Diapositive 1

1
From surface science to technological
performance the case example of adhesive joints
M-G. Barthés-Labrousse CNRS - Université Paris
Sud
2
Overview

• 1. Introduction
• 1.1. Epoxy-amine/ metal adhesive joints
• 1.2. The interphase
• 1.3. A simple strategy

2. Mechanisms of interaction of DAE with Al
surfaces in UHV 2.1. Bonding mechanisms 2.2.
Terminology 2.3. Bonding stability
3. Interaction of DAE with Al surfaces in real
world environment 3.1. Organic media 3.2. Aqueous
solutions
4. Surface complexes and adhesive bond
performance 4.1. Interphase formation 4.2.
Adhesive bond properties
5. Conclusions
3
1. Introduction

• 1.1. Epoxy-amine/ metal adhesive joints
• 1.2. The interphase
• 1.3. A simple strategy

4
1. 1. Epoxy-amine/metal adhesive joints (1/4)
Amine-cured epoxy systems

• used as adhesives (aeronautics, automotive),
  paints, varnish
• two-component paste or liquid system

DGEBA diglycedylether of bisphenol A

• Epoxy precursor

• Amine hardener

DETA diethylene triamine
NH2-CH2-CH2-NH-CH2-CH2-NH2
5
1. 1. Epoxy-amine/metal adhesive joints (2/4)
Two-step process

• Partly cured system (secondary amine)

• Fully cured system (tertiary amine)

6
1. 1. Epoxy-amine/metal adhesive joints (3/4)
Curing cycle
7
1. 1. Epoxy-amine/metal adhesive joints (4/4)
Amine cured epoxy/metal bond
INTERPHASE
Bond performance
Need to understand the formation and control the
properties of the interphase
8
1. Introduction
1.1. Epoxy-amine/ metal adhesive joints 1.2. The
interphase 1.3. A simple strategy
9
1. 2. The interphase (1/3)
Reactions with the metal surface are possible at
any stage Are they equally important?
NH2-CH2-CH2-NH-CH2-CH2-NH2
10
1. 2. The interphase (2/3)
XPS study of adsorption of mimic molecules on a
metal (Ti, Al, Cu) surface

• Uncured system Phenyl-2,3-epoxypropyl ether

• Diamine hardener1,2-diaminoethane (DAE)

NH2-CH2-CH2-NH2

• Part-cured system N-Methyl-1-amino-2-hydroxyetha
  ne

• Fully cured system N-Methyldiethanolimmine

Only nitrogenous molecules are adsorbed Strong
interaction observed with the diaminous hardener
(chelate???) Expected thickness for interphase ?
few nm
J. Marsh, L. Minel, M-G. Barthés-Labrousse and
D. Gorse, Appl. Surf. Sci. 133 (1998) 270
11
1. 2. The interphase (3/3)
Interphase thickness
J. Bouchet, A.A. Roche and E. Jacquelin J. Adhes.
Sci. Technol. 15 (2001) 321
12
1. Introduction
1.1. Epoxy-amine/ metal adhesive joints 1.2. The
interphase 1.3. A simple strategy
13
1. 3. A simple strategy (1/5)

• 1,2 diaminoethane (DAE)
• the simplest diamine which can adsorb as a
  chelate

NH2CH2CH2NH2

• Various Al surfaces
• prepared in UHV (clean, oxidised, hydroxylated)
• boehmited, anodised
• mechanically polished and aged in darkness 7 days

ICP-OES
OCP
XPS
14
1. 3. A simple strategy (2/5)
X-ray Phototelectron Spectroscopy (XPS)
15
1. 3. A simple strategy (3/5)
Open circuit potential (OPC)
Ref el.
V f(t)
Counter el.
Working el. (sample)
16
1. 3. A simple strategy (4/5)
Inductively Coupled Plasma Optical Emission
Spectroscopy (ICP-OES)
Continuous flow setting
17
1. 3. A simple strategy (5/5)
OCP ICP-OES
K. Ogle and S. Weber, J. Electrochem. Soc. 147
(2000) 1770
18
2. Interaction DAE / Al in UHV
2.1. Bonding mechanisms 2.2. Terminology 2.3.
Bond stability
19
2. 1. Bonding mechanisms (1/4)

• Decomposition of peaks in XPS in not
  straigthforward
• Guidelines (fingerprints of the different
  components) is needed

???
20
2. 1. Bonding mechanisms (1/4)

• DAE adsorption on clean Al in UHV

Binding energy (eV)
21
2. 1. Bonding mechanisms (2/4)
Adsorption modes
N2- / Al
396,7eV

9L
398eV
NH- / Al
399,3eV
NH2 / Al
9. 108 L
400,5eV
NH2 / Al 3
401,7eV
NH3 / OH
22
2. 1. Bonding mechanisms (3/4)

• Adsorption in UHV on real world specimens

NH2 / Al 3
400,2eV
NH3 / OH
401,7eV
NH3 / OHcont
402,6eV
23
2. Interaction DAE / Al in UHV
2.1. Bonding mechanisms 2.2. Terminology 2.3.
Bond stability
24
2.2. Terminology (1/2)

• Lewis-like interactions

• Brønsted-like interactions

NH2 - CH2 - CH2 - NH2
or
CH2 - CH2 - CH2 - NH2
Bidendate
Monodendate
25
2.2. Terminology (2/2)
DAE 9L
PA 800L

• Same bonding mechanisms but much weaker
  adsorption of propylamine

? Only bidentate species stable in UHV
Mononuclear
Binuclear
26
2. Interaction DAE / Al in UHV
2.1. Bonding mechanisms 2.2. Terminology 2.3.
Bond stability
27
2.3. Bond stability (1/1)

• Stability under UHV

Stability under UHV depends on bonding mechanism
MBSC gt HBSC
28
Summary to 2

• XPS provides a convenient way to identify bonding
  mechanisms of DAE on Al surfaces,
• On clean Al surfaces, interaction takes place via
  the molecular amine termination or partly or
  fully deprotonated amine termination,
• On (hydr)oxidised Al, interaction of the amine
  termination with the aluminium cations (Lewis
  acids) lead to the formation of MBSC,
• On (hydr)oxidised Al, interaction of the amine
  termination with the hydroxyl species (Brønsted
  acids) lead to the formation of HBSC,
• MBSC are more stable than HBSC in UHV,
• Bidentate species are more stable than
  monodentates in UHV.

29
3. DAE /Al interactions in real
world environment
3.1. Organic media 3.2. Aqueous solutions
30

• Mechanicaly polished and aged in darkness Al

(Hydr)oxide thickness 4.3 ? 0.4 nm
31
3.1. Organic media (1/8)
ICP-OES with 0.5 mol.L-1 DAE in xylene

• only DAE leads to dissolution ? bidendate
  (mononuclear chelate)

D. Mercier, JC. Rouchaud and MG
Barthés-Labrousse., Appl. Surf. Sci. (2008) in
press
32
3.1. Organic media (2/8)
partial dissolution (1.5 nm) ? specific reactive
sites for chelate formation
33
3.1. Organic media (3/8)
FT-IR characterisation of boehmited Al (10min in
boiling 16 MO.cm water) in contact with 10-3
mol.L-1 DAE in xylene
disappearance of Al-OH bonds (840, 1070 and 3665
cm-1)
? specific role of Al-OH bonds in oxide
dissolution
34
3.1. Organic media (4/8)

• Structural similarity of Al13 complex with Al
  oxides
• Similarity in dissolution mechanisms

AlO4(AlO6)12(H2O)127(aq)
12 ?1-OH2 sites 2 sets of µ2-OH 4 oxo groups (µ4
O)
W.H. Casey et al., Geochim. et Cosmo. Acta, 64
(2000) 2964
35
3.1. Organic media (5/8)

• Dissolution related to ligand exchange with water

Exchange by labilisation of bridging hydroxyls
At RT kex for OH ? water
1100 ? 300 s-1 for ?1 sites 1.6 ? 0.4. 10-2 s-1
for µ2 1.6 ? 0.1. 10-5 s-1 for µ2 0 for µ4
?1 gtgt µ2 gtgt µ2
Same mechanism for other ligand exchange
36
3.1. Organic media (6/8)
Ligand exchange rate coefficient high for
?1-OH,-OH2 , lower for µ2-OH (?1-OH,-OH2 gt µ2-OH)
No ligand exchange for µ3-O and µ4-O
W.H. Casey, B.L. Phillips, J.P. Nordin, D.J.
Sullivan, Geochim. et Cosmo. Acta, 62 (1998) 2789
37
3.1. Organic media (7/8)
Dissolution mechanism by formation of a MBSC with
non-bridging ?1 sites
H
Dissolution mechanism by formation of a MBSC with
bridging µ2 sites
38
3.1. Organic media (8/8)
Summary to 3.1
In non-aqueous environment

• diamines react with some specific sites and
  undergo a ligand exchange mechanism with hydroxyl
  species
• to form a mononuclear metal bound surface
  complexes (chelate)
• which can desorb and leads to dissolution of the
  (hydr)oxide surface,

In pure organic media, limited dissolution In
real conditions water is present
39
3. DAE /Al interactions in real
world environment
3.1. Organic media 3.2. Aqueous solutions
3.2.1. Diamines as corrosion inhibitors 3.2.2.
Acidic solutions (pH3) 3.2.3. Alkaline solutions
(pH13)
40
3.2.1. Diamines as corrosion inhibitors (1/4)

• Inhibition favoured by formation of a chelate
  structure

2,2 Bypiridine No inhibition
9,10 Phenanthroline Provides inhibition
A. Weisstuch, D.A. Carter and C.C. Nathan,
Materials protection and Performance, 10 (1971)11
41
3.2.1. Diamines as corrosion inhibitors (2/4)

• Inhibition effectiveness depends on chelate ring
  size

H2N (CH2)n NH2 / carbon steel in 3 NaCl
solutions
n 2, 3, 4
Differential inhibitive efficiency
5-membered rings most efficient
M. Duprat and F. Dabosi, NACE, 37 (1981) 89
42
3.2.1. Diamines as corrosion inhibitors (3/4)

• Low aqueous solubility of the surface chelate
  necessary

A chelating agent can act as an inhibitor or
accelerator of corrosion
A. Weisstuch, D.A. Carter and C.C. Nathan,
Materials protection and Performance, 10 (1971)11
B.W.Samuels, K. Sotoudeh and R.T. Foley, NACE, 37
(1981) 92

• But

• only adsorption via NH2 termination usually
  considered
• other terminations are possible (pH)
• other bonding mechanisms are possible

????
43
3.2.1. Diamines as corrosion inhibitors (4/4)

• pH effect in aqueous solutions
• metal substrate stability
• molecule termination

NH2CH2CH2NH2
pH 3 NH3
pH 13 NH2
44
3. DAE /Al interactions in real
world environment
3.1. Organic media 3.2. Aqueous solutions
3.2.1. Diamines as corrosion inhibitors 3.2.2.
Acidic solutions (pH3) 3.2.3. Alkaline solutions
(pH13)
45
3.2.2. Acidic solution pH3 (1/10)
Polished and aged Al in 10-3 mol.L-1 H2SO4
OCP measurements
1-exp(-t/?)
46
3.2.2. Acidic solution pH3 (2/10)
Polished and aged Al Various DAE in 10-3
mol.L-1 H2SO4
47
3.2.2. Acidic solution pH3 (3/10)
DAE pitting corrosion inhibitor (adsorption
mechanism)
48
3.2.2. Acidic solution pH3 (4/10)
DAE generalised corrosion accelerator
49
3.2.2. Acidic solution pH3 (5/10)
OCP-OES
Total thickness dissolved nm (Native oxide 4.3
nm)
50
3.2.2. Acidic solution pH3 (6/10)
Total thickness dissolved 0.6 nm for DAE 0.1
mol.L-1 0.3 nm for DAE 0.5 mol.L-1
Native oxide thickness 4.3 nm
DAE generalised corrosion inhibitor
51
3.2.2. Acidic solution pH3 (7/10)
From polarisation resistance DAE is a corrosion
accelerator
?
From ICP-OES DAE is a corrosion inhibitor
?????
52
3.2.2. Acidic solution pH3 (8/10)
Pure Na2SO4
With DAE
4.3?0.3 nm OH/O 1.3 No N1s
4.3?0.3 nm OH/O 1.3 No N1s
native
t1
t2

• DAE addition leads to the formation of a thinner
  film with a different chemical composition
  (modifies Rp)
• No N1s ? surface complex unstable in UHV (HBSC)

5,1 nm 1,9 No N1s
3,6 nm 3,5 No N1s
t3
53
3.2.2. Acidic solution pH3 (9/10)
vs
NH2-CH2-CH2-NH2
CH2-CH2-CH2-NH2
DAE ? PA Adsorption as a monodentate HBSC
54
3.2.2. Acidic solution pH3 (10/10)
Summary to 3.2.2.

• In acidic aqueous solutions, corrosion inhibition
  (localised, general) is due to blocking of the
  reactive sites by adsorption of DAE (PA) and
  formation of a monodentate HBSC
• The oxide film growth is delayed
• The oxide film properties (chemical composition)
  are modified

55
3. DAE /Al interactions in real
world environment
3.1. Organic media 3.2. Aqueous solutions
3.2.1. Diamines as corrosion inhibitors 3.2.2.
Acidic solutions (pH3) 3.2.3. Alkaline solutions
(pH13)
56
3.2.3. Alkaline solution pH13 (1/14)
Polished and aged Al in pure 10-1 mol.L-1 KOH
OCP measurements
Pure KOH
57
3.2.3. Alkaline solution pH13 (2/14)
S. I. Pyun and S.M. Moon, J. Solid State
Electrochem. (2000) 267
58
3.2.3. Alkaline solution pH13 (3/14)
S. Adhikari and K.R. Hebert, Corrosion Sci. 50
(2008) 1414

• Emin determined by Nernst potential of hydride
  oxidation (-1.9 eV at pH13)

• corrosion rate determined by kinetics of
  cathodic reaction (2nm/s at pH13.5)

• potential increase due to hydride accumulation
  and impurities enrichment

59
3.2.3. Alkaline solution pH13 (4/14)

• Emin -1.6 V/SCE

• Fe observed in XPS

• constant oxide thickness

60
3.2.3. Alkaline solution pH13 (5/14)

• complete dissolution of the native oxide (4.3?0.3
  nm) is achieved after 40s immersion (close to
  time corresponding to Emin (30-35s))
• at tgt400s dissolution rate is ? 1.8 nm/s
  (comparable to Hebert model)

61
3.2.3. Alkaline solution pH13 (6/14)

• The most likely scheme for Al corrosion in KOH at
  pH13
• initial dissolution of the native oxide
• formation of hydride species by reaction with Al
  metal
• dissolution due to anodic oxidation of the
  hydride to form aluminate ions
• accumulation of the Fe impurities at the surface
  (leading to anodic polarisation of the specimen)
• It is unclear whether the specimen remains partly
  covered by a thin oxide film

62
3.2.3. Alkaline solution pH13 (7/14)
Polished and aged Al Various DAE in 10-1mol.L-1
KOH
Same general behaviour for all DAE
63
3.2.3. Alkaline solution pH13 (8/14)
DAE 0.1 mol.L-1

• accumulation of Fe clearly visible

• oxide thickness constant

64
3.2.3. Alkaline solution pH13 (9/14)
Polarisation resistance

• low values of Rp indicate strong corrosion rates
• Rp increases with DAE would suggest that DAE is
  a corrosion inhibitor (adsorption type)

65
3.2.3. Alkaline solution pH13 (10/14)
OCP-OES
XPS
DAE 0.1 mol.L-1

• there is no effect of DAE on the long term
  dissolution, but a strong increase in initial
  dissolution is observed

• there is no N1s peak in the XPS data at long time
  immersion

Variations in Rp probably due to variations in
film composition
66
3.2.3. Alkaline solution pH13 (11/14)
Initial dissolution depends on DAE concentration
but is more severe than in pure KOH or in DAE in
organic media
Synergistic effects DAE-OH
67
3.2.3. Alkaline solution pH13 (12/14)

• Monodentates also leads to enhanced dissolution
• Chelates more efficient for initial dissolution

68
3.2.3. Alkaline solution pH13 (13/14)

• dissolution by chelates is instantaneous and
  rapidly stops
• dissolution by monodentates is slower and last
  for longer time before it stops

69
3.2.3. Alkaline solution pH13 (14/14)
Summary to 3.2.3.

• In alkaline solutions, DAE accelerates initial
  dissolution due to synergistic effects with OH,
• The formation of chelates complexes induces
  strong instantaneous dissolution,
• Monodentate complexes are also formed which can
  lead to slower dissolution,
• Long-term dissolution is not influenced by the
  presence of DAE. This is due to the disappearance
  of the suitable reactive sites and can be due to
  the formation of an hydride layer.

70
Conclusion in aqueous environment

• NH3 termination corrosion inhibitor
• NH2 termination corrosion accelerator
• Both chelate and monodentate complexes can lead
  to dissolution
• Synergistic effect amine/OH

• During the bonding process, interaction of the
  diamine hardener with the metal surface can lead
  to dissolution of the surface and formation of
  metal-organic complexes which can diffuse in the
  propolymer liquid
• Dissolution effects are enhanced by the presence
  of water at the interface and sufficient Al can
  be released to form an interphase several
  hundreds of microns thick.

71
4. Surface complexes and adhesive bond performance
4.1. Interphase formation 4.2. Adhesive bond
properties
From Roche and co-workers
72
4.1. Interphase formation (1/5)
following contact with metal
Pure IPDA
Precipitation
Organic-metal needles
S. Bentadjine, R. Petiaud, A.A. Roche and V.
Massardier, Polymer 42 (2001) 6271 A.A. Roche, J.
Bouchet, S. Bentadjine, Int. J. Adhes. Adhes. 22
(2002)431
73
4.1. Interphase formation (2/5)
S. Bentadjine, PhD dissertation, 2000

• Contact of the hardener with metal modifies the
  polymer properties

74
4.1. Interphase formation (3/5)

• Interactions can only occur before curing

• The interphase thickness should depend on
  contact time before curing

Contact before curing
75
4.1. Interphase formation (4/5)

• The interphase thickness increases with contact
  time before curing

• The interphase thickness decreases when DGEBA
  viscosity increases

M. Aufray and A.A. Roche, Int. J. Adhesion Adhes.
27 (2007) 387
76
4.1. Interphase formation (5/5)
Summary to 4.1.

• The amine hardener react with the metal surface
  to form needles consisting of organic-metal
  complexes,
• These organic-metal complexes can diffuse in the
  liquid pre-polymer to form the interphase.

77
4. Surface complexes and adhesive bond performance
4.1. Interphase formation 4.2. Adhesive bond
properties
From Roche and co-workers
78
4.2. Interphase macroscopic properties (1/8)

• The Young modulus is much higher in the
  interphase than in bulk polymer

J. Bouchet, A.A. Roche and E. Jacquelin, J.
Adhesion Sci. Techn. 16 (2002) 1603
79
4.2. Interphase macroscopic properties (2/8)

• The residual stresses are higher close to the
  metal surface

J. Bouchet, A.A. Roche and E. Jacquelin, J.
Adhes. Sci. Technol. 15 (2001) 321
80
4.2. Interphase macroscopic properties (3/8)

• Modifications in the mechanical properties of the
  polymer are due to the precipitation of the
  organic-metal complex needles
• These needles can act as reinforcement fibres

• If this is the case, mechanical properties should
  depend on the kinetics of formation and diffusion
  of the needles, i.e. on the contact time with
  prepolymer (liquid phase) before curing

81
4.2. Interphase macroscopic properties (4/8)
J. Bouchet, A.A. Roche and E. Jacquelin, J.
Adhesion Sci. Techn. 16 (2002) 1603
82
4.2. Interphase macroscopic properties (5/8)

• As long as the limit of solubility of the organic
  metal complex is not reached, the needles are not
  formed and the mechanical properties are not
  affected (but the interphase still have modified
  properties (Tg))

M. Aufray and A.A. Roche, J. Adhesion Sci. Techn.
20 (2006) 1889
83
4.2. Interphase macroscopic properties (6/8)

• Other properties (durability) are also affected
  by the presence of the interphase

A interphase
B no interphase
Ageing time in distilled water at 70C
P. Montois et al., Int. J. Adhesion Adhes. 27
(2007) 145
84
4.2. Interphase macroscopic properties (7/8)

• Precipitation of the needles is related to the
  nature of the amine hardener and can be achieved
  on any metal (with the exception of gold?)

A.A. Roche, J. Adhesion 78 (2002) 799
85
4.2. Interphase macroscopic properties (8/8)
Summary to 4.2.

• The mechanical properties of the interphase
  strongly differ from those of the bulk polymer,
• This is due to the presence of organic-metal
  needles which can act as reinforcement fibres,
• Other properties of the bond (durability) can
  also be affected.

86
5. Conclusions
87
5. Conclusions

• Diamines can interact with oxidised
  (hydroxylated) metal surfaces and form surface
  chelate complexes (MBSC), leading to the
  dissolution of the metal surface,
• Accumulation of the organic-metal complexes in
  the vicinity of the metal surface modifies the
  properties of the polymer and lead to the
  formation of the interphase,
• Precipitation of small needles can be observed.
  These needles are responsible for the modified
  mechanical properties of the interphase,
• Controlling the amine/metal interactions at a
  molecular scale can lead to tailoring (some of)
  the adhesive bond properties.