# Presentation: 792695

## THE NIST SANS USER RESEARCH

**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 

- 	PEO: -CH2CH2O- is hydrophillic
- 	PPO: -CH2CH2(CH3)O- is hydrophobic

**1. SANS FROM PLURONICS**

## P85 Pluronic forms micelles at high temperatures

- P85 Pluronic forms micelles at high temperatures

## GUINIER PLOT

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

- Guinier region

- Guinier region

## Slide 6

## 		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

**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

**Single sphere**

**Solution of spheres**

- Percus Yevick Model

## Slide 9

## Fit SANS Data to a Model of 

**Concentrated Core-Shell Particles**

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

Thermodynamics:	ST-1(Q=0) =   (1/kBT)(2G/12); G: Gibbs Free Energy.

The Random Phase Approximation:

			ST-1(Q) =  1/(n11v1P(QRg1) + 1/(n22v2P(QRg2) -2 12(T)/v0 

**Thermodynamics:**	ST-1(Q=0) =   (1/kBT)(2G/12); G: Gibbs Free Energy.
**The Random Phase Approximation:**
- 			ST-1(Q) =  1/(n11v1P(QRg1) + 1/(n22v2P(QRg2) -2 12(T)/v0

**2. POLYMER BLENDS THERMODYNAMICS**** **

- 0.1 m

- 1 nm

**Mixed polymer blend**

**Phase separated blend**

## Gibbs Free Energy

## Slide 13

## 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

## Slide 15

## ZIMM PLOT 

**ZIMM PLOT**** **

## Slide 17

## 0.1 m

- 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.** **

## Slide 20

## UV

**UV**

## SANS

**SANS**

## POROD PLOT	I(Q) ~ C/Qm 

## NONLINEAR LEAST-SQUARES FIT

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

## Solvation Intensity

## Correlation Length

## Porod Exponent

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

## POROD EXPONENTS 

**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