THE NIST SANS USER RESEARCH

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THE NIST SANS USER RESEARCH
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SANS RESEARCH TOPICS Boualem HammoudaNational
Institute of Standards and TechnologyCenter for
Neutron Research
1. SANS from Pluronics 2. Polymer Blend
Thermodynamics 3. Helix-to-Coil Transition in
DNA
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1. SANS FROM PLURONICS
Pluronics are triblock copolymers
PEO-PPO-PEO PEO -CH2CH2O- is
hydrophillic PPO -CH2CH2(CH3)O- is hydrophobic
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P85 Pluronic forms micelles at high temperatures
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GUINIER PLOT
I(Q) I(0) exp(-Q2Rg2/3)
Guinier region
Guinier region
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SINGLE PARTICLE AND INTER-PARTICLE STRUCTURE
FACTORS

• I(Q) (NA/V)VA2 (bA/vA-bB/vB)2 P(Q) S(Q)
• NA number of particles, VA particle volume,
  V sample volume
• (bA/vA-bB/vB)2 contrast factor
• P(Q) single-particle structure factor
• S(Q) inter-particle structure factor

P(Q) F(QR)2 3sin(QR)/(QR)3-cos(QR)/(QR)22
for sphere of radius R. P(Q)
2exp(-Q2Rg2)-1Q2Rg2/(Q2Rg2)2 for polymer of
radius of gyration Rg. S(Q) given by Percus
Yevick model for solution of hard spheres. S(Q)
given by the Random Phase Approximation model for
polymer mixtures.
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Solution of Spheres
Percus Yevick Model
Solution of spheres
Single sphere
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Fit SANS Data to a Model of Concentrated
Core-Shell Particles
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2. POLYMER BLENDS THERMODYNAMICS

• SANS Intensity I(Q) dS(Q)/dW (b1/v1-b2/v2)2
  ST(Q)
• Thermodynamics ST-1(Q0) (1/kBT)(d2G/df12)
  G Gibbs Free Energy.
• The Random Phase Approximation
• ST-1(Q) 1/(n1f1v1P(QRg1) 1/(n2f2v2P(QRg2)
  -2 c12(T)/v0

Mixed polymer blend
Phase separated blend
0.1 mm
1 nm
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Gibbs Free Energy
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SANS FROM POLYMER BLEND MIXTURES
Polymers Polyethylbutylene / Polymethylbutylen
e hPEB -(C6H12)- / dPMB -(C5H5D5)- Molecular
Weights Mw44,100 g/mole Mw88,400
g/mole Volume Fractions fhPEB0.57 fdPMB0.43

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ZIMM PLOT
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1 nm
0.1 mm
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3. HELIX-TO-COIL TRANSITION IN DNA
DNA is the basic building block for life. It
encodes for the synthesis of proteins.
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HELIX-TO-COIL TRANSITION IN DNA
UV
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SANS
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POROD PLOT I(Q) C/Qm

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NONLINEAR LEAST-SQUARES FIT
Functional form I(Q) C/1(QL)m
Background C solvation intensity L
correlation length m Porod exponent
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Solvation Intensity
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Correlation Length
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Porod Exponent
Reference B. Hammouda and D. Worcester, The DNA
Denaturation Transition of DNA in Mixed
Solvents, Biophysical Journal (accepted 2006).
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POROD EXPONENTS
Porod region
1D object
2D object
3D object
1/Q1
1/Q2
1/Q4
1/Q1.67
1/Q2
1/Q3
1/Q3
1/Q4
MASS FRACTALS
SURFACE FRACTALS
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CONCLUSIONS
-- The SANS technique is a valuable
characterization method. -- SANS has been
effective in complex fluids, polymers, biology,
etc. -- SANS can determine structures, phase
transitions, and morphology. -- The NG3 SANS
instrument at NIST gets over 150 users per year,
resulting in over 40 publications per year.
ACKNOWLEDGMENTS
NSF-DMR, Steve Kline, Nitash Balsara, David
Worcester.
CHECK IT OUT http//www.ncnr.nist.gov/programs/
sans/ http//www.ncnr.nist.gov/staff/hammou
da/ hammouda_at_nist.gov