shape and size of highly concentrated micelles ctab/nasal...

Center for the Exploration of Energy and Matter

And Department of Physics

Shape and size of highly concentrated micelles CTAB/NaSal by small angle neutron scattering

Narayan C Das, Hu Cao, Helmut Kaiser, Paul E. Sokol

Center for the Exploration of Energy and Matterp gyIndiana University, Bloomington IN 47408

Joseph GladdenDepartment of Physics and Astronomy

University of Mississippi, University, MS 38677

UCANS II 2011 8 July 2011



Surfactants and Micelles

CMC

Surfactants and Micelles

or CMC

Aggregates of surfactant molecules self-assembled in aqueous solutions → micelles

A surfactant molecule (organic amphiphilic)= surface active agent

ellipsoidal

Size of head group; length and number of tails; charge on surfactant; temperature;

LamellaeCylindrical Hexagonally packed rods


g p; g ; g ; p ;concentration; pH; ionic strength; flow conditions



Applications of micellesApplications of micellesOil field applications:

Viscoelastic type micelles used for fracturing fluids in the oil yp gfields. Small molecule; recovers back; fewer additives req.

Hydrodynamic engineering (drag reducing agent):yd ody c e g ee g (d g educ g ge ):Heating-cooling fluid. Warm-like micelles: dynamicassociated structure-like living polymers

Rheological modifiers for paints detergents lubricantRheological modifiers for paints, detergents, lubricant…

Home and personal cares:Viscoelastic property-Warm-like micelles. c.g., hard


surface cleaners and drain-opener liquid plumber.



SANS about CTAB/NaSalSANS about CTAB/NaSalCTAB =0.2wt.% (5.5mM), R=[SAL-1]/[CTAB+1]

25mM CTAB (x mM NaSal)L d likLong rod-like Micelles (L>>r)

I(Q)~ exp(-(Qr)^2/4)/Q

q-1

rb=22±1Å, L=250±25Å

100 mM CTAB (x mM NaSal)Ellipsoid Micelles

Interacting spherical micelles

rb=22±1Å, ra=44+5Å


J F Berret Molecular Gels, 667, 2006 Aswal et al. J. Phys. Chem. B, 102, 2469, 1998



M ti ti d Obj tiRheological Relaxation time measurements

Motivation and Objective

Ellipsoidal -> wormlike transition?

Major axis: 22 →250Å(ellipsoidal → worm like micelles)

Ref: Small Angle Neutron Scattering BATAN


Joseph (Josh) Gladden, Dept. of Physics, University of Mississippi



Low Energy Neutron Source at Indiana UniversityLow Energy Neutron Source at Indiana University

SEAMS Accelerator 13 MeV

Moderator Coupled < 20 K solid methaneSANS Moderator Coupled < 20 K solid methane

Wavelength Range 4 Å - 14 Å

Q Range 0.005 to 0.3 A -1

Pulse Width 600usPulse Width 600us

Source Frequency 10 to 30 Hz

Collimation Circular pinhole collimationArea Detector (3He 2D ORDELA)ORDELA)

Active Volume 64 x 64 cm2, 4.4 cm thickPixel Size 1 x 1 cm2

Detector Efficiency

71% for 5 Å neutrons, 52% for 3 Å neutrons

SANS Science ApplicationsPolymersMolecular self-assembly and interactions in complex fluids; Colloids and microemulsions; Micelles;

Efficiency 52% for 3 Å neutrons

Count-Rate Capability 104 n/s for 10% coincidence losses (105 n/s max.)

Integrated Flux on S l

2*104 n/cm2/s (at fulll f 13 kW)

Materials SciencePhase separation in alloys and glasses; Morphologies of superalloys; NanocompositesBiological Macromolecules


Sample accelerator power of 13 kW)Size and shape of proteins; macromolecular complexesHierachical biological structures; Biomembranes



Preliminary Evaluation of Micelles Structures

100 Micelles CTAB/NaSal (=0.60), T = 2930C

Possible Shapes: •Spheres

10

100

-1)

•Ellipsoid

1

10

ensi

ty (c

m-

0.1

1

tterin

g In

te

100/60mM 200/120mM 400/240mM

0 01 0 10.01

Sca

t 600/360mM 800/480mM A*exp(-(Q*r)2/4)/Q (rodlike)


0.01 0.1

Q (A-1)



SANS Data Modeling

810

2

ts]Particles F(Q x)– Ellipsoid b

SANS Data Modeling100/60mM CTAB/NaSal, 200CbkgdQSQFVn

dd

msmm )()()( 222

4

6

81

2

4

6

nsity

[cm

-1 o

r arb

itrar

y un

itParticles F(Q,x) Ellipsoid

cos)]1(1[/)cos(sin3)( 2/1223 uxQruuuuuxQF

3/4)( 2abm rrbV

Form factor-

Density-Neutron Contrast-

mn Volume-2)( sm

rr /

ra

r b

Spheroid (HSP)rb=25A, ra/rb=3.23R0=50A

0.1

2

4

Inte

n

2 3 4 5 6 7 8 90.1

2

Q [A-1]

Experimental Model for wave1

cos,)]1(1[,/)cos(sin3),( uxQruuuuuxQF b

Size Distribution – Gaussian)2/)(exp(

21)( 22

02

rrrf bb

Structural Factor S(Q) – Hard Sphere Model

ba rr / R0 50A

2Structural Factor S(Q) Hard Sphere Model

1.2

1.0

0.8

0.6ture

Fac

tor

)( ru,

0, r≥ 2R0

0, r<2R0

1

2

3

456

10

2

nsity

(cm

-1) Rodlike

R=25AIn solution the single particle form factor

Interparticle potential

bkgddxQSxQFdrrfrVndd

bbbmsmm

)()],([)()()(1

222

0.4

0.2

Stru

c

0.250.200.150.100.05 q ( -1)

Percus-Yevick Hard-Sphere (Phys. Rev. 1958)

0.1

2

3

456

1

Inte

n

5 6 7 8 90.01

2 3 4 5 6 7 8 90.1

2

L=88AIn solution the single particle form factor must be averaged over all angles to give the form factor:


d 0

1. Irena Package from the USAXS at APS, ANL: http://usaxs.xor.aps.anl.gov/staff/ilavsky/irena.html2. SANS Igor Pro from SANS at NCNR, NIST: http://www.ncnr.nist.gov/programs/sans/data/red_anal.html

Q (A-1)



T t d d f tt i i t itTemperature dependence of scattering intensity

20.5C(b) 200/120mM

40

m-1)

20.0C (a) 100/60 mM Q > 0.08Å

30.0C 40.5C 49.9C 58.8C

20

30

ing

Inte

nsity

(cm 20.0C

30.0C 40.5C 52.0C 60.0C

QShort axis remainconstant

Q < 0 08Å

40

1 ) 20.4C (c) 400/240 mM

(d) 600/360mM

0

10

scat

teri Q < 0.08Å

Long axis changewith temperature

↓shorter with temp

20

30

g In

tens

ity (c

m-1 30.4C

40.4C49.5C60.0C

20.5C

shorter with temp.

0.01 0.10

10

Sca

tterin

g

Q (A-1)0.01 0.1

1

20.5C 30.0C 40.0C 50.0C 60.0C


Q (A ) Q (A-1)Q > 0.08Å Q > 0.08Å



T t d d f tt i i t it40

100/60mM200/120mM

Temperature dependence of scattering intensity

30si

ty (c

m-1)

200/120mM 400/240mM 600/360mM 800/480mM Rodlike A*exp(-(Q*r)2/4)/Q

(r=25A, A=0.65)Ellipsodal Model FittingRodlike

10

20

erin

g In

tens Ellipsodal Model FittingRodlike

0 01 0 10

10

Sca

tte

(a) T=20.5C0.01 0.1

Q (A-1)Short ellipsoidal axis ~

length of the surfactant molecule (20~26Å)


g ( )



Model fitting

30

40

20.5C 30.0C 40.5C 49.9Cm

-1)

200/120mM(b)

1E17

*cm

3 )] 20.5C 30.0C40.5C

Model fitting

20

49.9C 58.8C Ellipsoidal Model

Fitting

ng In

tens

ity (c

m

Dis

tribu

tion

[1/(A 49.9C

58.8C

0.01 0.10

10

Scat

teri

Q (A-1)

18 20 22 24 26 28 301E16

Num

ber D

r (A)Q (A ) rb (A)

Model: Ellipsoid form, a hard sphere structure factor and Gaussian size distribution

Fitting parameters (7): total scattering volume of micelles, the semiminor axis rb, widthof Gaussian function (δ) aspect ratio (γ=r /r ) the radius (R ) and volume fractionof Gaussian function (δ), aspect ratio (γ=ra/rb), the radius (R0) and volume fraction(η=4πR0

3nm/3) of hard sphere, and background (bkgd).

Width (δ) of Gaussian function ~ 0.001 Å, the semiminor length of the ellipsoidal particle might be simply equal to the length of the surfactant molecule and these ellipsoidal particles could be


simply equal to the length of the surfactant molecule and these ellipsoidal particles could be monodispersed



0.50.3

( )28

(b)4

( )

Temperature dependence of fitting parameters of Micelles

0.3

0.4

0 250 500 750 10000.0

0.1

0.2

0.3

Volu

me

(cm

3 )

Concentration of CTAB (mM)

100/60mM 200/120mM 400/240mM 600/360mM 800/480mM

e (c

m3 )

(a)T=20oC

26

20 40 600.5

1.0

1.5

Num

. Dis

t. (1

017(A

*cm

^3)-1

)

0

200/120mM100/60mM

200/120mM 400/240mM 600/360mM 800/480mM

(A)

(b)

3

100/60mM 200/120mM 400/240mM 600/360mM 800/480mM

tio (

r a/r b

)

(c)

0.0

0.1

0.2Concentration of CTAB (mM)

Vol

ume

10 20 30 40 50 60 7022

24T (0C)

r b (

10 20 30 40 50 60 702

Asp

ect R

at

Temp (C)10 20 30 40 50 60 70

T (oC)Temp (C)

Linear decrease in both the semiminor axis rb and aspect ratio (ra/rb): Micelles begin to condense with increase in temperature: Micelles begin to condense with increase in temperature: 100/60 mM shows the largest particle size:ra (growth direction) shortens faster than rb: Volume remains constant-micelles break- and extra broken begin to recombine: number density increases with heating


: number density increases with heating



0.25

Temperature dependence of fitting parameters of Micelles

60

70 100/60mM 200/120mM 400/240mM 600/360mM 800/480mM

(a)

Equivalent Radius: (rarbrb)

0 15

0.20

100/60mM 200/120mM 400/240mM 600/360mM 800/480mM

(HS

A)

(b)

40

50

R0 (H

SA

)

0.10

0.15

me

Frac

tion

(10 20 30 40 50 60 70

30mM

mM

10 20 30 40 50 60 700.00

0.05

Vol

u

Temp (C) T (oC)

R0→ 50 to 33Å (100/60 to 400/240 mM)HAS works well for ellipsoidal or more spherical micelles

Volume fraction: 4R03nm/3


p p

Temperature effect on size of micelles and number density



Summary Highly concentration CTAB/NaSal formed ellipsoidal

i ll Elli id l i ll h b i ti t d b

Summary

micelle. Ellipsoidal micelles have been investigated by small angle neutron scattering.

SANS results suggests that this micelles solution fall in the SANS results suggests that this micelles solution fall in the ellipsoidal regime and micelles shape are independent on the concentration and temperature.

Micelles size decreases with concentration and temperature whereas total volume of micelles remain constant, indicating that long micelles start to break on heating and brokenthat long micelles start to break on heating and broken surfactant molecules coalesce again to form more micelles.

No structural transitions (linear change) in the studied


( g )temperature range for highly concentration CTAB/NaSal.

shape and size of highly concentrated micelles ctab/nasal...

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