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RESOLVING NANOMETER STRUCTURESUSING SMALL-ANGLE NEUTRON SCATTERING
OR
SANS FOR TEACHERS
Boualem Hammouda
National Institute of Standards and Technology Center for Neutron Research
Gaithersburg, MD 20899
COVER TWO CONCEPTS
1 10 100 1000
the millimeter
1 10 100 1000 the micrometer
1 10 100 1000 the nanometer
The nanometer scale
red likes water (hydrophilic)blue dislikes water (hydrophobic)
Amphiphile molecules
( or surfactants or soap)
micelles form
2
10 100 103 104 105 106 107
Length Scales (nanometers)
108 109
1 meter1 millimeter1 micrometer
1
1 nanometer
THE NANOMETER
• Thickness of a hair = 100 microns• Thickness of a sheet of paper is 100 microns
• Size of a human cell = 10 microns• Size of bacteria = 1 to 10 microns
• Size of viruses = 10 to 100 nanometers• Thickness of the cell membrane = 5 nanometers
• Size of the atom = 0.1 nanometer
TYPICAL SIZES
3
10-5 10-3 0.1 10 103 105 107 109
γ raysX rays
VisInfrared
RadarRadio
UVNeutrons
Wavelength (nanometers)
VARIOUS RADIATIONS
THE CELL
Membrane
The nucleus
DNA
Proteins
hydrophilic = likes water
hydrophobic = dislikes water
micrometers
4
THE CELL MEMBRANE
nanometers
alpha helixprotein
glycolipid
cholesterol
hydrophilic phospholipids
globularprotein
hydrophobic tails
coil
• Optical microscope. Magnification of 100 to 1,000• Discovered during the time of Galileo
• Electron microscope. Magnification of 1,000 to 1,000,000• Discovered over the past century
• Neutron scattering discovered some 50 years ago
• Electron microscopy and neutron scattering probe nanoscale structures
• They both have advantages and disadvantages
MAGNIFICATION
5
OPTICAL MICROSCOPY
Optical micrograph of an oil-in-water microemulsion.
micrometers
ELECTRON MICROSCOPY
Electron micrograph of microbial micelles
nanometers
6
• Microscopy shows direct images
• Scattering is measured in the “scattering space”. Mathematical models are used to resolve structures
• Neutrons are produced in nuclear reactors (Oak Ridge, NIST) and spallation source (Los Alamos)
• Small-angle neutron scattering (SANS) resolves nanometer size structures
• Deuteration is an advantage of neutron scattering
NEUTRON SCATTERING
Zero contrast
Multiple contrasts Contrast match
Finite contrast
The Deuteration Method consists In replacing hydrogen by deuterium
neutron
The Hydrogen Atom
proton
Electron
proton
Electron
The Deuterium Atom
0.1 nm
7
NIST GUIDE HALL
SANS: SMALL-ANGLE NEUTRON SCATTERING
Google search with “Center for Neutron Research” and “SANS” as keywords resulted in some 85,000 hits.
Incident Beam
Neutron Detector
Scattered Beam
Sample
Q
MonochromaticNeutron Beam
15 m 15 m
0.2 o to 20 o
Q is the scattering variable
8
10% P85 Pluronic
in d-water at 60oC
SANS Data
Inte
nsity
Scattering Variable Q (nm-1)
THE NANOSCALE
0.10.01 1 10
10100 1
10-310-4
103104105
Length Scale (nm)
Scattering Variable Q (nm-1)
9
PLURONICS IN DEUTERATED WATER
PEO-PPO-PEO structure:Poly(ethylene oxide) or PEO monomer -CH2CH2O-Poly(propylene oxide) or PPO monomer -CH(CH3)CH2O-Deuterated water D2O
Interactions:-CH2- is hydrophobic, -O- is hydrophillic (hydrogen bonding).
Upon heating PPO becomes more hydrophobic. Micelles form.
PEO
PEO
PPO
Coil
Dissolved moleculeat low temperature
Micelles form athigh temperature
PEO
PEO
PPO
hydrophobichydrophilic
PEO PPO
PEO
Dissolved Pluroniccopolymers at low temperatures
PLURONICS
10
PLURONICS ARE USED…
-- as detergents, -- as foaming and emulsification agents, -- for the separation and solubilization of organics in aqueous solutions, -- for the protection of microorganisms from damage in bioprocessing, -- for the solubilization, and the controlled release of drugs,-- as templates for catalyst formation.
Search of the ACS Publications Database with “Pluronics”as keyword resulted in 600 published papers.
0.1
1
10
100
0.1 1
0.5 % P85 in d-water
100 oC
90 oC80 oC
70 oC60 oC
50 oC40 oC30 oC
20 oC10 oC S
catte
ring
Inte
nsity
(cm
-1)
Scattering Variable Q (nm-1)
cylindrical micelles
spherical micelles
coils
lamellar micelles
SANS DATA
11
0.1
1
10
100
0.1 1
0.5 % P85 in d-Water
100 oC
90 oC
70 oC
50 oC
10 oC S
catte
ring
Inte
nsity
(cm
-1)
Scattering Variable Q (nm-1)
MICELLES PHASES
sphericalmicelles
cylindricalmicelles
lamellarmicelles
coils
FIT SANS DATA TO A MODEL OF CORE-SHELL SPHERICAL PARTICLES
RA=4.26 nm
RB=7.14 nm
core region A
shell region Bsolvent region C
10% P85 Pluronic/D2O, 40 oC
In the core:2,795 PPO monomers690 PEO monomers490 D2O molecules
In the shell:2,943 PEO monomers34,167 D2O molecules
12
PHASE DIAGRAM
P85 Fraction (%)
P85 in d-water
10 20 30 40 50 60 70 80 90 1000
20
40
60
80
0
Coils
SphericalMicelles
Cylindrical Micelles
Lamellar Micelles
• Weigh and mix two P85 Pluronic samples in deuterated water:
0.5 % sample – 0.01 g P85 in 1.99 g d-water10 % sample – 0.2 g P85 in 1.8 g d-water
• Describe the titanium cells and the quartz windows
• Assemble the cells and fill them
WHAT WILL BE DONE IN THE LAB
13
• Describe the instrument, talk about configurations
• Load sample cells in the heating block
• Start data acquisition, see live data being collected
• Check out the various sample environments
• Check out the posters
• Ask lots of questions
WHAT WILL BE DONE AT THE INSTRUMENT
14
• Do fits to the Guinier-Porod model for the SANS data from 0.5 % P85 in deuterated water
• Use the Porod plot to get clues about the formed structures
• Show effect of temperature on SANS data
• Show the phase diagram
DATA ANALYSIS
0.1
1
10
0.1 1
0.5 % P85/d-water, T = 50 oC
SANS DataGuinier-Porod Model Fit
Sca
ttere
d In
tens
ity (c
m-1
)
Scattering Variable Q (nm-1)
SPHERICAL MICELLES AT 50 OC
R = 6.1 nm
sphericalmicelles
15
0.1
1
10
100
0.1 1
0.5 % P85/d-water, T = 70 oC
SANS DataGuinier-Porod Model Fit
Sca
ttere
d In
tens
ity (c
m-1
)
Scattering Variable Q (nm-1)
CYLINDRICAL MICELLES AT 70 OC
R = 5.2 nm
cylindricalmicelles
0.1
1
10
100
0.1 1
0.5 % P85/d-water, T = 90 oC
SANS DataGuinier-Porod Model Fit
Sca
ttere
d In
tens
ity (c
m-1
)
Scattering Variable Q (nm-1)
LAMELLAR MICELLES AT 90 OC
T/2 = 4.7 nm
lamellarmicelles
16
PHASE DIAGRAMP85 in d-water
P85 Fraction (%)
LamellarDisordered
hexagonalCylindrical
Micelles
SphericalMicelles
cubic
Coils
10 20 30 40 50 60 70 80 90 1000
20
40
60
80
0
Lamellar Micelles
RELATED SANS RESEARCH
17
WAX BUILDUP IN DIESEL ENGINES
Polyolefin copolymer additive reduces wax buildup at low temperatures.
Diesel engines do not run well in cold climates (below 10 oC). Filters clog up due to wax crystal buildup.
CONSERVATION SCIENCE
Special gels (called nanosponges) are applied to paintings to clean and restore them to a healthier condition. The clear (left) portions have been cleaned and the dark (right) portions have not.
Nanosponges have also been applied to the cleaning of Mayan wall paintings (Mexico).
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THE SANS PROGRAM AT NIST– 200 experiments per year– 15 doctoral theses per year– 80 publications per year
THIS PRESENTATION CAN BE FOUND AT
http://www.ncnr.nist.gov/staff/hammouda/SANS_for_teachers/
FINAL WORDS
THANK YOU