Rheology Under the Microscope:Rheology Under the Microscope:gy pgy pTracking Changes of a Networked Associative Tracking Changes of a Networked Associative Polymer Under Shear at the Molecular LevelPolymer Under Shear at the Molecular Levelyy

Howard SiuHoward Siu3030thth Annual IPR SymposiumAnnual IPR Symposium

University of WaterlooUniversity of WaterlooMay 13May 13thth, 2008, 2008

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OutlineOutlineOutlineOutline

Associative polymers (APs)Associative polymers (APs)p y ( )p y ( )

Pyrene labelled APsPyrene labelled APs

Fraction of aggregated pyrenes (Fraction of aggregated pyrenes (ffaggagg) (Py) (Py--PDMA)PDMA)

Application to PyApplication to Py--HASE systemHASE systemApplication to PyApplication to Py HASE systemHASE system

Combined fluorometer/rheometer systemCombined fluorometer/rheometer system

ConclusionsConclusions IPR 20

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Associative PolymersAssociative PolymersAssociative PolymersAssociative Polymers

WaterWater--soluble polymers with a small amountsoluble polymers with a small amountWaterWater soluble polymers with a small amount soluble polymers with a small amount (<5 mol%) of hydrophobic pendants(<5 mol%) of hydrophobic pendants

In water, hydrophobes cluster to form In water, hydrophobes cluster to form aggregatesaggregates

In WaterIn Water

Hydrophobe Water-soluble polymerIP

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Associative PolymersAssociative PolymersAssociative PolymersAssociative Polymers

Above C* (semiAbove C* (semi--dilute regime), intermolecular dilute regime), intermolecular (( g ),g ),bridging creates a polymeric network that bridging creates a polymeric network that increases the solution viscosityincreases the solution viscosity

Used in paints and coatings as colloidal Used in paints and coatings as colloidal stabilizers and viscosity modifiers stabilizers and viscosity modifiers

Above C*IPR 20

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Rheology (Flow/Deformation) of AP SolutionsRheology (Flow/Deformation) of AP SolutionsPolymer

Hydrophobe

10000Shear hi i

100

1000

.s)

thinning

10η(P

a .

0.1

1

0.0001 0.001 0.01 0.1 1 10 100 1000

shear rate (s-1)

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Important Parameters in Modeling Important Parameters in Modeling Rheology of AP Solutions Rheology of AP Solutions

Residence time of hydrophobes in aggregatesResidence time of hydrophobes in aggregates

Average number of hydrophobes per aggregate Average number of hydrophobes per aggregate ((NN ))((NNaggagg))

Overall level of association of hydrophobes in Overall level of association of hydrophobes in solution (solution (ffaggagg))gggg

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Defining the Network byDefining the Network by NN andand ffDefining the Network by Defining the Network by NNaggagg and and ffaggagg

•fagg gives the fraction of hydrophobes in aggregates

•Knowing fagg and Nagg gives the # of junction points, thus the extent of network

•For same fagg, having highfagg, g gNagg values results in a less extended network

Thus, it is essential to know both fagg and Nagg in order to characterize the network effectively

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Determination ofDetermination of ff andand NNDetermination of Determination of ffaggagg and and NNaggagg

NNaggagg can be determined for a pyrene labelled AP by can be determined for a pyrene labelled AP by aggagg py ypy yfluorescence quenching studies*fluorescence quenching studies*

R lR l ff h b d i d b flh b d i d b flRecentlyRecently ffaggagg parameter has been determined by fluorescence parameter has been determined by fluorescence measurements for pyrene labelled APs**measurements for pyrene labelled APs**

NNaggagg has also been determined for a pyrene labelled AP from has also been determined for a pyrene labelled AP from fluorescence, using fluorescence, using ffaggagg and information obtained from the and information obtained from the fluorescence blob model (FBM)**fluorescence blob model (FBM)**fluorescence blob model (FBM)**fluorescence blob model (FBM)**

*Siu, H.; Prazeres, T. J. V.; Duhamel, J.; Olesen, K.; Shay, G. Macromolecules 2005, 38, 2865.

**Siu, H.; Duhamel, J. Submitted to J. Phys. Chem. B, Manuscript # JP-2008-011059

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Pyrene FluorescencePyrene FluorescencePyrene FluorescencePyrene Fluorescence

120

hν + Py + Py Py* + Py (PyPy)*1/τM 1/τE

<k1>

CH2O

80

100

y (a

.u.)

120

20

40

60

Inte

nsity

Monomer Excimer

I I

IE/IM

0350 400 450 500 550 600

Wavelength (nm)

IM IEIPR 20

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Excimer Lifetime DecaysExcimer Lifetime DecaysExcimer Lifetime DecaysExcimer Lifetime DecaysAggregatesDiffusion

hν + Py + Py Py* + Py (PyPy)*<k1> (PyPy) + hν

1/τM 1/τE

100000

Aggregates (no rise time)

1000

10000

ount

s

100

Co

Diffusion (rise time)

100 100 200 300 400

Time (ns)

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The Fluorescence Blob Model (FBM)The Fluorescence Blob Model (FBM)The Fluorescence Blob Model (FBM)The Fluorescence Blob Model (FBM)

Blob = Volume probed by an excitedBlob Volume probed by an excited pyrene can probePy

<n>: Average number of pyrenes per blob

PyPyPy

kbl b: Rate of encounter of excited

Py PyPy

Pyk kblob: Rate of encounter of excited

pyrene with one ground-state pyrene

Py* kblob

The fluorescence blob model is useful to model diffusional encounters of pyrene pendants attached to a polymer

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Pyrene Species Present in SolutionPyrene Species Present in SolutionPyrene Species Present in SolutionPyrene Species Present in Solution

ffaggagg: Fraction of associated : Fraction of associated pyrene pendants in pyrene pendants in solutionsolutionPyPy

ffdiffdiff: Fraction of pyrenes : Fraction of pyrenes f i i if i i iforming excimer via forming excimer via diffusion (FBM)diffusion (FBM)Py Py

fffreefree: Fraction of pyrenes that : Fraction of pyrenes that never form excimer never form excimer (e(e--t/t/ττMM))(e(e // MM))Py

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Determination of Pyrene Fluorescence FractionsDetermination of Pyrene Fluorescence FractionsDetermination of Pyrene Fluorescence FractionsDetermination of Pyrene Fluorescence Fractions

By relating the curvature of the monomer decay to the rise time By relating the curvature of the monomer decay to the rise time y g yy g yof the excimer decay, the fractions , , and can be of the excimer decay, the fractions , , and can be determined.determined.

aggf freef difff

f f

aggf

difff difff

-t/τM

freefe-t/τM

Siu, H.; Duhamel, J. Macromolecules (Technical Note) 2004, 37, 9287.

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Ideal Case ScenarioIdeal Case ScenarioIdeal Case ScenarioIdeal Case Scenario

P rene randoml labelled onto pol (P rene randoml labelled onto pol (NN NN dimeth ldimeth lPyrene randomly labelled onto poly(Pyrene randomly labelled onto poly(NN,,NN--dimethyl dimethyl acrylamide) (PyPDMA)acrylamide) (PyPDMA)

n m<<n

N O HN O

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Analysis of Fluorescence DecaysAnalysis of Fluorescence DecaysAnalysis of Fluorescence DecaysAnalysis of Fluorescence DecaysMonomer Decay Excimer Decay

g 10(I

E)

g 10(I

M)

[Py-PDMA] = 0.09 g/L

645 μmol pyrene/g polymerLo

g

Log

MonomerTime, ns Time, ns

Resid

uals

Resid

uals

λex = 340 nm

λem = 375 nm

utoc

orr.

utoc

orr.

Time, ns Time, ns Excimerλex = 340 nmλ = 510A

u

Au

Time, ns Time, ns

λem = 510 nmIP

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PyPy--PDMA Pyrene FractionsPDMA Pyrene FractionsPyPy PDMA Pyrene FractionsPDMA Pyrene Fractions

Pyrene Content OD

[Py-PDMA]

μmol/g g/Lfreef aggfdifff

Py PyPyPy

Py

1.0

6451 0.09 0.07 ±

0.010.00 ±0.00

0.93 ±0.01

30 2.2 0.06 ±0 01

0.00 ±0 00

094 ±0 02

0.7

0.8

0.9

f agg

30 2.2 0.01 0.00 0.02

479

0.1 0.01 0.18 ±0.03

0.02 ±0.00

0.80 ±0.03

0.7 0.08 0.18 ±0 02

0.02 ±0 00

0.81 ±0 02

0.5

0.6

0 100 200 300 400 500 600 700

Pyrene Content, mmol/g polymer0.02 0.00 0.02

15 1.8 0.17 ±0.02

0.01 ±0.00

0.82 ±0.02

263 30 4.8 0.25 ±0.02

0.06 ±0.01

0.69 ±0.03

Model was able to determine the pyrene fractions in solution

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NN for Pyfor Py--PDMAPDMANNaggagg for Pyfor Py PDMAPDMAKnowing the total pyrene concentration and the Knowing the total pyrene concentration and the fractions of the species we can obtain [fractions of the species we can obtain [PyPy ]] [[PyPy ]]fractions of the species we can obtain [fractions of the species we can obtain [PyPydiffdiff]]00, [, [PyPyaggagg]]00

F FBM b i <F FBM b i < > hi h i h b f> hi h i h b fFrom FBM we obtain <From FBM we obtain <nn>, which is the number of >, which is the number of groundground--state pyrene species per blob or:state pyrene species per blob or:

/][][ NPP][

/][][ 00

blobNPyPy

n aggaggdiff +=><

Assuming [Assuming [blobblob] = ] = cc xx [[PolyPoly], we can rearrange to get:], we can rearrange to get:

0][11][ PyPolyn ×><

0

0

0 ][][11

][][

diff

agg

aggdiff PyPy

NccPyPolyn

×+=

×><IP

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NN for Pyfor Py--PDMA (cont’d)PDMA (cont’d)NNaggagg for Pyfor Py PDMA (cont d)PDMA (cont d)5.0

ol

3 0

4.0ff

] o, g

/mo

2.0

3.0

ly]/[

Pydi

f

][11][ PP l1.0

<n>

[Pol

0

0

0 ][][11

][][

diff

agg

aggdiff PyPy

NccPyPolyn

×+=

×><

0.00 5 10 15 20

[Py agg ]o /[Py diff ]o

<

From the slope and intercept: Nagg = 3.1 ± 1.6IP

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Application to HASE SystemApplication to HASE SystemApplication to HASE SystemApplication to HASE System

Apply method used to determine Apply method used to determine ffaggagg and and NNaggagg for Pyfor Py--PDMA PDMA pp ypp y ffaggagg aggagg yysystem to Pysystem to Py--HASE associative polymer systemHASE associative polymer system

M i d i ll l (HASE l d iM i d i ll l (HASE l d iMore industrially relevant system (HASE polymer used in More industrially relevant system (HASE polymer used in latex paints as thickening agent)latex paints as thickening agent)

Relate Relate ffaggagg and and NNaggagg to physical properties of Pyto physical properties of Py--HASE HASE solutions under sheared conditionssolutions under sheared conditionsIP

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HASE PolymersHASE Polymers

Hydrophobically modified Alkali Swellable Emulsion Hydrophobically modified Alkali Swellable Emulsion

HASE PolymersHASE Polymers

(HASE) polymer (HASE) polymer

H C C

C4H9

S CH C

CH3

CHHC CH C

CH3

HH7C3 C

C4H9

S CH2 C

COOH

CH2 C

COOC2H5

CH2 C H

H3C

X Y Z

H3CH3C

NHO

Polymer properties can be fine tuned by controlling Polymer properties can be fine tuned by controlling

OOH2CH2CCH2R n

y p p y gy p p y gratio of X:Y:Z, PEO length n, and hydrophobe Rratio of X:Y:Z, PEO length n, and hydrophobe R

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Pyrene Labelled HASE PolymerPyrene Labelled HASE PolymerPyrene Labelled HASE PolymerPyrene Labelled HASE Polymer

C4H9 CH3 CH3

H7C3 C

C4H9

S CH2 C

COOH

CH2 CH

COOC2H5

CH2 C H

X Y Z

H3CH3C

NHOP

OOH2CH2CH2C n

Pyrene

•Pyrene is a hydrophobe

•Pyrene is a chromophoreIP

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Proposed Study Proposed Study Effect of Shear on Level of Association Effect of Shear on Level of Association

Application of shear breaks up hydrophobic aggregatesApplication of shear breaks up hydrophobic aggregatesApplication of shear breaks up hydrophobic aggregatesApplication of shear breaks up hydrophobic aggregates

Disrupts network leading to a drop in viscosity (shear Disrupts network leading to a drop in viscosity (shear thi i )thi i )thinning)thinning)

AppliedApplied Shear

Break up of aggregates leads to a change inBreak up of aggregates leads to a change inGoal: Map the changes in level of association Goal: Map the changes in level of association Break up of aggregates leads to a change in Break up of aggregates leads to a change in networknetwork

((ffagg agg and and NNaggagg) while the system is under ) while the system is under shear shear using the proposed setupusing the proposed setup

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Example of Fluorometer/Rheometer SetupExample of Fluorometer/Rheometer SetupExample of Fluorometer/Rheometer SetupExample of Fluorometer/Rheometer Setup

Optical fibers

S dS d fl f AP l ifl f AP l iSteadySteady--state fluorescence measurements of AP solutions state fluorescence measurements of AP solutions located inside a rheometerlocated inside a rheometer

Richey, B.; Kirk, A.B.; Eisenhart, E.K.; Fitzwater, S.; Hook, J. J. Coat. Technol.1991, 63, 31.

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Proposed Fluorometer/Rheometer SetupProposed Fluorometer/Rheometer SetupProposed Fluorometer/Rheometer SetupProposed Fluorometer/Rheometer Setup

Steady-state/Time-resolved Fl tFluorometer

Emission

E it tiExcitation

Optical fibers

Gap width = 0.2 mm

S dS d d id i l d fll d fl

Rheometerp

SteadySteady--state and timestate and time--resolved fluorescence resolved fluorescence measurements of pyrene labeled HASE solutions measurements of pyrene labeled HASE solutions

l d i id hl d i id hlocated inside a rheometer located inside a rheometer IP

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Experimental Coupled SetupExperimental Coupled SetupExperimental Coupled SetupExperimental Coupled SetupEmission Excitation

Rheometer Site

Exc

itatio

nE

mission

Single Photon Counter Steady State Fluorometer

E

Single Photon Counter Steady-State Fluorometer

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Experimental ConditionsExperimental ConditionsExperimental ConditionsExperimental Conditions

PyPy--HASE with a pyrene content of 65HASE with a pyrene content of 65 μμMMPyPy HASE with a pyrene content of 65 HASE with a pyrene content of 65 μμM M pyrene/g polymerpyrene/g polymer

Solvent is 0.01 M NaSolvent is 0.01 M Na22COCO33, pH 9 solution, pH 9 solution

[Py[Py--HASE] = 5 w/w%HASE] = 5 w/w%[ y[ y ] /] /IPR 20

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Rotation Experiment for PyRotation Experiment for Py--HASEHASERotation Experiment for PyRotation Experiment for Py HASEHASE

1,000,000

10,000

100,000

Pa.s

10

100

1,000

Vis

cosi

ty, P

η ~ 2 Pa.s

0

1

10V η ~ 800 Pa.s

01E-05 0.0001 0.001 0.01 0.1 1 10 100 1000

Shear Rate, 1/s

0.2 mm gap width between plates IP

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Preliminary SteadyPreliminary Steady--State/Rheometer DataState/Rheometer DataPreliminary SteadyPreliminary Steady State/Rheometer DataState/Rheometer Data

10000150

6000

8000

a.u.

Uncorrected Spectrum100ns

ity, a

.u. Shear rate = 0

Shear rate = 100 1/sShear rate = 0.1 1/s

4000

6000

Inte

nsity

, a

p

50aliz

ed In

ten

0

2000

I

Blank

0

Nor

ma

0350 400 450 500 550 600

Wavelength, nm

0350 400 450 500 550 600

Wavelength, nm

Little change in steady-state fluorescence despite 400x drop in viscosity

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Preliminary SPC/Rheometer DataPreliminary SPC/Rheometer DataPreliminary SPC/Rheometer DataPreliminary SPC/Rheometer DataMonomer Decay Excimer Decay

10000

100000

Shear rate = 0.1 1/sShear rate = 100 1/s

10000

100000

Shear rate = 0.1 1/sShear rate = 100 1/s

100

1000

Cou

nts

100

1000

Cou

nts

1

10

0 200 400 600 800Time, ns

1

10

0 500 1000 1500Time, ns

Monomer and excimer fluorescence decays also exhibit LITTLE DIFFERENCE despite change of 400x inLITTLE DIFFERENCE despite change of 400x in viscosity (fagg and Nagg likely are unchanged)!

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Conclusions for FluorometerConclusions for Fluorometer––Rheometer ExperimentsRheometer Experiments

Concept for both single photon counter and steadyConcept for both single photon counter and steady--p g p yp g p ystate fluorometer coupled with the rheometer proven state fluorometer coupled with the rheometer proven to be feasibleto be feasible

Optimization of procedure/setup is required to improve Optimization of procedure/setup is required to improve signal to the detectorsignal to the detector

N d b ildN d b ildNeed to build a more permanent setupNeed to build a more permanent setupIPR 20

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Conclusions for FluorometerConclusions for Fluorometer––Rheometer Experiments (cont’d)Rheometer Experiments (cont’d)

Little change observed in timeLittle change observed in time--resolved and steadyresolved and steady--gg yystate preliminary data indicating that little to no state preliminary data indicating that little to no change in change in ffaggagg and and NNaggagg with change in shear ratewith change in shear rate

Implies a switching between intraImplies a switching between intra-- and intermolecular and intermolecular associations with formation/disruption of network (energy associations with formation/disruption of network (energy transfer experiment)transfer experiment)

More measurements varying setup parameters More measurements varying setup parameters (measurement depth, gap width, concentration, etc.) need (measurement depth, gap width, concentration, etc.) need to be performed to verify this resultsto be performed to verify this results

Introduce latex particles (found to affect steadyIntroduce latex particles (found to affect steady--state state spectra in the presence of shear according to Richey et al.)spectra in the presence of shear according to Richey et al.)

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AcknowledgementsAcknowledgementsAcknowledgementsAcknowledgements

Dr. Jean DuhamelDr. Jean DuhamelDr. Jean DuhamelDr. Jean Duhamel

DOW Chemical for the PyDOW Chemical for the Py--HASE and PyPEOHASE and PyPEO

Telmo PrazeresTelmo Prazeres

h l d G h b Gh l d G h b GDuhamel and Gauthier Lab GroupsDuhamel and Gauthier Lab Groups

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QUESTIONS?QUESTIONS?

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