Talk from the 2011 American Oil Chemist's Society meeting (Surfactants and Detergents Division). Reviews the basics of FT-IR spectroscopy and how it can be used in a wide range of applications to surfactant science. How can FT-IR deal with aqueous solutions? How can shifts in wavenumber be interpreted? What is a significant shift in wavenumber?

1. Applications of Fourier Transform Infrared
Spectroscopy to Studies of Surfactant Behavior
AOCS Meeting – May, 2011
D.R. Scheuing – Clorox

2. Outline
How Does a Fourier Transform IR work?
Working with Aqueous Systems – Really?
How Can I Use FT-IR to Probe Structure and Properties of Surfactant Aggregates
Interfacial Behavior of Surfactants = Performance!

3. Michelson Interferometer Recombines Split Beams with Different
Pathlengths
Fixed Mirror
Distance – Fixed to
Beamsplitter
Moving
Mirror
Direction
IR
source
Beamsplitter
Distance – Fixed
to Moving Mirror
Optical Retardation =
Difference in Beam Paths Measured in cm !
=
To Detector
Phases of Two
Beams
Output

4. Modern FT-IR Benches Are Compact, Deliver High Energy
Throughput and Versatility for Sampling Optics
EM drive for moving
mirror (voice coil)
Laser
source
IR source
Moving Mirror
Beamsplitter
IR
detectors
Beam
Focus in
Sample
Area
Laser
detector

5. Record I’gram - FT to Single Beam - Ratio Sample/”Background” Single Beams
Fourier Transform =
from cm to cm-1
Sample
Background
Ratio Single Beam Spectra
5 mAU !
An adsorbed
polymer layer

6. Spectra of Surfactants in Water Are Possible with “Short”
Pathlengths ! (Transmission or ATR)
Jacket for
circulating fluid or
heaters.
Sample as film
between windows
CH
deformation
C=O stretch
CH stretch
C-O-C
stretch
S-O
stretch

7. Innovations with Surfactants Require Understanding
(Controlling) - Aggregate Structures = “Bulk Properties”
Micelle Size, Shape – Packing Parameter
AND Interfacial Activity of Aggregates =
Detergency, Surface Modification, Solubilization

8. Monitoring Sphere – Rod Transitions with FT-IR
Decreasing “tail disorder” =
“Straighter” tails
GraphicO'Reilly R Phil. Trans. R. Soc. A
2007;365:2863-2878
Increasing “tail disorder” = more gauche conformers
Dluhy, R.A., Mendelsohn,R., Casal, H.L., Mantsch,H.H.
Biochemistry, (1983), 22, 1170-1177
Snyder,R.G, Strauss, H.L., Elliger,C.A., J.Phys.Chem,
(1982), 86,5145

9. Shape/Position of CH2 Bands Correlate to “Disorder” in
Methylene Chains & Packing Parameter
“Center of gravity” of peak
can be calculated
Peak Locations Can Be
Measured to +/- 0.05 cm-1
(Laser reference!)
Cameron,D.G., Kauppinen,J.K., Moffatt,D., Mantsch, H.H, Applied Spec, (1983) 36,245

10. Mixed SDS – DTAC (quat) Micelles (B = -25!)
“Tail Ordering” Increases with Aggregation Number
CH2 str.
Asymm.
Increasing
Mole Frac.
SDS
CH3 str.
Asymm.
CH2 str.
symm
Separated CH2 and CD2 Bands Show
Same Trends
Scheuing,D.R., Weers, J.G. Langmuir, (1990) 6,3, 665-671

11. S-O Bands Sensitive to Counterion Type, Location –
Vibrational Modes Have Direction
Asymmetric S-O stretch, 1220 cm-1
δ−
δ−
Net Transition
Moment Vector
O
O
O
S
δ
−
δ+
δ+
O
δ−
O
+
-
δ−
Net Transition
Moment Vector
+
- +
+
+
++
- +
- ++ +
+
+
+
+
- + +
- - - - +
+
Symmetric S-O stretch, 1061 cm-1
δ−
δ−
+
+
δ−
O
S
δ+
Mantsch,H.H. et.al., J.Phys.Chem. 1980,84,227
δ+
Scheuing,D.R., Weers,J.G., Langmuir,1990,6,665

12. Shifts in S-O Bands Confirm Lateral Crowding of
Headgroups in SDS/DTAC rods
Difference Spectra*
SDS-rich
(Spectrum A) – X (Spectrum B)
X=Subtraction Scalar
S-O
symm.
stretch
DTAC -rich
DTAC rich minus SDS
S-O
asymm.
stretch
S-O symm.
stretch
SDS rods – SDS spheres
SDS-rich minus SDS
Scheuing,D.R., Weers,J.G., Langmuir,1990,6,665
* Cameron, D.G., Casal, H.L., Mantsch, H.H., Biochemistry, (1980) 19,3665

13. Interfacial Activity of Aggregates

14. Internal Reflection Optics Key To Analysis of Surfaces – Including the
IRE Surface Itself !
IRE
(Ge)
Air
Refractive index = n1=
4.0
θ
Refractive index = n2 = 1.5
n21=n2/n1
Sampling depth, dp= 736
nm at 1650 cm-1
dp = λ/2π (sin2 θ − n21 2 )1/2

15. Multiple Reflections Aid Sensitivity with Versatile
Horizontal IRE
Add a layer of
nanoparticles to study
adsorption on them!
Add a layer of “model solid soil” for
detergency studies
Trough on Horizon rig
50 mm

16. Solid Fats – Major Challenge in Detergency at
Lower Temperatures!
Beta-tristearin differs from alpha form – even in thin layers on Ge IRE.
Extensive FT-IR literature available for interpretation of changes.
Before and after
exposure to water
for 15 minutes
Beta crystal
structure –
most stable,
high m.p.

17. Time-resolved Analysis of Soil-Solution Interface
During Detergency Process
Tristearin Removal from Ge Surface By Alcohol
Ethoxylate (C12E8) in DI Water - High and Low
Conc.
0.3%
0.03%
25
30
0.8
0.6
0.4
0.2
0
0
5
10
15
20
35
Time, min.
Triste arin Removal from Ge Surface By Alcohol
Ethoxylate (C12E8) in DI Water - High and Low
Conc.
Normalized Absorbance, CH2 Def.
Band
(TS on IRE under surfactant solution) – X (water
only on IRE) = Spectrum of solid soil and
adsorbed surfactant every 20 seconds!
Normalized Absorbance, C=O Ester
1
1
0.3%
0.03%
0.8
0.6
0.4
0.2
0
0
10
20
Time, min.
30
40

18. Ironically – Strong Interaction of Alcohol Ethoxylate Induces
Formation of Beta -TS – Slowing Detergency!
Sequential difference spectra = (Spectrum of Interface at longer times)
– X (First spectrum of Interface under surfactant solution)
Scheuing, D.R., Langmuir (1990),6, 312-317

19. Using ATR – Structure of Mixed CTAB/d-SDS Hemi-micelles on
Fumed TiO2 Surfaces Determined
Quantitative Adsorption on particles
Determined from CH2 and CD2 Bands
Lateral Headgroup Interactions
Derived from S-O stretching
and CH3-N+ Deformation
Bands by H.Li & C.P.Tripp
Li, H., Tripp, Carl P., J.Phys.Chem B. 2004, 108, 18318-18326

20. Surface Compositions Assessed With FT-IR
How Does Modification of Surfaces (within 5 minutes)
Depend on Location in Phase Boundary Diagram ?
“Formulation” = Surfonic L12-8 (alcohol ethoxylate)
+ Fluorinated oxetane + pDADMAC
Cationic Polymer
= pDADMAC
Thomas, R.R., et. al, Langmuir, 2002, 18, 5933-5938

21. Poly(DADMAC) Adsorbed on Ge – Adequate Detection
Limit < 0.5 mg/m2
DADMAC Detection Limit (CH3-N+) < 0.3 mAU
Freely Adsorbed from 3 mM
Solution
Intense “coupled” S-O
and C-F bands used to
detect fluorosurfactant

22. Maximum Adsorption Near Boundaries, But High [Salt], Net
Anionic Complexes Inhibit Adsorption
AT 1002/Surfonic Interactions
with 0.3 mM DADMAC
clr
2, clr + coacervate
DADMAC CH3-N
C-F 1136
0.01
2, clr+ppt
0.6
Absorbance
0.008
0.5
0.4
NaCl, M
C-F 1236
0.3
0.006
0.004
0.002
0.2
0
0
1
2
3
4
5
6
7
Equivalents, Anionic/Cationic
R = anionic charges from fluorinated
surfactant/cationic charges from DADMAC
8
R=
0
R= .40
0. 0 M
9
R= 8, Na
0
R= 7.86 M Cl
0. 0 NaC
R= 40 M l
0. 0.1 Na
9
R= 4, 0 M Cl
1. .1 NaC
R= 70 M N l
0. 0.1 aC
R= 40 M l
0. 0.5 Na
9
R= 8, 0 M Cl
1. .5 NaC
86 M l
0. Na
5
M Cl
Na
Cl
0
0.1

23. Modern FT-IR Spectrometers “It’s All Done With Mirrors”.
Can Drive Fundamental Understanding of
Aggregate Structures in Water
Probe the actions of surfactants and formulations
at solid interfaces
Can Help Us Drive Innovations In –
Surfactant structure/performance
Formulation cost/performance

24. Will You Ask More of Your Spectroscopist and
Spectrometer?

25. Thanks
AOCS – Analytical, S&D Divisions
Clorox
You –
The Audience & Consumer!