4.3 Hydrothermal Treatment
Hydrothermal processes have been used to synthesize metal oxides such as titanium
oxide and zinc oxide and to modify the material properties [26, 91]. Zhou et al.
reported that hydrothermal treatment converted graphene oxide to a stable graphene
solution [92]. Jung et al. studied the structural transformation of organic copper
phthalocyanine NWs into hollow rectangular NTs during a hydrothermal process
[93]. Recently, Lee et al. reported that the structural and optical properties of P3HT
NPs prepared by reprecipitation [48] can be controlled through hydrothermal
treatment at different temperatures [94]. In their study, an autoclave served as the
chamber for the hydrothermal process. Pristine (i.e., before hydrothermal treatment) P3HT NPs dispersed in deionized water were placed in a Teflon beaker in the
chamber, which was heated in an oven to a temperature between 60
C and 150
C.
In this process, external pressure is applied on the P3HT NPs, roughly estimated to
be 15 bar at 100
C [95]. Then, the chamber was allowed to cool naturally. A
homogenous dispersion of NPs was obtained by sonicating the P3HT NP solution
with a high-power ultrasonicator.
Figure 17a and its insets show the SEM and TEM images, respectively, of P3HT
NPs in the pristine state and after hydrothermal treatment at various temperatures.
The numerical labels of the hydrothermally treated (HT) samples (HT060, HT090,
HT110, HT120, HT130, and HT150) indicate the temperature of treatment in
degrees Celsius. The diameters of the pristine, HT060, HT110, and HT150 P3HT
NPs were 77 (Æ11), 88 (Æ11), 184 (Æ50), and 471 (Æ107) nm, respectively. The
shape and degree of aggregation for P3HT NPs treated at temperatures of 110
C
and above were clearly different from those of the pristine and HT060 NPs.
Figure 17b shows the normalized UV–vis absorption spectra of the pristine and
hydrothermally treated P3HT NPs. The absorption peaks were observed at 510,
550, and 610 nm for the pristine P3HT NPs, which coincide with those of spincoated P3HT films [90, 96, 97]. The UV–vis absorption spectra changed with
increasing hydrothermal temperature, as shown in Fig. 17b: the peaks shifted to
longer wavelengths and their relative intensities changed. The absorption peak at
~510 nm was dominant for the pristine, HT060, and HT090 samples. However,
with increasing temperature, the absorption intensity at ~550 nm gradually
increased, as seen for the HT110, HT120, and HT130 samples. The peak at
610 nm, corresponding to the 0–0 transition, was the strongest for the HT150
P3HT NPs. A long-wavelength tail also progressively developed with increasing
hydrothermal temperature owing to the scattering effect. These results are
attributed to the interchain interactions and ring planarity in the P3HT main chains
that are strengthened owing to the higher pressure applied during the hydrothermal
process with increasing temperature [98–100].
Figure 17c shows the normalized LCM PL spectra for single pristine and HT
P3HT NPs averaged over 20 different dry NPs. The intensity and position of the 0–1
emission peak at 692À708 nm were different for the individual NPs and varied with
the hydrothermal temperature. Its dominance increased for the HT060 and HT110
Synthesis, Characteristics, and Applications of Intrinsically Light-Emitting. . .
221
Hydrothermal processes have been used to synthesize metal oxides such as titanium
oxide and zinc oxide and to modify the material properties [26, 91]. Zhou et al.
reported that hydrothermal treatment converted graphene oxide to a stable graphene
solution [92]. Jung et al. studied the structural transformation of organic copper
phthalocyanine NWs into hollow rectangular NTs during a hydrothermal process
[93]. Recently, Lee et al. reported that the structural and optical properties of P3HT
NPs prepared by reprecipitation [48] can be controlled through hydrothermal
treatment at different temperatures [94]. In their study, an autoclave served as the
chamber for the hydrothermal process. Pristine (i.e., before hydrothermal treatment) P3HT NPs dispersed in deionized water were placed in a Teflon beaker in the
chamber, which was heated in an oven to a temperature between 60
C and 150
C.
In this process, external pressure is applied on the P3HT NPs, roughly estimated to
be 15 bar at 100
C [95]. Then, the chamber was allowed to cool naturally. A
homogenous dispersion of NPs was obtained by sonicating the P3HT NP solution
with a high-power ultrasonicator.
Figure 17a and its insets show the SEM and TEM images, respectively, of P3HT
NPs in the pristine state and after hydrothermal treatment at various temperatures.
The numerical labels of the hydrothermally treated (HT) samples (HT060, HT090,
HT110, HT120, HT130, and HT150) indicate the temperature of treatment in
degrees Celsius. The diameters of the pristine, HT060, HT110, and HT150 P3HT
NPs were 77 (Æ11), 88 (Æ11), 184 (Æ50), and 471 (Æ107) nm, respectively. The
shape and degree of aggregation for P3HT NPs treated at temperatures of 110
C
and above were clearly different from those of the pristine and HT060 NPs.
Figure 17b shows the normalized UV–vis absorption spectra of the pristine and
hydrothermally treated P3HT NPs. The absorption peaks were observed at 510,
550, and 610 nm for the pristine P3HT NPs, which coincide with those of spincoated P3HT films [90, 96, 97]. The UV–vis absorption spectra changed with
increasing hydrothermal temperature, as shown in Fig. 17b: the peaks shifted to
longer wavelengths and their relative intensities changed. The absorption peak at
~510 nm was dominant for the pristine, HT060, and HT090 samples. However,
with increasing temperature, the absorption intensity at ~550 nm gradually
increased, as seen for the HT110, HT120, and HT130 samples. The peak at
610 nm, corresponding to the 0–0 transition, was the strongest for the HT150
P3HT NPs. A long-wavelength tail also progressively developed with increasing
hydrothermal temperature owing to the scattering effect. These results are
attributed to the interchain interactions and ring planarity in the P3HT main chains
that are strengthened owing to the higher pressure applied during the hydrothermal
process with increasing temperature [98–100].
Figure 17c shows the normalized LCM PL spectra for single pristine and HT
P3HT NPs averaged over 20 different dry NPs. The intensity and position of the 0–1
emission peak at 692À708 nm were different for the individual NPs and varied with
the hydrothermal temperature. Its dominance increased for the HT060 and HT110
Synthesis, Characteristics, and Applications of Intrinsically Light-Emitting. . .
221