longer wavelengths (red)
Light and its properties
Light is an oscillating wave of electric and magnetic fields
Characterized by frequency, wavelength and phase
• Polarization: direction
of electric field oscillation
• Intensity:
Generic Light Scattering Setup
What Can LS Measure?
• By investigating pattern
of scattered light
10
10
−2
−3
0
Intensity
I/I
– Molar mass, M
– Radius of gyration rg
– Second virial coefficient,
A2 (interaction potential)
– Aggregate shapes &
structures
10
10
−4
−5
10
6
7
10
q (1/nm)
1/Angle
10
8
What Can LS Measure?
70
pH = 1
60
intensity at 90° [kcps]
– Translational/rotational
diffusion coefficient
– Hydrodynamic radius &
polydispersity (fast
dynamics)
– Aggregation &
sedimentation (slow
dynamics)
Intensity
• By investigating
dynamics of scattered
light
50
40
30
20
10
0
0
2
4
6
8
10
Time
time [hours]
12
14
16
18
Polarized light
• Incident laser light is
polarized
• Scattering from nonspherical particles alters
polarization of the light
What Can DLS Measure?
•
•
•
•
Hydrodynamic Sizes
Size Distributions
Aggregation Rates
Critical Micelle Concentration
DLS reveals Brownian motion of a certain size range
532 nm
900
Types of Materials:
suspensions, emulsions,
microemulsions, polymers,
19
micelles