6/12/2012 1 SANS BASICS Boualem Hammouda National Institute of Standards and Technology Center for Neutron Research [email protected]OUTLINE • 1. The SANS Technique • 2. SANS Data Analysis Standard Plots (Guinier, Porod) SANS Models Inverse Fourier Transform Shape Reconstruction Method • 3. SANS Research Topics A- Phase Transitions in Pluronic P85 Solutions B- Role of Chirality in Peptide Biogels C- Structure of SDS Micelles • 4. Final Points VSANS and USANS Final Words
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6/12/2012
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SANS BASICS
Boualem Hammouda
National Institute of Standards and Technology Center for Neutron Research
In the core:2,795 PPO monomers690 PEO monomers490 D2O molecules
In the shell:2,943 PEO monomers34,167 D2O molecules
Material Balance Equations: Results for 10% P85 at 40 oC:
B- Role of Chirality in Peptide Biogels
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Faraday Rotation
Substances rotate linearly polarized light to the left (L-type) or to the right (D-type)
- A molecule is chiral if it is different from its mirror image
- Human hands are chiral
- Non-biological substances are heterochiral . They can be of the L-type or D-type
- Biological substances are homochiral. They are either of the L-type or of the D-type
- Proteins are of the L-type. Sugars are of the D-type. DNA is of the D-type. The reason is still a mystery
Chirality
Right handedLeft handed
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- Proteins are responsible for most biological function. They are made out of peptides. Peptides are made out of amino acids. There are 20 amino acids.
- Examples of amino acids include Lysine (K), Glutamate (E), Tryptophan (W) and Alanine (A)
- Most proteins rotate polarized light to the left. They are left handed or L-type
Proteins
DNA- DNA is the blueprint for life. It is the template for the synthesis of proteins
- DNA is made out of nucleotides. There are 4 DNA nucleotides: A, C, T and G
- The human genone contains 6 billion nucleotides making up some 23,000 genes
- Most DNA rotate polarized light to the right. They are right handed or D-type
- Peptides can be synthesized to be L-type or D-type
- Series of L-type and D-type short peptide sequences (11 amino acids) were synthesized.
- These were combined to give L-D- or D-L- heterochiral mixtures and L-L- or D-D- homochiral mixtures
- The resulting gels were investigated using mechanical testing (shear response) and SANS measurements
Peptide Biogels
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Mechanical Testing
- Heterochiral samples gel faster. Homochiral samples are slow to gel.
- Homochiral gels are initially weaker then become stronger
0 10 20 30 40 50100
101
102
103
104
105
Ela
stic
Modulu
s, P
a
Time, hrs
heterochiral
homochiral
SANS Data
Homochiral
Heterochiral
- Heterochiral gels scatter differently from homochiral ones
- They are all characterized by fibrilar structure
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SANS Data Analysis
Homochiral
Heterochiral
Heterochiral
Homochiral
- Homochiral fibers are thicker and denser than heterochiral ones
Shape ReconstructionFiber cross sections
Inverse FourierTransform
heterochiralhomochiral
webFiber
- Peptide biogel is formed of fibers joined by a web
Fiber-Web Structure
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- Chirality plays a role in the mechanical properties and structure of biogels
- Homochirality confers higher strength (shear modulus) and yield stress value. Right-right hand-shake is stronger.
- Biogel structure consists of main fibers held together by a web of cross fibers
- Fibers for homochiral biogels are thicker and denser
- Advantages conferred to homochirality lead to enhanced stability
Results
C- Structure of SDS Micelles
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- Surfactants are formed of a hydrophilic head and a hydrophobic tail
- Micelles form when enough surfactants aggregate (above the critical micelle concentration or CMC)
- SDS surfactants form micelles in water (or deuterated water)
Micelle Formation
0.1
1
10
0.01 0.1
68 oC
20% SDS10% SDS5% SDS2% SDS1% SDS0.5% SDS
Sca
tte
red
In
ten
sit
y (
cm-1
)
Scattering Variable Q (Å-1)
SANS from SDS Micelles
- Ellipsoidal micelles form
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0.1
1
10
0.01 0.1
5 % SDS, 49 oC
Model FitSANS Data
Sca
tte
red
In
ten
sit
y (
cm-1
)
Scattering Variable Q (Å-1)
Bd
)Q(d
Q
A)Q(I
ellipsoidsn
)Q(S)Q(PV2
ellipsoidsd
)Q(dIP
Ellipsoid Micelles Model Fit
- Power law (low-Q) + ellipsoidal micelles (high-Q) model fits well
1.5 104
2 104
2.5 104
3 104
3.5 104
4 104
4.5 104
280 300 320 340 360
10 % SDS5 % SDS 2 % SDS 1 % SDS 0.5 % SDS
Elli
ps
oid
Vo
lum
e (Å
3 )
Temperature (K)
Some Fit Results
- Micelles become smaller at higher temperatures and lower volume fraction
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10
15
20
25
30
35
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
1% SDS/d-Water, 21 oC
Ra Rb
Elli
pso
id H
alf
Ax
es (
Å)
NaCl Salt Fraction (mol/L)
More Fit Results
- Salt addition affects lateral growth only
-0.2
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100
1 % SDS/d-Water
SDS fraction in the micellesD
2O fraction in the micelles
SD
S a
nd
D2O
Fra
cti
on
s in
th
e M
icel
les
Temperature (oC)
Material Balance Equations
- SDS surfactant fraction remains constant above the CMC
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SDS MASS FRACTION (%)
T E M P E R A T U R E
(oC)
25
50
75
100
25 50 75 10000
lamellar phase
intermediates
spherical micelles
hydrated SDS crystals
hexagonalphase
intermediates+ crystals
hexagonal phase+ crystals
lamellar phase+crystals
Phase Diagram
- SDS/water phase diagram from calorimetry
4. Final Points
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Upgrade and VSANS
30 m SANS
Present Guide Hall
New Guide Hall
30 m SANS
40 m VSANS
10 m SANS
USANS
ConfinementBuilding
USANS Instrument
SANS, VSANS and USANS Ranges
VSANS
0.01
1
100
104
106
108
1010
10-5 0.0001 0.001 0.01 0.1 1
4% PEO/d-Ethanol,
Mw=42,900 g/mole, T=25oC
USANS DataSANS Data
Sca
tte
red
In
ten
sity
(cm
-1)
Q (Å-1)
SANS
USANS
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0.0001
0.01
1
100
104
106
108
1010
10-5 0.0001 0.001 0.01 0.1 1
Crosslinked CTVB Micelles
gel with no excess oil gel with excess octane gel with excess toluene
Sca
tte
red
In
ten
sity
(c
m-1
)
Q (Å-1)
SANS and USANS Data
VB-
CTA+
Final Words
THE SANS PROGRAM AT NIST
200 experiments per year
15 theses per year
80 publications per year
REFERENCES- B. Hammouda, “Probing Nanoscale Structures – The SANS Toolbox”, (2009). Book available online.- M. Taraban, Y. Feng, B. Hammouda, L. Hyland and B. Yu, “Chirality-Mediated Mechanical and Structural Properties ofOligopeptide Hydrogels”, Chemistry of Materials (2012)
ACKNOWLEDGMENTSSteve Kline, Marc Taraban, Bruce Yu