6. Thesis outline
2.3. Results and discussion
2.3.1. Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/
Table 2-1. Preparation of RF-(VM-SiO3/2)n-RF/h-BN nanocomposites
As shown in Scheme 2-1 and Table 2-1, the expected RF-(VM-SiO3/2)n-RF/h-BN
composites were obtained in 70 – 78% isolated yields under alkaline conditions at room
temperature. Sol–gel reaction under acidic conditions also afforded the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites in 53 – 80% isolated yields. These obtained
nanocomposites were found to exhibit a good dispersibility and stability toward the traditional organic solvents such as methanol, ethanol 2-propanol, 1,2-dichloroethane, N,N-dimethylformamide, dimethyl sulfoxide, and aliphatic fluorinated solvents [1: 1 mixed
Run Oligomer h-BN Yield
1 20 100 5
2 50 100 5
3 100 100 5
4 200 100 5
12 12 12 12
MeOH Catalyst
(mg) (mg) (mL) (mL) (mg)
94 (78)a) 105 (70)a) 143 (72)a) 215 (72)a)
5 20 100 5
6 50 100 5
7 100 100 5
8 200 100 5
12 12 12 12
96 (80)a) 80 (53)a) 139 (70)a) 199 (66)a)
Size of nanocomposites b) (nm) ± STD
a)Yield (%) based on oligomer and h-BN
b)Determined by dynamic light scattering measurements (DLS) in methanol at 25 °C 160.4 ± 39.3 102.6 ± 17.3 217.0 ± 50.8 102.3 ± 17.3 250.4 ± 67.9 89.4 ± 9.4 100.3 ± 17.1 127.8 ± 31.8 Product
25% aq. NH3
1 N HCl
2, 2, 3, 3-pentafluoropropane] including water; although the RF-(VM-SiO3/2)n-RF
oligomeric nanoparticles, which were prepared in the absence of h-BN nanoparticles under the similar sol–gel reaction illustrated in Scheme 2-1, cannot provide the dispersibility toward water.
In fact, Figure 2-1 and Figure 2-2 show that the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Table 2-1) prepared under alkaline and acidic conditions, respectively, have a good dispersibility toward water and the usual organic media such as methanol, 2-propanol, and AK-225 TR.
Figure 2-1. Photograph of the well-dispersed RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Table 2-1) in water (a), methanol (b), 2-propanol (c), 1:1 mixed solvents (AK-225TR) of 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,2,2,3,3-pentafluoropropane (d).
H2O MeOH 2-Propanol AK-225TR
(a) (b) (c) (d)
Figure 2-2. Photograph of the well-dispersed RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 7 in Table 2-1) in water (a), methanol (b), 2-propanol (c), 1:1 mixed solvents (AK-225TR) of 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,2,2,3,3-pentafluoropropane (d).
Thus, the size of well-dispersed methanol solutions containing the nanocomposite particles was measured by the use of dynamic light scattering measurements at 25 °C, and the results are shown in Table 2-1. Table 2-1 shows that each composite (Runs 1 – 4) has nanometer size-controlled particles from 89 to 250 nm, and the size of the composites (103
– 217 nm), which were obtained under acidic conditions, was similar to that under alkaline conditions.
In order to clarify the formation of the composite particles, the methanol solutions H2O MeOH 2-Propanol AK-225TR
(a) (b) (c) (d)
2-1) were observed by the field emission scanning electron micrograph (FE-SEM). The results are shown in Figure 2-3. The FE-SEM picture of the original h-BN particles is also shown in Figure 2-3, for comparison.
Figure 2-3. FE-SEM (Field Emission Scanning Electron Microscopy) image of well-dispersed methanol solutions of original h-BN nanoparticles (a), RF-(VM-SiO3/2)n-RF/ h-BNnanocomposites: Run 3 in Table 2-1 (b) and Run 7 in Table 2-1 (c).
(b) 100 nm (c) 100 nm
100 nm (a)
As shown in Figure 2-3-(b), FE-SEM images show that the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Table 2-1) are very fine nanoparticles, although the original h-BN particles can observe partly agglomeration or aggregation with each other [see Figure 2-3-(a)]. In particular, the h-BN nanoparticles (mean diameter: 55 nm) are mostly
encapsulated into fluoroalkyl end-capped oligomeric silica nanoparticle cores to produce the corresponding fluorinated oligomeric silica/h-BN nanocomposites (Run 3 in Table 2-1; average diameter size: 100 nm) as depicted in the TEM (Transmission Electron Microscopy) images (Figure 2-4).
Figure 2-4. TEM (Transmission Electron Microscopy) image of well-dispersed methanol solutions of the R -(VM-SiO ) -R /h-BNnanocomposites (Run 3 in Table 2-1).
100 nm
On the other hand, the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 7 in Table 2-1) are mainly composed of the linearly arrayed nanocomposite particles [Figure 2-3-(c)], quite different from the very fine nanoparticles prepared under alkaline conditions illustrated in Figure 2-3-(b).
To verify the presence of h-BN particles in the fluorinated oligomeric silica nanocomposites, two kinds of RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7) have been studied by using the XRD spectra measurements. The results are shown in Figure 2-5 and Figure 2-6.
As shown in Figure 2-5 and Figure 2-6, two kinds of RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Table 2-1) were found to afford the same diffraction
peaks as that of the original h-BN nanoparticles, although the corresponding RF-(VM-SiO3/2)n-RF oligomeric nanoparticles exhibit the amorphous structure, indicating
the presence of h-BN in each fluorinated nanocomposite.
Figure 2-5. X-ray diffraction patterns of the RF-(VM-SiO3/2)n-RF/h-BNnanocomposites [(a): Run 3 in Table 2-1], RF-(VM-SiO3/2)n-RF oligomeric nanoparticles (b), and the original h-BN nanoparticles (c).
Figure 2-6. X-ray diffraction patterns of the R -(VM-SiO ) -R /h-BNnanocomposites
Intensity (a.u.)
2 𝜃/deg (b) RF-(VM-SiO3/2)n-RF oligomeric nanoparticles (a) RF-(VM-SiO3/2)n-RF/h-BN
nanocomposites (Run 3)
(c) Original h-BN nanoparticles
2 𝜃/deg
Intensity (a.u.)
(b) RF-(VM-SiO3/2)n-RF oligomeric nanoparticles (a) RF-(VM-SiO3/2)n-RF/h-BN
nanocomposites (Run 7)
(c) Original h-BN nanoparticles
2.3.2. Thermal stability of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/hexagonal boron nitride nanocomposites [RF-(VM-SiO3/2)n-RF/h-BN]
The thermal stability of the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 1 – 8 in
Table 2-1) was studied by the use of the thermogravimetric analyses (TGA), in which the weight loss of the nanocomposites was measured by raising the temperature around 800 °C (the heating rate: 10 °C min-1) in air atmosphere. Thermal stability of the original h-BN particles and the original RF-(VM-SiO3/2)n-RF oligomeric nanoparticles was also studied, for comparison. The results are shown in Figure 2-7 and Figure 2-8.
Figure 2-7. Thermogravimetric analyses of the parent h-BN nanoparticles, parent RF-(VM-SiO3/2)n-RF oligomeric nanoparticles, RF-(VM-SiO3/2)n-RF/h-BNnanocomposites
prepared under alkaline conditions (Run 1 - 4 in Table 2-1). a) Weight loss (%) at 800 °C.
Figure 2-8. Thermogravimetric analyses of the parent h-BN nanoparticles, parent RF-(VM-SiO3/2)n-RF oligomeric nanoparticles, RF-(VM-SiO3/2)n-RF/h-BNnanocomposites
prepared under acidic conditions (Run 5 - 8 in Table 2-1). a) Weight loss (%) at 800 °C.
Temperature (°C)
Weight loss (%) Parent h-BN (~ 0 %)a)
Run 3 (35 %)a)
Parent RF-(VM-SiO3/2)n-RF oligomeric nanocomposites(75 %)a)
Run 2 (20 %)a) Run 1 (12 %)a)
Run 4 (46 %)a) 0
10 20 30 40 50 60 70 80 90 100
0 100 200 300 400 500 600 700 800
0 10 20 30 40 50 60 70 80 90 100
0 100 200 300 400 500 600 700 800
Temperature (°C)
Weight loss (%) Parent h-BN (~ 0 %)a)
Run 7 (30 %)a)
Parent RF-(VM-SiO3/2)n-RF oligomeric nanocomposites(75 %)a)
Run 6 (23 %)a) Run 5 (14 %)a)
Run 8 (44 %)a)
Original h-BN nanoparticles can keep no weight loss even after calcination at 800 °C, and the parent RF-(VM-SiO3/2)n-RF oligomeric nanoparticles provide a weight loss (75%) at 800 °C corresponding to the content of organic moieties in the nanoparticles as shown in Figure 2-7 and Figure 2-8. On the other hand, each weight loss value at 800 °C of the
RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 1 – 4) was found to increase from 12 to 46%, increasing with greater feed ratio of the oligomer in oligomer/h-BN shown in Table 2-1 (see Figure 2-7). A similar result was obtained in the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 5 – 8), and the weight loss values of the nanocomposites increased from 14 to 44% (see Figure 2-8). From these weight loss values, the contents of h-BN in the nanocomposites are estimated as follows:
The contents of h-BN in the nanocomposites were found to decrease from 84 to 39%
(or 81–41%) with the increase in the feed amounts of the oligomer from 20 to 200 mg in Table 2-1, indicating that the composite reactions of the fluorinated oligomer with h-BN
Run no.
1 2 3 4
Content of h-BN (%) 84
73 53 39
5 6 7 8
81 69 60 41
Run no. Content of h-BN (%)
illustrated in Scheme 2-1 should smoothly proceed to afford the expected RF-(VM-SiO3/2)n-RF/h-BN nanocomposites.
2.3.3. Applications of the fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/hexagonal boron nitride nanocomposites [RF-(VM-SiO3/2)n-RF/h-BN] for surface modification of traditional organic polymers
It was previously reported that fluoroalkyl end-capped oligomers [RF-(M)n-RF; RF =
fluoroalkyl group; M = radical polymerizable monomer] have an excellent surface arrangement ability toward the traditional organic polymers such as PMMA to exhibit a
good oleophobic property imparted by fluoroalkyl groups on the modified surface.26, 27)
From this point of view, it is strongly expected that h-BN in the present RF-(VM-SiO3/2)n-RF/h-BN nanocomposites should be arranged on the modified PMMA
surface to provide the unique property related to the h-BN on the surface. Thus, the
2-9. As shown in Figure 2-9, the transparent colorless-modified films have been prepared by using the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Table 2-1), similar to that of the original PMMA film.
Figure 2-9. Photograph of the modified PMMA films treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Table 2-1) and original
PMMA film.
The dodecane contact angle values of these transparent colorless-modified PMMA film surface and reverse sides were measured, and the results including their photography of the dodecane droplet are depicted in Tables 2-2 and 2-3.
Run 3 Run 7 Original PMMA film
Table 2-2. Contact angle of dodecane on the modified PMMA film surface an reverse sides treated with RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Table 2-1)
Table 2-3. Photograph of the dodecane droplet on the modified PMMA film surface treated with the RF-(VM-SiO3/2)n-RF/h-BNnanocomposites
Run Film thickness (µm) Contact Angle (°) Dodecane
Surface side Reverse side
3 200 31 0
7 200 33 32
Original
PMMA film 165 0 0
Run 3
Run 7 Run*
Original PMMA
Contact angle (Degree) Dodecane
Surface side Reverse side
31° 0°
33° 32°
0° 0°
Dodecane contact angle value:
Dodecane contact angle value:
Dodecane contact angle value:
Surface side Reverse side
Surface side Reverse side
Table 2-2 and Table 2-3 show that each surface side of modified PMMA films treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7) can give a good oleophobic property imparted by fluoroalkyl segments in the composites because the dodecane contact angle values are 31 – 33 degrees. These values are quite similar to that
(33 degrees) of the highly oleophobic PTFE [poly(terafluoroethylene)] sheet surface.28) On
the other hand, the reverse side of the modified PMMA film by using the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3) prepared under alkaline conditions
exhibited an oleophilic property (dodecane contact angle value: 0 degrees), quite similar to that of the original PMMA film. Of particular interest, the reverse side of the modified PMMA film treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 7) prepared under acidic conditions can give a similar oleophobic property (dodecane contact angle value: 32 degrees) to that (33 degrees) of the surface side.
It is well-known that h-BN can exhibit the fluorescent characteristic through the
excitation absorption around 215 nm, and the electronic structure of h-BN has been also
studied by the use of photoluminescence in detail.29 ~ 32) It has been very recently reported
that the fluoroalkyl end-capped acrylic acid oligomer [RF-(CH2CHCOOH)n-RF]/h-BN
nanocomposites can afford the fluorescent peak around 370 nm when the well-dispersed
nanocomposite methanol solutions were excited at 220 nm.33)
Now, the dispersed methanol solution containing the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Table 2-1) were tried to observe visibly the fluorescence emission (excitation: 330 – 385 nm) related to the encapsulated h-BN. The results were shown in Figure 2-10. As shown in Figure 2-10-(b), a clear fluorescent light related the present of h-BN can be observed by the use of the dispersed methanol solution containing the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Table 2-1).
Figure 2-10. Optical (a) and fluorescent (b) microscopy images of the dispersed methanol solution containing the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Table 2-1).
100 µm 100 µm
(a) (b)
Thus, the modified PMMA films surface and reverse sides treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 3 and 7 in Figure 2-9 and Table 2-2)
have been studied by the use of the fluorescent spectra in order to clarify the presence of the h-BN on the modified PMMA surfaces. The results are shown in Figure 2-11 and Figure
2-12. The fluorescence spectra of both the modified PMMA film surface and reverse sides treated with the RF-(VM-SiO3/2)n-RF oligomeric nanoparticles prepared under alkaline conditions are also measured, for comparison. The results are shown in Figure 2-11.
Figure 2-11. Fluorescence spectra of the modified PMMA film surface (a) and reverse (b) sides treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3 in Figure 2-9 and Table 2-2), the modified PMMA film surface (c) and reverse side (d) treated with the RF-(VM-SiO3/2)n-RF oligomeric nanoparticles, and the dispersed original h-BN nanoparticles (e) methanol solution (25 mg/dm3) (Ex. 220 nm).
0 50 100 150 200 250
300 310 320 330 340 350 360 370 380 390 400
Intensity (a. u.)
Wavelength (nm) (a)
(e)
(c)
(d) (b)
Figure 2-12. Fluorescence spectra of the modified PMMA film surface (a) and reverse (b) sides treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 7 in Figure 2-9 and Table 2-2) (Ex. 220 nm).
As shown in Figure 2-11-(a), when the cast film surface of PMMA treated with the
RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Run 3) is excited (l = 220 nm), the surface of
the film yields a strong fluorescent intensity with a peak maximum at around 376 nm [see
Figure 2-11-(a)]. This fluorescent peak is similar to that of the original h-BN nanoparticles [see Figure 2-11-(e)]. In contrast, the fluorescent intensity of the reverse side of the cast film was significantly lower [see Figure 2-11-(b)], than that of the surface. The modified
0 50 100 150 200 250
300 320 340 360 380 400
Intensity (a. u.)
Wavelength (nm) (a)
(b)
fluorescent intensity on the surface and even on the reverse sides under similar conditions [Figure 2-11-(c), (d)]. These findings suggest that the encapsulated h-BN should be arranged regularly on the PMMA film surface during the cast film formation. However, unexpectedly, the cast film treated with the RF-(VM-SiO3/2)n-RF/h-BN nanocomposites (Runs 7) can afford the same fluorescent intensity toward not only the surface (l = 379 nm)
but also the reverse sides (l = 380 nm) under the similar excitation conditions [Figure
2-12-(a), (b)], indicating that the encapsulated h-BN should be uniformly dispersed in the PMMA film during the cast film formation.
2.3.4. Study on the surface arrangement behavior of the fluoroalkyl end-capped