FT-IR & Phase Behavior Studies of Polymer-Surfactant Interactions

FT-IR and Phase Behavior
Studies of Polymer-Surfactant
Interactions
David R. Scheuing
Clorox Technical
Center

Objectives
Probe Effects of Polymer MWD, polydispersity with
“clean” SDS

Compare SDS and Dowfax 2A1 (commercial
“gemini”)
Develop method, probe structures of adsorbed layers
with FT-IR

System Description
Poly(diallyl dimethyl ammonium chloride) = pDADMAC
Aldrich – low, medium, high MW

Constant concentration = 0.1 wt%

Mixed anionic/nonionic micelles
Nonionic = Surfonic L12-8 – 20mM, constant and -

Either Sodium dodecylsulfate (SDS), single headgroup or
Dowfax 2A1, dual headgroup
NaCl – 0.05 – 0.60 M

Well above cmc of mixed system
Approximately 100 – 150 micelles/polymer chain

Materials - Details
Dowfax 2A1
R = C12, branched
MW = 576, cmc = 0.007% (12mM) in 0.1M NaCl

SDS – “Electrophoresis grade”
MW = 288.3, cmc = 8 mM in water

Aldrich pDADMAC – characterization by SEC/MALLS
“Low” – Mn = 80.2 x 103, Mw = 145 x 103, D = Mw/Mn=1.81
“Medium” – Mn = 128 x 103, Mw = 399 x 103, D = 3.1

“High” – Mn =200 x 103, Mw =636 x 103, D = 3.2

Experimental – Phase Samples
Vary Mole fraction anionic in micelles at constant
[NaCl], [polymer]
Total [surfactant] increases in a series (1% – 2.6%, 20 – 50 mM)

Made on 10 – 20 ml scale from stocks
Immediate vortexing
No viscosity or order of addition effects noted
Aged at ambient temp. = 23-25 C minimum 12 hrs
Centrifuged at 3000 rpm, 20 C, 30 to 60 minutes

Anionic Stock
60 mM surfactant
NaCl, [x] M

10 ml Stock 1
0.1% pDADMAC
20mM Nonionic
NaCl, [x] M

Y mL
Y mL

Stock 2
0.2% pDADMAC
20mM Nonionic
NaCl, [x] M

Coacervate formation
Initial binding of micelles to polymer required
Polymer-surfactant complexes must reach a certain total “molecular
weight” or size
Complexes achieve near neutral overall charge
Association of large intrapolymer complexes can yield interpolymer
complexes, yielding –
Macroscopic phase separation, sensitive to –
Polymer MW
Micelle charge (composition)
Overall complex charge

Electrolyte screening

Coacervate region, fixed [polymer]
Triton X-100/SDS micelles with pDADMAC

Y=mole
fraction
anionic
in micelle

r=
cationic/anionic
charge ratio
From Dubin, P.L., et.al, Macromolecules, 2000, 33, 3324-3331

Titration Phase Boundaries, pDADMAC (0.1%)
Triton X100 (20mM) /SDS Mixed Micelles
0.6

NaCl, M

0.5

2, clr + coacervate

1, Soluble Complexes

0.4

1, Soluble Complexes
1 Liquid
"No Interactions"

0.3

2, clr+ppt.

0.2

0.1
0
0

0.1

0.2

0.3

0.4

0.5

Y, Mole Fraction SDS in Micelle
Redrawn from Dubin, P.L., et.al, Macromolecules, 1999, 32, 7128-7134

0.6

0.1% DADMAC (6.2mM) High MW Interacting with 20mM
Surfonic L12-8 /SDS Mixed Micelles
0.6
Liq. + coacervate

0.5
1, clear

NaCl, M

0.4
0.3
Liq. + ppt.

0.2
0.1
0

0

0.1

0.2

0.3

0.4

Y, Mole Fraction SDS

0.5

0.6

0.1% DADMAC (6.2mM) High MW Interacting with
Surfonic L12-8 (20mM)/Dowfax Micelles
0.6
0.5
1 clear Liq.

NaCl, M

0.4
Liq. + coacervate

0.3
0.2

Liq. + ppt.

0.1
0
0

0.2

0.4

0.6

0.8

Equivalents Anionic/Moles Surf

1

1.2

Y, Mole Fraction SDS or Dowfax

Critical Y for Clear to Coacervate, Effect of
DADMAC Molecular Weight
Hi MW,SDS
Low MW SDS
Med MW,Dowfax

0.5

Med MW SDS
Hi MW, Dowfax
Low MW,Dowfax

0.45
0.4

0.35
0.3
0.25
0.2
0.15
0.1
0.05

0
0

0.1

0.2

0.3
0.4
NaCl, M

0.5

0.6

0.7

Y, Anionic Equivalents/Mole Total Surfactant

Critical Y for Clear to Coacervate, Effect of
DADMAC Molecular Weight
Hi MW,SDS
Hi MW, Dowfax
Triton X-100/SDS

Med MW SDS
Med MW,Dowfax

0.5
0.4

0.3
0.2
0.1

0
0

0.1

0.2

0.3
NaCl, M

0.4

0.5

0.6

Surfonic L12-8/Anionic Mixed Micelle Diameters (nm) from
DLS, 25 C – Indicate approximately constant size
Y, mole fraction
anionic

0.1 M

0.4 M

0.6 M

NaCl

NaCl

NaCl

0

7.9

13.5

9.3

0.17 SDS

10.6

8.2

9.3

0.3 SDS

6.4

7.1

8.0

0.4 SDS

7.8

8.0

9.4

0.17 Dowfax

11.4

8.0

8.2

0.3 Dowfax

9.0

8.6

7.9

0.4 Dowfax

7.3

8.6

7.0

Phase Study Conclusions
pDADMAC with broad MWD
Enhances precipitate formation in binding with mixed micelles
“Re-dissolution” or “charge reversed” complexes not observed

Dowfax “gemini” vs SDS
Enhances coacervate formation at lower mole fraction due to
larger micelle charge density
Larger effect of electrolyte vs. SDS – “weaker” binding of
polymer at high [salt]
Structure of complexes probably differs from SDS systems
• Electrostatic repulsions increase “headgroup” area?

Experimental – FT-IR
Attenuated Total Reflectance (ATR) optical rig
aka Internal reflection or multiple internal reflection
spectroscopy (IRS, MIRS)
Enables characterization of monolayers, even sub-monolayers
of surfactants, polymers – adsorbed directly on internal
reflection element (IRE)
In “thin film” case (<200 nm) Absorbance ~ layer thickness

Substrate for adsorption = Ge surface (model “polar”
surface) = the IRE !
Adsorption time = 5 minutes
Remove sample, rinse 20x with water

Multiple reflections enhance sensitivity to monolayers.
A horizontal IRE at bottom of a “trough” enables a variety of
experiments.
Trough on Horizon rig

Classical multiple IRE

50 mm

S-O Bands Sensitive to Counterion
Type, Location
Asymmetric S-O stretch, 1215 cm-1
O

O

O

O

Net Transition
Moment Vector

O
O

S

+ +

S

+

+
+

+
+

Symmetric S-O stretch, 1061 cm-1 Net Transition
Moment Vector

O

O

O

+

+

+

+
-

-

+
-

-

-

O
O

O
S

+

+

S
Mantsch,H.H. et.al., J.Phys.Chem. 1980,84,227
Scheuing,D.R., Weers,J.G., Langmuir,1990,6,665

.2

S-O asymm.
1220.96
1249.19

.15

Absorbance

S-O symm.
1060.86
.1
1083.45

SDS micelles in 0.1M NaCl
.05

Solid SDS on Ge
0
1500

1400

1300

1200
Wavenumber (cm-1)

1100

1000

Headgroup motions, spacing in micelles shifts asymm. S-O. Increased
headgroup – Na+ distance shifts symm. S-O.

All to same scale

S-O Asymm.

.012
SDS 60 mM micellar soln

Absorbance

.01

.008
S-O symm
.006

SDS Adsorbed onto pDADMAC
"Layer by Layer"

.004
pDADMAC adsorbed layer
.002

Ge, exposed to 60 mM SDS

0
1500

1400

1300

1200
Wavenumber (cm-1)

1100

1000

Approximate monolayer of SDS adsorbs onto preadsorbed pDADMAC layer.

.0012

All to same scale

asymm. S-O
.001

SDS Adsorbed onto pDADMAC
"Layer by Layer"

Absorbance

.0008

Ge, exposed to 60 mM SDS

.0006 CH2,CH3 def.

CH3-N-CH3
.0004

.0002

C-N-C
CH3 def.

0

1500

1400

1300

1200
Wavenumber (cm-1)

1100

1000

pDADMAC adsorbs in presence of Surfonic L12-8 micelles. SDS can
adsorb onto the pDADMAC layer, confirmed not to adsorb on Ge. No strong
evidence for adsorption of alcohol ethoxylates

Absorbance

.003

asymm. S-O
SDS micelles

symm. S-O

.0025

.002
Adsorbed Layers

Y=

0.294
0.257

.0015

0.222
0.170

.001
0.119
"LBL"

.0005

0.069

pDADMAC

0
1500

1400

1300

1200
Wavenumber (cm-1)

1100

1000

SDS and pDADMAC adsorb on Ge from systems containing mixed
micelles over wide range of Y. No evidence for adsorption of alcohol
ethoxylates.

Absorbance

asymm. S-O

.002

symm. S-O

SDS micelles
.0015

.001

Adsorbed Layers

Y=
0.294, clear
0.330, coacervate
0.406, coacervate

.0005

0.501, ppt.
pDADMAC

0
Adsorbed Layers

1500

1400

1300

Solid SDS
1200
Wavenumber (cm-1)

1100

1000

In adsorbed layers - SDS “headgroups” are laterally closer, more
“ordered”, relative to micelles. No (few) Na+ counterions.

CH2 asymm

.14

CH2 symm.

.12

Absorbance

.1
SDS micelles
.08
.06

Y= 0.294, clear

Adsorbed Layers

0.330, coacervate

.04

0.406, coacervate
0.501, ppt.

Adsorbed Layers

.02

Solid SDS

0

pDADMAC

3050

3000

2950
Wavenumber (cm-1)

2900

2850

Width and wavenumber of CH2 stretching bands – well established as related
to chain “melting” or “disorder”.
SDS “tails” in adsorbed layers are disordered, similar to micelles.

S-O asymm.

.03

S-O symm
C-O-C
aromatic C-H

Absorbance

.02

CH2 def., ring

60mM Dow fax 2A1 micelles, 0.4M NaCl

.01

0
Solid Dow fax

-.01
1500

1400

1300
1200
Wavenumber (cm-1)

1100

1000

Shifts of S-O bands of Dowfax from solid to micelle consistent
with those of SDS.

Absorbance

All to same scale
S-O asymm.

Dowfax adsorbed on pDADMAC
"Layer by Layer"

.002

.0015
.001

.0005

0
Ge, exposed to 60mM Dowfax
1500

1400

1300
1200
Wavenumber (cm-1)

1100

1000

Dowfax adsorbs onto pDADMAC layer, but not Ge. No significant
adsorption of alcohol ethoxylate.

Absorbance

.006

C-O-C

.005

S-O asymm.

S-O symm


.004

Y=
0.171

.003
0.144
0.105

.002

0.0409

.001
"LBL"

0

pDADMAC

Solid Dow fax

-.001
1500

1400

1300
1200
Wavenumber (cm-1)

1100

1000

Adsorption of Dowfax/pDADMAC from Y = 0.04 ! Loss of interaction with
Na+ counterions, similar to SDS case.

Absorbance

C-O-C

S-O asymm.

S-O symm.

.008

.006
Y=

.004

0.259 c oacervate
0.192 c oacervate

.002

0.181 c oacervate

0.171 c lear

0
"LBL"
pDADMAC

-.002
Solid Dow fax

1500

1400

1300
1200
Wavenumber (cm-1)

1100

1000

Adsorption of Dowfax/pDADMAC from supernatants of coacervate phase!
Evidence of headgroup crowding/rearrangements as Y increases.

Conclusions – FT-IR Study
Adsorbed layers formed from mixed anionic/nonionic micelles
contain only pDADMAC and anionic
Layers form quickly, over wide range of “Y”
Very active at solid surface even at low “Y”, low micelle charge

SDS – pDADMAC layer structure not a simple precipitate
“Ordered” headgroups with no Na+ counterions

Disordered tails resemble micelles
Adsorbed “rod micelles” with extended pDADMAC counterions?

Dowfax – pDADMAC layers –
Both sulfonate groups bound to pDADMAC – and
Headgroup spacing/crowding depends on “Y” value

Acknowledgments
Ms. M. Mehta – SEC of pDADMAC
Mr. M.Brutschy, Dr. E.Szekeres – DLS of micelles
Clorox management

Thanks !
S+D Session organizers, AOCS
Chairperson
YOU – for your attention !

FT-IR & Phase Behavior Studies of Polymer-Surfactant Interactions

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