Fluorescent polymeric Nanoparticles Fabricated by plasma
polymerization Under Atmospheric Pressure and Room temperature
Ping Yang1, Jing Zhang2, Ying Guo2
1 College of Material Science and Engineer, Donghua University, Shanghai, 200051
2 College of Scinece, Donghua University, Shanghai, 200051
Abstract: Fluorescent pyrrole nanoparticles were first synthesized through plasma polymerization
under atmospheric pressure and room temperature. The fine spherical polypyrrole nanoparticles with a
diameter of 100-200 nm are uniformly distributed. FTIR was used to investigate the structure of
atmospheric pressure plasma polymerized polypyrrole nanoparticles (AP-PPy nanoparticles). The
structure analysis indicates that the nanoparticles keep a better retention of the pyrrole structure. The
effect of power on the optical properties of AP-PPy nanoparticles were analysised with UV-Visble
absorption and PL spectra. Polarization induced coplanarization of pyrrole and high level of chain
stock during the nucleation and growth of nanoparticles. This leads to a better conjugation of chains,
and avoids the aggregation quench. Thus polypyrrole nanoparticles exhibit a strong fluorescence
emission at the range of 415nm to 450nm with different power. This technology will help the
realization of practical optoelectronic nanodevice applications of fluorescent polymeric nanoparticles.
Keywords: atmospheric pressure plasma polymerization, polypyrrole nanoparticles, fluorescence
1. Introduction
Fluorescent organic polymer-based nanoparticles have become the research hotspot in recent years,
as a result of their large diversity in molecular structure and optical properties that are of potential use
in optoelectronics and biologics [1-8]. This research has, to date, principally focused on colloidal-state
fluorescent organic nanoparticles, which can readily be prepared with simple reprecipitation methods
[1-9]. To explore the collective properties of fluorescent organic nanoparticles as well as to realize
practical device applications, however, reliable methods of transferring and aligning them with large
surface areas on solid substrates are required. Electrophoretic deposition [10], lithographic patterning
[11], and ink-jet printing of organic/inorganic nanoparticles [12] have been proposed as methods
appropriate to this purpose. As all these methods are based on the strategy of transferring preformed
fluorescent organic nanoparticles onto the substrate, which demands separate nanoparticle synthesis
and complicated handling, we decided to explore the possibility of in-situ generation of fluorescent
organic nanoparticles on large-area substrate.
Herein, fluorescent AP-PPy nanoparticles have been first fabricated from nonfluorescent pyrrole
monomer
by atmospheric
pressure
plasma
polymerization.
Atmospheric
pressure
plasma
polymerization has many advantages. The utmost advantage is that atmospheric plasma technology
allows the circumvention of one of the major drawbacks of current low-pressure plasma technologies,
namely the need for expensive and limited-volume vacuum equipment. Besides these advantages,
plasma polymerization under atmospheric pressure has some other advantages over deposition under
low pressure. Since the chance that a gas molecule collides with another is higher under atmospheric
pressure than under vacuum, energy transfer is more efficient. Under vacuum, the monomer molecules
are often fragmented because the plasma species are highly energetic. The lower energy of plasma
species under atmospheric pressure results in a better retention of the chemical structure [13]. This
technology will integrated in traditional microelectronic fabrication process and help the realization of
practical optoelectronic nanodevice applications of fluorescent polymeric nanoparticles.
The fluorescent AP-PPy nanoparticles in this paper were synthesized by a homemade
nonequilibrium atmospheric plasma reactor using pyrrole as the precursor and Ar as the carrier gas. The
morphology and chemical structure of the polypyrrole nanoparticles have been characterized using
SEM, FTIR (NEXUS670 spectrophotometer). The UV-visible absorption (PerkinElmer Lambada 35)
and PL spectra (Hitachi F-4500) were used to investigate the optical properties of the polypyrrole
nanoparticles.
2. Results and Discussion
In the plasma area, the monomer molecules are converted into active radicals as a consequence of
electron collision. Effect by the electric field of plasma, the radicals were be polarized. Then these
charged radicals become precursors of chain reactions leading to nucleation process. When the pyrrole
molecules get closer to nucleation and growth, coplanarization of pyrrole and high level of chain stock
can be induced by polarization. After synthesis, uniform nanoparticles were grown on the glass
substrate. Figure 1 (a) shows the morphology of the typical nanoparticles obtained at the power of
480W, the fine spherical polypyrrole nanoparticles with a diameter of 100-200 nm are uniformly
distributed over the surface of the glass substrate. As shown in Figure 1(b), the diameter of the
polypyrrole nanoparticles obtained by laser particle analyzer was in the range of 100-200 nm, mainly in
150 nm, this is in accordance with the results get from SEM.
During formation of nanoparticles, the coplanarization of pyrrole and high level of chain stock leads
to a better conjugation of chains. This avoids the aggregation quench. Thus AP-PPy nanoparticles show
different optical properties from bulk polypyrle. The AP-PPy nanoparticles show a broad peak at 340
nm (with width of 23nm). Compared with the electrical polymerized polypyrrle, we believe that this
peak correspond to the
    transition of undecomposed PPy backbone [14]. With the increase
40
mean number/%
35
30
25
20
15
10
5
0
0
40
80
120
160
200
240
280
particle size/nm
(b)
(a)
Fig. 1. Scanning electron micrograph of polypyrrole nanoparticles (a) and particle size distributing obtained by
laser particle size analyzer (b).
436.4
16
0.20
0.15
390W
420W
450W
480W
500W
510W
438.8
443
444.9
424
Intensity (a.u)
Intensity (a.u)
416
390W
420W
450W
480W
500W
510W
0.25
12
8
4
0.10
0
280
300
320
340
360
350
380
400
450
500
550
600
Wavelength/nm
Wavelength/nm
(a)
(b)
Fig. 2. (a) UV-visible absorption and (b) fluorescence spectra of polypyrrole nanoparticles.
of discharge power from 390W to 480W the absorption intensity decrease, however, when the
discharge power increase from 480W to 510W, the intensity increase. The plasma polymerization
leading to the formation of spherical nanoparticles is accompanied by dramatic fluorescence changes.
Obvious fluorescence was detected in nanoparticles of nonfluorescent polypyrrole. When excited by
laser with wavelength of 350nm, the polypyrrole nanoparticles exhibit a fluorescence emission at the
range of 415nm to 450nm, with the increased power from 390W to 510W. Contrary to the UV-visible
spectra, the fluorescence intensity of the AP-PPy nanoparticles was increased versus the increase of
discharge power, company with the red-shift of the fluorescence peak. The increase of fluorescence
intensity may induced by the increased conjugated length of the AP-PPy, as the increase of discharge
power.
FTIR spectrum of the polypyrrole nanoparticles was displayed in Figure 3. There are mainly
three broad absorption peaks, at 3200-3580cm-1、1570-1700 cm-1 and 950-1200 cm-1, respectively. The
broad peaks at approximately 3427 cm-1 is assigned to typical N-H/C-H stretching vibration [15]. The
broad peak at 1570-1700 cm-1 are a combination of a number of absorptions corresponding to C=C and
％ Transmittance
100
90
784
2928
80
70
1632
60
50
1384
3427
40
4000
1052
3500
3000
2500
2000
1500
1000
-1
Wavenumbers(cm )
Fig. 3. Fourier transform infrared spectra of polypyrrole nanoparticles
C=N in plane vibrations in the pyrrole structures, and C=O stretching vibration cause by
oxidation.Amine salts may also contribute to this absorption [16]. The peaks at 950-1200cm-1 are
related to =C-H in plane vibration in the pyrrole structures and NH 2 wag, respectively [17]. The C-H
asymmetry stretching shows a slender peak at 2928 cm-1. When the pyrrole rings are broken, branching
and crosslingking reactions tend to occur predominatly. Thus, primary and secondary amines appear in
polypyrrole nanoparticles. This induces the appearance of weak peak at the 1384 cm -1 which attribute
to the secondary amines C-N stretching [18]. The appearance of peak at 784 cm-1 is also likely to be
due to different substitution effects.
3. Conclusion
Fluorescent pyrrole nanoparticles were first synthesized through plasma polymerization under
atmospheric pressure and room temperature. The fine spherical polypyrrole nanoparticles with a
diameter of 100-200 nm are uniformly distributed over the surface of the glass substrate. FTIR analysis
indicated that the polypyrrole keep a better retention of pyrrole structure. The AP-PPy nanoparticles
show a broad peak at 340nm, which correspond to
    transition of undecomposed PPy
backbone. With the increase of discharge power from 390W to 480W the absorption intensity decrease,
however, when the discharge power increase from 480W to 510W, the intensity increase. When the
pyrrole molecules, radicals and ions get closer to nucleation, growth and formation of nanoparticles,
coplanarization of pyrrole and high level of chain stock can be induced by polarization. This leads to a
better conjugation of chains, and avoids the aggregation quench. The AP-PPy nanoparticles exhibit a
fluorescence emission at the range of 415nm to 450nm, with the increased power from 390W to 510W.
Contrary to the UV-visible spectra, the fluorescence intensity of the AP-PPy nanoparticles was
increased versus the increase of discharge power, company with the red-shift of the fluorescence peak.
The increase of fluorescence intensity may induced by the increased conjugated length of the AP-PPy,
as the increase of discharge power. Atmospheric pressure plasma polymerization can accomplish in-situ
generation of fluorescent organic nanoparticles on large-area substrate. The better retention of
monomer chemical structure helps it achieve the results that achieved by chemical methods and avoids
environmental concerns arising from solvent usage.
Thus this technology will help the realization of
practical optoelectronic nanodevice applications of fluorescent polymeric nanoparticles.
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