the surface analysis laboratory interfacial chemistry and adhesion phenomena… · 2018-03-07 ·...

The Surface Analysis Laboratory

Interfacial Chemistry and Adhesion Phenomena:

How to Analyse and How to Optimise

John F Watts

Department of Mechanical Engineering Sciences


The Role of Surface Analysis in

Adhesion Studies

• Assessing surface characteristics (cleaning/pretreatment)

• Forensic analysis of failed joints, coatings etc.

• Fundamental studies of adhesion

o Sectioning of real systems

o XPS and ToF-SIMS of thin films

o Adsorption isotherms


Surface Analysis


The Problem Faced by the Analyst

ARXPS d ~10nm

X-ray spectroscopies d ~200nm

RBS d ~1μm

d

Interface Region

Substrate

Adhesive or Coating 10’s m - mm

100’s m - mm


The Buried Interface

Obtaining analytical

information from intact

interfaces is very difficult.

Carrying out in-situ

experiments within the

spectrometer can be useful

but only rarely is the

interphase chemistry

exposed in this manner

J F Watts, Surf Interf Anal, 12, 497-503, (1988)


TEM/PEELS Cross-Sections

A J Kinloch, M Little, J F Watts, Acta Materialia, 48, 4543, (2000)

PAA treated joint PAA + primer joint

abrupt interface diffuse interphase


Epoxy + GPS/Aluminium Joint

Fig. 2. Composite image of the cross-section of a

sample containing 1% (w/w) of APS showing the

aluminium/adhesive interface from several TEM

images.

Fig. 3. EELS spectrum of the core loss region of the oxygen

K edge along the aluminium oxide layer for a sample

containing 0.5% (w/w) of APS.

Fig. 5. Graph representing the relative oxygen content over the

oxide layer for the various APS concentrations, obtained from

EELS spectra. At 0.5% APS, the oxygen profile is bi-lobar,

whilst at 1% and 2% the oxygen concentration has only one

maximum, near the silane and near the Al respectively.

J Bertho, V Stolojan, M-L Abel, J F Watts, Micron, 41, 130, (2010)


Oxide Stripping + Depth Profiling

Chemical removal

of metal substrate,

depth profiling of

oxide in situ by ion

sputtering.

Interphase can

then be analysed

directly

J F Watts, J E Castle, J Mat Sci, 18, 2987, (1983)


Interface Chemistry

Fe(II)

Fe(II) satellite

Iron 2p3/2 spectrum

showing Fe(II)

component at

interface. Oxide is

entirely Fe(III).


Ultra Low Angle Microtomy

Angle Sectioning Block

12 x 12 x 7 mm3

+ 25 m = 0.03O

+ 50 m = 0.07O

+ 100 m = 0.15O

+ 200 m = 0.33O

Microtome Knife

Angled Sectioning Block

Polypropylene Block


ULAM Geometry

XPS

spot

size/m

ULAM taper angle/o

0.03 0.33 2.0

100 60 600 3500

15 13 100 500

Depth Resolution ULAM/nm

Coating

Small area XPS analysis mode

(100 m)

Substrate q

S J Hinder, C Lowe, J T Maxted, J F Watts, J Mater Sci, 40, 285, (2005)

Depth resolution attainable depends on the taper angle and

the size of the analytical probe. In XPS small area XPS in

the range 15 -500 m, for ToF-SIMS < 1 m


XPS Line Scan Along Taper

0

2

4

6

8

10

12

14

16

18

20

0 0.013 0.026 0.039 0.052 0.065 0.078 0.091 0.104 0.117 0.13 0.143 0.156 0.169

Depth / um

Ato

mic

%

0

0.5

1

1.5

2

2.5

3

3.5

4

Fluorine

Nitrogen

PVdF Polyurethane

X-ray Spot = 15m

Step Size = 18 m

13nm

F: DZ = 50 nm

N: DZ = 27 nm

PVdF Topcoat on Polyurethane Primer

13

ToF-SIMS Line scan

500 µm

500 µm - 128 pixels

𝑝𝑖𝑥𝑒𝑙 𝑖𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦

𝑝=128

𝑝=1

0

0.2

0.4

0.6

0.8

1

0 1 2

Rel

ativ

e p

eak

inte

nsi

ty

Depth (µm)

For each of the 128 rows Pixel depth = f(cutting angle)

Positive ToF-SIMS image,

characteristic ion of the primer formulation

14

Stitched Images: Two Coat System

Negative ToF-SIMS images : 8 (500 µm x 500 µm) squares

1 mm

Large scale overview of the interface and species migration

Primer Topcoat

1 mm

15

Line Scan : Species Segregation

500 µm - 128 pixels

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5

rela

tive

pe

ak in

ten

sity

depth (µm)

Line scan

Characteristic fragment

of a primer component

Characteristic

fragment

of the topcoat


ToF-SIMS of ULAM Section

d)

b) a)

c)

1

3

2

+ve SIMS -ve SIMS

Polyurethane ions

PVdF ions

(a) m/z = 149: C8H5O3+

(b) m./z = 26: CN-

(c) m/z = 59: C3H4F+

(d) m/z = 19: F-

FoV is 500 m

500 m

250 nm

S J Hinder, C Lowe, J T Maxted, J F Watts, Surf Interf Anal, 36, 1575, (2005)


ToF-SIMS Anions from Images

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

a) 25

41-42

49

66

100

121

0

1500

3000

4500

6000

7500

9000

10500

12000

13500

15000

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

c) 19

49

39

85

Point 2: Bulk Polyurethane

Point 1: Bulk PVdF

c)

1

3

2


ToF-SIMS at Interface

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120 140 160 180 200

m/z

Co

un

ts

b) 19

31

55 71

87

85

121

185 141

Point 3: PU and PVdF at Interface c)

1

3

2

PCA on Positive Spectra from Interfacial Region to Identify

Those that are not Characteristic of PVdF or PU

Negative ToF-SIMS


Minor Additive

0

300

600

900

1200

1500

1800

2100

2400

2700

3000

30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

m/z

Co

un

ts31

55

71

85

185

41

A negative ion ToF-SIMS mass spectra of the pure acrylic co-resin

component of the PVdF topcoat formulation in the mass range 30-200m/z.

x10


ToF-SIMS Images of Acrylic Ions

a) b)

e) f)

d) c)

Negative Ion Mass

Selected Images

(a) m/z = 31: CH3O-

(b) m/z = 55: C3H3O-

(c) m/z = 71: C3H3O2-

(d) m/z = 85: C4H5O2-

(e) m/z = 87: C4H7O2-

(f) m/z = 141: C9H13O4-


Coil Coating: Adhesion Promoter

500 µm

128 pixels= 16 strips x 8 pixels

128 pixels

RoI: Region of Interest

∑8 x 128 of Recording Relative

Intensity (RI) for each

specific fragment

RI vs. RoI

Convert RoI to Depth

RI vs. Depth √ = 2°

8 pixels = 15.6 µm

1.08 µm

Red: Top coat

Green: Primer

Blue: HDGS

500 µm

25 µm

ULAM

Approximately same

area is used for XPS

line scan.

Depth profile of a various fragments

obtained by reconstruction of SIMS spectra

across the top coat/primer/metal area from

16 regions of interest.


XPS Line Scan: ULAM Section

The region associated with the primer

layer can be determined considering the

change in the elements concentration:

Analysis point at a depth of ~18 µm

where the concentration of carbon starts

to decrease.

Analysis point at a depth of ~25µm where

Zn signal is observed to become more

intense.

Having Characterised all the individual

components present in the formulation,

it can be concluded that nitrogen is

associated with the adhesion promoter

molecule.

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35 40

Su

rfac

e C

on

cen

trat

ion

%

Depth (µm)

C Co N O Zn

Changes in C, O, Zn, Co and N elemental

concentration traversing a ULAM taper which

has exposed the buried topcoat/primer/metal

substrate interfaces of the sample with higher

concentration of adhesion promoter.

|------------Topcoat-----------Primer--------------HDGS------|


0

10

20

30

40

50

0 2 4 6 8 10 12

RP

I x 1

00

00

C2H6N C3H8N C4H10N

C5H10NO2 Molecular ion x 50 Zinc

Depth (µm)

Depth profile of the fragments originating from

the adhesion promoter molecule obtained by

reconstruction of SIMS spectra across the

metal/primer/topcoat area from 16 regions of

interest. the intensity of molecular ion reaches

the maximum intensity at the primer/topcoat

interface (the intensity of the molecular ion

has been multiplied by 50).

Adhesion promoter segregates to the primer

surface when added to the primer

formulation at the higher concentration.

Adsorption studies on this molecule proves

that there is no chemical interaction between

the metal substrate and adhesion promoter

molecule.

The concentration of the adhesion promoter

at the higher level is beyond the critical

miscibility limit of the primer and the

adhesion promoter is rejected from the

formulation towards the outer surface.

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Surf

ace

Co

nce

ntr

atio

n%

Depth (µm)

C N O Zn

Correlative Surface Analysis:

XPS and ToF-SIMS


The Thin Film Approach

d

Interface Region

Substrate

Adhesive or Coating 10’s m - mm

100’s m - mm

thin (< 2 nm film on substrate)

select sample from the plateau

region of the adsorption isotherm


PMMA on Oxidised Metals

S R Leadley, J F Watts,

J Adhes, 60, 175, (1997)

0.2 eV


Polymer Conformation

J F Watts, S R Leadley, J E Castle, C J Blomfield,

Langmuir, 16, 2292, (2000).

PMMA on Oxidized Si and Al


Organosilane Adhesion Promoters

Molecular Dynamics Models of:

(a) Epoxy

(b) Amino

(c) Vinyl


High Resolution ToF-SIMS

The intense SiOAl+

peak is indicative of a

covalent bond between

the aluminium oxide

and the organosilane

adhesion promoter


Specific Interactions

SiHO

OH

O

(CH2)3 O CH2 CH CH2

OH

Al

O H

SiHO

OH

O

(CH2)3 O CH2 CH CH2

O

Al


Flame Treatment Used for

Many Years


Flame Treatment of Automotive

Polypropylene


Example XPS Spectra

XPS spectra for Sample A untreated (lower) and treated

(upper).

C1s

O1s


As Received PP Samples

Sample B

Sample C

Sample A

Sample D

C1s

O1s


Mono XPS Valence Band

Untreated

1 Pass

3 Passes

7 Passes

characteristic of pendant methyl group


XPS/Cluster Profiling

X-ray photoelectron spectroscopy performed

using the Thermo Scientific K-Alpha system

• Monochromated X-ray source

• Fully automated acquisition

MAGCIS (monatomic and gas cluster ion source)

used to produce craters

• Ar Cluster size up to 2000 atoms

• Ion energy = 2 - 8 keV

• Monatomic Ar ion beam


Depth Profiling

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Ato

mic

perc

en

t (%

)

Etch Depth (nm)

C1s

O1s (5x)

Analysis on a K-Alpha using large cluster ions to etch (Ar1000)

Depth calculation using estimate from Irganox reference.


ToF-SIMS Identification of

Oxygenation

C3H5O

C4H9

untreated

treated


mass / u69.00 69.05 69.10

4x10

2.0

4.0

Inte

nsit

y

4x10

1.0

2.0

Inte

nsit

y

4x10

0.5

1.0

1.5

Inte

nsit

y

4x10

1.0

2.0

Inte

nsit

y

4x10

1.0

2.0

Inte

nsit

y4x10

1.0

2.0

Inte

nsit

y

C3HO2

C4H5O C5H9 8 passes

6 passes

3 passes

2 passes

1 pass

Untreated

ToF-SIMS of Oxidation Process


Additives: ToF-SIMS Spectra

Additive Chemical structure Characteristic peaks

Ethylene Bis-steramide 282, 310

Irganox™ 1010 57, 203, 219, 259


Ablation of Additives

C18H36NO

C20H40NO C15H23O

C17H23O

Ethylene Bis-steramide Irganox™ 1010

untreated untreated

treated treated


Conclusions

• Chemical analysis of interfaces responsible for adhesion

requires careful sample preparation.

• In model systems explicit bond formation can be identified.

• In commercial systems the inter-diffusion and segregation of the

individual components in a formulation may be equally (or even

more) important.

• The use of this films allows bonding, configuration and bond

density to be established.

• For extruded products residual processing aids or additives as

well as low functionality may compromise adhesion.

• Pretreatments must remove the former and enhance the latter.

the surface analysis laboratory interfacial chemistry and adhesion phenomena… · 2018-03-07 ·...

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