Poly(vinyl

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Ultrasound Responsive Behavior of Gelatinous Ionic Liquid-Poly(vinyl alcohol) Composites Kai Li, Sarara Noguchi, and Takaomi Kobayashi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b02264 • Publication Date (Web): 29 Aug 2016 Downloaded from http://pubs.acs.org on August 30, 2016

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Industrial & Engineering Chemistry Research

Ultrasound Responsive Behavior of Gelatinous Ionic Liquid-Poly(vinyl alcohol) Composites Kai Li, Sarara Noguchi, Takaomi Kobayashi*

Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata, 940-2188, Japan

*

Corresponding Author: E-mail: [email protected].

ABSTRACT Poly(vinyl alcohol)/ionic liquid (PVA/[BMI]Cl) gelatinous composites were prepared and used to study ultrasound (US) responsive behavior in the shear viscosity, viscoelasticity and FT-IR spectra before and after 43 kHz US exposure. PVA with different molecular weights were mixed with imidazole ionic liquid in aqueous solution to form the gelatinous complex. The shear viscosity and viscoelasticity of PVA/[BMI]Cl composites decreased under US exposure and increased gradually to the original value after removing the US exposure. The FT-IR results showed that the US enhanced the intensities of OH stretching region in 3000-3600 cm-1. Two-dimensional correlation spectroscopy and the deconvolution of the FT-IR spectra suggested that the US exposure 1

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deformed hydrogen bonds in the composites of the PVA/[BMI]Cl. These results showed that hydrogen bonds formed between [BMI]Cl and PVA were broken by the US exposure. As a result, the composites of PVA/[BMI]Cl could respond to US exposure.

INTRODUCTION Ionic liquid (IL) has attracted attention for decades, because IL behaves as liquid under the temperature below 100 °C.1, 2 Since the unique properties of negligible vapor pressure, negligible flammability, high conductivity and high thermal stability of ILs,1 ILs are regarded as “designer solvent” or “green solvent”. In addition, the possibility of combining different cations and anions in ILs structures endows ILs specific properties for different purposes. Therefore, ILs have been used as interesting materials in various fields, such as reaction medium,2 catalyst in organic reaction,3 electrolyte in electrochemistry,4 and in polymer science.5 Among above applications, polymer in IL medium attracts increasingly interests recently. Since the fascinating properties of ILs and polymer materials,6 polymer/IL binary composite provided a unique platform for designing materials.7, 8 Polymer/IL binary composite combines the distinguish properties of polymer and IL together, which was valuable in the materials science. Incorporating the IL into the polymer networks can 2


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provide conductivity and enhancement of chemical and mechanical properties of the polymers. One of the polymer/IL binary composites is iongel, which is made from swelling the polymeric network in an IL medium.9,

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Compared with the organic

solvent-based electrolyte, iongel is nonvolatile with thermal stability and high electro conductivity.9, 10 Besides, such iongel could be used as polymer electrolyte

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and

dielectrics in organic thin film transistors.12 Another polymer-IL binary is utilizing IL as plasticizer for polymers, such as poly(ethylene oxide),13 poly(vinylidene fluoride)14 and poly(vinyl alcohol) (PVA).15 In these binary polymer/ILs composites, PVA having OH side groups and hydrophilic nature acts as a promising candidate to form polymer/IL composites. Saroj et al reported 1-ethyl-3-methylimidazolium ethylsulfate/PVA complex based polymer electrolytes.16 The thermal, dielectric and conductive properties were strongly depended on the IL concentration in the composite. Paţachia investigated the hydrogel behavior of PVA and 1-butyl-3-methylimidazolium tetrafluoroborate.17 Liew and co-works revealed that polymer electrolytes made of PVA and 1-butyl-3-methylimidazolium chloride ([BMI]Cl) had excellent thermal characteristics.18, 19 The PVA/IL composites had the potential to be used as polymer electrolyte in fuel cells and supercapacitors. Here, hydrogen bonds between the PVA and IL behaved as an important driving force in the

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complex. Therefore, it would be attractive to control the hydrogen bonding by external stimulus like ultrasound (US). More recently, US effect on aqueous ILs was investigated and revealed that the US acted as an environmental trigger to influence the hydrogen bonds.20 Similar experiments were described in aqueous polymer solution,21 slurry,22 and poly(ionic liquid).23 Especially, US could break hydrogen bonds in aqueous IL solution with different counter anions.20 Recently, Yuan et al investigated the influence of US on the gelation behavior of poly(vinylidenefluoride-co-hexafluoropropylene) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.24 However, the report on the US effect on the properties of polymer/IL binary composite is still rare. In the present work, the US responsive behavior of the polymer/IL binary composite was focused in PVA/[BMI]Cl composites (Figure 1a). Atamas et al reported that Cl- anion of IL played an important role in forming hydrogen bond and suggested Cl-···OH formed strong hydrogen bond for imidazolium IL with Cl- anion.25 Therefore, the hydrogen bonds between PVA and the Cl- of [BMI]Cl could be formed as shown in scheme 2, meaning that PVA/[BMI]Cl can form gelatinous composites. The present work investigated the effect of US on PVA/[BMI]Cl properties of shear viscosity, viscoelasticity and FT-IR spectroscopy under the US exposure.

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EXPERIMENTAL SECTION Materials.

All reagents were used directly after purchasing without any further

purification. Table 1 lists the information of the PVAs used in the present study. Four PVAs with different molecular weights of 13000-23000, 31000-50000, 88000 and 146000-180000 (Table 1) were named as PVA13, PVA31, PVA217 and PVA117, and their hydrolysis degrees were 87%, 87%, 80% and 98-99%, respectively. PVA13, PVA31 and PVA117 were purchased from Sigma-Aldrich (USA). PVA217, 1-methylimidazole (98%) and 1-chlorobutane (98%) were purchased from TCI Co., Ltd. (Japan).

1-butyl-3-methylimidazole

chloride

([BMI]Cl)

was

prepared

with

1-methylimidazole and 1-chlorobutane as reported previously.26 The structure of [BMI]Cl was confirmed by 1H NMR (400 MHz, D2O), δ 8.69 (s, 1H), 7.45 (s, 1H), 7.41 (s, 1H), 4.18 (t, 2H), 3.87 (s, 3H), 1.90-1.71 (m, 2H), 1.37-1.21 (m, 2H), 0.90 (t, 3H). The aqueous PVA and [BMI]Cl solution were mixed with stirring, and then, water was vapored through heating at 110 °C in the air for 2 days. After this process, the samples were dried in vacuum at 80 °C for 24 h until the constant weight. Then gelatinous viscous liquid was formed as shown in Figure 1b.

Shear viscosity measurement in the absence and presence of US The shear viscosity was measured using a rheometer (Physica MCR 301, Anton Paar)

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as illustrated in Scheme 1a. Here, the round ultrasound water bath (Φ: 86 mm with 65 mm depth) having a transducer (Honda Electronics Co., Ltd.), which was directly attached to the stage of the rheometer, was used. The shear viscosity was tested in the absence and presence of US with the PP25-cone (Φ: 25 mm). The water bath temperature was maintained at 25 °C by flowing water with thermostat (Ecoline E100, Lauda-Brinkmann, LP). The sample of PVA/[BMI]Cl composite (weight ratio of PVA/[BMI]Cl = 1:5) was added on the plate and exposed by 43 kHz US with the power of 12.5 W for 5 min. The gap between the cone and the plate was fixed at 1.0 mm. The shear viscosity was measured continuously in the absence and presence of the US every 10 second. Each sample was exposed by US for three times and observed the change of shear viscosity.

Viscoelasticity measurement in the absence and presence of US The viscoelasticity of PVA/[BMI]Cl composites in the presence and absence of US was tested using a rheometer (Physica MCR 301, Anton Paar) as showed in Scheme 1a with the PP25-cone (Φ: 25 mm), which was similar with the setup in the shear viscosity. A constant frequency of 1 Hz and constant strain of 1 % were applied in these experiments. The sample of PVA/[BMI]Cl composite (PVA/[BMI]Cl = 1:5) was added on the plate and exposed by 43 kHz US with the power of 12.5 W at 25 °C for about 5 6


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min and then stopped the US exposure. Here, the gap between the cone and the plate was 1.0 mm. The process was repeated for three times. The storage moduli G' and loss moduli G'' were recorded continuously with and without US exposure every 10 second.

Determination of FT-IR spectra for the US effect FT-IR spectra were recorded using a JASCO FT-IR/4100 spectrometer before and after the US exposure. In these experiments, two CaF2 plates with diameter of 30 mm and thickness of 2 mm (Pier Optics Co. Ltd.) were used for making PVA/[BMI]Cl samples. The details of the FT-IR measurement were reported previously.27, 28 As shown in Scheme 1b (upper), the PVA/[BMI]Cl composite was put on a CaF2 plate and covered with another one. The samples were sealed with Teflon tape (0.1 mm × 13 mm, Sanyo, Japan) to prevent water penetration into the sample, when it was put in US water bath (Scheme 1b, bottom). After the sample was immersed in the water bath, it was exposed by 43 kHz US with 50 W for 1, 3, 5 and 10 min. The temperature of water bath was controlled at 25 °C using water circulation with thermostat (Lauda ecoline E100). After US exposure, FT-IR spectra were recorded immediately with a 4 cm-1 spectral resolution. For peak deconvolution, the FT-IR spectra were fitted with Gaussian function using Origin software.

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Two-dimensional (2D) correlation analysis Two-dimensional correlation method, which has been used in many different spectroscopies, such as FT-IR, Raman, UV-vis, chromatography, NMR and so on,29-31 was useful for analyzing the interaction between different compounds.32, 33 Through 2D correlation analysis in FT-IR spectra.30 2D synchronous and 2D asynchronous maps could be obtained. In the 2D correlation maps, autopeaks and cross-peaks were able to analyze the different interaction for the sample. In the present study, generalized 2D correlation analysis of FT-IR spectra with different US exposure time was carried out by using the software “2D shige” (Shigeaki Morita, Kwansei-Gakuin University, Japan) for the PVA/[BMI]Cl sample. The FT-IR spectra before and after US exposure were smoothed and baseline corrected using the software (Spectra Manager 2.0) in the FT-IR equipment. Moreover, the 2D correlation maps were drawn with Origin software. In the 2D maps, the shaded areas were defined as the negative correlation intensities, and the unshaded area represented the positive correlation intensities.

RESULTS AND DISCUSSION Effect of US on the shear viscosity and viscoelasticity of PVA/[BMI]Cl composites US effect on the shear viscosity of PVA/[BMI]Cl composites was studied in the absence and presence of US exposure as illustrated in Scheme 1a. Figure 2 shows the change of the shear viscosity of the PVA/[BMI]Cl composites containing different 8


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molecular weights of PVA with and without US exposure. Here, US power was 12.5 W with 43 kHz frequency. It was seen that the shear viscosity of four PVA/[BMI]Cl composites decreased under the US exposure and returned to the original values after removing the US exposure within about 5 min. After the values of shear viscosity returned to the original ones, the composites were exposed to the US for a second and third time. The similar change on shear viscosity was observed. These three cycles indicated that US changed the shear viscosity of the PVA/[BMI]Cl periodically and the PVA/[BMI]Cl composites responded to the US exposure. Moreover, the value of shear viscosity increased with the increasing of molecular weight (Mw). And the decrements of the shear viscosity are bigger for the composites made from low Mw PVAs such as PVA13 and PVA31 as compared with the result of composites made from high Mw PVA of PVA117 and PVA 217. It was reported that the change of shear viscosity reflected the change of hydrogen bonds in the system.27, 28 Therefore, it was concluded that the US influenced the hydrogen bonds in the PVA/[BMI]Cl composites. The effect of the US on the viscoelasticity is shown in Figure 3. In Figure 3(a), it was seen that the storage moduli G' and loss moduli G'' decreased for four PVA/[BMI]Cl composites under the US exposure. Moreover, the values the G' and G'' returned to the original ones after stopping the US exposure. This phenomenon was seen

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in the second and third cycles, which indicated that the PVA/[BMI]Cl composites responded to the US exposure. Moreover, the value of G' and G'' increased with the increasing of Mw. On the basis of change in the PVA molecular weight, the viscoelasticity data suggested that higher Mw of the composites had larger G', meaning the gelatinous condition was more stable, while lower Mw showed a flow liquid. As it was well known that, Tan δ = G''/G', reflected the gelatinous property of the material. The change of Tan δ in the presence and absence of US is plotted in Figure 3(b). It was seen that the value of Tan δ for PVA217/[BMI]Cl and PVA117/[BMI]Cl composites were smaller than 1, meaning that the PVA217/[BMI]Cl and PVA117/[BMI]Cl composites behaved more like a gel other than a liquid. Whereas the value of Tan δ for PVA13/[BMI]Cl and PVA31/[BMI]Cl became larger than 1, indicating that the behavior of the PVA13/[BMI]Cl and PVA31/[BMI]Cl composites was like a liquid. These were reflected from the viscosity values of the four composites in Figure 2. On the other hand, the value of Tan δ increased under the US exposure and returned to the original values after stopping US exposure. The changed pattern was observed in the second and third cycles, which means the PVA/[BMI]Cl composites response to the US exposure. The increase in value of Tan δ under US exposure indicated these four composites behaved much more like a liquid under the US exposure, which could be explained by the

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breakage of hydrogen bonds in the composites under the US exposure. These results were consistent with the results of shear viscosity change.

Effect of US on FT-IR spectra of PVA/[BMI]Cl composites. In order to investigate the US effect in the view of the chemical change in the PVA/[BMI]CL composites, FT-IR spectroscopy was applied. Figure 4 compares FT-IR spectra of PVA13, [BMI]Cl and their composites containing PVA/[BMI]Cl with different weight ratio of 1:1, 1:5 and 1:10. In the spectrum of [BMI]Cl, the characteristic bands of CH in the imidazole ring are 3137 cm-1 (C4(5)-H) and 3051 cm-1 (C2-H).34 As seen, the broaden band at 3000-3700 cm-1 belonged to OH stretching. In the PVA spectrum (bottom), the broaden band of OH stretching in the range of 3000-3600 cm-1 was observed. The CH band at 2700-3000 cm-1 also appeared. After mixing PVA with [BMI]Cl together at PVA/[BMI]Cl =1:10, it was seen that the CH band peak, which centered at 3051 cm-1 and 3137 cm-1 in pure [BMI]Cl, was shifted toward the higher wavenumber of 3097 cm-1 and 3149 cm-1, respectively. Moreover, with the increasing of the PVA content in the composites, these two peaks shifted toward longer wavenumber region. For the pure [BMI]Cl, the imidazolium cation and Cl- anion are strong hydrogen bonded, while the addition of PVA disrupted the hydrogen bonding network in pure [BMI]Cl and hydrogen bonds formed between [BMI]Cl and PVA. Moreover, with the 11



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increasing of PVA content, which can be treated as a dilute process for [BMI]Cl, the stretching of C-H blue shifted to higher wavenumber. Similar blue shifted of C-H stretching phenomena was observed by Zhang et al.35 In their study, the increased in wavenumber of C-H stretching was observed while dilute ionic liquid with water, since the formation of hydrogen bond between water and ionic liquid. Therefore, the shift of the CH stretching in the imidazole ring was caused by the formation of C-H…O hydrogen bond.34-36 The same tendency was observed in the PVA31/[BMI]Cl, PVA217/[BMI]Cl, and PVA117/[BMI]Cl. These strongly suggested that hydrogen bonds between PVA and [BMI]Cl were formed after mixing them together. From the results of the shear viscosity and viscoelasticity, it was concluded that the US broke the hydrogen bonds in the PVA/[BMI]Cl composites. In order to confirm the results of the shear viscosity and viscoelasticity change, the FT-IR spectra before and after the US exposure were recorded. Here, these PVA/[BMI]Cl composites were exposed to the US for 1-10 min. As shown in Figure 5, FT-IR spectra of the PVA13/[BMI]Cl with different content of PVA were measured before and after the US exposure. In addition, the results of PVA31, PVA217, and PVA117 were compared in Figure 6, when PVA/[BMI]Cl=1:5. From the results of Figure 5, it was seen that with the increasing of the PVA13 content in the composites, OH band became broader in the

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region of 3000-3700 cm-1. In addition, after the US exposure, the OH band intensities were enhanced relative to the result before US exposure. The intensities increased as the increasing of the exposure time from 1 to 10 min. In the PVA/[BMI]Cl composite, the spectra of OH stretching band in 3200-3700 cm-1 indicated that the OH groups can be divided into free OH groups and bonded OH groups. The enhancement of OH stretching after US exposure meant that the increasing of the OH components groups was resulted in the US exposure. Therefore, the hydrogen bonds formed in PVA/[BMI]Cl were broken by US exposure. The strong electron-withdrawing properties of the O atom of PVA and the Cl counter anion of the [BMI]Cl made them easy to form hydrogen bonds with hydrogen atoms in the OH groups of PVA. As illustrated in Scheme 2a, different pairs of hydrogen bonds were formed in the PVA/[BMI]Cl. The intensities enhancement in the O-H stretching region indicated that the hydrogen bonds in the PVA/[BMI]Cl composites were broken by the US exposure. In the composites, additionally, there are other possibilities of PVA and [BMI]Cl interactions, which reflect on the spectra. It might be due to the transition of hydrogel from kosmotropic state to chaotropic state, which was caused by temporary distance between water and the PVA backbone.37 The dehydration might be also influenced in the spectra change after US exposure. Actually, Venegas-Sanchez et al reported US

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effect on hydrogen bonds of aqueous PVAs.21 In addition, the aqueous [BMI]Cl has US response in the FT-IR spectra.20 Therefore, the change of spectra was cause by the change of hydrogen bond in the PVA/[BMI]Cl composites. Furthermore, as shown in Figure 5, the ratio of PVA and [BMI]Cl influenced the OH band enhancement after the US exposure. When the weight ratio of PVA and [BMI]Cl was changed to 1:5 and 1:10, similar enhancement of the OH stretching region in their spectra was observed (Figure 5 b and c). In order to compare these, the enhancement degree, It/I0, was measured at different US exposure time for different weight ratios (Figure 5d). Here, the I0 and It referred to the intensities of the OH stretching band before US exposure and after US exposure for t minutes, respectively. It showed that the larger change in the OH band intensities was observed in the ratio of 1:5. Similar experiments were conducted for other PVA/[BMI]Cl composites, namely PVA31/[BMI]Cl, PVA217/[BMI]Cl and PVA117/[BMI]Cl. Figure 6 shows the FT-IR results of three PVA/[BMI]Cl composites, after the 43 kHz US exposure from 1 to 10 min. Here, the weight ratio of PVA and [BMI]Cl in the composites was fixed at 1:5. It was seen that the intensities of OH stretching region were enhanced after US exposure, and the intensities increased with the increase of US exposure time as shown in Figure 7.

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It was appeared that the ratio of these three PVA/[BMI]Cl composites with different PVA contents was enhanced after the US exposure. The enhancement in the ratio was observed with the increasing of the US exposure time for these three PVA/[BMI]Cl composites. These results indicated that the US effect on these composites increased with the US exposure time. According to the studies before,21, 27 the intensified OH stretching indicated the breakage of hydrogen bonds in the composites by the US exposure. Therefore, it was concluded that the US exposure broke the hydrogen bonds in the PVA/[BMI]Cl composites. To evaluate the characteristics of wavenumber of each FT-IR peak in the spectra, 2D correlation was carried out. The FT-IR spectra of each PVA/[BMI]Cl composites, which was measured before and after the US exposure, were analyzed in the 2D correlation. Results of the synchronous maps and asynchronous maps are shown in Figure 8 in the range of 3200-3700 cm-1. In the synchronous map of the PVA13/[BMI]Cl (Figure 8a), one autopeaks of (3450, 3450), two cross-peaks of (3648, 3450) and (3580, 3450) were observed. In the asynchronous map of PVA13/[BMI]Cl (Figure 8b), four cross-peaks lied on (3648, 3450), (3580, 3450), (3529, 3410) and (3410, 3245), respectively. Because of the formation of hydrogen bonds between PVA13 and [BMI]Cl, the OH stretching band was broadened and overlapped to each

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other. Through analyzing the autopeaks and cross-peaks in the OH stretching band, it was seen that the OH band of PVA13/[BMI]Cl was split into six bands in the OH stretching region, namely 3245, 3410, 3450, 3529, 3580 and 3648 cm-1. In other PVA/[BMI]Cl composites, for PVA31/[BMI]Cl, the synchronous map (Figure 8c) had one autopeak of (3396, 3396) and two cross-peaks of (3648, 3396) and (3610, 3396). For the asynchronous map (Figure 8d), four cross-peaks at (3648, 3396), (3565, 3396), (3520. 3396) and (3287, 3396) were observed. For the PVA217/[BMI]Cl, the synchronous map (Figure 8e) contained one autopeak at (3396, 3396) and in the asynchronous map, five cross-peaks of (3648, 3396), (3615, 3396) and (3566, 3396), (3494, 3396) and (3283, 3396) were found in Figure 8f. In the synchronous map of PVA117/[BMI]Cl (Figure 8g), the autopeak was at (3396, 3396) and the three cross-peaks at (3647, 3396), (3610, 3396) and (3565, 3396) were obtained. In the asynchronous map of PVA117/[BMI]Cl (Figure 8h) was seen that the cross-peaks were observed at (3647, 3396) and (3565, 3396). As mentioned above, the breakage of hydrogen bonds in the composites was occurred after the US exposure. However, the OH stretching band was highly overlapped in the spectra of PVA and [BMI]Cl. Therefore, deconvolution of the FT-IR spectra was also conducted to analyze the change of each component. Here, the FT-IR

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spectra before and after US exposure were deconvoluted into Gaussian components based on their second derivatives, and combined with the results of 2D correlation analysis at the same time. Table 2 lists the peaks information of the fitting curves. Figure 9 shows the deconvolution results of the pure PVA films. According to the reports before,21 the peaks 1, 2, and 3 were assigned to the OH group of PVA hydrogen bonded with the neighbor OH groups, OH group of PVA hydrogen bonded with intermolecular crosslinking of the PVA segments and the free OH group, respectively, for 1, 2 and 3 (Scheme 2a). Moreover, for the PVA217, additional peak 4 was obtained from the deconvolution. On the basis of the results of the 2D correlation of PVA/[BMI]Cl composites, it was seen that there were six components involved in the overlapped OH stretching region. Figure 10 shows the deconvolution results for the FT-IR of the PVA/[BMI]Cl composite before and after the US exposure for 10 min. The peak assignment in Scheme 2a were listed as followed.21 Peak 1 belonged to the OH group hydrogen bonded with the neighbor OH group and the peak 2 for the OH group hydrogen bonded with intermolecular crosslink of PVA. Peak 3 referred to the free OH group and the peak 4 was the OH group hydrogen bonded with the Cl- anion of [BMI]Cl. Peak 5 and 6 belonged to the OH group hydrogen bonded with the C2-H and C4(5)-H in the

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imidazolium ring, respectively. As seen in Figure 10 a and b for the deconvolution results of PVA13/[BMI]Cl composite before and after the US exposure, FT-IR intensities of the peaks of 1, 2, 3, 4 and 5 were intensified after the US exposure. Especially, the observation of the peaks of 3, 4 and 5, implied that the US exposure broke hydrogen bonds between PVA13 and [BMI]Cl. As assigned above, these peaks belonged to the OH group hydrogen bonded with the neighbor OH group, intermolecular OH group, Cl- and C2-H of imidazolium ring. After the US exposure, the free OH groups were released from the breakage of hydrogen bonds, and this was reflected from the enhancement of the peak 3, which belonged to the free OH groups of the PVA. For the PVA31/[BMI]Cl (Figure 10 c and d) and PVA217/[BMI]Cl, similar change was observed for the fitting peaks. The peaks of 1, 2, 3 and 4 were intensified, whereas peaks of 5 and 6 decreased after the US exposure. These indicated that the hydrogen bonds were formed by the neighbor OH group (peak 1), OH groups between different PVA chains (peak 2), and the OH group with Cl- (peak 4) were broken by the US exposure. Deconvolution results of PVA117/[BMI]Cl composites in Figure 10 e and f showed that the peaks of 1, 2, 3 and 4 intensified after the US exposure. Especially in the peak 2,

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the intramolecular hydrogen bond was highly intensified. Peak 1 and 4 belonged to the hydrogen bond formed by the neighbor OH groups and the OH group with Cl-. These meant that the US broke these hydrogen bonds. Therefore, it was resulted in the enhancement of peak 3, which belonged to the free OH group. Moreover, it was noted that the US influenced the intermolecular hydrogen bonds. It was seen through the doconvolution results that the hydrogen bonds formed the neighbor OH groups, the OH groups in different PVA chains, and the OH group with the Cl- anion were easily influenced by the US exposure.

CONCLUSION In this study, US effect on the PVA/[BMI]Cl composites was investigated on the basis of shear viscosity, viscoelasticity and FT-IR spectroscopy. The shear viscosity of the PVA/[BMI]Cl complex decreased under US exposure and increased gradually to the original value. The viscoelastic behavior changed periodically in the absence and presence of US exposure. This meant that the US destroyed the gelatinous structure between PVA and the [BMI]Cl. The results of FT-IR showed that the intensities of OH stretching region were enhanced after the US exposure. These results showed that US exposure could break the hydrogen bonds in PVA/[BMI]Cl composites, and the hydrogen bonds formed by the neighbor OH groups, the OH groups in different PVA 19



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chains, and the OH group with the Cl- anion were easily influence by the US exposure.

REFERENCES (1) Welton, T., Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chem. Rev. 1999, 99, 2071-2084. (2) Hallett, J. P.; Welton, T., Room-temperature ionic liquids: Solvents for synthesis and catalysis. 2. Chem. Rev. 2011, 111, 3508-3576. (3) Liu, X.; Ma, H.; Wu, Y.; Wang, C.; Yang, M.; Yan, P.; Welz-Biermann, U., Esterification of glycerol with acetic acid using double SO3H-functionalized ionic liquids as recoverable catalysts. Green Chem. 2011, 13, 697-701. (4) Rupp, B.; Schmuck, M.; Balducci, A.; Winter, M.; Kern, W., Polymer electrolyte for lithium batteries based on photochemically crosslinked poly(ethylene oxide) and ionic liquid. Eur. Polym. J. 2008, 44, 2986-2990. (5) Winterton, N., Solubilization of polymers by ionic liquids. J. Mater. Chem. 2006, 16, 4281-4293. (6) Ueno, K.; Fukai, T.; Nagatsuka, T.; Yasuda, T.; Watanabe, M., Solubility of poly(methyl methacrylate) in ionic liquids in relation to solvent parameters. Langmuir 2014, 30, 3228-3235. (7) Lodge, T. P., A unique platform for materials design. Science 2008, 321, 50-51. (8) Freemantle, M., Designer liquids in polymer systems. Chem. Eng. News 2004, 82, 26-29. (9) Susan, M. A. B. H.; Kaneko, T.; Noda, A.; Watanabe, M., Ion gels prepared by in situ radical polymerization of vinyl monomers in an ionic liquid and their characterization as polymer electrolytes. J. Am. Chem. Soc. 2005, 127, 4976-4983. (10) He, Y.; Lodge, T. P., Thermoreversible ion gels with tunable melting temperatures from triblock and pentablock copolymers. Macromolecules 2008, 41, 167-174. (11) Ueki, T.; Watanabe, M., Macromolecules in ionic liquids: Progress, challenges, and opportunities. Macromolecules 2008, 41, 3739-3749. (12) Lee, J.; Panzer, M. J.; He, Y.; Lodge, T. P.; Frisbie, C. D., Ion gel gated polymer thin-film transistors. J. Am. Chem. Soc. 2007, 129, 4532-4533. (13) Singh, P. K.; Bhattacharya, B.; Mehra, R. M.; Rhee, H.-W., Plasticizer doped ionic 20


Page 21 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


liquid incorporated solid polymer electrolytes for photovoltaic application. Curr. Appl. Phys. 2011, 11, 616-619. (14) Guo, L.; Liu, Y.; Zhang, C.; Chen, J., Preparation of PVDF-based polymer inclusion membrane using ionic liquid plasticizer and Cyphos IL 104 carrier for Cr(VI) transport. J. Membr. Sci. 2011, 372, 314-321. (15) Yoon, J.; Lee, H.-J.; Stafford, C. M., Thermoplastic elastomers based on ionic liquid and poly(vinyl alcohol). Macromolecules 2011, 44, 2170-2178. (16) Saroj, A. L.; Singh, R. K., Thermal, dielectric and conductivity studies on PVA/Ionic liquid [EMIM][EtSO4] based polymer electrolytes. J. Phys. Chem. Solids 2012, 73, 162-168. (17) Paţachia, S.; Friedrich, C.; Florea, C.; Croitoru, C., Study of the PVA hydrogel behaviour in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. Express Polymer Letters 2011, 5. (18) Liew, C.-W.; Ramesh, S.; Arof, A. K., A novel approach on ionic liquid-based poly(vinyl alcohol) proton conductive polymer electrolytes for fuel cell applications. Int. J. Hydrogen Energy 2014, 39, 2917-2928. (19) Liew, C.-W.; Ramesh, S.; Arof, A. K., Good prospect of ionic liquid based-poly(vinyl alcohol) polymer electrolytes for supercapacitors with excellent electrical, electrochemical and thermal properties. Int. J. Hydrogen Energy 2014, 39, 2953-2963. (20) Li, K.; Kobayashi, T., A FT-IR spectroscopic study of ultrasound effect on aqueous imidazole based ionic liquids having different counter ions. Ultrason. Sonochem. 2016, 28, 39-46. (21) Venegas-Sanchez, J. A.; Tagaya, M.; Kobayashi, T., Ultrasound stimulus inducing change in hydrogen bonded crosslinking of aqueous polyvinyl alcohols. Ultrason. Sonochem. 2014, 21, 295-309. (22) Ngoc, N. L.; Kobayashi, T., Ultrasound stimulus effect on hydrogen bonding in networked alumina and polyacrylic acid slurry. Ultrason. Sonochem. 2010, 17, 186-192. (23) Li, K.; Kobayashi, T., Ultrasound response of aqueous poly(ionic liquid) solution. Ultrason. Sonochem. 2016, 30, 52-60. (24) Yuan, C.; Zhu, X.; Su, L.; Yang, D.; Wang, Y.; Yang, K.; Cheng, X., Preparation and characterization of a novel ionic conducting foam-type polymeric gel based on polymer PVdF-HFP and ionic liquid [EMIM][TFSI]. Colloid. Polym. Sci. 2015, 293, 1945-1952. (25) Atamas, N. A., Local structure of ionic liquid–monohydric alcohol solutions. J. Struct. Chem. 2016, 57, 121-127. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 37

(26) Dupont, J.; Consorti, C. S.; Suarez, P. A. Z.; Souza, R. F. d., Preparation of 1-butyl-3-methylimidazolium based room temperature ionic liquids. Org. Synth. 2002, 79, 236-239. (27) Venegas-Sanchez, J. A.; Tagaya, M.; Kobayashi, T., Ultrasound effect used as external stimulus for viscosity change of aqueous carrageenans. Ultrason. Sonochem. 2013, 20, 1081-1091. (28) Venegas-Sanchez, J. A.; Tagaya, M.; Kobayashi, T., Effect of ultrasound on the aqueous viscosity of several water-soluble polymers. Polym. J. 2013, 45, 1224-1233. (29) Noda, I., Generalized two-dimensional correlation method applicable to infrared, raman, and other types of spectroscopy. Appl. Spectrosc. 1993, 47, 1329-1336. (30) Noda, I.; Dowrey, A. E.; Marcoli, C.; Story, G. M.; Ozaki, Y., Generalized two-dimensional correlation spectroscopy. Appl. Spectrosc. 2000, 54, 236A-248A. (31) Noda, I., Progress in two-dimensional (2D) correlation spectroscopy. J. Mol. Struct. 2006, 799, 2-15. (32) Morita, S., Hydrogen-bonds structure in poly(2-hydroxyethyl methacrylate) studied by temperature-dependent infrared spectroscopy. Frontiers in Chemistry 2014, 2, 10. (33) Zhou, Y.; Zheng, Y.; Sun, H.; Deng, G.; Yu, Z., Hydrogen bonding interactions in ethanol and acetonitrile binary system: A near and mid-infrared spectroscopic study. J. Mol. Struct. 2014, 1069, 251-257. (34) Chang, H.-C.; Jiang, J.-C.; Chang, C.-Y.; Su, J.-C.; Hung, C.-H.; Liou, Y.-C.; Lin, S. H., Structural organization in aqueous solutions of 1-butyl-3-methylimidazolium halides: A high-pressure infrared spectroscopic study on ionic liquids. J. Phys. Chem. B. 2008, 112, 4351-4356. (35) Zhang, L.; Xu, Z.; Wang, Y.; Li, H., Prediction of the solvation and structural properties of ionic liquids in water by two-dimensional correlation spectroscopy. J. Phys. Chem. B 2008, 112, 6411-9. (36) Masunov, A.; Dannenberg, J. J.; Contreras, R. H., C-H bond-shortening upon hydrogen bond formation: Influence of an electric field. J. Phys. Chem. A. 2001, 105, 4737-4740. (37) Kudo, K.; Ishida, J.; Syuu, G.; Sekine, Y.; Ikeda-Fukazawa, T., Structural changes of water in poly(vinyl alcohol) hydrogel during dehydration. The Journal of Chemical Physics 2014, 140, 044909.

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(b)

Figure 1. (a) The structures of PVA and [BMI]Cl and (b) the picture of the PVA/[BMI]Cl gelatinous composites after placing upside down for 1h (PVA/[BMI]Cl =1:5).

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Table 1. PVA/[BMI]Cl composites used in the present study. . Weight ratio

PVA

Mn

Alcoholysis degree

PVA13

13000-23000

87%

1:1, 1:5, 1:10

PVA31

31000-50000

87%

1:1, 1:5, 1:10

PVA217

80000

80%

1:1, 1:5, 1:10

PVA117

146000-180000

98%

1:1, 1:5, 1:10

(PVA: [BMI]Cl)

24


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Scheme 1. Experimental setup for (a) measuring shear viscosity and (b) making sample preparation for the FT-IR spectra and US experiment.

25



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Figure 2. Shear viscosity change with and without US for PVA/[BMI]Cl composites. (The weight ratio of PVA and [BMI]Cl was 1:5).

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Figure 3. (a) Viscoelasticity and (b) tan δ change in the absence and presence US exposure for PVA/[BMI]Cl composites. (The weight ratio of PVA and [BMI]Cl was 1:5).

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Figure 4. FT-IR results for the [BMI]Cl, PVA and PVA13/[BMI]Cl composites.

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Figure 5. The FT-IR results for the PVA13/[BMI]Cl composites with different PVA13/[BMI]Cl ratios (a-c) and (d) the enhancement degree of these composites after US exposure for different time.

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Figure 6. The FT-IR results for the PVA/[BMI]Cl composites before and after US exposure for different time. (a): PVA31/[BMI]Cl, (b): PVA217/[BMI]Cl, (c) PVA117/[BMI]Cl)

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Figure 7. The enhancement degree of PVA/[BMI]Cl composites after US exposure for different time. (a) PVA/[BMI]Cl = 1:1, (b) PVA/[BMI]Cl = 1:5, and (c) PVA/[BMI]Cl = 1:10.

31



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Figure 8. Synchronous (a, c, e and g) and asynchronous (b, d, f and h) 2D correlation IR spectra of different PVA/[BMI]Cl composites.

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Table 2. Peaks center of the fitting curves. PVA Dry film [a]

PVA/IL composites before US

PVA/IL composites after US

PVA

PVA

PVA

PVA

PVA

PVA

PVA

PVA

PVA

PVA

PVA

PVA

13

31

217

117

13

31

217

117

13

31

217

117

1

3244

3219

3245

3229

3262

3297

3282

3283

3263

3283

3283

3282

2

3302

3301

3302

3308

3383

3392

3396

3396

3383

3392

3396

3396

3

3411

3420

3410

3403

3460

3494

3494

3493

3460

3494

3494

3493

3523

3565

3565

3565

3524

3566

3566

3565

5

3585

3607

3607

3607

3586

3612

3607

3607

6

3648

3648

3648

3648

3648

3648

3648

3648

Peak

4

3480

[a]. Venegas-Sanchez, J. A., et al. Ultrason. Sonochem.2014, 21, 295-309.

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Figure 9. Deconvolution results for different PVA dry films. (a) PVA13, (b) PVA31, (c) PVA117 and (d) PVA217.

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Figure 10. Deconvolution results for PVA/[BMI]Cl composites before (a, c, e and g) and after (b, d, f and h) the US exposure for 10 min.

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(a)

(b)

Scheme 2. (a) The interaction mode between PVA and [BMI]Cl and (b) chemical structure change of PVA/[BMI]Cl composite during with and without US epxosure.

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For Table of Contents Only 84x47mm (300 x 300 DPI)


Poly(vinyl

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