ft-ir & phase behavior studies of polymer-surfactant interactions
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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 !
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