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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
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
g p; g ; g ; p ;concentration; pH; ionic strength; flow conditions
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
surface cleaners and drain-opener liquid plumber.
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
J F Berret Molecular Gels, 667, 2006 Aswal et al. J. Phys. Chem. B, 102, 2469, 1998
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
Joseph (Josh) Gladden, Dept. of Physics, University of Mississippi
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
Sample accelerator power of 13 kW)Size and shape of proteins; macromolecular complexesHierachical biological structures; Biomembranes
Center for the Exploration of Energy and Matter
And Department of Physics
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)
UCANS II 2011 8 July 2011
0.01 0.1
Q (A-1)
Center for the Exploration of Energy and Matter
And Department of Physics
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:
UCANS II 2011 8 July 2011
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)
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
Q (A ) Q (A-1)Q > 0.08Å Q > 0.08Å
Center for the Exploration of Energy and Matter
And Department of Physics
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)
UCANS II 2011 8 July 2011
g ( )
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
simply equal to the length of the surfactant molecule and these ellipsoidal particles could be monodispersed
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
: number density increases with heating
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
p p
Temperature effect on size of micelles and number density
Center for the Exploration of Energy and Matter
And Department of Physics
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
UCANS II 2011 8 July 2011
( g )temperature range for highly concentration CTAB/NaSal.