Preparation and applications of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/chemically modified cellulose fibers composites

Abstract

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R_F-(CH₂-CHSi(OMe)₃) _n -R_F: n = 2, 3; R_F = CF(CF₃)OC₃F₇: R_F-(VM) _n -R_F] was found to undergo the sol-gel reaction under alkaline conditions in the presence of chemically modified cellulose fibers treated with N-methylglucamine units ( MeGlu ) [Cellu-fiber- MeGlu ] and treated with iminodiacetic acid units ( ImDia ) (Cellu-fiber- ImDia ) to provide the corresponding fluorinated oligomeric silica/Cellu-fiber- MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu ] and /Cellu-fiber- ImDia composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia ], respectively. Dodecane and water contact angle measurements showed that these obtained composites can supply a superamphiphobic characteristic on their composite powders surface. The R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites were applied to the packing material for the column chromatography to separate the mixture of hydrocarbon and fluorocarbon oils. In addition, the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites were found to have more effective removal ability for fluorinated aromatic compounds than that for the corresponding non-fluorinated ones from aqueous methanol solutions. Interestingly, it was demonstrated that the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders are also applicable to the fabrication of liquid marbles, which are millimeter-sized liquids such as water, glycerine, ethylene glycol and dodecane stabilized by the adsorbed composite powders at air-liquid interfaces.

Keywords

Fluorinated oligomeric composite iminodiacetic acid unit-containing cellulose fiber superamphiphobicity selective removal of fluorinated aromatic compounds liquid marble

Introduction

Much attention has been focused on the use of the cellulose fibers in the fields of wastewater treatment and chemical industries as an inexpensive alternative to the adsorbents such as activated carbon due to their large surface area around 200 m²/g.¹ Chemically modified cellulose fiber derivatives treated with polyethyleneimine have been already applied to the mercury removal from wastewater.² N-methylglucamine-type cellulose fiber derivatives were also applied to the removal of boron (III) from wastewater with a higher removal rate.³ From the increased applicable viewpoint of these chemically modified cellulose fiber derivatives into a wide variety of fields, it is of particular interest to explore the novel composite materials based on these cellulose fiber derivatives and organic polymers, especially fluorinated polymers possessing a unique surface active characteristic related to longer fluoroalkyl groups, which cannot be achieved by the corresponding non-fluorinated polymers. However, to our knowledge, such studies have been very limited so far. During our comprehensive studies on the fluorinated polymers possessing a surface active characteristic,^4-9 we have already found that two fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica nanocomposites [R_F-(CH₂CHSiO_3/2) _n -R_F; R_F = CF(CF₃)OC₃F₇: R_F-(VM-SiO_3/2) _n -R_F], which were prepared by the sol-gel reaction of the corresponding oligomer [R_F-(CH₂CHSi(OMe)₃) _n -R_F: R_F-(VM) _n -R_F] under alkaline conditions, can exhibit an oleophobic/superhydrophobic characteristic on their modified glass surface.¹⁰ R_F-(VM) _n -R_F oligomer can also undergo the sol-gel reaction in the presence of alkyl-modified cellulose (AM-Cellu) under alkaline conditions to supply the corresponding fluorinated oligomeric silica/AM-Cellu nanocomposites [R_F-(VM-SiO_3/2) _n -R_F/AM-Cellu].¹¹ These obtained nanocomposites have been applied to the surface modification of filter paper to provide a superoleophilic/superhydrophobic property on the modified surface, demonstrating that the modified filter paper is effective for the separation membrane for W/O emulsion to isolate the transparent colorless oil.¹¹ Here we report that R_F-(VM) _n -R_F oligomer can undergo the sol-gel reaction under alkaline conditions in the presence of chemically modified cellulose fibers treated with N-methylglucamine units ( MeGlu ) [Cellu-fiber- MeGlu ] and with iminodiacetic acid units ( ImDia ) (Cellu-fiber- ImDia ) to provide the corresponding fluorinated oligomeric silica/Cellu-fiber- MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu ] and /Cellu-fiber- ImDia composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia ], respectively. These obtained composites can give a superamphiphobic characteristic on their composite powders surface, applying to the packing material for the column chromatography to separate the mixture of hydrocarbon and fluorocarbon oils. Such unique surface characteristic related to the composite powders enables the composites to provide not only a selective removal ability for fluorinated aromatic compounds from aqueous methanol solutions, but also the fabrication of liquid marbles, which are millimeter-sized liquids such as water, glycerine, ethylene glycol and dodecane at air-liquid interfaces. These results will be described in this article.

Experimental

Measurements

Field emission scanning electron micrograph (FE-SEM) was recorded by using JEOL JSM-7000F (Tokyo, Japan). Energy dispersive X-ray (EDX) spectra were obtained using JEOL JSM-7000F (Tokyo, Japan). The contact angles were measured by the use of Kyowa Interface Science Drop Master 300 (Saitama, Japan). Ultraviolet–visible (UV–vis) spectra were measured using Shimadzu UV-1600 UV–vis spectrophotometer (Kyoto, Japan).

Materials

Chemically modified cellulose fibers treated with N-methylglucamine units ( MeGlu ) [Cellu-fiber- MeGlu ] and with iminodiacetic acid units ( ImDia ) (Cellu-fiber- ImDia ) were kindly supplied from Chubu Chelest Co., Ltd. (Mie, Japan). Vinyltrimethoxysilane was used as received from Dow Corning Toray Co., Ltd. (Tokyo, Japan). 2’, 3’, 4’, 5’, 6’-pentafluoroacetophenone was purchased from Sigma Aldrich Japan Co., Ltd. (Tokyo, Japan). Dodecane, perfluorohexane, bisphenol A (BPA), bisphenol AF (BPAF), and acetophenone were received from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan), respectively. 1,4-Bis[(4-methylphenyl)amino]-9,10-anthracenedione (Quinizarin Green SS), acid blue 112, and PS Red G were received from Chugai Kasei Co., Ltd. (Fukushima, Japan). 25 wt % ammonia was provided by FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan). Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R_F-(CH₂-CHSi(OMe)₃) _n -R_F: the mixture of dimer and trimer; R_F = CF(CF₃)OC₃F₇ (R_F-(VM) _n -R_F); Mn = 780] was synthesized by reaction of fluoroalkanoyl peroxide with the corresponding monomer according to our previously reported method.¹² Aluminum crucibles (40 μl; Material No: 27311) was purchased from Mettler-Toledo Co., Ltd. (Tokyo, Japan).

Preparation of the fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/Cell-fiber-MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu]

A typical procedure for the preparation of R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites is as follows: To methanol solution (5.0 ml) containing fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R_F-(CH₂-CHSi(OMe)₃) _n -R_F: n = 2, 3; R_F = CF(CF₃)OC₃F₇: R_F-(VM) _n -R_F] (50 mg) was added Cellu-fiber- MeGlu (10 mg). The mixture was stirred with a magnetic stirring bar at room temperature for 10 min. 25 wt % aqueous ammonia solution (2.0 ml) was added to this mixture, and successively was stirred at room temperature for 5 hr. After the removal of solvent, the obtained product was dried under vacuum at 50°C for 1 day to afford the expected product [54 mg; isolated yield based on the used oligomer (50 mg) and Cellu-fiber- MeGlu (10 mg): 90%]. The material loss (6 mg) would be due to the recovery process of the expected composites. Other composites were also prepared under similar conditions. The results are demonstrated in Table 1.

Table 1.

Preparation of R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites and R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites.

Run	Cellu-fiber-MeGlu (or Cellu-fiber-ImDia) (mg)	Product Yield^a (%)
	Cellu-fiber- MeGlu
1	10	90
2	20	79
3	30	85
4	40	89
	Cellu-fiber- ImDia
5	10	80
6	20	68
7	30	72
8	40	56
9	50	71
10	100	78
11	150	76

^a Yield was based on oligomer and Cellu-fiber- MeGlu (or Cellu-fiber- ImDia ).

Contact angle measurements of dodecane and water on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu composite powders surface

The R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (2 mg) were added into the aluminum crucible (volume: 40 μl). The contact angles of dodecane and water were measured by the deposit of each droplet (2 μl) on the composite powders surface at room temperature. The contact angle measurements of dodecane and water on the other composite powders surface were conducted under the similar conditions.

Removal of aromatic compounds from aqueous methanol solution by using the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-ImDia composites

R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites (20 mg) and bisphenol AF (160 mg/dm³) were added in aqueous methanol solution [5 ml: H₂O/MeOH: 94/6 (vol/vol)] and successively stirred with a magnetic stirring bar at room temperature for 1 day. After stirring, the composite powders in the mixture were separated by using the membrane filter to isolate the transparent aqueous methanol solution. The residual bisphenol AF in this solution was analyzed by UV-Vis spectra measurements. Residual amounts of the other aromatic compounds were also studied under similar conditions. The results are shown in Figures 7 –9.

Preparation of liquid marbles

Liquid marbles were prepared by rolling the liquid drops on the composite powders layer. The amount of all liquid drops was adjusted to 10 μL, and the liquid marbles thus obtained were transferred onto another substrate by careful manipulation with a micro spatula [see Figure 10-(a)].

Results and discussion

Preparation and surface wettability of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/Cellu-fiber- MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu ] and /Cellu-fiber- ImDia composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia ]

Sol-gel reaction of fluoroalkyl end-capped vinyltrimethoxysilane oligomer: R_F-(CH₂-CHSi(OMe)₃) _n -R_F: n = 2, 3; R_F = CF(CF₃)OC₃F₇: R_F-(VM) _n -R_F] proceeded under alkaline conditions in the presence of chemically modified cellulose fibers treated with N-methylglucamine units ( MeGlu ) [Cellu-fiber- MeGlu ] and treated with iminodiacetic acid units ( ImDia ) (Cellu-fiber- ImDia ) at room temperature to supply the corresponding fluorinated oligomeric silica/Cellu-fiber- MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu ] and /Cellu-fiber- ImDia composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia ], respectively. The results are shown in Figure 1 and Table 1.

Figure 1.

Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/Cellu-fiber- MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu ] and /Cellu-fiber- ImDia composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia ].

As shown in Figure 1 and Table 1, the expected composites were obtained in 56–90% isolated yields. FE-SEM (Field Emission Scanning Electron Microscopy) photographs of the composites (Runs 1 and 5 in Table 1) have been recorded in order to clarify the formation of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites. The results are illustrated in Figures 2 and 3.

Figure 2.

FE-SEM (Field Emission Scanning Electron Microscopy) pictures of pristine Cellu-fiber- MeGlu (a) and R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites (Run 1 in Table 1) (b), and EDX (Energy Dispersive X-ray) mapping micrograph of the fluorine atoms (c) and the silicon atoms (d) on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites [(b): Run 1 in Table 1].

Figure 3.

FE-SEM (Field Emission Scanning Electron Microscopy) pictures of pristine Cellu-fiber-ImDia (a) and R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites (Run 5 in Table1) (b), and EDX (Energy Dispersive X-ray) mapping micrograph of the fluorine atoms (c) and the silicon atoms (d) on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites surface [(b): Run 5 in Table 1).

Figures 2-(a) and 3-(a) show that the pristine Cell-fiber- MeGlu and Cell-fiber- ImDia consist of fibers with a length of ca. 500 µm and a width of ca. 100 μm, respectively. The R_F-(VM-SiO_3/2) _n -R_F/Cell-fiber- MeGlu composites and the R_F-(VM-SiO_3/2) _n -R_F/Cell-fiber- ImDia composites show that the R_F-(VM-SiO_3/2) _n -R_F oligomeric fine particles are uniformly coated on each Cell-fiber surface to provide the corresponding fluorinated oligomeric silica/Cell-fiber composites as illustrated in Figures 2-(b) and 3-(b).

In addition, we have measured the energy dispersive X-ray analyses (EDX) of these composites to verify the presence of the fluorinated oligomer in the composites. The results are shown in Figures 2-(c), -(d) and 3-(c), -(d). EDX measurements also show that the atomic contents of carbon, nitrogen, oxygen, fluorine, and silicon related to the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites are as follows (see Table 2).

Table 2.

The atomic contents of carbon, nitrogen, oxygen, fluorine, and silicon of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites (Run 1 in Table 1) and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites (Run 5 in Table 1).

Atomic contents (atm, %)
	C	N	O	F	Si
R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites
	56.9 ± 0.0	4.5 ± 0.3	21.0 ± 0.1	15.7 ± 0.1	1.9 ± 0.0
(Pristine Cellu-fiber- MeGlu )
	(62.2 ± 0.0	9.9 ± 0.6	27.9 ± 0.2	—	—
R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites
	58.9 ± 0.0	5.5 ± 0.4	23.8 ± 0.1	10.7 ± 0.1	1.0 ± 0.0
(Pristine Cellu-fiber- ImDia )
	(57.2 ± 0.0	3.9 ± 0.4	39.0 ± 0.1	—	—

EDX mapping micrographs on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites (Run 1 in Table 1) and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites (Run 5 in Table 1) show that fluorine (green-colored area) and silicon (blue-colored area) related to the fluorinated oligomer in the composites are uniformly dispersed on the Cellu-fiber- MeGlu or Cellu-fiber- ImDia surface [see Figures 2-(c), -(d) and 3-(c), -(d)]. Additionally, the content values of fluorine (15.7 and 10.7 atm %) and silicon (1.9 and 1.0 atm %) also indicate the presence of fluorinated oligomeric silica particles in the composites (see Table 2).

Next, we tried to study on the surface wettability of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders and the R_F-(VM-SiO_3/2) _n -R_F/Cellu- ImDia composite powders depicted in Table 1 through the dodecane and water contact angle measurements. The results are shown in Table 3.

Table 3.

Dodecane and water contact angle values on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders surface and the R_F-(VM-SiO_3/2) _n -R_F/Cellu- ImDia composite powders surface.

Run^a Contact angle (Degree)
Feed ratio (mg/mg)		Dodecane	Water
Pristine Cellu-fiber- MeGlu		0	0	—
1	50/10	180	180
2	50/20	180	180
3	50/30	180	180
4	50/40	180	180
Pristine Cellu-fiber- ImDia		0	0	—
5	50/10	180	180
6	50/20	180	180
7	50/30	180	180
8	50/40	180	180
9	50/50	180	180
10	50/100	180	180
11	50/150	180	180

^a Each Run No. corresponds to that of Table 1.

As shown in Table 3, dodecane and water contact angle values of the pristine Cellu- MeGlu and Cellu- ImDia are 0 degree, respectively, in each case. However, we cannot deposit dodecane and water droplets on each R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders surfaces in Table 3. In fact, as shown in Figure 4, the dodecane and water droplets were not placed on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powder surface (Run 9 in Table 3), due to the superamphiphobic (superoleophobic/superhydrophobic) characteristic even after the pull-up process of the needlepoint from surface [see Figure 4-(b) and -(d); in these cases, we defined that such wettability corresponds to the superamphiphobic surface (water and dodecane contact angle values are 180 degrees, respectively, for convenience)].

Figure 4.

Photograph of the water and dodecane droplets on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (Run 9 in Table 3); (a) and (c) correspond to water and dodecane droplets, respectively; (a): water and (c): dodecane droplets on the needlepoint; (b) and (d): pull-up of needlepoint from the composite powders surface.

Heretofore, it is well-known that the fabrication of superamphiphobic surface can be realized by lowering the surface energy and enhancing the surface roughness.^13-19 Thus, it is suggested that such surface wettability can be realized by enhancing the surface roughness, of whose surface would be easily prepared through the sol-gel process of the present R_F-(VM) _n -R_F oligomer illustrated in Figure 1. Especially, the Cellu-fibers are very convenient for the architecture of such roughness surface owing to their micrometer-size controlled fibers, and the longer fluoroalkyl groups on the Cell-fiber composite surface [see EDX mapping illustrated in Figures 2-(c) and 3-(c)] should enable each composite powder to create the superamphiphobic characteristic, due to the good surface arrangement ability of fluoroalkyl group on the composite surface.

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites to the separation of the mixture of hydrocarbon oil and fluorocarbon oil

In order to clarify such unique wettability (superamphiphobic property) related to the present fluorinated composites, we tried to apply the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (Run 10 in Table 1) to the packing material for the column chromatography to separate the mixture of hydrocarbon oil (dodecane) and fluorocarbon oil (perfluorohexane). The results are shown in Figure 5.

Figure 5.

Separation of the mixture (A) of blue-colored hydrocarbon oil (dodecane) and fluorocarbon oil (perfluorohexane) by using the pristine Cellu-fiber- ImDia powders (B) and the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (Run 10 in Table 1) (C) as packing materials, respectively.

As shown in Figure 5-(C), it was verified that the present R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders are effective for the separation of the mixture of blue-colored hydrocarbon oil (dodecane) and fluorocarbon oil (perfluorohexane) [see Figure 5-(A)] to isolate the transparent colorless fluorocarbon oil; although we failed to separate the mixture of hydrocarbon oil and fluorocarbon oil by using the original Cellu-fiber- ImDia powders as the packing material depicted in Figure 5-(B). This finding is due to the effective fluorophilic – fluorophilic interaction between the longer fluoroalkyl groups in the composites and the fluorocarbon oil, because the present composites can exhibit a superamphiphobic characteristic on the composite surface.

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites to the removal of organic aromatic compounds from aqueous methanol solutions

In this way, it was clarified that the present fluorinated composite powders can provide the superamphiphobic (superoleophobic and superhydrophobic) property on the composite surface. Such unique wettability would enable the present composites to interact predominately with fluorinated organic molecules in aqueous solutions. Thus, we tried to study on the removal ability of fluorinated aromatic compounds from aqueous methanol solutions by using the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders possessing the superamphiphobic characteristic. We have also tried to study on the removal of the corresponding non-fluorinated ones under similar conditions, for comparison. Schematic outline for the removal process of fluorinated aromatic compounds by using the composite powders is illustrated in Figure 6.

Figure 6.

Schematic outline for the analysis of the removal ratio of aromatic compounds by the use of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (20 mg) (Runs 5, 9, and 11 in Table 1) and the pristine Cellu-fiber- ImDia powders (20 mg) from aqueous methanol solutions [5 mL: H₂O/MeOH = 94/6 (vol/vol)].

Firstly, we tried to study on the removal ability of bisphenol AF(BPAF) and bisphenol A (BPA) by the use of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (Run 11 in Table 3) at room temperature based on the process shown in Figure 6. The results are shown in Figure 7.

Figure 7.

UV-vis spectra of BPAF (101 mg/dm³)[(A) and (B)] and BPA (50 mg/dm³) [(C) and (D)] in aqueous methanol solutions [5 ml: H₂O/MeOH (94/6 (vol/vol)) in the presence of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (20 mg: Run 11 in Table 3); (A) and (C): in the absence of the composites; (B) and (D): in the presence of the composites.

As shown in Figure 7, UV-vis spectra show that the effective decrease of the absorbance related to BPAF and BPA can be observed by the addition of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites. Especially, more effective decrease of the absorbance was observed in the case of BPAF. Similarly, the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites can decrease the absorbance of 2’, 3’, 4’, 5’, 6’-pentafluoroacetophenone (PF-AP) effectively, compared to that of AP as depicted in Figure 8.

Figure 8.

UV-vis spectra of PF-AP (10 mg/dm³) [(A) and (B)] and AP (10 mg/dm³) [(C) and (D)] in aqueous methanol solutions [5 ml: H₂O/MeOH (94/6 (vol/vol)) in the presence of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (20 mg: Run 11 in Table 3); (A) and (C): in the absence of the composites; (B) and (D): in the presence of the composites.

We have studied on the removal ability of these aromatic compounds by using some of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites in Table 1 under similar conditions. The results are summarized in Figure 9.

Figure 9.

Removal ratio (%) of BPAF and BPA [see (a)] and PF-AP and AP [see (a)] in aqueous methanol solutions by using the pristine Cellu-fiber- ImDia and the R_F-(VM-SiO_3/2) _n -R_F /Cellu-fiber- ImDia composite powders (Runs 5, 9 and 11 in Table 3). *Each Run No. corresponds to that of Table 3.

Figure 9 shows that each R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite can exhibit a good removal ability for the aromatic compounds illustrated in Figure 6, and a higher removal ability was observed in the fluorinated aromatic compounds (BPAF and PF-AP), not the corresponding non-fluorinated ones (BPA and AP) in each case. Especially, the composites (Run 5), which were prepared under a greater feed ratio of oligomer in oligomer/Cellu-fiber- Dia , were found to afford the highest ability for the removal of fluorinated aromatic compounds from aqueous methanol solutions. This finding is due to the effective fluorophilic – fluorophilic interaction between the fluorinated oligomer in the composites and the trifluoromethyl units in BPAF or the pentafluorobenzene units in PF-AP in aqueous methanol solutions, because the present composites can provide a superoleophobic/superhydrophobic (superamphiphobic) characteristic on each composite powder surface illustrated in Table 3.

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu composites and -I mDia composites to the fabrication of liquid marbles

Hitherto, it is well-known that the rolling of a hydrophilic liquid drop on a hydrophobic powder layer makes it possible to prepare a liquid marble, of whose powder can self-assemble at the liquid-air interface.^20-23 Liquid marbles are in general millimeter-sized liquid drops, and there has been a great interest in liquid marbles, due to their high potential application into numerous fields such as sensors, microfluidics, and material delivery carriers.^24-32 Therefore, it is suggested that our present fluorinated composite powders possessing a superamphiphobic property enwrapping the water drop or the traditional oil drops would allow the fabrication of not only water marble but also oil marbles. From the applicable point of view of the present fluorinated composites possessing a superamphiphobic characteristic, it is of particular interest to fabricate liquid marbles by using the present fluorinated composite powders. Firstly, we tried to study on the fabrication of water marble stabilized by the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (Run 1 in Table 3), of whose fabrication process is due to the rolling of water drop on the solid substrate covered with the layer of the corresponding powders [see Figure 10-(a)], and the results are shown in Figure 10-(b).

Figure 10.

Fabrication process of water marble by using the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (Run 1 in Table 3): (a), photograph of 10–100 µL composite powders–coated water marbles: (b), and photograph of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (Run 1 in Table 3)–coated water marble on the air-water interface: (c); (I): water marble on the micro spatula; (II): water marble on the air-water interface.

As shown in Figure 10-(b), we have succeeded in the fabrication of several kinds of water marbles coated with the composite powders by rolling the water drops (water volumes: 10 ∼ 100 μL) on the layer of white-colored composite powders. Interestingly, our present composite powders (Run 1 in Table 3)-coated water (volume: 10 μL) marble was found to be stable enough on the air-water interface illustrated in Figure 10-(c).

Similarly, the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders possessing a similar wettability (Run 11 in Table 3) were effective for the fabrication of 20 ∼ 100 µL water marble coated by the corresponding powders as shown in Figure 11.

Figure 11.

Photograph of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composite powders (Run 11 in Table 3)–coated water marbles.

As indicated above, our present composite powders can exhibit not only a superhydrophobic but also superoleophobic property on their surface. Thus, it is suggested that the present composite powders should be applicable to the fabrication of several type of oil marbles. In fact, we have succeeded in the fabrication of stable liquid marbles from oil drops such as glycerine, ethylene glycol and dodecane by using the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (Run 1 in Table 3) as shown in Figure 12.

Figure 12.

Photograph of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composite powders (Run 1 in Table 3)-coated glycerine, ethylene glycol, and dodecane marbles; Glycerine was colored with acid blue 112 and ethylene glycol was colored with PS Red G.

Conclusions

R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- MeGlu composites and R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites were prepared by the sol-gel reactions of the corresponding oligomer in the presence of the Cellu-fiber- MeGlu and Cellu-fiber- ImDia under alkaline conditions at room temperature, respectively. These composite powders thus obtained were found to exhibit a superamphiphobic characteristic on the composite powders surface. The fluorinated composite powders possessing such unique wettability were applied to the separation of the mixture of hydrocarbon and fluorocarbon oils to isolate the transparent colorless fluorocarbon oil. In addition, a higher removal ability of fluorinated aromatic compounds than that of the corresponding non-fluorinated ones from aqueous methanol solutions was observed by using the present composite powders. Interestingly, it was clarified that a superamphiphobic characteristic related to the present composite powders enables the present composites to fabricate not only water marble but also several type of oil marbles. Therefore, our present fluorinated Cellu-fiber composites will have high potential application to the development of novel fluorinated composite materials imparted by such unique superamphiphobic characteristic.

Footnotes

Acknowledgment

The authors are sincerely grateful to Chubu Chelest Co., Ltd. (Mie, Japan) for supplying Cellu-fiber- MeGlu and Cellu-fiber- ImDia .

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partially supported by a Grant-in-Aid for Scientific Research 19K05027 from the Ministry of Education, Science, Sports, and Culture, Japan.

ORCID iD

Hideo Sawada

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Preparation and applications of fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/chemically modified cellulose fibers composites

Abstract

Keywords

Introduction

Experimental

Measurements

Materials

Preparation of the fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/Cell-fiber-MeGlu composites [RF-(VM-SiO3/2) n -RF/Cellu-fiber-MeGlu]

Contact angle measurements of dodecane and water on the RF-(VM-SiO3/2) n -RF/Cellu-fiber-MeGlu composite powders surface

Removal of aromatic compounds from aqueous methanol solution by using the RF-(VM-SiO3/2) n -RF/Cellu-fiber-ImDia composites

Preparation of liquid marbles

Results and discussion

Application of the RF-(VM-SiO3/2) n -RF/Cellu-fiber- ImDia composites to the separation of the mixture of hydrocarbon oil and fluorocarbon oil

Application of the RF-(VM-SiO3/2) n -RF/Cellu-fiber- ImDia composites to the removal of organic aromatic compounds from aqueous methanol solutions

Application of the RF-(VM-SiO3/2) n -RF/Cellu-fiber-MeGlu composites and -I mDia composites to the fabrication of liquid marbles

Conclusions

Footnotes

Acknowledgment

Declaration of conflicting interests

Funding

ORCID iD

References

Preparation of the fluoroalkyl end-capped vinyltrimethoxysilane oligomeric silica/Cell-fiber-MeGlu composites [R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu]

Contact angle measurements of dodecane and water on the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu composite powders surface

Removal of aromatic compounds from aqueous methanol solution by using the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-ImDia composites

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites to the separation of the mixture of hydrocarbon oil and fluorocarbon oil

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber- ImDia composites to the removal of organic aromatic compounds from aqueous methanol solutions

Application of the R_F-(VM-SiO_3/2) _n -R_F/Cellu-fiber-MeGlu composites and -I mDia composites to the fabrication of liquid marbles