An Investigation of the Phase Behavior of SDS in water using

NG3 SANS

Group II – 2012 NCNR Summer School

Kiyo Akabori, Greg Barnett, Kiersten Batzli, Vishal Javvaji, Ricky Lam, Halil Oztop, Jessie Sun, Charlezetta Wilson

Objectives

• Hands on experience using Small angle neutron scattering (SANS) @ NG3

• Determine the shape and size of Sodium dodecyl sulfate (SDS) micelles

• Determine the effects of temperature and concentration on the phase behavior of SDS

SDS Phase Diagram

(Hydrophobic Tail)

(Hydrophilic Head)

Surfactant

http://www.ncnr.nist.gov/staff/hammouda/the_SANS_toolbox.pdf

Incident Beam

Area Detector

Scattered

Beam Sample Q

Source

Aperture Sample

Aperture

Monochromatic

Neutron Beam

Monochromation Collimation Scattering Detection

NG3 SANS Setup

velocity selector collimation

sample area

area detector beam shutter

15 m 15 m

cold neutrons

BEAM BEAM ON OFF

http://www.ncnr.nist.gov/staff/hammouda/sans_tutorial/SANS_nuts_and_bolts.pdf

Experimental Design

• SDS micelles were prepared

– 10wt% to 80wt% in 10wt% increments

• SANS measurements were performed

– 10°C to 80°C in 10° increments

• Data was analyzed using IGOR

– NCNR Analysis Macros

70% SDS Phase Structures

7

1

2

3

4

5

67

10

2

3

4

5

67

100

2

I(q

)

4 5 6 7 8 9

0.012 3 4 5 6 7 8 9

0.12 3 4 5

q (Å-1

)

X70__sds_20c_ABS_i X70__SDS_30C_ABS_i X70__sds_40c_ABS_i X70__sds_50c_ABS_i X70__sds_60c_ABS_i X70__sds_70c_ABS_i X70__sds_80c_ABS_i

T

E

M

P

E

R

A

T

U

R

E

(oC)

SDS MASS FRACTION (%)

25

50

75

100

25

0

500

75

0

1000

0 0

lamellar

phase

intermediates

spherical

micelles

hydrated

SDS crystals

hexagonal

phase

intermediates

+ crystals

hexagonal phase

+ crystals

lamellar

phase

+crystals

30 C 20 C

40 C 50 C

60 C 70 C

80 C

Old Diagram

T

E

M

P

E

R

A

T

U

R

E

(oC)

SDS MASS FRACTION (%)

25

50

75

100

25

0

500

75

0

1000

0 0

lamellar

phase

intermediates

spherical

micelles

hydrated

SDS crystals

hexagonal

phase

intermediates

+ crystals

hexagonal phase

+ crystals

lamellar

phase

+crystals

SDS Mass Fraction (%)

Indexing Peaks

Micelles Crystals

Hexagonal Lamellar

Indexing Peaks

• Structural info

– Lamellar (1, 4)

– Hexagonal (1, 3, 4, 9, 12, …)

– Crystals

• Updating phase diagram accordingly

• Or a combination of structures

Old vs New Phase Diagram

0

20

40

60

80

100

0 20 40 60 80

Tem

pe

ratu

re (

oC

)

SDS Mass Fraction (%)

spherical

micelles

hexagonal

phase

hydrated SDS crystals

lamellar

phase

intermediates

lamellar

phase +

crystals

hexagonal phase

+ crystals

intermediates

+ crystals

a

a

b

a

a

b

b

c

c

c

c

a a

a

a

a

b'

c'

d'

e

e

d'

a

a

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

a

a

b'

c'

e

f

e

d'

T

E

M

P

E

R

A

T

U

R

E

(oC)

SDS MASS FRACTION (%)

25

50

75

100

25

0

500

75

0

1000

0 0

lamellar

phase

intermediates

spherical

micelles

hydrated

SDS crystals

hexagonal

phase

intermediates

+ crystals

hexagonal phase

+ crystals

lamellar

phase

+crystals

SDS Mass Fraction (%)

Prolate vs Oblate

Oblate Ra = 15.1 Å Rb = 26.2 Å Χ2 =6.58

Prolate Ra = 36.4 Å Rb = 17.7 Å Χ2 =7.52

Rotational axis (Ra)

Rotational axis (Ra)

Smeared ellipsoid model fit

http://en.wikipedia.org/wiki/Spheroid

http://en.wikipedia.org/wiki/Spheroid

Radius vs. Temperature

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100

Rad

ius

(A)

Temperature

R(a)

R(b)

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100

Rad

ius

(A)

Temperature

R(A)

R(b)

Increasing Temperature = Decreasing Size (both Ra and Rb)

Temp (C) Ra (Ǻ) Rb (Ǻ) X2

30 36.3985 17.733 7.51724

50 32.6245 17.5374 7.09351

80 29.2232 16.9808 4.76725

Prolate model (20% mass fraction) Oblate model (20% mass fraction)

Temp (C) Ra (Ǻ) Rb (Ǻ) X2

30 15.0739 26.2076 6.57489

50 14.8203 25.1155 5.40358

80 14.5007 23.8827 3.61079

Model Comparison Sphere Model Sphere Model + Power Law Model

Ellipsoid Model Ellipsoid Model + Power Law Model

Model Comparison Sphere Model Sphere Model + Power Law Model

Ellipsoid Model Ellipsoid Model + Power Law Model

Radius A: 36.2 Ang Radius B: 17.7 Ang

Radius A: 36.4 Ang Radius B: 17.7 Ang

The Great Prolate Oblate State Debate!!

?

http://en.wikipedia.org/wiki/Spheroid

Old vs New Phase Diagram

0

20

40

60

80

100

0 20 40 60 80

Tem

pe

ratu

re (

oC

)

SDS Mass Fraction (%)

spherical

micelles

hexagonal

phase

hydrated SDS crystals

lamellar

phase

intermediates

lamellar

phase +

crystals

hexagonal phase

+ crystals

intermediates

+ crystals

a

a

b

a

a

b

b

c

c

c

c

a a

a

a

a

b'

c'

d'

e

e

d'

a

a

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

a

a

b'

c'

e

f

e

d'

T

E

M

P

E

R

A

T

U

R

E

(oC)

SDS MASS FRACTION (%)

25

50

75

100

25

0

500

75

0

1000

0 0

lamellar

phase

intermediates

spherical

micelles

hydrated

SDS crystals

hexagonal

phase

intermediates

+ crystals

hexagonal phase

+ crystals

lamellar

phase

+crystals

SDS Mass Fraction (%)

0

20

40

60

80

100

0 20 40 60 80

Tem

pe

ratu

re (

oC

)

SDS Mass Fraction (%)

spherical

micelles

hexagonal

phase

hydrated SDS crystals

lamellar

phase

intermediates

lamellar

phase +

crystals

hexagonal phase

+ crystals

intermediates

+ crystals

a

a

b

a

a

b

b

c

c

c

c

a a

a

a

a

b'

c'

d'

e

e

d'

a

a

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

b

a

a

b'

c'

e

f

e

d'

SDS Mass Fraction (%)

Summary

• Learned to use SANS to determine structure!!

SDS Micelle Project • Re-evaluated Phase Diagram

• Prolate vs Oblate?

• Indexed Peaks for micelle structure

• Further Work for Phase Diagram