Allylamine was widely applied as a coating layer on biomaterials such as
polyethyleneterephtalate [26], polystyrene and polyethylene powder [27], stainless
steel stents or on aluminum [28], also in the fields of sensor technology [29], as well
as for DNA immobilization [30].
The mechanism of allylamine plasma polymerization has been reported and reviewed
by different research groups [25,31]. However, the comparisons among plasma
polymerizations with other C3 amine molecules, i.e. propylamine [32,33] and
propargylamine [32], were less reported.
Plasma polymerization of amine-containing thin films and the studies on the
deposition kinetics
Introduction:
Plasma polymers differ from the conventionally synthesized polymers with
their highly complex structure, with branched or crosslinked chains [15].
The course of plasma polymerization involves the generation and dissociation
of complicated reactive species such as electrons, ions, radicals, atoms and molecules.
Therefore, only limited supporting literature detailed the relationships
between the deposition kinetics with the physical–chemical properties
of plasma polymers [34–36].
Although the potential applications of plasma polymers rely considerably
on their stability, only a few works focusing on the stability of
plasma polymers were found.
Plasma polymerization of amine-containing thin films and the studies on the
deposition kinetics
Introduction:
In this study,
- we prepared amine-containing plasma polymers from three C3 amine precursors with
different conjugation degree.
- The triple and double bonded propargylamine and allylamine presented more than
5.6 and 1.8 folds deposition rate than that of the saturated propylamine, respectively.
- The amine functionalities of the three plasma polymers, on the other hand, revealed
a different correlation to the saturation degree.
- It was observed that the overall deposition rate of the three plasma polymers were
controlled mainly by the plasma applied power.
- Moreover, the slight change in the chemistry of precursor resulted in significant
difference in deposition kinetics.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Introduction:
-The principal molecular structure of precursor that resulted in the difference in
deposition kinetics was presumably the amine bond dissociation energy (NH2 BDE).
- Furthermore, we found that the created amine plasma polymers showed direct effects
on the growth of L-929 fibroblast cells where the higher N/C ratio and imine/amine
contents promoted higher cell density on plasma polymers.
- The results, integrating experimental data and mathematical calculations, have
detailed how greatly the chemical structure of precursors influenced the physical–
chemical properties of the prepared plasma polymers and their direct applications.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Experimental section:
2.2. Plasma polymerization
The polymerization of C3 amines
was conducted in a plasma system
which was modified from
the previous work [42].
The system consists of three main parts:
(i) a reaction chamber;
(ii) a radio-frequency generator
(Huttinger, model PFG 300 RF, Germany);
(iii) a vacuum system.
In the plasma reactor, a stainless steel anode with 2 cm thickness was placed at the central part of
the vacuum chamber, and its upper part was located by 10 cm above the pumping outlet.
The anode was separated by 7 cm air gap from the shower-type cathode. Both electrodes were
circular with a diameter of 15 cm. The deposition of all monomers was set at 100 mTorr, 20 sccm,
heating temperature at 40 °C, for 60 min.
The vaporized monomer was introduced into the chamber and was polymerized with different
applied power (5, 10, 30, and 50 W) on quartz, KBr pellet, and Si wafer.
Due to overheating occurred for the applied power higher than 50 W in this plasma apparatus, the
experimental parameter was controlled at the applied power up to 50 W
2.4. Surface characterizations
The chemical functionality of the fabricated amine-containing plasma polymers was characterized by
Fourier-transformed infrared spectrometry (FTIR), model FTS-3500, Bio-Rad Digilab.
The amount of the deposited polymers on quartz substrate was quantified by quartz crystal microbalance
(ANT Technologies Co., model ANTQ3000, Taiwan). (deposition rate)
The wettability of the surface was evaluated by measuring the static contact angles (Sindatek) with
deionized water. At least five droplets were measured for each position, with droplet volume of 3 μL.
The surface morphology of C3 amine plasma polymers was observed by using tapping-mode atomic force
microscope (Digital Instruments, Nanoscope III, 125 μm AFM scanning head) with scan resolution of 2×2
nm2 .
The cell morphology of L-929 fibroblasts on different surfaces was observed by using scanning electron
microscope (SEM, JEOL JSM- 6300).
The chemical composition of the plasma polymerized thin films was determined by electron spectroscopy
for chemical analysis (ESCA). Thermo VG Scientific Theta Probe Instrument with monochromatic source of
Al-Kα (1,486.6 eV) as excitation source was operated, with pass energy of 50 eV. Ar ion gun was employed
with 3 kV voltage and 1 mA current. The characterizations of samples were taken under takeoff angle of 53°,
with under X-ray spot size of 400 μm.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Experimental section:
3.1. The deposition of the C3 amine plasma polymers
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
In this study,
the experiments were conducted in a precursor-sufficient (energydeficient) region which generally
demonstrated a linear trend for the deposition rate as function of the applied power
3.2. Identification of amine functionalities by FTIR
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
It is noted that the intensity of the characteristic peaks increased proportionally with the modulated power.
In comparison with the FTIR spectra of PPP, one special signal was detected especially at high power (30 W
and 50 W) at 2240 cm−1 , corresponding to the non-conjugated triple-bond structures of N\(\R\C`N) and
(R\C`C\R) for PPA and PPG. The results revealed that more unsaturated C, N bindings were deposited from
allylamine and propargylamine under the higher applied powers.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Experimental section:
The surface concentration of primary (NH2) and secondary (NH) amines was determined by
the derivatization technique employing trifluoromethyl benzaldehyde (TFBA) and
trifluoroacetic anhydride (TFAA), with the derivatization mechanism reported elsewhere [25].
The derivatization was performed by exposing the plasma polymers 30 and 10 min with TFBA
and TFAA vapor, respectively, in a sealed container at an ambient condition [43]. The amine
concentrations were then calculated by applying Eqs. (1a) and (1b).
[F] and [C] are the fluorine and carbon concentrations determined by ESCA after the reactions with TFBA.
[F′] and [C′] are the fluorine and carbon concentrations determined by ESCA after the reactions with TFAA.
TFBA derivatization + XPS (ESCA)
TFAA derivatization + XPS (ESCA)
The authors did not consider the contribution of OH groups in the derivatization results and
correlated the fluorine concentration after the reaction only with amines. While OH groups
could have contributed to those results, we have found here that hydroxyls do not play an
important role in aging of pp-allylamine.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
3.3. ESCA surface characterizations
Fig. 3. ESCA high-resolution
C1s spectra of PPP (a), PPA (b),
and PPG (c), deposited
at 20 sccm flowrate,
100 mTorr pressure,
50 W for 60 min.
PPA possessed the highest nitrogen content, in particular CIII (17.1%),
than that of PPP and PPG (16.5 and 14.2%, respectively).
It was reported that nitrile (C\C`N) and alcohol (C\O) component were the
minor constituents in the CIII peak [47], while imine (\C=N) was the major
functional groups (more than 50%) [32].
The N/C ratio from the wide scan corresponded proportionally to the CIII
content, suggesting that the deposition of PPA introduced significantly
higher imine functionalities than that of PPP and PPG
Fig. 3. ESCA high-resolution C1s spectra
of PPP (a), PPA (b), and PPG (c),
deposited at 20 sccm flowrate, 100
mTorr pressure, 50 W for 60 min.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
3.3. ESCA surface characterizations
It was demonstrated that the PPA incorporates
the highest amount of primary and secondary
amines into the corresponding thin films
compared to those synthesized from PPP and
PPG.
Moreover, the density of the secondary amine
was more than five folds higher than the
primary amine.
3.4. Surface morphology and stability of plasma polymerized C3 amine thin films
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
Fig. 4. Surface roughness of PPP (a), PPA (b), and PPG (c),
deposited as function of the applied power
(lines are drawn only to guide eye).
The surface morphology of the
plasma polymerized polymers
prepared from three C3 amine
precursors under various applied
power was analyzed by AFM.
The surface of the PPG thin film
revealed a roughness of 0.34 nm
which is higher than that of PPA
(0.28 nm) and PPP (0.23 nm),
suggesting that the higher surface
roughness of the deposited films
was resulted from the higher
unsaturation degree in precursor.
The stability tests were performed by preparing two sets of plasma polymers from the three
precursors independently under the experimental conditions of 20 sccm, 10 W, and 60 min.
After immersing the deposited amine-containing specimens in PBS for 48 h,
dissolution and swelling were not observed.
ESCA characterizations confirmed that there was no significant change in chemical composition
for the films after the immersion.
3.4. Surface morphology and stability of plasma polymerized C3 amine thin films
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
For all the three plasma polymers, more than 95% of carbon and nitrogen content were
preserved and only slight oxidation was detected by about 5% for PPP, and 7% for PPA and PPG
which is presumably due to the sample immersion in oxidative condition.
It is therefore reasonable to conclude that all of the prepared amine-containing plasma
polymers were exceptionally stable that the superior properties can assist further applications
in surface coatings and surface functionalization of biomedical devices.
3.4. Surface morphology and stability of plasma polymerized C3 amine thin films
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
Fig. 6. Cell behavior of L-929 fibroblasts on surfaces of bare Si wafer (a), PPP (b), PPA (c), and
PPG (d).
4.2. Cell response related to surface chemistry of C3 amines plasma polymers
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Results:
Fig. 7. Relationship between surface chemistry of C3 amines plasma polymers towards
L-929 fibroblast cell density
4.2. Cell response related to surface chemistry of C3 amines plasma polymers
Amine-containing plasma polymer thin films were successfully prepared from three
types of C3 amine precursors with different saturation degree.
Notable difference in deposition rates of more than two and six folds was observed
from allylamine and propargylamine comparing with propylamine precursors.
FTIR and ESCA characterizations identified the increase of the intensity of amine
functionalities as function of the applied power for the three C3 amine precursors.
Further analyses on the three C3 amine precursors revealed that the amine bond
dissociation energy of precursor governed the polymerization kinetics by showing a
linear relationship with the deposition constant Kdep.
Moreover, the cell responses on the C3 amine polymerized thin films demonstrated
that the imine content and amine contents as well as the N/C ratio play a pivotal role
in promoting cell adhesion.
With the exceptional stability, controllability, and biocompatibility, the aminecontaining
plasma polymers possess vast potential for the application in surface
coating and the surface modifications for biomaterials.
Plasma polymerization of amine-containing thin films and the studies on the deposition
kinetics
Conclusions:
Thank you
with the derivatization mechanism reported elsewhere [25]: