This document describes a study that used time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging and non-negative matrix factorization (NMF) to characterize the spatial distribution of treatment on an atmospheric plasma-treated polypropylene sample. The researchers analyzed samples treated with plasma at different standoff distances and gas mixtures. NMF identified four distinct treatment components and showed the treatment was more homogeneous with an 8 mm standoff distance compared to 4 mm. Mixing the plasma gas with atmosphere also influenced the treatment effects. The results demonstrate the ability of this methodology to characterize plasma polymer treatment patterns.

1. Analysis of atmospheric plasma treated polypropylene by large
area ToF-SIMS imaging and NMF
Wednesday, 04 October 2017 1
Gustavo F. Trindade1*, David F. Williams1,2, Marie-Laure Abel1 and John F. Watts1
1The Surface Analysis Laboratory, University of Surrey, UK
2TWI Ltd Granta Park Great Abington, Cambridge CB21 6AL, UK

2. Outline
Wednesday, 04 October 2017 2
Introduction Experimental Data
processing
Results Conclusion &
Future work

3. Introduction
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Energetic surface treatment of polymers used for years
Flame, plasma, corona

4. Introduction
Wednesday, 04 October 2017 4
more recently
cold atmospheric plasma (low cost, in situ, vacuum not required, flexible)
Argon Helium:Nitrogen
Courtesy of TWI

5. Introduction
Wednesday, 04 October 2017 5
- Very surface sensitive
- Oxidised species
- Detection of additives
- Depth of treatment with dual beam
depth profiling
ToF-SIMS is a great technique to characterise plasma treated polyolefins
No reports of spatial distribution of treatment using large area
capabilities of ToF-SIMS

6. Introduction
Wednesday, 04 October 2017 6
Objectives
Characterise distribution/reactivity zones of an atmospheric plasma treated polymer
(using ToF-SIMS large area imaging)
(generates large datasets)
Apply/adapt previously developed* MVA methodology to a “real life” sample
*

7. Experimental
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Samples: automotive grade polypropylene
(PP copolymer + carbon black)
Undergo plasma treatment prior to paint application
(surface segregation of additives might hinder the adhesion process)
Supplied as 5 mm thick injection moulded plaques and cut into small coupons
0.5cm

8. Experimental
Wednesday, 04 October 2017 8
Plasma kit
Plasma Tact system (Ad-Tec Europe)
Modification that allows the use of argon or
helium as a primary gas and has an additional
input to allow doping of the inlet gas with other
gases.
For this work a Argon was set as the input gas
inlet gas flor rate: 8 min-1
torch velocity: 150 mm/min.
(set accordingly to unpublished work carried out
at TWI)
2 different standoff distances for this particular experiment:
torch at 4 mm and 8 mm from sample’s surface

9. Experimental
Wednesday, 04 October 2017 9
ToF-SIMS analysis
Iontof’s TOF.SIMS 5
at Surrey
 Positively charged secondary ions
 25 keV Bi3
+ (high current bunched)
 0.3 pA
 Stage raster mode: total area of 1 x 1 cm2
containing 2000 x 2000 pixels which comprise of
20 x 20 patches of 500 x 500 µm2 areas and sized
100 x 100 pixels each.
 Final dataset was binned down to 100 x 100 pixels

10. Data processing
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Data compression
Keeps high resolution information
(no mass binning)

11. Data processing
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Alignment issue
Alignment of spectra from
different pixels
Automated large area ToF-SIMS has to give up
adjustments such as height and reflector voltage
corrections at every patch measured.
For this reason, the sample must be homogeneous
both in terms of charging and topography (not the
case here).
This led to different detected time-of-flight for ions
of the same mass coming from different regions,
resulting ultimately in misaligned spectra at different
pixels.

12. ii) Align the spectra of all pixels
to a reference pixel spectrum
(data).
i) Mount samples over thick
glass to ensure homogeneous
charging (experimental).
Data processing
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Alignment issue
Approaches to overcome
the misalignment problem

13. Data processing
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Alignment issue
C5H9
+
C4H5O+
C3HO2
+
C5H9
+
C4H5O+
C3HO2
+
Before After

14. Data processing
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Multivariate analysis
The pre-processed data were loaded into s i m s M V A for multivariate analysis
s i m s M V A
www.mvatools.com

15. Data processing
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Method of choice: Non-negative matrix factorisation (NMF)

16. Data processing
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To overcome time and memory limitations:
Sub-sampling (training set)
Surf. Interface. Anal 2016

17. Results (NMF with 4 components)
Wednesday, 04 October 2017 17

18. Results
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Torch distance influence homogeneity (important for industrial application)
8mm standoff 4mm standoff

19. Results
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Effects of plasma mixing with atmosphere
(8mm standoff)

20. Conclusion & Future work
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Successful methodology to characterise distribution of treatment
- Importance of standoff distance
- Mixing with atmosphere
Future work
- Dataset is rich, more to explore aided by MVA (such as additives)
- Use a humid plasma with D2O to separate contributions

21. Sponsors
- CAPES
- Science without borders
- UKSAF
Acknowledgements
Supervisors
- Prof. John F. Watts
- Dr. Marie-Laure Abel
Thank you for your attention!
s i m s M V A
www.mvatools.com