THE NIST SANS USER RESEARCH

1. THE NIST SANS USER RESEARCH

2. SANS RESEARCH TOPICSBoualem HammoudaNational Institute of Standards and TechnologyCenter for Neutron Research 1. SANS from Pluronics 2. Polymer Blend Thermodynamics 3. Helix-to-Coil Transition in DNA

3. 1. SANS FROM PLURONICS Pluronics are triblock copolymers: PEO-PPO-PEO PEO: -CH2CH2O- is hydrophillic PPO: -CH2CH2(CH3)O- is hydrophobic

4. P85 Pluronic forms micelles at high temperatures

5. GUINIER PLOT I(Q) = I(0) exp(-Q2Rg2/3) Guinier region Guinier region

6. SANS from Pluronics Micelles PPO PEO PEO PEO PEO low temperature high temperature Polymer Sphere Sphere and polymer PPO PPO

7. SINGLE PARTICLE AND INTER-PARTICLE STRUCTURE FACTORS I(Q)=(NA/V)VA2(bA/vA-bB/vB)2P(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 = 3[sin(QR)/(QR)3-cos(QR)/(QR)2]2 for sphere of radius R. P(Q) = 2[exp(-Q2Rg2)-1+Q2Rg2]/(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.

8. Solution of Spheres Percus Yevick Model Solution of spheres Single sphere

9. Solution of Spheres with Polymers PPO PPO PPO PPO PPO PEO PEO PEO PEO PEO PEO PEO PEO PEO PEO

10. 10% P85 Pluronic/D2O, 40 oC solvent region C shell region B In the core: 2,795 PPO monomers 690 PEO monomers 490 D2O molecules core region A In the shell: 2,943 PEO monomers 34,167 D2O molecules (b/v)C = 6.4*10-6 Å-2 (b/v)B = 5.9*10-6 Å-2 (b/v)A = 1*10-6 Å-2 RA=42.6 Å RB=71.4 Å Fit SANS Data to a Model of Concentrated Core-Shell Particles

11. 2. POLYMER BLENDS THERMODYNAMICS SANS Intensity: I(Q) = dS(Q)/dW = (b1/v1-b2/v2)2 ST(Q) Thermodynamics: ST-1(Q=0) = (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 1 nm 0.1 mm

12. Gibbs Free Energy

14. SANS FROM POLYMER BLEND MIXTURES Polymers: Polyethylbutylene / Polymethylbutylene hPEB -(C6H12)- / dPMB -(C5H5D5)- Molecular Weights: Mw=44,100 g/mole Mw=88,400 g/mole Volume Fractions: fhPEB=0.57 fdPMB=0.43

16. ZIMM PLOT

18. 1 nm 0.1 mm

19. THE DNA MOLECULE Amine bases Phosphate group Sugar Purines Pyrimidines H H N O H H3C N N N H N N O H H N HOCH2 OH O H H O H H Adenine (A) Thymine (T) H H O O P HO H O H H D-desoxyribose O N H N N N H H N N H N O N H H H Guanine (G) Cytosine (C) Nucleotide H H N H N Base O H O N O Phosphate group P O CH2 O Sugar O C C H H H H C C H HO 3. HELIX-TO-COIL TRANSITION IN DNA DNA is the basic building block for life. It encodes for the synthesis of proteins.

20. THE DNA HELIX T A G Major groove A T Pitch 30-40 Å T A A T G C A Minor groove C A C G Repeat distance per base pair=3.4 Å A

21. HELIX-TO-COIL TRANSITION IN DNA UV

22. SANS

23. POROD PLOT I(Q) ~ C/Qm

24. NONLINEAR LEAST-SQUARES FIT Functional form: I(Q) = C/[1+(QL)m] + Background C: solvation intensity L: correlation length m: Porod exponent

25. Solvation Intensity

26. 12.3 Å 12.3 Å 8.5 Å 8.5 Å Correlation Length

27. Porod Exponent Reference: B. Hammouda and D. Worcester, “The DNA Denaturation Transition of DNA in Mixed Solvents”, Biophysical Journal (accepted 2006).

28. 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

29. 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/hammouda/ hammouda@nist.gov