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Porous TiO2 nanoparticles derived from titanium Metal-Organic Framework and its improved electrorheological performance Kai He, Qingkun Wen, Chengwei Wang, Baoxiang Wang, Shoushan Yu, Chuncheng Hao, and Kezheng Chen Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00846 • Publication Date (Web): 03 May 2018 Downloaded from http://pubs.acs.org on May 4, 2018

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Industrial & Engineering Chemistry Research

Porous TiO2 nanoparticles derived from titanium Metal-Organic Framework and its improved electrorheological performance Kai He a, Qingkun Wen a, Chengwei Wang a, Baoxiang Wang a,b,*, Shoushan Yu a, Chuncheng Hao a, b and Kezheng Chen a a) College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China b) State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi'an, 710049, PR China

Abstract: A simple method for synthesis of porous TiO2 nanoparticles was developed via a two-step route using titanium metal-organic framework (MOF) as a precursor, in which MOFs were firstly prepared by a cetyltrimethyl ammonium bromide (CTAB) assisted solvothermal method and then calcined in air at 500 °C. After pyrolysis of precursor MOFs, the anatase TiO2 inherited the porosity of precursor MOF and possessed a large surface area and uniform pore distribution, which was subsequently adopted as an electrorheological (ER) material by dispersing in silicone oil. ER activities of MOFs and porous TiO2 based suspensions under the applied electric fields were investigated in a controlled shear rate (CSR) mode. In contrast to MOFs based ER fluids, the suspension of porous TiO2 exhibited a higher ER efficiency and lower leakage current. Furthermore, the improvement of dielectric properties was found to be responsible for the enhanced ER activity through an investigation of dielectric spectrum.

Key words:

Ti-MOF, Electrorheological fluid, Porous Nanostructures,

Solvothermal method.

*To whom correspondence should be addressed. Tel: 86-532-84022509. Fax: 86-532-84023773.

E-Mail: [email protected] 1

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1. Introduction Electrorheological fluid is a two-phase suspension system, which is typically composed of polarized particles dispersing in an insulating medium. The ER effect, instantaneous and reversible changing in rheological and mechanical properties of the suspensions under an external electric field, arises from the chain-like structures formed among neighboring polarized particles, resulting in a rapid transformation from a fluid-like state to solid-like one

[1-4]

. Owing to the intrinsic advantages of

instantaneous and tunable rheological properties in response to electric stimuli, the ER material promises wide range applications in electrically controllable devices

[5-7]

.

Various conducting materials have been employed to act as the dispersion phase of ER fluids, ranging from conducting polymers to inorganic semiconductor

[8-14]

.

Among them, TiO2 has received considerable attention currently owing to its relatively high permittivity, non-toxic, chemical stability, etc

[15-17]

. However, the

practical applications of ER fluids are still limited by the sedimentation of suspended particles, narrow operation temperature, and large leaking current and insufficient yield stress. It is well-accepted that the TiO2 with a regular shape does not exhibit an appropriate ER effect caused by its intrinsic weak polarization. To overcome those limitations, the nanosize TiO2 is commonly prepared to increase the surface area in order to lead to an enhancement of interfacial polarization. In addition, designing mesoporous TiO2 with a large and active interface structure may be another available way to lead further improvement of ER activity

[18-21]

. The TiO2 nanoparticles with a

mesostructure not only play a crucial role in possessing a large surface area to induce the improvement of interfacial polarization, but also provide a stable chain-like structure to resist shearing under an applied electric field. As previous literature reported by Zhao’s group, an ER fluid of wormhole-like mesoporous TiO2 has been prepared and exhibits a superior ER effect. Besides, Zhao’s group also synthesized mesoporous anatase TiO2 hollow microspheres by sol-gel method. The results indicated that increasing the specific surface area of TiO2 microspheres not only 2


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enhances the ER performance but also improves the suspension stability of ER fluids. [22-23]

. Metal-organic framework (MOF), established as a new class crystalline

microporous material, is constructed by metallic ion and organic ligands, which attracts increasing attention due to their intrinsic porosity, tunable framework and adjustable pore size [24, 25]. Cu3(BTC)2 was used as an ER material by Choi’ group and exhibited excellent anti-shearing properties under the action of applied electric ﬁeld [25]

. In contrast to TiO2, MIL-125 (a form of the Ti-incorporated MOF), formulated as

Ti8O8(OH)4(BDC)6 and equipped with TiO2 clusters assembled with organic ligands, possesses tunable porosity to accelerate the rate of interfacial polarization and induce the strong polarizable ability of particles for the synergistic ER effects [26]. Moreover, using MOFs as a novel precursor is a feasible approach to prepare porous metal oxide with a desirable framework recently

[27-29]

. Furthermore, the metal oxide can convert

from MOF completely inheriting a certain degree of porosity after pyrolyzation because of the periodical arrangement of atoms inside the structure [30-32]. Herein, we proposed a facile strategy to prepare porous TiO2 nanoparticles derived from the precursor MIL-125 using CTAB as a surfactant. The porous TiO2 was obtained after calcination of MIL-125 in an air atmosphere flow. Compared with the ER suspension of MIL-125, the porous TiO2 based ER fluid displayed an outstanding ER performance under the action of an applied electric field with a relatively low leaking current. With the role of the electric field, the yield stress of TiO2 was observably enhanced and the ER fluid exhibited strong shearing resistance. At last, the improved ER performance was further investigated through the measurement of dielectric properties of ER fluids. The large difference of permittivity and a suitable dielectric relaxation was found to be the cause of ER properties improvement.

2. Experimental Section 2.1 Materials Titanium

tetrabutoxide

(TBT,

Beijing

Chemicals,

3


Beijing,

China),

1,


4-benzenedicarboxylic acid (BDC, Sinopharm Chemical Reagent Corporation, Shanghai, Chian), cetyltrimethyl ammonium bromide (CTAB, Tianjin Bodi Chemical Co. Ltd., Tianjin, China), dimethylformamide (DMF, Laiyang Fine Chemical Factory, China), anhydrous methanol (Tianjin Fuyu Fine Chemical Co. Ltd., Tianjin, China)， acetic acid (Tianjin Ruijinte Co.,Ltd., Tianjin, China) and silicone oil (Tian Jin Damao limited company, Tianjin, China) were purchased. All reagents were of analytical grade and used as received without further treatment. 2.2 Synthesis of MIL-125 The MIL-125 was synthesized by a facile CTAB-assisted solvothermal method using TBT and BDC as the metallic ion source and organic linkers, respectively. In a typical procedure, 5 g BDC and a certain amount of CTAB were firstly dissolved in a mixed solution of 100 mL DMF and 15 mL anhydrous methanol. Then 5 mL acetic acid was added before the addition of TBT to prevent the titanium precursor from hydrolysis. After the 15 min of the addition of acetic acid, 3 ml TBT was added into above mixing solution and stirred for 1 h. The resulting solution was transferred into an autoclave and reacted at 150 °C for 24 h. After cooling down to room temperature naturally, the white precipitate was harvested by centrifuging with DMF and anhydrous methanol 3 times to remove the unreacted surfactant and dried in an oven at 65 °C overnight. In order to investigate the effect of CTAB on the crystal size and morphologies, the amount of CTAB added in the solution was turned from 0 to 3 g. For a given amount of CTAB (0 g, 0.5 g, 1 g, 2 g, 3 g,) the corresponding samples were denoted by S0, S0.5, S1, S2, S3, respectively. 2.3 Synthesis of porous TiO2 (P-TiO2) Generally speaking, the ER properties can be altered by many factors, including size, surfactant and morphology, etc

[30-31]

. In this point of view, the precursor S1 was

chosen to prepare P-TiO2. To prepare P-TiO2, the as-synthesized S1 nanoparticles were calcined at 500 °C for 3 h under air flow with a heating rate of 5 °C min-1. Upon cooling down naturally, the resulting white powder of porous TiO2 was collected. 2.4 Synthesis of ER fluids 4


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The 10 wt% ER fluids were prepared by separately dispersing the as-obtained S0, S1 and P-TiO2 in silicone oil. The density of samples S0, S1 and P-TiO2 was measured by a pycnometer method. The measured particle densities of S0, S1 and P-TiO2 are 2.18, 2.11 and 1.96 g cm-3, respectively. The particle concentration of the samples based ER fluid is 10 wt%, so their calculated volume fraction for S0, S1 and P-TiO2 is about 4.6, 4.7 and 5.1 vol%. 2.5 Characteristics Field emission scanning electron microscope (SEM) and Transmission electron microscopy (TEM) were used to reveal the morphological properties of as-synthesized particles. SEM images were collected on a JEOL JSM-6700F and TEM was performed on the JEM-2100 with operating voltage at 200 kV. The XRD patterns were recorded on a powder X-ray diffractometer (Rigaku D/max-rA) equipped with a rotating anode and a Cu Kα1 radiation source (λ=1.5406Å). The thermal behavior of as-synthesized sample was investigated by a thermal analyzer (Netzsch, STA449C) at a heating rate of 5 °C min-1 under air flow. The porous structure was determined by using a nitrogen adsorption measurement (ASAP 2020). 2.6 Measurement of ER properties and dielectric properties The rheological properties of ER fluids were tested by using a rotational rheometer (HAAKE Rheo Stress 6000). The dielectric properties of ER fluids were detected by implementing a broadband dielectric spectroscopy equipment (Novocontrol Concept 40).

3. Result and Discussion The MIL-125 nanoparticles with different morphologies and particle sizes were prepared by the reaction of TBT and BDC under the solvothermal condition with or without the assistance of CTAB. And the morphologies and particle sizes of as-synthesized S0, S0.5, S1, S2, S3 particles were observed by SEM images and TEM images. As Fig. 1 and Fig. S1 showed, in the synthesis without CTAB, a large number of tetragonal plate morphology particles were obtained with an irregular size in length between 300-800 nm and 200 nm in thickness and their surfaces were relatively 5



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smooth with no tiny particles attachment (Fig. 1a). Under the identical experimental condition, except for the addition of 0.5 g CTAB, a new plane in the particular direction paralleled with the plate started to grow, resulting the formation of truncated octahedron morphology. Simultaneously the size of particles reached a stable value at 800 nm (Fig. 1b). Furthermore, as the SEM images showed (Fig. 1c-e), the morphology of particles had no significant development but a decrease in the particle size from 800 nm to 350 nm as the amount of CTAB further increased to 3 g. In addition, the as-prepared MIL-125 nanoparticles with different morphologies of tetragonal plate and truncated octahedron were further characterized by TEM in Fig. S2. The tetragonal plate with round corners was clearly observed in the synthesis without addition of CTAB (Fig. S2a). Then the truncated octahedron shape with a new plane appearance and sharp edges was obtained in the synthesis with assistance of 1 g CTAB (Fig. S2b). It is well-know that CTAB can affect the morphology and size of MIL-125 crystals in the course of crystallization, as indicated in previous literatures. Especially, CTAB was recently employed to synthesize MOF and caused modulation of morphology and particle size

[33-34]

. However, the morphology of MIL-125 can be

varied by many factors. For example, NH2-MIL-125 with different morphologies from tetragon to octahedron was prepared by modulating the concentration of the reactant. The same group also showed the decrease of the crystal size in the synthesis of NH2-MIL-125 was ascribed to the addition of CTAB

[35-36]

. In this case, CTAB not

only acted as a morphology-direct agent, but also induced the decrease in particle size. As displayed in Fig. 2 (a, b), the XRD patterns of S0 and S1 powders, whether with or without CTAB, were corresponded well with the previous report about MIL-125

[37]

.

Meanwhile, the XRD patterns suggested that the addition of CTAB did not change the crystalline structure of S0. For the TiO2 derived from MOF precursor, as displayed in Fig. 2c, all the diffraction peaks were indexed to anatase phase TiO2 (JCPDS 21-1272), proving the complete transformation from MOF to TiO2 after calcination at 500 °C. The thermal behavior was investigated by TGA analysis of S1 sample. The TGA curve of S1 in Fig. S3 was similar to the result reported in previous literature. 6


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The weight loss was mainly ascribed to the decomposition of residual reactant and decomposition of terephthalic acid from the framework and production of TiO2 crystal [38]

. As the temperature further increases, there is no further weight loss observed,

which also indicated the complete destruction of framework and complete conversion from MIL-125 to TiO2 crystal. The SEM image in Fig. 3a showed that the P-TiO2 obtained after heat treatment maintained the initial morphology in spite of undergoing a process of framework collapse but a particle size decrease to 400 nm. The TEM image, as showed in Fig. 3b, revealed that the P-TiO2 particle was constructed with nanosize particles. And the nanotunnels on the surface of TiO2 particle were also observed, which played an important role in the interfacial polarization. The pore structure of TiO2 crystal was further determined by N2 adsorption-desorption isotherms characterization, as showed in Fig. 3(c, d). The isothermals were classified as a typical Ⅳ type with a distinct hysteresis loop. The BET surface area was 56 m2 g-1 for porous TiO2 nanostructure. The corresponding pore size distribution curve indicated that TiO2 crystal had an average pore size value of 16 nm. The porous TiO2 derived from MOF exhibited superior ER performance which was considered to be due to its unique structure, as illustrated in Fig. 3e. Firstly the anatase TiO2 can inherit the porosity of precursor and display a porous structure composed of nanoparticles, which could be beneficial for promoting the interaction of polarized particles by reducing the polarized distance. Secondly, the nanosized tunnels through the framework structure can promote the mobility of polarized particles, which is helpful to accelerate the rate of chain-like structure organization. The ER properties were measured in a controlled shear rate (CSR) mode to verify the flow behaviors of S0, S1 and P-TiO2. The flow curves of S0, S1 and P-TiO2 under the absence and presence of an applied electric field were presented in Fig. 4a-c. ER fluids behaved like Newtonian fluids without electric stimuli, whose shear stress increased with the shear rate linearly. When exposed to the applied electric field, the shear stresses exhibited a dramatic enhancement

[39-44]

. Because of the chain-like

structure formed between the adjacent particles, the fluids exhibited a strong flow 7



resistance. Under high intensity of electric field, the S1 and P-TiO2 based ER suspensions exhibited an enhanced shear stress and plateau area in the flow curve. When shear rate was in the low range, the electrostatic attraction between adjacent polarized particles developed by an applied electric field was predominant compared with hydrodynamic force. As the shear rate further increased, the rate of chain-like structures destroyed by flow shearing and reformed with the assistance of electric field was almost equal; the competition between hydrodynamic force and electrostatic interactions tended to be balanced. As soon as the shear rate beyond the critical value, the competition between hydrodynamic force and electrostatic interactions was out of balance, and the shear stress increased in proportion to shear rate again. It was worth to notice that the plateau region of P-TiO2 based ER fluid was wider than that of the ER fluid of S1, which means that the porous TiO2 particles organize into columnar structure fast enough to maintain a stable shear stress. The high and stable shear stress indicated that the ER fluid of P-TiO2 showed a better ER performance. In order to determine the morphology effect on ER behavior, S0 sample was also calcined into TiO2 and compared with P-TiO2, as showed in fig. S4. The calcined product showed a similar rheological curve with P-TiO2. Although the shear stress value was lower than P-TiO2, the electric breakdown did not occur during the ER test from 0-3 kV/mm, indicating the calcined treatment and a well-defined morphology has a positive impact on ER activity. Fig. 4d-f displayed the shear viscosity versus shear rate curves for three types ER fluids. The typical Newtonian fluid behaviors were observed for all the suspensions when electric field was absent. The thinning phenomenon was observed under various electric conditions, which was a classic pseudoplastic fluid characteristic. Under the action of electric field, the shear viscosity elevation was found for three types ER fluids. However, the elevation for P-TiO2 based ER fluid was more significant, which indicated a strong resistance to flow shearing. Fig. 5 displayed the dependence of yield stress on electric field strength of S1 and P-TiO2 suspensions, in which the yield stress was regarded as the extrapolation of the shear stress to a shear rate minimum limit from CSR curves. In contrast to S1, the 8


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P-TiO2 based ER fluid exhibited a higher yield stress of approximately 70 Pa at 3 kV/mm indicating a better ER effect under the applied electric field. The power equation is normally adopted to correct the dependence of yield stress on electric field strength, which can be described as follows: τy∝Eα

(1)

The value of α in the power law distinguishes the conduction model and polarization model. The value of α in this work is determined to be 1.1 and 1.2 for S1 and P-TiO2, respectively. The deviation from conducting model may be ascribed to the porous structure and conductivity mismatch of particles and oil medium. Additionally, the ER efficiency, given as: e= (τE-τ0)/τ0 (where the τE and τ0 mean the value of shear stress under the applied electric field and without electric field), is a critical parameter to evaluate the intensity of ER effect. The e of P-TiO2 based ER fluid is higher than the other two kinds of ER fluids (16 for P-TiO2 at 3 kV/mm, 10.9 for P-TiO2 at 2.5 kV/mm, 3.5 for P-TiO2 at 1.5 kV/mm, 3.2 for S1 at 2.5 kV/mm and 1.6 for S0 at 1.5 kV/mm, respectively) as the shear rate was fixed at 10 s-1. Leaking current density is another critical parameter to distinguish the behaviors of ER materials, which could lead to a breakdown of ER fluids. The leaking current density of three types ER fluids was listed in Table 1. It can be seen that the current density of P-TiO2 ER fluid is lower than those of S0 and S1 ER fluid obviously, which should be ascribed to the lower conductivity of TiO2 compared with S0 and S1. For the S0 and S1 based ER fluids, the leaking current is sufficient to lead to a breakdown of ER fluids under 2 kV mm-1 and 3 kV mm-1. Generally speaking, the strength of electric field can cause a huge impact on the electrorheological properties. Under a high strength of electric field, the particles in the ER fluid can form a strong chain-like structure to resist breakup under the shear force, and therefore the shear stress exhibits a significant enhancement. On the other hand, the enhancement in shear stress is very limited under a low strength of electric field. As a consequence, the large leaking current density of S0 and S1 ER suspensions restricts the ER performance greatly. Thus, the ER efficiency of S0 and S1 is much lower than that of P-TiO2. As reported previously from our group [45], the anatase TiO2 with exposed (100) facets 9



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was synthesized and exhibited an improved ER performance. In addition, it was found that the anisotropic characteristic resulted from the exposure of (100) facets was the mainly responsibility for the improvement of ER effect. Although the strong interfacial polarization was induced by a large surface area, TiO2-(100) does not exhibit intrinsic porosity. In comparison with conventional TiO2, P-TiO2 derived from MOF not only possesses a large surface area, but also exhibits a porous structure. The effect of uniform pore structure on ER performance was indicated in other reports. This effect is expected to produce a fast polarization within the nanochannals and a strong attraction between particles and consequently induce a higher shear stress and ER efficiency. Additionally, the dielectric properties of materials are tightly associated with their ER performance, which greatly affect the polarization ability under an external electric field. As reported in previous literature

[46-49]

, a high dielectric constant and a proper

dielectric loss have a positive influence on ER activity. To investigate the change of dielectric properties after calcination process of S1, the dielectric constant and dielectric loss were determined as functions of frequency at room temperature, as showed in Fig. 6. And the Cole-Cole’s equation was employed to analyze the behavior of dielectric spectrum, as described below: ∆ε 1-α （1 + iωλ ）

ε ∗ (ω ) = ε '+ iε ' ' = ε ∞ +

where ε' and ε" are dielectric constant and dielectric loss factor of ER suspensions. The dielectric constant difference (∆ε=ε0-ε∞) is related to the strength of interfacial polarization of ER fluid, in which ε0 and ε∞ are the permittivity of ER fluid at zero frequency and infinite frequency, respectively. The relaxation time is defined as: λ=1/2πfmax, where fmax is the frequency at dielectric loss factor peak.

[50-52]

. It is

generally accepted that a higher ∆ε and a proper λ are beneficial for better ER performance

achievement

[53-57]

.

From

the

dielectric

spectrum,

a

large

∆ε=3.9-2.89=1.01 is obtained in the case of P-TiO2 based ER fluid. Compared with the ER fluid of S1, the larger ∆ε indicated that a stronger chain structure was formed and reorganized when exposed to an external electric field. On the other hand, the 10


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dielectric loss factor peak of P-TiO2 based ER fluid located within the range of 103-104 Hz, which was required for a good ER effect. In addition, the relaxation time λ was calculated as 0.037 ms, which was very short for ER response. On the contrary, no peak was found in the dielectric loss curve of S1 within the frequency range of 10-1-106, reflecting that the polarization rate was improved after calcination process. The detailed parameters on dielectric constant, dielectric loss peak, and relaxation time of S1 and P-TiO2 are listed in Table 2. In the ER fluid system, the dielectric constant of silicone oil carrier is independent of the electric field strength. Therefore, the improvement of dielectric properties is contributed from the polarization of porous TiO2, which should be responsible for the enhanced ER performance.

4. Conclusions In conclusion, the porous TiO2 nanoparticles derived from MIL-125 were successfully synthesized by using a solvothermal method with an assistance of CTAB and a following heat treatment. In the synthesis of MIL-125 based on a surfactant templating strategy, it was found that the amount of CTAB played a key role on controlling the morphology of MIL-125 particle and reducing the particle size. After calcination, the anatase TiO2 retained the initial morphology and inherited the porous framework of MIL-125. Under applied electric fields, the porous TiO2 exhibited a superior ER performance and a lower leaking current density compared with the suspension of MIL-125 particles. The dielectric measurements revealed that the porous TiO2 displayed a larger dielectric constant enhancement and a clear dielectric loss peak. Based on the result of dielectric spectrum, the improvement of ER activity is considered to be ascribed to the enhanced dielectric interfacial polarization. Acknowledgment This work was supported by State Key Laboratory of Electrical Insulation and Power Equipment (Xi'an Jiaotong University, EIPE17205) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry. Supporting Information. SEM images of S0 (a), S0.5 (b), S1 (c), S2 (d), S3 (e); TEM images of S0 (a) and P-TiO2 (b);TGA curve for S1; The electrorheological curve for the sample calcined 11



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from S0.

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17



The list of figure Fig. 1 The representative SEM images of S0 (a), S0.5 (b), S1 (c), S2 (d), S3 (e). Fig. 2 XRD patterns of as-synthesized S0 (a), S1 (b) and P-TiO2 (c). Fig. 3 SEM (a) and TEM (b) images of P-TiO2, N2 adsorption-desorption isotherms (c)of P-TiO2, the corresponding pore size distribution (d), scheme for evolution of structure from S1 to P-TiO2 (e). Fig. 4 Shear stress and shear viscosity as functions of shear rate for three types ER fluids: S0 (a, d), S1 (b, e) and P-TiO2 (c, f). Fig. 5 The yield stress as functions of strength of electric field for S1 and P-TiO2. Fig. 6 Dielectric constant (a) and dielectric loss (b) of the S1 and P-TiO2 based ERFs

Fig. S1 The representative SEM images of S0 (a), S0.5 (b), S1 (c), S2 (d), S3 (e). Fig. S2 The representative TEM images of S0 (a) and P-TiO2 (b). Fig. S3 TGA curve for S1. Fig. S4 The electrorheological curve for the sample calcined from S0.

The list of table Table 1 Leaking current density (µA/cm2) of three types ER fluids under various applied electric field. Table 2 The detailed dielectric properties of samples S1 and P-TiO2.

18


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Table of Contents graphic

19



Page 20 of 27

Table 1. Electrical field strength (kV/mm) Samples

1.0

1.5

2.0

2.5

3.0

S0 S1

21.8 0

62.4 6.2

× 23.9

50.9

×

P- TiO2

0

3.1

4.1

6.2

7.2

20


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Table 2 Samples

ε0

ε∞

∆ε

fmax

λ

S1

3.69

2.87

0.82

×

×

P-TiO2

3.9

2.89

1.01

4210 Hz

0.037 ms

21



Fig. 1


Page 22 of 27

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


c

Intensity [a.u.]

Page 23 of 27

b a 0

10

20

30

40

50

60

2 theta [degree]

Fig. 2


70

80


dV/dlog(D) pore volume [cm /g]

0.5 160

adsorption desorption

140

3

Quantity Adsorbed (cm3/g)

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 24 of 27

120 100

c

80 60 40 20

0.4

0.3

d

0.2

0.1

0.0

0 0.0

0.2

0.4

0.6

0.8

1.0

1

Relative Pressure (P/P ) °

10

100

Pore diameter [nm]

e

Fig .3


Page 25 of 27

100

10

0.0 kV/mm 1.0 kV/mm 1.5 kV/mm

1

0.1 1

10

100

shear stress/Pa

shear stress/Pa

100

0.0 kV/mm 1.0 kV/mm 1.5 kV/mm 2.0 kV/mm 2.5 kV/mm

10

1 1

shear rate/s

10

100

shear rate/s

-1

-1

a)

b)

shear stress/Pa

100

shear viscosity/Pa*s

1000

0.0 kV/mm 1.0 kV/mm 1.5 kV/mm

100

0.0 kV/mm 1.0 kV/mm 1.5 kV/mm 2.0 kV/mm 2.5 kV/mm 3.0 kV/mm

10

1 1

10

10

1 1

100

10

100

shear rate/s

-1

shear rate/s

-1

c)

d)

0.0 kV/mm 1.0 kV/mm 1.5 kV/mm 2.0 kV/mm 2.5 kV/mm

100

10

1 1

10

shear rate/s

-1


1000

1000


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


0.0 kV/mm 1.0 kV/mm 1.5 kV/mm 2.0 kV/mm 2.5 kV/mm 3.0 kV/mm

100

10

1 1

100

10

shear rate/s

-1

e)

f)

Fig. 4


100


100 80 60

yield stress/Pa

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 26 of 27

40

20

S1 P-TiO2 1

2

3 -1

electric field/kV*mm

Fig. 5


4

5

Page 27 of 27

0.06 4.0

Dielectric loss[e "]

P-TiO2 S1

3.8

Dielectric constant[e ']

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


3.6

3.4

3.2

a

P-TiO2 S1 0.04

b 0.02

3.0

2.8 0.1

1

10

100

1000

10000

100000 1000000

1E7

Frequency/Hz

1

10

100

1000

10000

Frequency/Hz

Fig. 6


100000

1000000

Porous TiO2 Nanoparticles Derived ... - ACS Publications

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