Use of the NG3 SANS Instrument at NIST

Polymers 50%Complex Fluids 26%Biology 11%Other Material Science 9%Condensed Matter 4%

Polymers

Complex Fluids

Biology

Other Materials Science

Condensed Matter

THE NIST SANS USER RESEARCH

SANS RESEARCH TOPICS

Boualem Hammouda

National Institute of Standards and TechnologyCenter for Neutron Research

1. SANS from Pluronics

2. Polymer Blend Thermodynamics

3. Helix-to-Coil Transition in DNA

Pluronics are triblock copolymers: PEO-PPO-PEO

PEO: -CH2CH2O- is hydrophillicPPO: -CH2CH2(CH3)O- is hydrophobic

0.01

0.1

1

10

100

0.001 0.01 0.1 1

10% P85 pluronic in d-water at 60 oC

SANS data

Scattering Vector (Å -1)

incoherent cross section

coherent cross section

1. SANS FROM PLURONICS

0.1

1

10

100

0.001 0.01 0.1 1

10% P85 Pluronic in d-water

60 oC

50 oC

40 oC

30 oC

20 oC

Scattering Vector (Å -1)

Guinier region

Porod region

P85 Pluronic forms micelles at high temperatures

GUINIER PLOT

I(Q) = I(0) exp(-Q2Rg2/3)

Guinier region

Guinier region

0

0.2

0.4

0.6

0.8

1

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016

Pluronics/d-water, 10 %, 20 oC

Guinier Plot

Q2 (A-2)

Rg = 34 Å

SANS from Pluronics Micelles

PEO

PEO

PPO

PEO

0.01

0.1

1

10

100

0.001 0.01 0.1 1

sphere

Scattering Wavenumber Q (Å-1)

0.01

0.1

1

10

100

0.001 0.01 0.1 1

polymer

Scattering Wavenumber Q (Å-1)

0.01

0.1

1

10

100

0.001 0.01 0.1 1

sphere and polymer

Scattering Wavenumber Q (Å-1)

Polymer Sphere Sphere and polymer

PPO

PEO

PPO

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+Q2Rg

2]/(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

0.01

0.1

1

10

100

0.001 0.01 0.1 1

sphere

Scattering Wavenumber Q (Å-1)

Single sphere Solution of spheres

0.01

0.1

1

10

100

0.001 0.01 0.1 1

Solution of Spheres

Scattering Wavenumber Q (Å-1)

Percus Yevick Model

Solution of Spheres with Polymers

PPOPEOPEO

PPOPEOPEO

PPOPEOPEO

PPOPEOPEO

PPOPEOPEO

0.01

0.1

1

10

100

0.001 0.01 0.1 1

solution of spheres with polymers

Scattering Wavenumber Q (Å-1)

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 monomers690 PEO monomers490 D2O molecules

In the shell:2,943 PEO monomers34,167 D2O molecules

10% P85 Pluronic/D2O, 40 oC

)Q(S)Q(

2

)A

F(QRAV)

BF(QR

BV

Cv

Cb

Bv

Bb

)A

F(QRAV

Cv

Cb

Av

Ab

V

N

dΩ

dI(Q)

SANS Intensity: I(Q) = d(Q)/d = (b1/v1-b2/v2)2 ST(Q)

Thermodynamics: ST-1(Q=0) = (1/kBT)(2G/1

2); G: Gibbs Free Energy.

The Random Phase Approximation:

ST-1(Q) = 1/(n11v1P(QRg1) + 1/(n22v2P(QRg2) -2 12(T)/v0

2. POLYMER BLENDS THERMODYNAMICS

0.1 m1 nm

Mixed polymer blend Phase separated blend

Gibbs Free Energy

-6 10-6

-5 10-6

-4 10-6

-3 10-6

-2 10-6

-1 10-6

0

1 10-6

2 10-6

0 0.2 0.4 0.6 0.8 1

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

270 K220 K200 K

Volume Fraction 1

spinodal points

binodal points

critical point

0

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

Volume Fraction 1

two-phase spinodal region

spinodal line

one-phase spinodal region

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: hPEB=0.57 dPMB=0.43

0

20

40

60

80

100

120

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

10 oC

20 oC

30 oC

40 oC

50 oC

Scattering Vector Q (Å-1

)

0

0.05

0.1

0.15

0.2

0 0.0005 0.001 0.0015 0.002 0.0025

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

Data at 10 oC

Q2 (Å-2)

intercept gives 1/I(Q=0)

slope gives radius of gyration

ZIMM PLOT

0.005

0.006

0.007

0.008

0.009

0.01

0.003 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

Inverse Temperature (K -1)

Ts = 220 K

0

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1

hPEB/dPMB, Mw=40,100 g/mole/88,400 g/mole

Volume Fraction 1

two-phase spinodal region

one-phase mixed region

spinodal line

critical point

0.1 m

1 nm

3. HELIX-TO-COIL TRANSITION IN DNA

DNA is the basic building block for life. It encodes for the synthesis of proteins.

H

H

H

H

H

H

P

O

C

C C

O

C

N

N

NH OO

HO

CH2

O

O

Nucleotide

H H

Phosphate group

Sugar

Base

P O

O

O

O

Phosphate group

SugarAmine bases

O

H

HHO

OHHOCH2

HH

D-desoxyribose

Purines Pyrimidines

HAdenine (A)

Guanine (G) Cytosine (C)

Thymine (T)

H HN

N

NN

NH

H

H

H

H

H H

HN

N

N

NN

OH

H

H

H

N

N

N O

H

H

H

O

ON

NH3C

THE DNA MOLECULE

THE DNA HELIX

A

A

A

A

A

A

A

T

T

T

T

G

G

G C

C

C

Pitch30-40 Å

Repeat distanceper base pair=3.4 Å

Major groove

Minor groove

HELIX-TO-COIL TRANSITION IN DNA

1.8

2

2.2

2.4

2.6

2.8

20 30 40 50 60 70 80 90 100

4 % DNA in d-ethylene glycol and in d-water, 0.1 M NaCl

4% DNA/d-ethylene glycol4% DNA/d-water

Temperature ( oC)

Transition Temperatures

First Temperature

Second Temperature

UV

0.1

1

10

0.01 0.1

4% DNA in d-ethylene glycol, 0.1M NaCl

25 oC

50 oC

Scattering Wavenumber (Å -1)

SANS

POROD PLOT I(Q) ~ C/Qm

-2.3

-2.2

-2.1

-2

-1.9

-1.8

-1.7

-1.6

-0.75 -0.7 -0.65 -0.6 -0.55 -0.5 -0.45 -0.4 -0.35

4% DNA in d-ethylene glycol,

0.1 M NaCl, T=50 oC

Porod Plot

Log(Q)

slope = -1.76

NONLINEAR LEAST-SQUARES FIT

0.08

0.09

0.1

0.2

0.04 0.06 0.08 0.1 0.3

4 % DNA in d-ethylene glycol,

0.1 M NaCl, 25 oC

SANS Data

Scattering Wavenumber ( Å -1)

background

solvation intensity C

Functional form: I(Q) = C/[1+(QL)m] + Background

C: solvation intensityL: correlation lengthm: Porod exponent

0.135

0.14

0.145

0.15

0.155

0.16

0.165

0.17

0 20 40 60 80

4 % DNA in d-ethylene glycol, 0.1 M NaCl

Temperature ( oC)

helix

coil

transition

Solvation Intensity

8

9

10

11

12

13

14

15

0 20 40 60 80 100

4% DNA in d-ethylene glycol, 0.1 M NaCl

Temperature ( oC)

helix

coil

transition

Correlation Length

12.3 Å

12.3 Å

8.5 Å

8.5 Å

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100

4 % DNA in d-ethylene glycol, 0.1 M NaCl

Temperature ( oC)

helix

coil

transition

Porod Exponent

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

1D object 2D object 3D object

1/Q1.67 1/Q2 1/Q3

MASS FRACTALS SURFACE FRACTALS

1/Q1 1/Q2 1/Q4

1/Q3 1/Q4

Porod region

POROD EXPONENTS

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