15 “Polymer–Oxide” Micro-/Nanocomposites: Background and Promises
267
It is of interest to note that behavior of the (ε / , ε // ) in the whole temperature
range is similar to temperature behavior of the viscoelastic characteristics (storage
modulus and tang δ) of hydroxypropyl cellulose composites reinforced with cellulose nanofibers [77–79]. The authors had related, measured by them, dependences
with two types of relaxations both involving large-scale molecular motions [77] and
changes of the amount of crystalline, amorphous, and intermediate-order phases
[77–79]. We suppose similar processes occur in the case of the MCC-oxide which
are under our study. Moreover, we think that relaxations which are realized in
the low temperature range, −125 to 25 ◦ C, promote to phase transformations of
mentioned above type, which take place in the higher temperature range 25–125 ◦ C.
Fitting of experimental ε / (T, f ) curves with corresponding theoretical dependencies in Debye approximation was performed for the temperature range −125 to
25 ◦ C (Fig. 15.9), and the energy barrier between two equilibrium positions, U,
have been evaluated. Corresponding values are accumulated in the Table 15.1. It
is easy to see that U-values show significant influence of the oxide component on
the relaxation conditions in cellulose matrix that confirm the role of the microfibril
surface molecular groups.
It is clear that these issues are far from their total understanding; that is why
further study in this direction has to be performed. Nevertheless, placed below
data concerning effect of oxide particles on luminescence properties of studied
composites confirm the role of the cellulose–oxide interactions.
Photoluminescence (PL) of the MCC and MCC-oxide composites is excited in
the wide spectral range from UV to yellow light (250–570 nm) (Figs. 15.11 and
15.12). The PL spectra consist of wideband that extends from 350 up to 750 nm (Fig.
15.11, curves 1, 2). Besides, the sets of relatively narrow lines are in the spectra of
the composites embedded with oxides doped with RE ions Sm 3+ (Fig. 15.4, curve
4) and Eu 3+ (Fig. 15.11, curves 5 and 6). Relative intensities of the wideband and
narrow lines depend on the sample composition. So, some traces of the fine structure
can be found in the spectral ranges 560–580, 580–615, and 645–665 nm of the PL
spectra of the 10-La 0.7 Sm 0.3 VO 4 composites (Fig. 15.11, curve 3). If oxide amount
is higher (100-La 0.7 Sm 0.3 VO 4 composite), the lines are significantly enhanced (Fig.
15.11, curve 4).
The shape and peak position (λ max ) of the wide PL band also depend on the
sample preheating and on the sample composition. Taking into account previously
found results [36, 37, 44], we can conclude that the wideband at least consists of four
strongly superposed components with λ max near 420–430, 505, 565, and 600 nm.
Contributions of these components to the total spectra change in different way after
MCC heating (Fig. 15.11, curve 2) or if oxide is embedded into MCC. The former
leads to the short wavelength side domination in the spectra (Fig. 15.4, curve 2).
As for the last, as a rule, short wavelength luminescence components dominate in
the spectra of composites; however, middle components become predominant when
amount of oxide increases (Fig. 15.11, curve 4).
The spectra of the wideband PL excitation similarly to emission spectra showed
complex structure (Fig. 15.12). As for starting MCC sample, excitation spectra
267
It is of interest to note that behavior of the (ε / , ε // ) in the whole temperature
range is similar to temperature behavior of the viscoelastic characteristics (storage
modulus and tang δ) of hydroxypropyl cellulose composites reinforced with cellulose nanofibers [77–79]. The authors had related, measured by them, dependences
with two types of relaxations both involving large-scale molecular motions [77] and
changes of the amount of crystalline, amorphous, and intermediate-order phases
[77–79]. We suppose similar processes occur in the case of the MCC-oxide which
are under our study. Moreover, we think that relaxations which are realized in
the low temperature range, −125 to 25 ◦ C, promote to phase transformations of
mentioned above type, which take place in the higher temperature range 25–125 ◦ C.
Fitting of experimental ε / (T, f ) curves with corresponding theoretical dependencies in Debye approximation was performed for the temperature range −125 to
25 ◦ C (Fig. 15.9), and the energy barrier between two equilibrium positions, U,
have been evaluated. Corresponding values are accumulated in the Table 15.1. It
is easy to see that U-values show significant influence of the oxide component on
the relaxation conditions in cellulose matrix that confirm the role of the microfibril
surface molecular groups.
It is clear that these issues are far from their total understanding; that is why
further study in this direction has to be performed. Nevertheless, placed below
data concerning effect of oxide particles on luminescence properties of studied
composites confirm the role of the cellulose–oxide interactions.
Photoluminescence (PL) of the MCC and MCC-oxide composites is excited in
the wide spectral range from UV to yellow light (250–570 nm) (Figs. 15.11 and
15.12). The PL spectra consist of wideband that extends from 350 up to 750 nm (Fig.
15.11, curves 1, 2). Besides, the sets of relatively narrow lines are in the spectra of
the composites embedded with oxides doped with RE ions Sm 3+ (Fig. 15.4, curve
4) and Eu 3+ (Fig. 15.11, curves 5 and 6). Relative intensities of the wideband and
narrow lines depend on the sample composition. So, some traces of the fine structure
can be found in the spectral ranges 560–580, 580–615, and 645–665 nm of the PL
spectra of the 10-La 0.7 Sm 0.3 VO 4 composites (Fig. 15.11, curve 3). If oxide amount
is higher (100-La 0.7 Sm 0.3 VO 4 composite), the lines are significantly enhanced (Fig.
15.11, curve 4).
The shape and peak position (λ max ) of the wide PL band also depend on the
sample preheating and on the sample composition. Taking into account previously
found results [36, 37, 44], we can conclude that the wideband at least consists of four
strongly superposed components with λ max near 420–430, 505, 565, and 600 nm.
Contributions of these components to the total spectra change in different way after
MCC heating (Fig. 15.11, curve 2) or if oxide is embedded into MCC. The former
leads to the short wavelength side domination in the spectra (Fig. 15.4, curve 2).
As for the last, as a rule, short wavelength luminescence components dominate in
the spectra of composites; however, middle components become predominant when
amount of oxide increases (Fig. 15.11, curve 4).
The spectra of the wideband PL excitation similarly to emission spectra showed
complex structure (Fig. 15.12). As for starting MCC sample, excitation spectra