THE NIST SANS USER RESEARCH

SANS RESEARCH TOPICS Boualem Hammouda National Institute of Standards and Technology Center for Neutron Research 1. SANS from Pluronics 2. Polymer Blend Thermodynamics 3. Helix-to-Coil Transition in DNA

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

P85 Pluronic forms micelles at high temperatures

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

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

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 = 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.

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

Solution of Spheres with Polymers PPO PEO

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

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

Gibbs Free Energy

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

ZIMM PLOT

1 nm 0.1 mm

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

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

HELIX-TO-COIL TRANSITION IN DNA UV

SANS

POROD PLOT I(Q) ~ C/Qm

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

Solvation Intensity

Correlation Length 12.3 Å 8.5 Å

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

POROD EXPONENTS Porod region 1D object 2D object 3D object 1/Q1 1/Q2 MASS FRACTALS SURFACE FRACTALS

CONCLUSIONS ACKNOWLEDGMENTS -- 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