1 April 19th 2011

Plasma polymers for reaching Plasma polymers for reaching

reversible metal / elastomer reversible metal / elastomer

adhesionadhesion

Institut de Chimie des Surfaces et Interfaces

UPR 9069 15 rue Jean Starcky, 68057 Mulhouse

Frederic SIFFERFrederic SIFFER

2 April 19th 2011

1 Background – Diels-Alder reaction, plasmas

2 Chemometric investigation of the effect of the process parameters during pulsed plasma polymerization of maleic anhydride

4 Synthesis of bi-functional molecules for interfacial Diels-Alder reactions

5 Following Diels-Alder reaction kinetics in solution on dienophile functionalized substrates

6 Interfacial Diels-Alder reaction between 2 substrates correctly functionalized

7 Conclusion & perspectives

Presentation agendaPresentation agenda

3 April 19th 2011

Plasma polymer functionalized substrate

Understand and control adhesion properties

BA

BackgroundBackground

Interfacial chemistry

4 April 19th 2011

BackgroundBackgroundDiels-Alder reaction overview

C

C

C

C CH2

C

C

H

H

H

R

C

C

H

H

H

R DienophileDienophile

C

C

C

C

CH2

DieneDiene

Transition state

C

C

C

C CH2

C

C

H

H

H

R

New C-C bonds formed

Concerted reaction

5 April 19th 2011

BackgroundBackground

Diels-AlderRetro

Diels-Alder

Goal :

Control adhesion properties between 2 surfaces functionalized by plasma

polymerization via Diels-Alder reaction

6 April 19th 2011

Plasma…Plasma…

Substrate

Electrode

Gas inlet

Vacuum

Electrode

Electrons Ions

Molecules

Recombinaison

Ionisation

Optical Emission

Radicals

ReactionsIons -molecules

sheath

7 April 19th 2011

Substrate

ExcitationsIonisations

Radiations

Dissociations

Recombinaisons

Surface

Neutrals Ionic species

Migration, Adsorption, Dissociation, Reaction

sheath

Bombardement

Diffusion Acceleration

Boundary

Desorption

Plasma…Plasma…

8 April 19th 2011

M i

M i

M i + M M i - MM i - M

+ M jM i M i - M jM i -

M i

M i - M jM k - +

M k

M k

M k + M

M k M j+

M k - M

M k - M j

P o l y m é r i s a t i o n b i c y c l i q u e

E x c i t a t i o n d u p l a s m a

C y c l e 1

C y c l e 2

M i

M iM i

M iM i + M M i - MM i - M

+ M jM i + M j+ M jM iM i M i - M jM i -M i - M jM i -

M iM i

M i - M jM k -M i - M jM k -M i - M jM k - +

M kM k

M kM k

M kM k + M

M kM k M jM j+

M k - MM k - M

M k - M jM k - M j

P o l y m é r i s a t i o n b i c y c l i q u e

E x c i t a t i o n d u p l a s m a

C y c l e 1

C y c l e 2

H. Yasuda. Plasma Polymerization, Academic Press, 1985

Plasma…Plasma…

Bicyclic polymerization

Plasma excitation

9 April 19th 2011

Po

wer

(W

)

Impulsion length (10-3 s – 10-6 s)

Substrate

Plasma offPlasma off

Vite

sse

de d

épos

ition

deposition

Plasma…Plasma…S

pec

ies

den

sity

Substrate

Plasma onPlasma on

Ions

UV Electrons

Radicals

Molecules

modification

deposition

ablation

10 April 19th 2011

Plasma polymerization setupPlasma polymerization setup

Schéma simplifié du mécanisme de polymérisation Schéma simplifié du mécanisme de polymérisation

OO OO

O

O

OO

OR.F. pulsées

30 min

R/R’ = -COOH -CH2OR -C=O -CH3

-OH

…

OO O

Maleic anhydride

High reactivity

MonomerMonomerPump

Liquid nitrogen

Fittings

Pressure gauge

Copper turns O-ring Gas

Matching

Substrate

Glass plate

Valve

R.F. generator

13,56 MHzbox

11 April 19th 2011

Pulsed plasma polymerizationPulsed plasma polymerization

Desired plasma coating properties :

-Highest concentration of maleic anhydride functionalities incorporated in polymer

- Low roughness

- Ultra thin plasma polymer coating

toff

ton

Variation of ton toff Pp

Variation of plasma polymer properties

Need to optimize plasma parameters

PuissancePp

Monitoring RF signal via an oscilloscope

12 April 19th 2011

200

400

600

800

200

400

600

800

1000

1200

0,4

0,8

1,2

200

400

600

800

200

400

600

800

1000

1200

0

20

Off – time (µs) On –tim

e (µs)

On –tim

e (µs)Off – time (µs)

% A

nh

ydri

de

Ra

(nm

)

200

400

600

800

200

400

600

800

1000

1200

200

400

600

800

200

400

600

800

1000

1200

0,4

0,8

1,2

0,4

0,8

1,2

200

400

600

800

200

400

600

800

1000

1200

200

400

600

800

200

400

600

800

1000

1200

0

20

Off – time (µs) On –tim

e (µs)

On –tim

e (µs)Off – time (µs)

% A

nh

ydri

de

Ra

(nm

)

Use of chemometric toolsUse of chemometric toolsParameter Low (-) Center (0) High (+)

Pp (peak power, W)

10 50 90

ton (µs) 20 410 800

toff (µs) 20 610 1200

Domain of variation of plasma parameters for DOE study

Parameter Low (-) Center (0) High (+)

Pp (peak power,

W)5 10 15

ton (µs) 13 26 39

toff (µs) 1200 1250 1300

Domain of variation of refined parameters for central composite design

Matrix of experiments

Response

ExperimentPp

(W)

ton

(µs)

toff

(µs)

Anhydride group

retention(%)

Thickness(nm)

Roughness

(nm)

1 - - - 19,0 191,3 0,44

2 + - - 12,8 120,1 0,39

3 - + - 12,3 114,2 0,99

4 + + - 0,0 0,0 0,06

5 - - + 30,0 38,7 0,19

6 + - + 15,8 128,7 0,21

7 - + + 11,2 42,0 0,10

8 + + + 10,3 87,5 0,20

9 0 0 0 11,15 84,9 0,55

10 0 0 0 11,25 89,0 0,88

11 0 0 0 11,83 87,2 0,61

Area of interest

13 April 19th 2011

Optimized conditions :Optimized conditions : 5W, 25µs on-time, 1200µs off-time

XPS IRRAS AFM

Anhydride group retention : Anhydride group retention : 32%

Film thickness :Film thickness : 15 nm

Roughness :Roughness : ~ 0.2 nm

AFM image - Phase z=3° - 2μm x 2μm

Plasma coating propertiesPlasma coating properties

Anhydride groups

C 1s

OO OOO OOO O

Elongation cycles

anhydride conjugués

Conjugated anhydrides – cycle

elongation

C-O-C elongation

C=O antisym. vibration C=O sym.

vibration

Wavenumber (cm-1)Binding energy (eV)

14 April 19th 2011

Influence of substrate on plasma coating Influence of substrate on plasma coating morphologymorphology

Silicon wafer

Sputtered gold

Mirror finish aluminum

EPDM

Model substratesModel substrates

Industrial substratesIndustrial substrates

Surface morphology prior to plasma polymerizationSurface morphology prior to plasma polymerization

Surface morphology after plasma coating depositionSurface morphology after plasma coating deposition

15 April 19th 2011

Plasma coating functionalizationPlasma coating functionalizationOO O

OO O

OO OOO OOO O

OO O

Aminolysis Aminolysis reactionreaction

O ONH

R

OH

OO O

NH2 R

O ONH

R

OH

O ONH

R

OH

O ONH

R

OH

Functionalization

R = Diene or Dienophile

Functionalized plasma coating

16 April 19th 2011

Bifunctional molecules Bifunctional molecules

NH2

NH2 R

Available commercially

No commercial availability

SYNTHESIS

17 April 19th 2011

Synthesis of the bifunctional diene Synthesis of the bifunctional diene

Targeted molecule :

NH2

Plasma polymer thin filmPlasma polymer thin filmAu

8

NH

F. Siffer, V. Roucoules, M.-F. Vallat, A. Defoin, “Synthesis of new functionalized cyclopentadienes to reach reversible bonding between two substrates”, Synthesis, 2008 (4), 515-518.

18 April 19th 2011

NO O

OH

O

NH

OH

O

NH

OH

O

NH

Plasma coating functionalizationPlasma coating functionalization

NO O

120°C – 2 hrs under vacuum

NH2

Gas phase

b)

c) Plasma coating

OO OOO OOO O

a) Plasma coating

NO O

d) Plasma coating

Plasma coating functionalized with dienophile groups

Wavenumber (cm-1)

Wettability measurements

Nature des échantillons

Advancing contact angle

Receding contact angle

Plasma coating(anhydride groups)

62° ± 2° < 10°

Plasma coating functionalized with allylamine - AMIDE

12° ± 2° < 10°

Plasma coating functionalized with allylamine - IMIDE

60° ± 2° < 10°

19 April 19th 2011

Diels-Alder reactionDiels-Alder reactionConcerted reaction :

C

C

C

C

CH2

DieneDieneTransition state

C

C

HH

H DienophileDienophile

Au

C

H

C

C

C CH2

C

C

H

H

Au

C

C

C

C CH2

C

C

H

H

H

Newly created C-C bonds

Au

20 April 19th 2011

Reaction kinetics of interfacial Diels-Reaction kinetics of interfacial Diels-Alder Alder

Diene used for this study

NO O

Si

NO O

Si

NO O

Si

Pulsed plasma polymer

NO O NO O NO O

Pulsed plasma polymer

Si

CPdSiSi

[(triméthylsilyl)methyl]cyclopentadiene

21 April 19th 2011

Following Diels-Alder reaction kineticsFollowing Diels-Alder reaction kinetics

59

64

69

74

79

84

89

0 1000 2000 3000 4000 5000 6000

Time (s)

Ad

van

cin

g c

on

tact

an

gle

(°)

294 K 308 K

318 K 328 K

278 K 288 K

Wettability measurements:Wettability measurements:

22 April 19th 2011

Functional group densityFunctional group density

NO O NO O NO O

Plasma polymer

NO O

Si

NO O

Si

NO O

Si

Plasma polymer

SiCyclohexane

θalkene = 60°

θbicyclo = 87°

θexpérimental

Cassie equation : Cos θexperimental = alkene . Cos θalkene + bicyclo . Cos θbicyclo

alkene

alkene bicyclo

bicyclo

23 April 19th 2011

Following Diels-Alder reaction kineticsFollowing Diels-Alder reaction kineticsXPS measurements – following Si/N ratio

Si/N = 1 when all dienophile groups have undergone a Diels-Alder

reaction

CP

S

Binding energy (eV)

NO O

Si

NO O

Si

NO O

Si

Polymère plasma

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

0 1000 2000 3000 4000 5000 6000

Time (s)

Si/N

rat

io (

area

un

der

pea

k)

293 K

308 K

328 K

24 April 19th 2011

Interfacial Diels-Alder reaction between solid Interfacial Diels-Alder reaction between solid substratessubstrates

Substrate 1aluminum

Substrate 2aluminum

orrubber

Plasma polymerization

Functionalization with diene groups

Functionalization with dienophile groups

Substrates assembledIn a curing press

Is the Diels-Alder reaction effective Is the Diels-Alder reaction effective between 2 functionalized substratesbetween 2 functionalized substrates

25 April 19th 2011

Disponibility of dienophile groupsDisponibility of dienophile groups

ImideAmide

DicumylDicumyleperoxyeperoxy

dede

AluminumAluminum

Crosslinking reaction

Press 170ºC - 40min – 3 MPa

AluminumAluminiumAluminum

1st step : verify that dienophile groups immobilized on aluminum are available to react during EPDM peroxide cure

EPDM EPDM

26 April 19th 2011

Disponibility of dienophile groupsDisponibility of dienophile groups

180 degree peel tests Interfacial fracture energy

-200

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Peeled length (mm)

W18

0 (J

/m²)

Amide

Imide (vacuum)

Imide (atmosphere)

Reference

20 mm/min5 mm/min

5 mm/min20 mm/min

EPDM cohesion

energy

Dienophile groups seem to be available for interfacial reaction

EPDM

Aluminum

180 degrees

27 April 19th 2011

Analysis of peeled substratesAnalysis of peeled substratesWettability measurements

Contact angle

Alu

min

um

EP

DM

(after peel test)

Advancing: 103º ± 2º

Receding : 42º ± 2ºAdvancing: 100º ± 2º

Receding : 35º ± 2°

Cohesive fracture located in EPDM

• Bare EPDM :• A: 103º R: 45º

28 April 19th 2011

Interfacial Diels-Alder reaction between Interfacial Diels-Alder reaction between functionalized EPDM / aluminumfunctionalized EPDM / aluminum

NO ONO O NO O NO O

Substrates assembled in a curing press for

different conditions of

pressure, time and temperature

EPDM EPDM

30°C – 70°C30min – 120 min

0,08 MPa – 0,32 MPa

DOE performed to optimize assembling

conditions

Pulsed plasma polymer Pulsed plasma polymer

Pulsed plasma polymer Pulsed plasma polymer

29 April 19th 2011

Interfacial Diels-Alder reaction between Interfacial Diels-Alder reaction between functionalized EPDM / aluminumfunctionalized EPDM / aluminum

Peeled length (mm)

Peel energy between 2 dienophile functionalized substrates

Aluminum

EPDM

ExperimentN°

Temperature(°C)

Time(min.)

Pressure(MPa)

Peel energy(J.m-2)

1 30 30 0,08 20

2 70 30 0,08 280

3 30 120 0,08 8

4 70 120 0,08 224

5 30 30 0,32 32

6 70 30 0,32 248

7 30 120 0,32 280

8 70 120 0,32 448

9 50 75 0,2 24

10 50 75 0,2 20

11 50 75 0,2 24

Peel energy between 2 substrates respectively functionalized with diene and dienophile groups

No interfacial bond formation

Interfacial Diels-Alder seem to proceed ! Interfacial Diels-Alder seem to proceed !

30 April 19th 2011

Interfacial Diels-Alder reaction – AFM images of Interfacial Diels-Alder reaction – AFM images of aluminum substrate before and after peel testaluminum substrate before and after peel test

EPDM

ALUMINIUM

Pelage 180°

Height image

Ra = 62.32 nm

Phaseimage

Phaseimage

Height image

Ra = 18.74 nm

Plasma coated Plasma coated aluminum substrate aluminum substrate (prior to peel test)(prior to peel test)

Aluminum substrate Aluminum substrate after peel testafter peel test

31 April 19th 2011

Interfacial Diels-Alder reaction – AFM Interfacial Diels-Alder reaction – AFM images of EPDM substrate before and after images of EPDM substrate before and after

peel testpeel test

EPDM

ALUMINIUM

180° peel test

Phaseimage

Phaseimage

Height image

Ra = 13.9 nm

Plasma coated EPDMPlasma coated EPDM(prior to peel test)(prior to peel test)

EPDM substrate after peel EPDM substrate after peel testtest

Height image

Ra = 60.6 nm

Height image

Ra = 16.1 nm

Phaseimage

Bare EPDMBare EPDM

32 April 19th 2011

Analysis of peeled substratesAnalysis of peeled substrates

Wettability measurements

Contact angles

Alu

min

um

EP

DM

(after peel test)

Advancing: 100º ± 2º

Receding : 40º ± 2ºAdvancing: 103º ± 2º

Receding : 42º ± 2°

Cohesive fracture located in EPDM

Bare EPDM :• A: 103º R: 45º

33 April 19th 2011

Retro Diels-AlderRetro Diels-AlderDiels-Alder reaction seem to proceed at interface

Is the reaction reversible

Reversibility test : 180 degree peel test performed while heating sample

Peeled length (mm)

Ambient temperature

34 April 19th 2011

Conclusion - perspectivesConclusion - perspectives

Diels-AlderRetro

Diels-Alder

• Plasma coating strongly adheres to EPDM, Al• Substrates easily functionalized with diene, dienophile groups• Solid-state Diels-Alder reaction seem to proceed• Indication that Retro Diels-Alder undergoes at high

temperature• Interfacial reaction can be extended to other types of

substrates