Mechanistic Studies of Plasma Polymerization of Allylamine
Andrei Choukourov, Hynek Biederman, Danka Slavinska, Luke Hanley, Andrey Grinevich, Hanna
Boldyryeva and Anna Mackova
J. Phys. Chem. B, 2005, 109, 23086-23095
30.5.2016
Author: Štěpánka Bittnerová

Content of publication
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•Analyses of amine-rich plasma polymers prepared in a glass tubular reactor with external ring
electrodes and standard excitation frequency of 13.56 MHz from allylamine monomer (2.5 sccm) under
working pressure 25 or 100 Pa.
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•For deposition were used pulsed-wave (PW) discharge mode and continuous (CW) mode (duty cycle 0.1
or 1), with average power in range 2-20 W
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•Used physical techniques for characterization  of plasma polymers: IR spectroscopy, XPS, AFM, RBS
•Chemical methods: derivatization.
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•Comparison of chemical composition for different depositions, stability of the surface in the air
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•Discussed polymerization mechanism=layer-by-layer growth: based on comparison of amine content for
PW and CW plasma polymers and AFM study of ultrathin (1-10 nm) layers
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Published results: Infrared spectroscopy
•Results of IR spectroscopy in publication: description of absorption peaks and changes dependent
on applied power (CW mode)
•Problems: it is impossible to determine number of primary and secondary amines
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•What I miss in the text:
–Details about data manipulation: problems with background
–Quantitative analysis of IR spectra: comparison of the intensity  of the paks or area under
specific absorption region according to the  thickness
–No discussion about NH2 scissoring first overtone
–No comparison of IR spectra of PW and CW layers
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X-ray photoelectron spectroscopy
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•Measurement:
–Wide scan survey spectrum: wide spectrum of binding energies (0-1300 eV) usually with lower
resolution; identification of the elements and finding possible charging effect=) determination of
elemental composition
–Narrow scan survey spectrum: higher resolution measurement including area of concrete peak (C 1s)
; determination of chemical bonds (chemical shifts to higher binding energies)

Chemical composition of the surface of allylamine polymers
•Elemental composition : high resolution XPS
•Primary and secondary amines: derivatization =) Binding energies of NH and NH2  are very close
~399.2 eV         in  N 1s environment .
•Principle of derivatization: chemical reaction of amine group with specific compound. Used
Trifluoromethyl benzaldehyde (TFBA) reacts only with NH2 .  Trifluoroacetic anhydride (TFAA) was
also used, however reacts  with NH2, NH, and OH.
•Discussion of the results:
–higher supplied (peak) power results decrease of nitrogen content and amine content
–For PW mode decreasing trend is not so strong
–The overall increase in amine concentration in the pulsed mode compared to CW according to the
supplied power (20 W) is attributed to secondary amines.
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•Atomic force microscopy
•IR spectroscopy and XPS does not allow determination of hydrogen content
•Thin films contain ~43 at. % =) about 20% less than in monomer (64%)
•Rutherford backscattering
•Usage of intermittent contact mode to eliminate artifacts induced by an AFM tip on a relatively
soft plasma polymer surface
•Scanned area: 1 x 1 μm and 5 x 5 μm; ultrathin layers (~10 nm)
•comparison of the films deposited under 25 and 100 Pa
•25 Pa: smooth layers,  roughness does not change with thickness.
•On the contrary, at 100 Pa, the film growth is more complex: roughness strongly dependent on
thickness.
•no indication of plasma polymer nucleation was observed within the AFM detection limit,=)the
allylamine film formation occurs predominantly via a layer-by-layer mechanism
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Possible  reactions during plasma polymerization in PW mode
Comparison with analyses of allylamine polymers
1)Plasma-off . Significant film formation (Yasuda studies). Plasma-induced polymerization of
allylamine goes via the successive reactions of the monomer molecules with the surface radicals.
The overall increase in amine concentration in the pulsed mode compared to CW (according to the
supplied power) is attributed to secondary amines. This indicates that reaction 1 alone cannot
account for all studied polymerization. 2)Plasma-on: in general, there is the hydrogen detachment
in plasma polymerization=) lower hydrogen content in polymer in comparison with monomer-RBS
3)Reactions with ions and radiation=) radicals
4)The surface radicals participate in polymerization reactions with the gas-phase species or with
each other to produce a highly cross-linked structure. The nitrogen radicals take part in chain
propagation reactions forming the secondary amine structures (observed in IR, on the surface) •5),
6)   The continuing loss of hydrogen with    formation of non-amine nitrogen species
1)
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Conclusion
•Positives:
–It is possible to prepare smooth amine-rich coatings by plasma polymerization of allylamine =)
possible usage for bioapplications
–Good stability of polymers in the air (surface chemistry)
–Discussion of plasma polymerization mechanism according to the
o experimental results: amines and hydrogen content and AFM study of surface structure
oprevious researches focused on plasma polymerization:  Yasuda H.: Plasma Polymerization;, Academic
Press: New York, 1985; p 432;
•     Beck A. J., Candan S., Short R. D., Goodyear A., Braithwaite, N. St: J. Phys.    Chem. B,
2001
•Negatives:
–Results of IR spectroscopy can be discussed in more detail, I miss comparison of PW and CW plasma
polymers
–Errors of chemical composition of the surface are not discussed
–AFM study of surface includes plasma polymers prepared under different working pressure=)
roughness comparison;  however  possible changes in chemistry are not mentioned
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Thank you for your attention
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