Institut de Chimie des Surfaces et Interfaces
UPR 9069
15 rue Jean Starcky, 68057 Mulhouse
Frederic SIFFER
Plasma polymers for reaching reversible
metal / elastomer adhesion
1
April 19th 2011
Presentation agenda
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
2
April 19th 2011
Background
Plasma polymer functionalized substrate
A
Interfacial
chemistry
B
Understand and control adhesion properties
3
April 19th 2011
Background
Diels-Alder reaction overview
Transition state
Diene
C
C
C
C
C
CH2
C
CH2
Concerted reaction
C
C
C
C
CH2
C
C
New C-C bonds formed
Dienophile
4
April 19th 2011
Background
Retro
Diels-Alder
Diels-Alder
Goal :
Control adhesion properties between 2
surfaces functionalized by plasma
polymerization via Diels-Alder reaction
5
April 19th 2011
Plasma…
Gas inlet
Electrode
Electrons
Recombinaison
Ions
Molecules
Reactions
Ions -molecules
Ionisation
Radicals
Optical
Emission
sheath
Substrate
Electrode
Vacuum
6
April 19th 2011
Plasma…
Excitations
Dissociations
Ionisations
Recombinaisons
Neutrals
Radiations
Ionic species
sheath
Boundary
Acceleration
Diffusion
Desorption
Bombardement
Surface
Migration,
Dissociation,
Adsorption,
Reaction
Substrate
7
April 19th 2011
Plasma…
Cycle 1
Mi
Mi + M
Mi - M
Mi + Mj
Mi - Mj
Mi
Mi
Mki - Mj
+
Polymérisation
bicyclique
Bicyclic polymerization
Mk
Excitation
Plasmadu
plasma
excitation
Mk
Mk + M
Mk - M
Mk + Mj
Mk - Mj
M
Cycle 2
H. Yasuda. Plasma Polymerization, Academic Press, 1985
8
April 19th 2011
Plasma…
Plasma on
Electrons
Molecules
Radicals
Ions
Power (W)
Substrate
Substrate
modification
deposition
ablation
Vitesse de déposition
Species density
UV
Plasma off
deposition
Impulsion length (10-3 s – 10-6 s)
9
April 19th 2011
Plasma polymerization setup
High reactivity
Pressure gauge
Copper turns
O
Valve
Gas
O-ring
Fittings
Substrate
Pump
O
O
Maleic anhydride
Monomer
Glass plate
R.F. generator
Matching
box
Liquid nitrogen
13,56 MHz
Schéma simplifié du mécanisme de polymérisation
O
O
O
O
R.F. pulsées
O
O
O
R
*
30 min
10
R'
n*
O
R/R’ = -COOH
-CH2OR
-C=O
-CH3
O
-OH
…
April 19th 2011
Pulsed plasma polymerization
ton
Puissance
Pp
Variation of ton toff Pp
toff
Variation of plasma
polymer properties
Monitoring RF signal via an oscilloscope
Desired plasma coating properties :
-Highest concentration of maleic anhydride functionalities incorporated in polymer
- Low roughness
- Ultra thin plasma polymer coating
Need to optimize plasma parameters
11
April 19th 2011
Use of chemometric tools
Parameter
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
Area of interest
High (+)
15
Roughness
39
(nm)
Domain of variation of refined
parameters for central composite design
1300
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
12
20
0
0
20
Of
f
% Anhydride
Matrix of
Parameter
Low (-)
CenterResponse
(0)
experiments
Pp (peak power,
5
Anhydride 10
W) Pp
toff
ton
group
Thickness
Experiment
ton (µs)(W)
13
retention 26 (nm)
(µs)
(µs)
(%)
toff (µs)
1200
1250
1
19,0
191,3
0
40
20
0
–t
0
60
im
e
s)
40
0
0
80
00
10
(µs
)
60
0
00
12
80
0
On
–
µ
e(
tim
April 19th 2011
Plasma coating properties
Optimized conditions : 5W, 25µs on-time, 1200µs off-time
C 1s
Anhydride
groups
C=O
sym.
vibration
C=O antisym. vibration
C-O-C elongation
Conjugated
anhydrides – cycle
elongation
Binding energy (eV)
Wavenumber (cm-1)
XPS
O
O
O O
Elongation
cycles
anhydride
conjugués
IRRAS
O
O O
O
O
AFM image - Phase z=3° - 2μm x 2μm
AFM
Anhydride group retention : 32%
Film thickness : 15 nm
Roughness : ~ 0.2 nm
13
April 19th 2011
Influence of substrate on plasma coating morphology
Model substrates
Silicon wafer
Surface morphology prior to plasma polymerization
Sputtered gold
Mirror
finish aluminum
Surface morphology after
plasma
coating deposition
EPDM
14
April 19th 2011
Plasma coating functionalization
O
O
O
O
O O
O
O
O
O
O
O
O
O
O
O
O
O
H2N
Aminolysis
reaction
Functionalization
O
R
R
R = Diene
or
Dienophile
O
O
R
R
OH HN
O
R
OH HN
OH HN
O
O
OH HN
O
O
O
O
O
Functionalized plasma coating
15
April 19th 2011
Bifunctional molecules
H2N
R
No commercial
availability
Available commercially
H2N
SYNTHESIS
16
April 19th 2011
Synthesis of the bifunctional diene
Targeted molecule :
NH2
8
Au
NH
Plasma polymer thin film
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.
17
April 19th 2011
Plasma coating functionalization
O
O
O
OO
a)
OO
O
O
NH2
Plasma coating
b)
Gas
phase
Wettability measurements
Nature des
échantillons
Advancing contact
angle
Receding contact
angle
Plasma coating
(anhydride groups)
62° ± 2°
< 10°
H
OH
H
N
OH
12° ± 2°
Plasma coating
functionalized with
allylamine - IMIDE
60° ± 2°
OH
N
O
O
O
Plasma coating
functionalized with
allylamine - AMIDE
H
N
< 10°
c)
Plasma coating
< 10°
120°C – 2 hrs
under vacuum
O
N
d)
OO
N
OO
N
O
Plasma coating
Wavenumber (cm-1)
Plasma coating functionalized with
dienophile groups
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April 19th 2011
Diels-Alder reaction
Concerted reaction :
Transition state
Diene
C
C
C
C
C
CH2
Newly created C-C bonds
C
CH2
C
C
C
C
CH2
C
C
Dienophile
Au
Au
Au
19
April 19th 2011
Reaction kinetics of interfacial Diels-Alder
Diene used for this study
Si
CPdSi
[(triméthylsilyl)methyl]cyclopentadiene
Si
Si
O
N
O O
N
O O
N
O
Si
Si
Pulsed plasma polymer
O
N
O O
N
O O
N
O
Pulsed plasma polymer
20
April 19th 2011
Following Diels-Alder reaction kinetics
Wettability measurements:
q
Advancing contact angle (°)
89
84
79
74
69
64
294 K
308 K
318 K
328 K
278 K
288 K
4000
5000
59
0
1000
2000
3000
6000
Time (s)
21
April 19th 2011
Functional group density
Cassie equation :
Cos θexperimental =
calkene . Cos θalkene + cbicyclo . Cos θbicyclo
c
N
O
N
O O
N
O O
alkene
O
θalkene = 60°
Plasma polymer
c
Si
alkene
c
bicyclo
Cyclohexane
θexpérimental
Si
Si
Si
c
O
N
O
O
N
O
O
N
bicyclo
θbicyclo = 87°
O
Plasma polymer
22
April 19th 2011
Following Diels-Alder reaction kinetics
XPS measurements – following Si/N ratio
O
Si
308 K
0,7
328 K
0,6
0,5
O
0,4
N
O
O
0,3
Polymère plasma
0,2
N
O
CPS
N
Si/N ratio (area under peak)
O
293 K
0,8
Si
Si
0,1
0
0
1000
Si/N = 1 when all
dienophile groups have
undergone a Diels-Alder
reaction
9000000
8500000
8000000
7500000
7000000
6500000
6000000
5500000
5000000
4500000
4000000
3500000
3000000
2500000
2000000
1500000 2000
1000000
500000
Angle of incidence : 90°
O 1s
C 1s
N 1s
CPS
0,9
Si 2s
3000
4000
5000
Si 2p 6000
Time (s)
600
400
200
0
Binding
Energy
Binding
energy
(eV)
23
April 19th 2011
Interfacial Diels-Alder reaction between solid substrates
Functionalization with diene groups
Substrate 1
aluminum
Plasma polymerization
Substrate 2
aluminum
or
rubber
Substrates assembled
In a curing press
Functionalization with
dienophile groups
Is the Diels-Alder reaction effective
between 2 functionalized substrates
24
April 19th 2011
Disponibility of dienophile groups
1st step : verify that dienophile groups immobilized on aluminum are
available to react during EPDM peroxide cure
EPDM
EPDM
Imide
Amide
Aluminum
Aluminum
Crosslinking reaction
Press 170ºC - 40min – 3 MPa
Dicumyle
peroxyde
Aluminum
Aluminum
Aluminium
25
April 19th 2011
Disponibility of dienophile groups
Interfacial fracture energy
180 degree peel tests
Amide
1200
180 degrees
Imide (vacuum)
20 mm/min
5 mm/min
Imide (atmosphere)
1000
Reference
EPDM
EPDM
cohesion
energy
800
W180 (J/m²)
Aluminum
600
400
20 mm/min
200
5 mm/min
0
0
20
40
-200
60
80
100
120
Peeled length (mm)
Dienophile groups seem to be available for interfacial reaction
26
April 19th 2011
Analysis of peeled substrates
Wettability measurements
Contact angle
(after peel test)
Aluminum
EPDM
q
Advancing: 103º ± 2º
Receding :
Cohesive fracture
located in EPDM
42º ± 2º
Advancing: 100º ± 2º
Receding : 35º ± 2°
• Bare EPDM :
•
A: 103º
27
R: 45º
April 19th 2011
Interfacial Diels-Alder reaction between
functionalized EPDM / aluminum
Substrates
assembled in a
curing press for
different conditions of
pressure, time and
temperature
Pulsed plasma polymer
O
N
O
O
N
Pulsed plasma polymer
Pulsed plasma polymer
O
O
30°C – 70°C
30min – 120 min
0,08 MPa – 0,32 MPa
EPDM
N
O
N
O
O
Pulsed plasma polymer
EPDM
DOE performed to
optimize assembling
conditions
28
April 19th 2011
Interfacial Diels-Alder reaction between
functionalized EPDM / aluminum
Peel energy between 2 dienophile
functionalized substrates
Peeled length (mm)
Aluminum
No interfacial
bond formation
EPDM
Peel energy between 2 substrates respectively
functionalized with diene and dienophile groups
Experiment
N°
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
Interfacial Diels-Alder seem to proceed !
29
April 19th 2011
Interfacial Diels-Alder reaction – AFM images of aluminum
substrate before and after peel test
Phase
image
Height image
Ra = 18.74 nm
Plasma coated
aluminum substrate
(prior to peel test)
Pelage 180°
EPDM
ALUMINIUM
Aluminum substrate
after peel test
Phase
image
Height image
Ra = 62.32 nm
30
April 19th 2011
Interfacial Diels-Alder reaction – AFM images of
EPDM substrate before and after peel test
Phase
image
Height image
Ra = 13.9 nm
Bare EPDM
Plasma coated EPDM
(prior to peel test)
180° peel test
Height image
EPDM
Ra = 60.6 nm
Phase
image
ALUMINIUM
EPDM substrate after peel
test
Height image
Ra = 16.1 nm
31
Phase
image
April 19th 2011
Analysis of peeled substrates
Wettability measurements
Aluminum
EPDM
Contact angles
(after peel test)
q
Advancing: 100º ± 2º
Receding :
Cohesive fracture
located in EPDM
40º ± 2º
Advancing: 103º ± 2º
Receding : 42º ± 2°
Bare EPDM :
•
A: 103º
32
R: 45º
April 19th 2011
Retro Diels-Alder
Diels-Alder reaction seem to proceed at interface
Is the reaction reversible
Reversibility test : 180 degree peel test performed while heating sample
Ambient temperature
Peeled length (mm)
33
April 19th 2011
Conclusion - perspectives
•
•
•
•
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
Diels-Alder
Retro
Diels-Alder
34
April 19th 2011