Sadeq M Al-Hazmy1,2, Yassine El-Ghoul1,3, Jameelah Al-Harby1, Haja Tar1, Fahad M Alminderej1. 1. Department of Chemistry, College of Science, Qassim University, Buraidah 51452, Saudi Arabia. 2. Department of Chemistry, College of Science, Sana'a University, Sana'a 1247, Yemen. 3. Textile Engineering Laboratory, University of Monastir, Monastir 5019, Tunisia.
Abstract
Currently, particular attention is paid to public health related to the field of γ-ray dosimetry, which is becoming increasingly important in medical diagnostic processes. Incorporating sensitive dyes as radiation dose sensors in different material hosts has shown promising radiation dosimetry application routes. In this perspective, the current study proposes a new fluorescent dye based on boron difluoride complex, the pyridomethene-BF2 named 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile (DBDMA) as an indicator for low γ-ray doses. The different optical and quantum chemical parameters and the spectral behavior of the selected fluorescent dye were first studied. Then, PVP/DBDMA electrospun nanofibers and PVA/DBDMA thin films were prepared. The different UV-vis spectrophotometric and fluorescence studies revealed a clear change after exposure to different γ-ray doses. Thermogravimetric analysis exhibited excellent thermal stability of the prepared nanocomposite films, showing altered thermal behavior after γ-ray treatment. Furthermore, the SEM evaluation displayed a significant modification in the surface morphology of the two designed nanomaterials with increased radiation dose intensity. These novel forms of dosimeter designed in nanoscale composites could therefore constitute a promising and efficient alternative for rapid and accurate detection of low doses of γ-rays in various medical applications.
Currently, particular attention is paid to public health related to the field of γ-ray dosimetry, which is becoming increasingly important in medical diagnostic processes. Incorporating sensitive dyes as radiation dose sensors in different material hosts has shown promising radiation dosimetry application routes. In this perspective, the current study proposes a new fluorescent dye based on boron difluoride complex, the pyridomethene-BF2 named 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile (DBDMA) as an indicator for low γ-ray doses. The different optical and quantum chemical parameters and the spectral behavior of the selected fluorescent dye were first studied. Then, PVP/DBDMA electrospun nanofibers and PVA/DBDMA thin films were prepared. The different UV-vis spectrophotometric and fluorescence studies revealed a clear change after exposure to different γ-ray doses. Thermogravimetric analysis exhibited excellent thermal stability of the prepared nanocomposite films, showing altered thermal behavior after γ-ray treatment. Furthermore, the SEM evaluation displayed a significant modification in the surface morphology of the two designed nanomaterials with increased radiation dose intensity. These novel forms of dosimeter designed in nanoscale composites could therefore constitute a promising and efficient alternative for rapid and accurate detection of low doses of γ-rays in various medical applications.
Radiation treatment is
a technique widely explored in several fields,
including polymerization, sterilization of surgical devices, food
irradiation, and diagnostic radiology.[1−5] Depending on the area of investigation, different level doses are
selected carrying a high, medium, or low intensity.The detection
or accurate quantification of the radiation dose
delivered has become a necessity and a significant challenge in various
applications. In particular low radiation doses constitute a real
problem today due to the non-availability of suitable dosimeters in
this range.[6,7] Several forms of dosimeters suitable for
various dose intensities have been studied and have made rapid progress,
such as photographic films and Geiger–Muller and proportional
counter.[8,9] Standard solutions having the properties
of color or oxidation state changes have been widely studied.[10,11] However, the complexity of handling the solution, the recording
time, and the need for heavy and expensive auxiliary instrumentation
for dose detection such as UV–vis, electron spin resonance,
NMR, infrared (IR), and thermoluminescence have intensified the need
to find more effective alternatives.[12,13] Nowadays,
it is beneficial to have practical and easy-to-explore dosimeters
offering a direct reading of doses without recourse to the auxiliary
instruments. The most obvious solution was to exploit the physical,
optical, and color changes following radiation treatment.[14,15] The most widespread solution was based on composite films whose
matrix is an easy-to-cast polymer that interacts with different host
molecules without affecting their colorimetric, physical, or optical
characteristics.[16,17] At present, functional polymers
are widely investigated in various fields.[18−22] Several polymers have been reported as matrices of
thin-film dosimeters, such as PVA, nylon-6, polystyrene, polymethyl
methacrylate, and polyvinyl chloride. Their possible doping using
different dyes preceding their irradiation was studied, and their
dosimetric efficiency was evaluated.[23−25] In line with this, the
investigation of PVA-doped films has shown great interest in several
studies and research.[26,27] PVA has shown more opportunities
due to its low cost, availability, nontoxicity, water solubility,
and ability to incorporate a wide range of transition metal salts
and dyes.[28−30] Currently, nanofibrous materials via different electrospinning
technologies are widely reported and proven effective in various biomedical
applications including tissue engineering, wound dressing, drug delivery,
regenerative medicine, disease modeling, and detection/biodetection.[30−33] These sustainable electrospun composites were effective due to their
ease of operation, nanoscale diameter, wide specific surface, high
porosity, cost-effectiveness, and the considerable adaptability for
engineering eco-friendly bioactive nanomaterials.[34,35] Electrospun nanomaterials synthesized by mixing high molecular weight
polymers and different sensitive dye molecules could be an effective
way to prepare various nanomaterials as dosimeters of different γ-ray
exposure levels.The current study aims to take part in the
excellent colorimetric,
optical potential, and spectral behavior of pyridomethene–BF2
complex (DBDMA) to synthesize γ-ray nanocomposite dosimeters
in different matrix hosts. The first is a film-based PVA polymer-doped
DBDMA and the second is a DBDMA incorporating electrospun PVP nanofibers.
Different parameters of film casting and nanofiber preparation are
first optimized. The two nanocomposite materials were then exposed
to various γ-radiation doses. After irradiation treatment, the
various chemical, structural, physical, and morphological changes
were evaluated via FTIR, UV, thermogravimetric analysis (TGA), and
SEM analyses. Moreover, the different response behaviors, revealed
by these characterizations, as a function of increasing γ-ray
doses applied to the two nanocomposite hosts were studied in order
to evaluate their dosimetric performances for the routine γ-irradiation
process.
Materials and Experimental Methods
Materials
The dye used in the present
study is 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene)
acetonitrile (DBDMA). It is kindly offered by Professor Ewald Daltrozzo
of the Faculty of Chemistry at the University of Konstanz in Germany.
It is also synthesized and characterized by Kubota et al.[36] PVA polymer (Mw:
89 000–98 000, 99%, with a hydrolysis degree of 85–90%)
and PVP (Mw: 1.300.000, 99.9%) were purchased
from Sigma-Aldrich (St. Louis, USA). Ultrapure water (Milli-Q Direct, Darmstadt, Germany) was used to prepare different
films and electrospun nanomaterials. All reagents were of analytical
grade and were used without further purification.
Characterization
The synthesized
nanofiber materials and nanocomposite films were characterized via
various techniques. The responses of raw and irradiated nanomaterials
at different doses were compared to assess their effectiveness as
low γ-ray dosimeters.FTIR characterization using the
attenuated total reflection mode was carried out to obtain IR spectra
of raw and irradiated nanomaterials. An IR spectrophotometer (Agilent
Technologies/Gladi-ATR, Santa Clara, CA, USA) was used in a fixed
range varied from 4000 to 400 cm–1. A resolution
of 4 cm–1 was set to measure different IR spectra.A UV–vis spectrophotometer (Shimadzu, UV-2501PC, Kyoto,
Japan) was explored to determine the absorption curves of the different
nanomaterial labels. The measurements were applied on a wavelength
scale varying from 200 to 700 nm. Steady-state measurements of the
DBDMA dye and the different prepared nanomaterials were carried out
using a JASCO FP-8200 spectrometer (JASCO, Riyadh, Saudi Arabia),
with an excitation bandwidth of 5 nm and an emission bandwidth of
5 nm, using a Xe lamp light source.Photochemical quantum yields
of DBDMA (φc) were measured
using a modified A. J. Lees’s method considering the decrease
in absorbance at the excitation wavelength as photo-irradiation proceeds.[37]
Fluorescence Quantum Yields
Fluorescence
quantum yields in liquid were determined using the optically dilute
solution relative method with either 9,10-diphenyl-anthracene or quinine
sulfate solutions, depending on the emission wavelength range. The
intensity of light was determined using ferrioxalate actinometry.[38,39] The following eq was
applied to calculate the fluorescence quantum yields.The integrals denote the corrected
fluorescence peak areas, “A” represents
the absorbance at the excitation wavelength, and “n” denotes the solvent’s refractive index. The subscripts
“s” and “r” indicate that this is a sample
and a reference.Thermal stability and different thermal characteristics
of prepared
thin-film nanocomposites were evaluated via thermogravimetric measurements
using a TA Instruments apparatus. The fixed parameters for different
TGA analyses were a heating rate of 10 °C min–1 and a temperature range from 25 to 600 °C.SEM analysis
was performed on raw and irradiated nanocomposite
films and electrospun nanofibers to evaluate their morphological behavior
after varied X-ray doses. SEM micrographs were accomplished via SEM
(JEOL JSM-5400 LV, JEOL Ltd., Akishima, Japan). The measurements were
carried out under an acceleration voltage of 5 kV. Magnifications
ranged from 100 to 2000×. To improve the surface conductivity
of the tested samples, a surface coating of a thin layer of Au was
applied before the analysis.
Preparation of PVA/DBDMA Nanocomposite Films
The film-based PVA polymer mixed with various amounts of DBDMA
filler was developed following a previously reported casting method
in our laboratory.[40] A 5% solution of PVA
dissolved in distilled water was prepared. The bulk solution was then
heated gently using a controlled temperature with a heater instrument.
The preparation was kept under continuous stirring at a constant temperature
of 80 °C. After 2 h, the polymer solution was cooled to an ambient
temperature, and DBDMA solution (0.04% dissolved in 10 mL of ethanol)
was poured into the clear, viscous solution of PVA. After 1 h of stirring
without heating, 20 mL of the solution was poured into glass Petri
dishes. The dishes were then set to dry in the dark (to avoid direct
exposure to light) at room temperature for 3 days. The thickness of
peeled films was then measured using a numerical thickness instrument.
The mean value of the thickness of films was around 100 μm.
The nanocomposite films were finally cut into small pieces of 2 cm
sides and stored in black envelopes away from any light to avoid their
possible deterioration and achieve thermal equilibrium before their
subsequent use.
Preparation of PVP/DBDMA Nanofiber Material
The formation of DBDMA-doped PVP nanofiber begins. When a critical
potential is reached, the jet solution is expelled from the Taylor
cone and deposited on the collector. A prepared solution of PVP polymer
(2 × 10–3 M) doped with DBDMA (1.2 × 10–6 M) was subjected to nanofiber fabrication using aY-flow Professional lab device Nanotechnology electrospinning
machine. The electrospinning procedure was conducted at a voltage
of 30 kV. A distance of 17 cm was set between the stationary collection
plate and the tip of the blunt syringe needle. The flow rate was set
at 5 L/min. The generated nanomaterial was collected on an aluminum
foil placed over the fixed collecting plate.
Results and Discussion
Effect of Media on the Spectral Characteristics
of the DBDMA Dye
The absorption spectrum of DBDMA in chloroform
shows narrow absorption bands with three absorption maxima similar
in shape to boron dipyrromethene dye.[41] The 0–0 band of a strong S0–S1 transition with a maximum appearing at 511 ± 3 nm. At the short
wavelength, the second maximum is centered at about 475 and 451 nm
and attributed to the same transition’s 0–n vibrational band. In addition, the S0–S2 transition is characterized by relatively low absorption value bands
at around 379 nm, as shown in Figure a.
Figure 1
Absorption spectra of 2.9 × 10–6 M DBDMA
in chloroform (a) and normalized red emdash absorption and black emdash
fluorescence spectra of 2.8 × 10–7 mol dm–3 in chloroform, λex = 512 nm (b).
Absorption spectra of 2.9 × 10–6 M DBDMA
in chloroform (a) and normalized red emdash absorption and black emdash
fluorescence spectra of 2.8 × 10–7 mol dm–3 in chloroform, λex = 512 nm (b).The high molar absorptivity of DBDMA and the mirror
image relationship
between excitation and fluorescence spectra are consistent with a
strongly allowed (π–π*) transition with a small
geometry change between electronic ground and excited states as shown
in Figure b for the
studied dyes in chloroform.[38] A slight
Stokes shift of 8 nm is observed, indicating a poor excited state.
The emission spectrum shows vibrational structure due to a lack of
ground-state solvation, as shown in Figure b.
Effect of Acidity on Absorption and Emission
Spectra
Methyl sulfonic acid (MSA) is a strong organic acid.
Its addition leads to the protonation of nitrogen heteroatoms, transforming
it from an electron-donating center into an electron-withdrawing center.
It is well known that electron-donating centers cause fluorescence
enhancement, whereas electron-withdrawing centers reduce fluorescence
efficiency. This explains the decrease in fluorescence intensities
upon increasing the MSA concentration. Unlike fluorescence, absorbance
is less affected by protonation. Figures and 3 show a robust
regular reduction in fluorescence of DBDMA by the addition of MSA
due to protonation. This excludes the possibility of pH tuning for
DBDMA as a laser dye.[42−44]
Figure 2
Emission spectra of 2.2 × 10–5 mol
dm–3 DBDMA in ethanol shows a decrease in emission
intensity
at increasing concentrations of sulfonic methyl acid (a) 0.0, (b)
2.1 × 10–4, (c) 2.6 × 10–4, and (d) 3.5 × 10–4 M. λex = 514 nm.
Figure 3
Fluorescence spectra of 1.4 × 10–5 M DBDMA
in CH3CN at different [H0] values. The
values of H0 at decreasing emission intensities:
(a) 0.0, (b) 0.18, (c) 0.37, (d) 0.74, (e) 1.1, and (f) 1.8 A.U.
Emission spectra of 2.2 × 10–5 mol
dm–3 DBDMA in ethanol shows a decrease in emission
intensity
at increasing concentrations of sulfonic methyl acid (a) 0.0, (b)
2.1 × 10–4, (c) 2.6 × 10–4, and (d) 3.5 × 10–4 M. λex = 514 nm.Fluorescence spectra of 1.4 × 10–5 M DBDMA
in CH3CN at different [H0] values. The
values of H0 at decreasing emission intensities:
(a) 0.0, (b) 0.18, (c) 0.37, (d) 0.74, (e) 1.1, and (f) 1.8 A.U.A corresponding decrease in the absorbance is observed
upon the
addition of MSA to 7.6 × 10–6 M DBDMA in acetonitrile
solution, as shown in Figure . This is related to the molecule’s allowedness and
forbiddenness of electronic transitions because of its protonation.
No extra bands were detected under prevailing experimental conditions.
Figure 4
Electronic
absorption spectra of 7.6 × 10–6 M DBDMA in
acetonitrile decreasing absorbance at increasing % of
MSA, green emdash 0.0%, red emdash 0.006%, voilet emdash 0.007% and
blue emdash 0.009%.
Electronic
absorption spectra of 7.6 × 10–6 M DBDMA in
acetonitrile decreasing absorbance at increasing % of
MSA, green emdash 0.0%, red emdash 0.006%, voilet emdash 0.007% and
blue emdash 0.009%.According to the half-height method, the protonation
constant of
the ground state (pKa) was determined
using fluorometric titration, as shown in Figure . The value of pKa was determined as 0.56 from emission spectra.[45,46]
Figure 5
lot
of emission intensities of 1.4 × 10–5 mol dm–3 DBDMA at λem = 528 nm
against pH values.
lot
of emission intensities of 1.4 × 10–5 mol dm–3 DBDMA at λem = 528 nm
against pH values.
Photostability of DBDMA
The photochemical
quantum yield (ϕc) values (∼0.003±) of
DBDMA in chloroform, thin-film, and nanofiber are summarized in Table . The low values of
ϕc indicate photostability against irradiations. Figure shows no change
in emission intensity of the studied dye upon irradiation using 365
nm for 24 h which is attributed to the rigidity of the molecules,
which has also been confirmed by the slight shift in the emission
and absorption wavelengths as the solvent’s polarities change.
The rigidity of the molecule is approved by the high fluorescence
quantum yield. This high fluorescence quantum yield indicates that
reabsorption is avoided. The remarkable DBDMA dye photostability and
its high fluorescence quantum yield (Φf) values allow
its potential application in many areas, including dye lasers and
solar cell collectors.[47,48]
Table 1
Fluorescence Quantum Yield (Φf) and Photochemical Quantum Yield (ϕc) in
Chloroform
solvent
λem max (nm)
λabs max (nm)
Φf λabs max
Φc
CHCl3
532
512
0.70
0.003
DBDMA-doped PVP
528
520
0.3
-
DBDMA-doped PVA
533
512
0.1
0.004
Figure 6
Fluorescence spectra of fresh and irradiated
1.4 × 10–6 mol dm–3 DBDMA
solution in ethanol.
Irradiation wavelength is 365 nm for 24 h.
Fluorescence spectra of fresh and irradiated
1.4 × 10–6 mol dm–3 DBDMA
solution in ethanol.
Irradiation wavelength is 365 nm for 24 h.
Spectral Characteristics of Dye-Doped PVP
Nanofiber and Dye-Doped PVA Films
DBDMA in solid hosts, including
electrospun nanofibers and PVA thin films, showed structured and peak-shifted
emission compared to the emission obtained for CHCl3 solution.
The structured criterion of the spectra is attributed to the restriction
of the rotational mode of molecular motion in solid matrices due to
the condensed phase cage effect.[49]A slight Stokes shift of 8 nm, a perfect coincidence between absorption
and excitation spectra, maximum wavelengths, and the full width at
half-maximum are observed between DMF solution and nanofiber structure
as shown in Figure . DBDMA-doped PVP nanofiber prepared from 1.2 × 10–6 mol dm–3 shows an absorption peak at 52 nm and
an apparent fluorescence emission with a structured band peak at 528
nm using λex = 450 nm, as shown in Figure . Low concentrations were used
to avoid reabsorption. This makes DBDMA-doped PVP of a promising application
in electronic devices. All these similar properties between absorption
and fluorescence spectra of DBDMA in both DMF solution and dye-doped
PVP nanofiber suggest the formation of neither aggregation in the
ground state nor an excimer in the excited state. As the difference
between the emission spectra of the same dye-doped PVP and that in
the ethanol solvent shows, a simple blue shift of 9 nm with the appearance
of resolved Franck–Condon fluorescence peak at 556 nm is observed
in Figure . A slight
change in the excitation spectrum is observed. The wavelength of the
band peaks was shifted by only 2 nm going with the dye from an ethanol
solution to dye-doped PVP nanofibers, as shown in Figure .
Figure 7
Normalized electronic
red emdash absorption and black emdash fluorescence
spectra of DBDMA in DMF solution, and blue hyphen absorption and pink
hyphen fluorescence spectra of DBDMA-doped PVP nanofiber, λex = 488 nm.
Figure 8
Absorption brown emdash, fluorescence green emdash spectra,
λex = 488 nm and excitation black emdash spectra,
λemmax = 540 nm of DBDMA-doped PVP nanofibers.
Figure 9
Normalized fluorescence spectra of orange emdash DBDMA-doped
PVP
nanofibers prepared from ethanol solution and blue emdash 2.9 ×
10–6 M DBDMA in ethanol, λex 500
nm.
Figure 10
Excitation spectra of DBDMA brown emdash ethanolic solution
2.9
× 10–6 M and blue emdash nanofabricated with
PVP polymer (4%).
Normalized electronic
red emdash absorption and black emdash fluorescence
spectra of DBDMA in DMF solution, and blue hyphen absorption and pink
hyphen fluorescence spectra of DBDMA-doped PVP nanofiber, λex = 488 nm.Absorption brown emdash, fluorescence green emdash spectra,
λex = 488 nm and excitation black emdash spectra,
λemmax = 540 nm of DBDMA-doped PVP nanofibers.Normalized fluorescence spectra of orange emdash DBDMA-doped
PVP
nanofibers prepared from ethanol solution and blue emdash 2.9 ×
10–6 M DBDMA in ethanol, λex 500
nm.Excitation spectra of DBDMA brown emdash ethanolic solution
2.9
× 10–6 M and blue emdash nanofabricated with
PVP polymer (4%).The emission spectrum of dye-doped PVA thin film
has a remarkable
decrease in the fluorescence quantum yield compared to its peers in
various media previously explained as given in Table . The normalized fluorescence spectra of
DBDMA-doped PVP nanofiber and DBDMA-doped PVA thin film show an emission
band peak at a shorter wavelength of 492 nm for DBDMA-doped PVP with
only a shoulder at 551 nm. In contrast, for DBDMA-doped PVA, there
is a peak at 551 nm and a disappearance of the peak at 492 nm for
and resolved Franck–Condon fluorescence peak at 551 nm, as
shown in Figure .[50]
Figure 11
Normalized fluorescence spectra of brown
emdash DBDMA-doped PVP
nanofiber and blue emdash DBDMA-doped PVA thin film, λex = 450 nm.
Normalized fluorescence spectra of brown
emdash DBDMA-doped PVP
nanofiber and blue emdash DBDMA-doped PVA thin film, λex = 450 nm.
γ-ray Effect on Nanofiber and Thin-Film
Composites
Absorption and Fluorescence Spectra
Irradiation of dye-doped PVP using γ-rays (dose = 420 mR) results
in the disappearance of a resolved Franck–Condon fluorescence
peak at 561 nm and a blue shift of 4 nm, as shown in Figure . However, irradiation of
the DBDMA-doped PVA thin layer using the same rays and duration increased
the emission intensity, as shown in Figure a. This increase is accompanied by the disappearance
of the resolved Franck–Condon peak in addition to a red shift
from 522 nm in the fresh sample to 563 nm in the irradiated sample.
It may be due to molecular aggregation or excimer formation because
of a mutation compound due to irradiation, see Figure b (normalized version of Figure a). This red shift and disappearance
of Franck–Condon peaks were not observed in the ground state,
as there was no change in the absorption spectrum. There was only
a decrease in the intensity of the absorbed light without any change
in the spectra. The changes in the positions of the emission peaks
together with the change in the fluorescence and absorption intensities
of DBDMA-doped PVP nanofiber and DBDMA-doped PVA thin film as a result
of exposure to very low doses of γ-rays (between 150 and 420
mR) confirm the efficacy of using this dye as a probe to identify
the presence of γ-rays as shown in Figure .
Figure 12
Normalized fluorescence spectra of DBDMA-doped
PVP brown emdash
fresh and blue emdash irradiated, dose: 220 mR (λex = 450 nm).
Figure 13
Normalized fluorescence (a) and fluorescence spectra (b)
of DBDMA-doped
5% PVA blue emdash fresh and brown emdash irradiated samples (dose
= 220 mR), λex = 500 nm.
Figure 14
Absorption spectra of DBDMA-doped PVA thin film, blue
emdash fresh
and irradiated using γ-rays, green hyphen 150 mR and brown hyphen
420 mR.
Normalized fluorescence spectra of DBDMA-doped
PVP brown emdash
fresh and blue emdash irradiated, dose: 220 mR (λex = 450 nm).Normalized fluorescence (a) and fluorescence spectra (b)
of DBDMA-doped
5% PVA blue emdash fresh and brown emdash irradiated samples (dose
= 220 mR), λex = 500 nm.Absorption spectra of DBDMA-doped PVA thin film, blue
emdash fresh
and irradiated using γ-rays, green hyphen 150 mR and brown hyphen
420 mR.
FTIR analysis
The irradiation of
the DBDMA-doped PVP nanofiber induced significant variations in the
structure of the sample, as indicated by FTIR spectra as shown in Figure . The broad band
at 3300–3500 cm–1, ascribed to the stretching
modes of overlap of CO–H vibrations, has been shifted to a
higher wavenumber after irradiation which implies the peak O–H
after irradiation. This finding may be due to the increasing extent
of hydrogen bonding or cross-linking. Again, the intensity of the
peak C=O stretching (at 1650 cm–1) was increased.
C–O (at 1050 cm–1) was increased in the irradiated
sample, proving the possibility of interchange between the two groups.
This could be due to the occurrence of keto–enol tautomerism
and hydride migration between carbon and oxygen within the network
of the PVP polymer.[51]
Figure 15
FTIR spectra of DBDMA-doped
PVP nanofibers fresh and irradiated
with 150 and 420 mR.
FTIR spectra of DBDMA-doped
PVP nanofibers fresh and irradiated
with 150 and 420 mR.The effect of the irradiation on the chemical structure
of the
thin-film DBDMA-doped PVA is illustrated in Figure , where the exposed films to different γ-ray
doses (150 and 420 mR) are compared with the non-irradiated sample.
A decrease in the intensity of the peaks of all functional groups
is observed in the irradiated samples. However, the positions of all
peaks remained basically in the same positions. Besides, no additional
peaks are observed in the irradiated samples. These results indicate
that irradiation with low γ-ray doses imposed limited influence
on the chemical structure of the thin-film DBDMA-doped PVA sample.
Figure 16
FTIR
spectra of DBDMA-doped PVA thin film, fresh, irradiated with
150 and 420 mR.
FTIR
spectra of DBDMA-doped PVA thin film, fresh, irradiated with
150 and 420 mR.
Thermal Analysis of the PVA/DBDMA Nanocomposite
Film
TGA was carried out on the fresh and irradiated PVA/DBDMA
thin films with the aim to determine the different thermal properties
and evaluate the stability of the casted nanocomposite films as well
as to assess the impact of the γ-irradiation exposure on the
thermal behavior and stability of the PVA/DBDMA film. Thermograms
in Figure show
that untreated PVA/DBDMA undergoes two principal steps of thermal
decomposition. The first occurs at a temperature range of 95–160
°C revealing a weight loss of 4.42% which refers to the removal
of moisture and residual solvent,[52] whereas
the temperature range at which the second decomposition step occurs
is 270–436 °C with a weight loss of 87.15% which represents
more significant weight loss due to the degradation of side group
(−OH) to give polyene[53] and also
the cleavage of (C–C) in the main chain of PVA (leading to
carbocation).[54] In addition, these thermal
findings showed more enhanced thermal properties of the casted and
blended PVA/DBDMA film compared to a pure PVA film reported in the
literature.[55] We notice that after irradiation
the thermal behavior decreased and the decomposition onset after irradiation
lowered from 270 to 240 °C. Moreover, the residual weight after
degradation of the fresh PVA/DBDMA film (8.43%) was higher than the
one observed with the irradiated film (0.12). This confirmed the thermal
stability of the prepared PVA/DBDMA film and the effect of the γ-irradiation
on its thermal behavior.
Figure 17
TGA thermograms of fresh and irradiated PVA/DBDMA
thin films (dose
210 mR).
TGA thermograms of fresh and irradiated PVA/DBDMA
thin films (dose
210 mR).
SEM Study of the PVP/DBDMA Nanofibers and
the PVA/DBDMA Nanocomposite Film
SEM micrograph in Figure a shows smooth
and regular nanofiber morphology without the appearance of clear nodes
or beads. This could be explained by the use of a low flow rate and
an appropriate needle-collector distance, allowing enough time for
solvent evaporation. Although, by using high flow rates, beads may
appear due to the short drying time.[56]
Figure 18
SEM
micrographs of PVP/DBDMA nanofibers before irradiation (a)
and γ-irradiated samples (b) (dose 150 mR) and (c,d) (at different
magnifications, dose 210 mR).
SEM
micrographs of PVP/DBDMA nanofibers before irradiation (a)
and γ-irradiated samples (b) (dose 150 mR) and (c,d) (at different
magnifications, dose 210 mR).The bead-free fibers revealed a relatively uniform
diameter size.
Most nanofibers’ average diameter ranges from 300 to 400 nm.
Moreover, the structure obtained from the above process parameters
showed continuous twisted and spaced nanofibers providing a surface
porosity which is a required property for various electrospun polymer
applications.This efficient fiber homogeneity in its global
morphology was due
to the excellent PVP polymer, and appropriate DBDMA selected concentrations
allowed suitable viscosity solution to the different applied electrospinning
parameters.After irradiating the nanofiber composite material
with the lowest
dose of 150 mR (Figure b), we noticed the appearance of nodes and beads on the nanofiber
structures. The low dose of γ-rays was so low as to cause degradation
of the interconnected fibers. By increasing the irradiation dose to
210 mR, nodes and beads became bigger and more apparent (Figures c,d). These findings
clearly showed the possibility of exploring these materials as sensitive
dosimeters with promising application in routine medical diagnostic
control.Morphological SEM analysis of control and irradiated
PVA/DBDMA
thin films was performed to assess the effect of the increased low-ray
doses on the surface morphology of the treated prepared films. Unirradiated
PVA/DBDMA film (Figure a) presents a smooth and homogeneous appearance with uniform
structural integrity and crack-free states. This obtained surface
morphology exhibited high compatibility of the two mixed compounds
(PVA and DBDMA) and good selection of different parameters for the
preparation of the composite film. After low dose γ-irradiation
of the PVA/DBDMA nanocomposite films (Figure b,c), we remarked the presence of some fluke-like
structures accompanied by some globules and surface stripes. These
apparently recorded that degradation and morphological changes on
the surface morphology of irradiated film composites appeared more
vigorous with the increase of the γ-ray applied dose from 210
to 420 mR (Figure d). The drastic change in surface morphology of irradiated thin films
exhibited high sensitivity of the PVA/DBDMA prepared films and their
promising application as low radiation dosimeters for medical diagnostic
systems.
Figure 19
SEM micrographs of the DBDMA/PVA raw thin film (a) and γ-irradiated
films (b,c) (dose 210 mR at different magnifications) and (d) (dose
420 mR).
SEM micrographs of the DBDMA/PVA raw thin film (a) and γ-irradiated
films (b,c) (dose 210 mR at different magnifications) and (d) (dose
420 mR).
Conclusions
Detection or further quantification
of the γ-ray dose to
tissues or organs is of great importance for risk estimation, but
such doses are arduous to assess directly in most situations. In the
current work, we proposed an alternative based on various nanomaterial
hosts doped with a new fluorescent dye as effective γ-ray dosimeters.
Poor excited-state solvation is indicated by a slight Stokes shift
of the studied dye. The valuable colorimetric and optical performances
(high optical stability, high fluorescent quantum yield, and short
excited-state lifetime value) and the excellent spectral behavior
obtained confirmed its ability to be a potent candidate as a sensitive
indicator and efficient sensor for dosimetric devices. To these findings,
PVP/DBDMA nanofiber materials and PVA/DBDMA thin films were designed,
and their preparation parameters were optimized. The dosimetric efficiency
of these two nanomaterials after irradiation with different doses
of γ-rays was evaluated. Indeed, both prepared materials revealed
clear changes in the characteristics of the fluorescence and absorption
spectra which became more significant with increased applied doses.
Additionally, the thermogravimetric study of PVA thin films via TGA
showed good thermal stability of the prepared films and the modification
of their thermal proprieties after irradiation. Furthermore, the morphology
of the dye-doped PVP and PVA nanomaterials exhibited gradual surface
degradation after exposure to increased low dose γ-rays. Therefore,
all these findings confirmed the possibility of exploring DBDMA-doped
PVP nanofibers and PVA/DBDMA thin films as sensitive dosimeters with
promising application in routine medical diagnostic control. Moreover,
photostable DBDMA can also be considered a potential laser dye and
solar cell collector.