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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

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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

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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

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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

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OPTICAL MICROSCOPY

Optical micrograph of an oil-in-water microemulsion.

micrometers

ELECTRON MICROSCOPY

Electron micrograph of microbial micelles

nanometers

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• 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

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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

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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)

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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

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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

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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

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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

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• 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

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• 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

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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

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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