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

10 ml Stock 1

0.1% pDADMAC

20mM Nonionic

NaCl, [x] M

Anionic Stock

60 mM surfactant

NaCl, [x] M

Stock 2

0.2% pDADMAC

20mM Nonionic

NaCl, [x] M

Y mL

Y mL

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

From Dubin, P.L., et.al, Macromolecules, 2000, 33, 3324-3331

Y=mole fraction

anionic in micelle

r = cationic/anionic

charge ratio

0 0.1 0.2 0.3 0.4 0.5 0.60

0.1

0.2

0.3

0.4

0.5

0.6

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

Y, Mole Fraction SDS in Micelle

NaC

l, M

1 Liquid"No Interactions"

1, Soluble Complexes

2, clr + coacervate

1, Soluble Complexes

2, clr+ppt.

Redrawn from Dubin, P.L., et.al, Macromolecules, 1999, 32, 7128-7134

0 0.1 0.2 0.3 0.4 0.5 0.60

0.1

0.2

0.3

0.4

0.5

0.6

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

Y, Mole Fraction SDS

Na

Cl,

M

1, clear

Liq. + coacervate

Liq. + ppt.

0 0.2 0.4 0.6 0.8 1 1.20

0.1

0.2

0.3

0.4

0.5

0.6

0.1% DADMAC (6.2mM) High MW Interacting with Surfonic L12-8 (20mM)/Dowfax Micelles

Equivalents Anionic/Moles Surf

NaC

l, M

Liq. + ppt.

Liq. + coacervate

1 clear Liq.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Critical Y for Clear to Coacervate, Effect of DADMAC Molecular Weight

Hi MW,SDS Med MW SDSLow MW SDS Hi MW, DowfaxMed MW,Dowfax Low MW,Dowfax

NaCl, M

Y,

Mo

le F

ract

ion

SD

S o

r D

ow

fax

0 0.1 0.2 0.3 0.4 0.5 0.60

0.1

0.2

0.3

0.4

0.5

Critical Y for Clear to Coacervate, Effect of DADMAC Molecular Weight

Hi MW,SDS Med MW SDSHi MW, Dowfax Med MW,DowfaxTriton X-100/SDS

NaCl, M

Y,

An

ion

ic E

qu

ivale

nts

/Mo

le T

ota

l S

urf

acta

nt

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

Y, mole fraction anionic

0.1 M

NaCl

0.4 M

NaCl

0.6 M

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

50 mm

Trough on Horizon rig

Classical multiple IRE

Multiple reflections enhance sensitivity to monolayers.

A horizontal IRE at bottom of a “trough” enables a variety of experiments.

S

OO

O

S

OO

O

Net Transition Moment Vector

Net Transition Moment Vector

Asymmetric S-O stretch, 1215 cm-1

Symmetric S-O stretch, 1061 cm-1

d-

d-

d+

d-

d+ d-

d-

d-

d-

S

OO

O

d+

d- d-

S

OO

O

d+

d-

d-

d- d-

d+

d-

++ +

+

+

+

+

+

++

+

+ +

+-

-- -

-

--

S-O Bands Sensitive to Counterion Type, Location

Mantsch,H.H. et.al., J.Phys.Chem. 1980,84,227

Scheuing,D.R., Weers,J.G., Langmuir,1990,6,665

0

.05

.1

.15

.2A

bsor

banc

e

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

SDS micelles in 0.1M NaCl

Solid SDS on Ge

S-O asymm.

S-O symm.

1083.45

1060.86

1249.19

1220.96

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

0

.002

.004

.006

.008

.01

.012

Abs

orba

nce

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

S-O Asymm.

S-O symm

SDS 60 mM micellar soln

pDADMAC adsorbed layer

All to same scale

SDS Adsorbed onto pDADMAC"Layer by Layer"

Ge, exposed to 60 mM SDS

Approximate monolayer of SDS adsorbs onto pre-adsorbed pDADMAC layer.

0

.0002

.0004

.0006

.0008

.001

.0012A

bsor

banc

e

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

pDADMAC adsorbed layer

All to same scale

SDS Adsorbed onto pDADMAC

"Layer by Layer"

Ge, exposed to 60 mM SDS

CH3-N-CH3

CH3 def.

CH2,CH3 def.

asymm. S-O

C-N-C

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

0

.0005

.001

.0015

.002

.0025

.003

Abs

orba

nce

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

asymm. S-O

symm. S-OSDS micelles

Y=Adsorbed Layers 0.294

0.257

0.222

0.170

0.119

0.069"LBL"

pDADMAC

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

ethoxylates.

0

.0005

.001

.0015

.002

Abs

orba

nce

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

asymm. S-Osymm. S-O

SDS micelles

Y=Adsorbed Layers0.294, clear

0.330, coacervate

pDADMAC

0.406, coacervate

0.501, ppt.

Solid SDSAdsorbed Layers

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

0

.02

.04

.06

.08

.1

.12

.14A

bsor

banc

e

3050 3000 2950 2900 2850 Wavenumber (cm-1)

Y= 0.294, clear

0.330, coacervate

0.406, coacervate

0.501, ppt.

Solid SDS

pDADMAC

SDS micelles

CH2 asymm

CH2 symm.

Adsorbed Layers

Adsorbed Layers

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.

-.01

0

.01

.02

.03A

bsor

banc

e

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

60mM Dowfax 2A1 micelles, 0.4M NaCl

Solid Dowfax

S-O asymm.

CH2 def., ring

S-O symmC-O-C

aromatic C-H

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

0

.0005

.001

.0015

.002

Abs

orba

nce

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

S-O asymm.

All to same scale

Dowfax adsorbed on pDADMAC"Layer by Layer"

pDADMAC adsorbed layer

Ge, exposed to 60mM Dowfax

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

-.001

0

.001

.002

.003

.004

.005

.006A

bsor

banc

e

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

60mM Dowfax 2A1 micelles, 0.4M NaCl

Solid Dowfax

S-O asymm.

Y=0.171

0.144

0.105

0.0409

"LBL"

pDADMAC

C-O-C S-O symm

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

-.002

0

.002

.004

.006

.008

Abs

orba

nce

1500 1400 1300 1200 1100 1000 Wavenumber (cm-1)

60mM Dowfax 2A1 micelles, 0.4M NaCl

Solid Dowfax

S-O asymm.

Y=

0.171 clear

0.181 coacervate

0.259 coacervate

0.192 coacervate

"LBL"

pDADMAC

C-O-CS-O symm.

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 !