Improving Dielectric Properties and Thermostability of CaCu3Ti4O12

Subscriber access provided by UNIV AUTONOMA DE COAHUILA UADEC

Article

Improving Dielectric Properties and Thermostability of CaCu3Ti4O12/Polyimide Composites by Employing Surface Hydroxylated CaCu3Ti4O12 Particles Chao Qian, Tianwen Zhu, Weiwen Zheng, Runxin Bei, Siwei Liu, Dingshan Yu, Zhenguo Chi, Yi Zhang, and Jiarui Xu ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.9b00010 • Publication Date (Web): 09 Apr 2019 Downloaded from http://pubs.acs.org on April 9, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 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

ACS Applied Polymer Materials

Improving Dielectric Properties and Thermostability of CaCu3Ti4O12/Polyimide Composites by Employing Surface Hydroxylated CaCu3Ti4O12 Particles Chao Qian1, Tianwen Zhu1, Weiwen Zheng1, Runxin Bei1, Siwei Liu1, Dingshan Yu1, Zhenguo Chi1, 2, Yi Zhang*1, and Jiarui Xu1 1

Laboratory of Polymeric Composite and Functional Materials, Guangdong Laboratory of High-

Performance Polymer Composites, Guangdong Engineering Technology Research Centre for High-performance Organic and Polymer Photoelectric Functional Films, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China. 2

State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry, Sun

Yat-sen University, Guangzhou 510275, China. *E-mail: [email protected]. Keywords: polyimide; high-k composite; surface hydroxylation; CCTO; heat resistance

ABSTRACT: Surface hydroxylation was implemented on CaCu3Ti4O12 (CCTO) particles to improve their interface compatibility and dispersibility in polyimide matrix. The surface

ACS Paragon Plus Environment

1

ACS Applied Polymer Materials 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

hydroxylated CCTO fillers (CCTO-OH) were obtained by treating the CCTO particles in the mixed solution of H2SO4 and H2O2. The experimental results showed that the CCTO-OH/PI composite films owned higher dielectric permittivity and lower coefficient of thermal expansion (CTE) than CCTO/PI composite films, which were mainly attributed to the well dispersion of CCTO-OH particles and the enhanced interfacial polarization between CCTO-OH particles and PI chains. Among these CCTO-OH/PI composite films, the composite film with 40 vol% CCTO-OH particles loading exhibited the highest dielectric permittivity (76.9, 102 Hz) and a low dielectric loss (0.2, 102 Hz) maintained. The maximum discharge energy density of the CCTO-OH/PI composite film with 25 vol% CCTO-OH reached 1.31 J/cm3, which was almost twice than that of pure PI (0.63 J/cm3). What’s more, the prepared CCTO-OH/PI composite films had excellent heat resistance and low CTE. The high-k property of the CCTO-OH/PI composites remains stable up to 300 oC, which is probably the most heat-resistant dielectric material reported in the literature and is absolutely critical for the manufacture of electronic devices facing extreme conditions.

INTRODUCTION High dielectric permittivity (high-k) materials are widely applied in the electrical industry due to the excellent charge storage capacity.1 According to the material type, high-k materials can be divided into high-k ceramic materials, high-k polymer materials and high-k polymer composite materials. Recently, a lot of efforts have been devoted in developing the high-k flexible polymer composites owing to their potential applications in the high charge storage capacitors, artificial muscles, smart skins, and apparatus for high-speed integrated circuits.2–17 To obtain the high-k polymer composite materials with outstanding comprehensive performance, the selection of polymer matrix and high-k fillers are vitally important. Some recent


2

Page 2 of 27

Page 3 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


researches used the ferroelectric polymer, such as poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)], or poly(vinylidene fluoridetrifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] as a host material for their higher dielectric permittivity compared with other polymers.18-23 However, these ferroelectric polymers have some deficiencies. Firstly, their k values show instability under different temperature. In general, the k values of the composites with ferroelectric polymers perform unsteady by increasing the environment temperature. Secondly, the fluorine atom in the ferroelectric polymer will form hydrofluoric acid under high temperature which will serious corrode the electronic device. Among numerous polymer materials, polyimide (PI) is considered as one of the best candidate for the host material in high-k polymer composite materials due to its excellent thermostability, flexibility and outstanding resistance to solvents.24 The high-k filler is also a very important part of high-k polymer composites. The high-k fillers can form micro-capacitor networks to acquire a distinctly enhanced dielectric permittivity when the content of the high-k fillers reached the percolation threshold. Many studies have reported the introduction of conductive fillers (such as graphene oxide (GO),25-28 carbon nanotubes (CNTs)2933

) or ceramic fillers (such as TiO2,34 Al2O335 and BaTiO336-38) into polymer substrates to form

high-k polymer composites. CaCu3Ti4O12 (CCTO) is a kind of ceramic material with an ultrahighk (> 104) due to its special microstructure.39,

40

Dang et al.41 added the CCTO particles into

polyimide to obtain high-k composite films. Because of the ultrahigh-k of the CCTO particles, the composite film with CCTO particles exhibited high-k (~49, 102 Hz) and low dielectric loss (< 0.2, 102 Hz) when the content of CCTO reached 40 vol%,. For polymer-based composites, the combination properties are very dependent on the interfacial compatibility and dispersibility between the polymer matrix and the fillers. The fillers can play the


3


best performance in the composites only with good interfacial compatibility and dispersibility. Although a lot of research has been done on mixing various polymers with different kinds of fillers to endow the composites with high performance, such as high dielectric permittivity, low loss tangent and excellent thermal stability, little research focuses on the influence of the interface between fillers and polymer matrix.18, 42-46 Actually, the interfacial interaction could significantly affect the interfacial compatibility and dispersibility of the high-k fillers in polymer matrix, which is a vitally important determinant of the k values of the composites. Here, surface hydroxylation was implemented on CCTO particles to improve their interface compatibility and dispersibility in polyimide matrix. The surface of CCTO particles was chemically modified by H2O2/H2SO4 treatment to introduce a lot of hydroxyl groups. The PI-based composites, which were filled with CCTO (CCTO/PI) and CCTO-OH (CCTO-OH/PI) were both prepared. It was found that the CCTO-OH/PI composites had higher k value and better heat resistant than CCTO/PI composites in the temperature range from room temperature to 300 oC. Higher dielectric breakdown strength and maximum discharge energy density were also found in the CCTO-OH/PI composites. Further studies proved that the formation of strong hydrogen bond between the CCTO-OH fillers and the precursor PAA was beneficial to the dispersion of CCTO-OH particles in the PI matrix. The better dispersion and the interfacial polarization between the CCTO-OH particles and the PI chains might be the reasons for the improvement of the dielectric properties. EXPERIMENTAL SECTION Materials. Pyromellitic dianhydride (PMDA), 4, 4’-diaminodiphenyl ether (ODA) and chromatographically pure dimethylacetamide (DMAc) were purchased from Aladdin Industrial Corporation.


4

Page 4 of 27

Page 5 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


CaCu3Ti4O12 (CCTO) (diameter: 1~3 μm) was purchased from Dianyang Industrial Corporation. All other solvents and reagents as analytical grade were purchased from Shanghai Aladdin Company and used without further purification. Surface modification of CCTO particles. To prepare the surface hydroxylated CCTO particles (CCTO-OH), 10 g CCTO particles were added into a mixed solution of H2O2 (35%, 100 mL)/H2SO4 (98%, 100mL), and the mixture was magnetic stirring at 110 oC for 12 h. Then centrifuged the reaction mixture and washed the precipitate by deionized water. At last the CCTO-OH particles were baked in an oven at 100 oC for 1 day. Preparation of CCTO-OH/PI composite films. The CCTO-OH particles were dispersed in DMAc under ultrasonic treating for 0.5 h. At the same time, equimolar PMDA and ODA were dissolved in DMAc with mechanical stirring to obtain a precursor poly(amic acid) (PAA) solution. Then the CCTO-OH solution was slowly added into the PAA solution and then the mixture solution was mechanical stirring for 8 h. Then the mixture solution was cast on a clean glass plate, and then the liquid film went through a thermal imidization process in a vacuum drying oven to obtain CCTO-OH/PI composite films. The temperature was set at 120 oC/1 h, 300 oC/1 h and 350 oC/1 h. The CCTO/PI composite films in this work were prepared by the similar process described above. The CCTO-OH/PI composite films and CCTO/PI composite films containing 5 vol%, 10 vol%, 25 vol% and 40 vol% of CCTO-OH or CCTO particles were obtained. RESULTS AND DISCUSSION


5


The characterization of CCTO-OH particles. FT-IR was used to evaluate the surface hydroxylation of the H2O2/H2SO4 treatment on the surface of the CCTO particles. The new band at 3430 cm-1 which is associated to the stretching mode of OH was appeared in Figure 1. This result indicates that the surface hydroxylation treatment of the CCTO particles with H2O2/H2SO4 can endow the surface of the CCTO particles with -OH groups. Figure 2 shows the morphology of CCTO and CCTO-OH particles. It can be seen that these is no obvious difference between the CCTO and CCTO-OH particles. The result indicates that the H2O2/H2SO4 treatment would cause no harm to the surface morphology of the CCTO particles. After the H2O2/H2SO4 treatment, the diameter of CCTO-OH particles still keep at 1~3 μm so that they can be well dispersed in PAA solution.

Transmittance (a.u.)

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 6 of 27

3430cm-1

CCTO CCTO-OH

-O-H

4000

3500

3000

2500

2000

1500 -1

Wavenumber (cm )

Figure 1. FT-IR spectra of CCTO and CCTO-OH particles.


6

1000

500

Page 7 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


Figure 2. SEM images of the (a) (b) CCTO and (c) (d) CCTO-OH particles.

The characterization of CCTO-OH/PI composite films. The manufacture route of the CCTO-OH/PI composite films is shown in Figure 3. The insets are the photographs of the CCTO-OH/PI composite film with 40 vol% CCTO-OH particles. As the schematic diagrams shown in Figure 3, the hydroxylation of CCTO by H2O2/H2SO4 treatment brings a lot of hydroxyl groups onto the CCTO surface. When the CCTO-OH particles are mixed with the precursor PAA solution, hydrogen bond will form between -CO-NH- or -COOH groups in the PAA main chains and the -OH groups on the surface of the CCTO-OH particles. Because of the hydrogen-bond interaction, the CCTO-OH particles have a good dispersion in PAA which can be retained in CCTO-OH/PI composites. The inset pictures show that the CCTO-OH/PI composite films possess good homogeneity and flexibility even when the volume fraction of CCTO-OH particles reached 40%, which might due to the excellent dispersion of the CCTO-OH particles in PI matrix.


7


Figure 3. Schematic diagrams of the preparation process of the CCTO-OH/PI composites. Insets: the photographs of the CCTO-OH/PI composite film with 40 vol% CCTO-OH. The photographs and SEM images of the CCTO-OH/PI composite films with different CCTOOH loading were shown in Figure 4. All the composite films present good flexibility and the CCTO-OH particles dispersed homogeneously in the PI matrix with no obvious aggregation. SEM images show clearer picture of the dispersion effect of CCTO particles in PI matrix. In CCTO/PI system (Figure 4(i)), the CCTO particles are separated from the PI matrix with obvious aggregation. However, the CCTO-OH particles are completely wrapped in PI matrix with no obvious aggregation (Figure 4(j)), which indicates that the hydroxyls on the surface of the CCTO particles can effectively increase the interaction between the fillers and PI matrix, and also enhance the dispersibility of the fillers in PI matrix.


8

Page 8 of 27

Page 9 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


Figure 4. Photographs and SEM images of CCTO-OH/PI composite films with CCTO-OH loading of (a) (e) 5 vol%, (b) (f) 10 vol%, (c) (g) 25 vol% and (d) (h) 40 vol%, respectively. (i) The crosssectional image of CCTO/PI composite film with CCTO loading of 25 vol%. (j) The crosssectional image of CCTO-OH/PI composite film with CCTO-OH loading of 25 vol%.

Table 1. The thermal properties of the CCTO-OH/PI composite film. Composite Films

Tga (oC)

Tdb (oC)

Residue ratec (%)

Pure PI

372

668

62

5 vol% CCTO-OH/PI

381

675

71

10 vol% CCTO-OH/PI

385

675

74

25 vol% CCTO-OH/PI

389

678

78

40 vol% CCTO-OH/PI

390

680

84

a

Measured by DMA at a heating rate of 10 oC/min.

b

Measured by TGA at a heating rate of 20 oC/min under nitrogen atmosphere.

c

Residual weight percentage at 800 oC under nitrogen atmosphere.


9


The thermal properties of the CCTO-OH/PI composite films were investigated by DMA, TMA and TGA. Analysis results are summarized in Table 1-2 and Figure S2. Compared with pure PI film, the CCTO-OH/PI composite films have higher glass transition temperature (Tg), thermal decomposition temperature (Td5%), residue rate and lower the coefficient of thermal expansion (CTE). These results indicated that the existence of CCTO-OH could observably improve the heat resistant properties of the CCTO-OH/PI composite films. By increasing the volume fraction of CCTO-OH particles, the glass transition temperature (Tg) of the CCTO-OH/PI composite films has been obviously increased, from 381 oC (5 vol% CCTOOH/PI) to 390 oC (40 vol% CCTO-OH/PI) (Table 1). The reason might be that the strong interaction between the CCTO-OH particles and PI matrix will limit the movement of the PI segments. With the quantity of CCTO-OH particles increasing, the inhibiting effect becomes stronger and stronger which severely confine the movement of the PI segments and thus Tg of the composite films increases. Precisely because of the movement confinement of the PI segments, the CTEs of the CCTO-OH/PI composite films decrease significantly (Table 2). When the volume fraction of CCTO-OH particles exceed 25%, the CTE of the CCTO-OH/PI composite films is less than 18 ppm/oC which perfectly matches the CTE of copper (Cu, 17~19 ppm/oC). What’s interesting is that when the volume fraction of CCTO-OH particles exceed 25%, the transition point of the dimension change at around glass transition temperature was disappeared, which means that the CCTO-OH/PI composite films can keep steady size even when the temperature reaches Tg (Figure 5).


10

Page 10 of 27

Page 11 of 27

Table 2. The CTE values of CCTO-OH/PI and CCTO/PI composite films.

a

Composite Films

CTECCTO-OH/PIa (ppm/oC)

CTECCTO /PIa (ppm/oC)

Pure PI

51

51

5 vol% CCTO-OH/PI

48

50

10 vol% CCTO-OH/PI

34

47

25 vol% CCTO-OH/PI

18

23

40 vol% CCTO-OH/PI

17

20

Measured at the temperature range from 100 oC to 250 oC by TMA. 1000

Dimension Change (m)

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


800 600 400

Pure PI 5 vol% CCTO-OH/PI 10 vol% CCTO-OH/PI 25 vol% CCTO-OH/PI 40 vol% CCTO-OH/PI

200 0 50

100

150

200

250

300

350

400

Temperature (C)

Figure 5. The TMA curves of CCTO-OH/PI composite films with different CCTO-OH particles loading. As shown in Table 2 and Figure S3, compared with the CCTO/PI composite films, the CTEs of the CCTO-OH/PI composite films decreased more obviously by increasing the filler loading. This can be attributed to that the dispersion of the CCTO-OH particles is better than the CCTO particles in PI matrix. As a result, the existence of CCTO-OH in PI matrix can effectively improve the heat-resistant properties and dimensional stability of the composite films, which make them become excellent potential candidates for electronic equipment, especially capacitors.


11


Dielectric properties of CCTO-OH/PI composite films. 3

100

10

pure PI 5 vol%-CCTO-OH/PI 10 vol%-CCTO-OH/PI 25 vol%-CCTO-OH/PI 40 vol%-CCTO-OH/PI

A

80 60

B

2

pure PI 5 vol%-CCTO-OH/PI 10vol%-CCTO-OH/PI 25vol%-CCTO-OH/PI 40vol%-CCTO-OH/PI

10

Dielectric Loss

Dielectric Permittivity

120

1

10

0

10

-1

10

40

-2

20

10

-3

0 2 10

3

10

4

5

10 10 Frequency (Hz)

10

6

10

2

3

10

10

4

5


6

10

Figure 6. (A) The dielectric permittivity of the CCTO-OH/PI composite films as a function of frequency at room temperature. (B) The dielectric loss of the CCTO-OH/PI composite films as a function of frequency at room temperature. 90

100 80

PI 5 vol% CCTO/PI 10 vol% CCTO/PI 25 vol% CCTO/PI 40 vol% CCTO/PI

A

60



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 12 of 27

40 20 0 2 10

75

B CCTO-OH/PI CCTO/PI

60 45 30 15 0

3

10

4

5


6

10

0

10 20 30 40 Volume fraction of filler (%)

Figure 7. (A) The dielectric permittivity of the CCTO /PI composite films as a function of frequency at room temperature. (B) The dielectric permittivity of the CCTO /PI composite films and CCTO-OH /PI composite films at 100 Hz as a function of volume fraction of filler at room temperature.


12

Page 13 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


As shown in Figure 6, the CCTO-OH/PI composite films with different CCTO-OH loading exhibit different dielectric permittivity and dielectric loss. when the volume fraction of CCTO-OH particles lower than 10%, the k values of the composite films do not change with the increase of frequency. When the volume fraction of CCTO-OH particles exceeds 25%, the k values of the composite films are obviously frequency dependent. Namely, the k values decrease dramatically with the increase of frequency. This phenomenon was also shown in CCTO/PI composite films (Figure 7) and it could be attributed to the semi-conductive characteristic of the CCTO-OH particles. As shown in Figure 6 (A), the dielectric loss of the composite films increases with the increase of the volume fraction of CCTO-OH particles which are attributed to the interfacial polarization between the PI matrix and the CCTO-OH particles. The k value of the CCTO-OH/PI composite film with 40 vol% CCTO-OH particles reaches 76.9, which is almost 23 times than pure PI, and the dielectric loss is less than 0.2 at 102 Hz. This result might be ascribed to a synergistic effect, namely a superposition of the internal boundary layer capacitance (IBLC) effect, electronic polarization, and interfacial polarization between CCTO-OH and PI.41,

47-49

Compared with

CCTO/PI composite films, the CCTO-OH/PI composite films have higher dielectric permittivity with a same filler loading (see Figure 7(B)). In other words, to achieve the same k value, the surface hydroxylation of CCTO can effectively reduce the addition of fillers. The CCTO-OH/PI composites films with 28 vol% CCTO-OH loading can get the same k value as the CCTO/PI composites films with 40 vol% CCTO particles loading. These phenomena can be attributed to two reasons. On one hand, the hydroxyl on the surface of the CCTO-OH particles can improve the compatibility between CCTO-OH particles and PI matrix, which results a better dispersion of CCTO-OH particles in PI matrix. On the other hand, the presence of hydroxyl may strengthen the interfacial polarization of the CCTO-OH particles and PI matrix. Both of the two effects could


13


Page 14 of 27

enhance the k values of the CCTO-OH/PI composite films. Compared with other ceramic particles in PI matrix, just like BaTiO3 nanofibers (k = 8.3)[50] and halloysite nanotubes (k = 17.3)

[51]

,

CCTO-OH/PI composites still show great superiority due to the ultrahigh-k of the CCTO-OH particles. In this work, PI was chosen as the host material due to its excellent stability, especially the heat resistance. As shown in Figure 8 (A), the k value of the CCTO-OH/PI composite film with 40 vol% CCTO-OH particles occurred a sharp increase at low frequency (102 ~ 104 Hz) only when the temperature over 300 oC. Figure 8 (B) shows the k value of the CCTO-OH/PI composite film with 40 vol% CCTO-OH particles at 102 Hz under different temperature. The dielectric permittivity maintains a slight fluctuation when the temperature below 300 oC. Namely, the CCTO-OH/PI composite film can maintain stable dielectric properties until the environment temperature exceed 300 oC. Figure 8 (C) shows the maximum service temperature and the k values of some commercial polymers for capacitors and high-k PI composites. Compared with the CCTO/PI composites reported in Ref. 41, the thermal stability of the as-prepared CCTO/PI and CCTO-OH/PI composite films has been greatly improved due to the optimization of the preparation process; and compared with the CCTO/PI composite with 40% CCTO content in this work, the k value of the CCTO-OH/PI composite was increased by 61% due to the enhancement of the interfacial interaction between the particles and the matrix by surface hydroxylation of CCTO particles. And as we can see, the CCTO-OH/PI composite film shows excellent thermal stability of dielectric properties compared with the commercial polymers for capacitors and some other common high-k PI composites.


14

Page 15 of 27

700 600

A

500 400 300 200 100 0 2 10

700

30 C 50 C 100 C 150 C 180 C 200 C 220 C 250 C 280 C 300 C 320 C 3

10

4

5


400 300 200 100 0

10

0

50

100 150 200 250 300 350 Temperature (C)

CCTO-OH/PI (this work)

CCTO/PS(ref.52)

60 40

500

C

80

B

600

6


100



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


CCTO/PI (this work)

CCTO/PI(ref.41) CCTO/PU(ref.53)

20 0 50

BT/PI(ref.51) PI

PVDF PP

100

PET

150

200

250

300

350

400

Maximum Service Temperature (C)

Figure 8. (A) The dielectric permittivity of the CCTO-OH /PI composite films with 40 vol% CCTO-OH particles as a function of frequency at different temperature. (B) The dielectric permittivity of the CCTO-OH /PI composite with 40 vol% CCTO-OH particles at 100 Hz as a function of temperature. (C) The maximum service temperature and dielectric permittivity of some commercial polymers for capacitors and high-k PI composites.

Breakdown strengths and energy storage properties of CCTO-OH/PI composite films.


15


0.4

Log(-Ln(1-P))

0.8

A

0.4

Pure PI 5 vol% CCTO-OH/PI 10 vol% CCTO-OH/PI 25 vol% CCTO-OH/PI 40 vol% CCTO-OH/PI

0.0

B

40.05

Log(-Ln(1-P))

0.8

-0.4 -0.8 -1.2

 = 20.4

1.0

1.2

1.4

1.6

26.7 1.8

20.7 2.0

Pure PI 5 vol% CCTO/PI 10 vol% CCTO/PI 25 vol% CCTO/PI 40 vol% CCTO/PI

0.0 -0.4 -0.8 -1.2

25.1 2.2

26.2 23.2

 = 47.7

1.0

2.4

1.2

Log E

) 3

250

C

CCTO-OH/PI CCTO/PI

200 150 100 50 0

0

10

20

1.4

1.6

1.8

25.1

28.6 2.0

2.2

2.4

Log E

30

40

Max Discharge Energy Density (J/cm

Breakdown Strength (kV/mm)

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 16 of 27

Volume fraction of CCTO-OH (vol%)

1.5

D

1.2

CCTO-OH/PI CCTO/PI

0.9 0.6 0.3 0.0

0

10 20 30 Volume fraction of CCTO-OH (vol%)

40

Figure 9. Weibull-distribution plots of breakdown strength for (A) CCTO-OH/PI; (B) CCTO/PI. (C) The breakdown strengths of composite films. (D) The maximum discharge energy density of composite films (102 Hz).

The breakdown strength (EB) and maximum discharge energy density (Ue) of the composite films have been discussed in detail in our previous work.51 The calculation process of the EB and Ue are described in Supporting Information. As shown in Figure 9, the CCTO/PI and CCTO-OH/PI composites exhibit high β values which indicate that the composite films have high quality. Figure


16

Page 17 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


9(C) shows the EB of the composites with different fillers loading. In general, the EB of the composite decreases along with increasing the contents of the fillers due to the degradation of the insulativity. As shown in Figure 9(D), the highest Ue is obtained both in CCTO/PI or CCTOOH/PI composite films with 25 vol% fillers. Compared with CCTO/PI composite films, the CCTO-OH/PI composite films have much higher Ue because of the better dispersion of the fillers. The Ue of the 25 vol% CCTO-OH/PI composite film reached 1.31 J/cm3 which is almost improved by 108% compared with that of pure PI (0.63 J/cm3).

CONCLUSION In conclusion, hydroxylation of CCTO particles has been realized by H2O2/H2SO4 treatment. Compared with the CCTO/PI composites films, the CCTO-OH/PI composite films show higher dielectric permittivity and heat resistance at the same filler loading. For the CCTO-OH/PI composite, increasing loading of fillers not only enhances the dielectric permittivity but also improves the dimensional stability of the materials. The CCTO-OH/PI composite film with 40 vol% CCTO-OH particles loading possesses the highest dielectric constant (76.9, 102 Hz) while a low dielectric loss (0.2, 102 Hz) maintained. The Ue value reaches 1.31 J/cm3 in the CCTO-OH/PI composite film with 25 vol% CCTO-OH particles loading. Briefly speaking, the existence of the hydroxyl groups on the surface of the CCTO-OH particles improved the dispersion of CCTO-OH particles in the PI matrix, strengthened the confinement of PI chains and enhanced the interfacial polarization of the CCTO-OH particles and PI matrix. All these effects make the CCTO-OH/PI composite films possess superior high-k properties and heat resisting properties. The high-k property of the CCTO-OH/PI composites remains stable up to 300 oC, which is probably the most heat-resistant dielectric material reported in the literature.


17


ASSOCIATED CONTENT Supporting Information. The following files are available free of charge. Instrumentation, experimental setup of the dielectric permittivity measurement, TGA and DMA curves of CCTO-OH/PI composite films and TMA curves of CCTO/PI composite films, the calculation of breakdown strength and maximum discharge energy density. (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The financial supports by the National 973 Program of China (No. 2014CB643605), the National Natural Science Foundation of China (No. 51373204 and 51873239), the Science and Technology Project of Guangdong Province (No. 2015B090915003 and 2015B090913003), the Leading Scientific, Technical and Innovation Talents of Guangdong Special Support Program (No. 2016TX03C295), the China Postdoctoral Science Foundation (No. 2017M612801), the Science and Technology planning project of Guangzhou (No. 201704020008) and the Fundamental Research Funds for the Central Universities (No. 161gzd08) are gratefully acknowledged. REFERENCES


18

Page 18 of 27

Page 19 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


(1) Dang, Z. M.; Yuan, J. K.; Zha, J. W.; Zhou, T.; Li, S. T.; Hu, G. H. Fundamentals, Processes and Applications of High-Permittivity Polymer-Matrix Composites. Prog. Mater. Sci. 2012, 57, 660-723. (2) Carpi, F.; Bauer, S.; De Rossi, D. Stretching Dielectric Elastomer Performance. Science 2010, 330, 1759-1761. (3) Zhang, Q. M.; Li, H. F.; Poh, M.; Xia, F.; Cheng, Z. Y.; Xu, H. S.; Huang, C. An All-Organic Composite Actuator Material with A High Dielectric Constant. Nature 2002, 419, 284-287. (4) Li, Q.; Chen, L.; Gadinski, M. R.; Zhang, S. H.; Zhang, G. Z.; Li, H. U.; Iagodkine, E.; Haque, A.; Chen, L. Q.; Jackson, T. N.; Wang, Q. Flexible High-Temperature Dielectric Materials from Polymer Nanocomposites. Nature 2015, 523, 576-579. (5) Mirfakhrai, T.; Madden, J. D. W.; Baughman, R. H. Pure and Doped Boron Nitride Nanotubes. Mater. Today 2007, 10, 30-38. (6) Brochu, P.; Pei, Q. B. Advances in Dielectric Elastomers for Actuators and Artificial Muscles. Macromol. Rapid Comm. 2010, 31, 10-36. (7) Fan, B.; Liu, F.; Yang, G.; Li, H.; Zhang, G.; Jiang, S.; Wang, Q. Dielectric Materials for High-temperature Capacitors. IET Nanodielectrics 2018, 1, 32-40. (8) Zhong, S. L.; Dang, Z. M.; Zhou, W. Y.; Cai, H. W. Past and Future on Nanodielectrics. IET Nanodielectrics 2018, 1, 41-47. (9) Zhu, N.; Liang, G.; Yuan, L.; Guan, Q.; Gu, A. Progress of Heat Resistant Dielectric Polymer Nanocomposites with High Dielectric Constant. IET Nanodielectrics 2018, 2, 67-79.


19


(10) Yang, M.; Hu, C.; Zhao, H.; Ashtiani, P. H.; He, D.; Yang, Y.; Yuan, J.; Bai, J. Core@doubleshells Nanowires Strategy for Simultaneously Improving Dielectric Constants and Suppressing Losses of Poly(vinylidene fluoride) Nanocomposites. Carbon 2018, 132, 152156. (11) Wu, J. G.; Xiao, D. Q.; Zhu, J. G. Potassium-Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries. Chem. Rev. 2015, 115, 2559-2595. (12) Dang, Z. M.; Zheng, M. S.; Zha, J. W. 1D/2D Carbon Nanomaterial-Polymer Dielectric Composites with High Permittivity for Power Energy Storage Applications. Small 2016, 12, 1688-1701. (13) Zhang, Y.; Zhang, C.; Feng, Y.; Zhang, T.; Chen, Q.; Chi, Q.; Liu, L.; Li, G.; Cui, Y.; Wang, X.; Dang, Z.; Lei, Q. Excellent Energy Storage Performance and Thermal Property of Polymer-based Composite Induced by Multifunctional One-dimensional Nanofibers Oriented In-plane Direction. Nano Energy 2019, 56, 138-150. (14) Chi, Q.; Ma, T.; Zhang, Y.; Chen, Q.; Zhang, C.; Cui, Y.; Zhang, T.; Lin, J.; Wang, X.; Lei, Q. Excellent Energy Storage of Sandwich-Structured PVDF-Based Composite at Low Electric Field by Introduction of the Hybrid CoFe2O4@BZT–BCT Nanofibers. ACS Sustain. Chem. Eng. 2018, 6, 403-412. (15) Chi, Q.; Wang, X.; Zhang, C.; Chen, Q.; Chen, M.; Zhang, T.; Gao, L.; Zhang, Y.; Cui, Y.; Wang, X.; Lei, Q. High Energy Storage Density for Poly(vinylidene fluoride) Composites by Introduced Core-Shell CaCu3Ti4O12@Al2O3 Nanofibers. ACS Sustain. Chem. Eng. 2018, 6, 8641-8649.


20

Page 20 of 27

Page 21 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


(16) Chi, Q.; Ma, T.; Zhang, Y.; Cui, Y.; Zhang, C.; Lin, J.; Wang, X.; Lei, Q. Significantly Enhanced Energy Storage Density for Poly(vinylidene fluoride) Composites by Induced PDACoated 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 Nanofibers. J. Mater. Chem. A 2017, 5, 16757-16766. (17) Zhang, C.; Wang, D.; He, J.; Liu, M.; Hu, G. H.; Dang, Z. M. Synthesis, Nanostructures and Dielectric Properties of Novel Liquid Crystalline Block Copolymers. Polym. Chem. 2014, 5, 2513-2520. (18) Zhou, T.; Zha, J. W.; Cui, R. Y.; Fan, B. H.; Yuan, J. K.; Dang, Z. M. Improving Dielectric Properties of BaTiO3/Ferroelectric Polymer Composites by Employing Surface Hydroxylated BaTiO3 Nanoparticles. ACS Appl. Mater. Inter. 2011, 3, 2184-2188. (19) Zhang, Q.; Bharti, V.; Zhao, X. Giant Electrostriction and Relaxor Ferroelectric Behavior in Electron-Irradiated Poly(vinylidene fluoride-trifluoroethylene) Copolymer. Science 1998, 280, 2101-2104. (20) Zhang, X.; Shen, Y.; Shen, Z.; Jiang, J.; Chen, L.; Nan, C. W. Achieving High Energy Density in PVDF-Based Polymer Blends: Suppression of Early Polarization Saturation and Enhancement of Breakdown Strength. ACS Appl. Mater. Inter. 2016, 8, 27236-27242. (21) Dang, Z. M.; Wang, L.; Wang, H. Y.; Nan, C. W.; Xie, D.; Yin, Y.; Tjong, S. Rescaled Temperature Dependence of Dielectric Behavior of Ferroelectric Polymer Composites. Appl. Phys. Lett. 2005, 86, 172905.


21


(22) Yuan, J. K.; Li, W. L.; Yao, S. H.; Lin, Y. Q.; Sylvestre, A.; Bai, J. High Dielectric Permittivity and Low Percolation Threshold in Polymer Composites Based on SiC-Carbon Nanotubes Micro/Nano Hybrid. Appl. Phys. Lett. 2011, 98, 032901. (23) Arbatti, M.; Shan, X.; Cheng, Z. Y. Ceramic-Polymer Composites with High Dielectric Constant. Adv. Mater. 2007, 19, 1369-1372. (24) Kriechbaum, K.; Cerrón-Infantes, D. A.; Stöger B.; Unterlass, M. M. Shape-Anisotropic Polyimide Particles by Solid-State Polycondensation of Monomer Salt Single Crystals. Macromolecules 2015, 48, 8773-8780. (25) Cho, S.; Kim, M.; Lee, J. S.; Jang, J. Polypropylene/Polyaniline Nanofiber/Reduced Graphene Oxide Nanocomposite with Enhanced Electrical, Dielectric, and Ferroelectric Properties for a High Energy Density Capacitor. ACS Appl. Mater. Inter. 2015, 7, 22301-22314. (26) He, F.; Lau, S.; Chan, H. L.; Fan, J. High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite Nanoplates. Adv. Mater. 2009, 21, 710-715. (27) Tian, M.; Ma, Q.; Li, X.; Zhang, L.; Nishi, T.; Ning, N. High Performance Dielectric Composites by Latex Compounding of Graphene Oxide-Encapsulated Carbon Nanosphere Hybrids with XNBR. J. Mater. Chem. A 2014, 2, 11144-11154. (28) Fang, X.; Liu, X.; Cui, Z. K.; Qian, J.; Pan, J.; Li, X.; Zhuang, Q. Preparation and Properties of Thermostable Well-Functionalized Graphene Oxide/Polyimide Composite Films with High Dielectric Constant, Low Dielectric Loss and High Strength via in Situ Polymerization. J. Mater. Chem. A 2015, 3, 10005-10012.


22

Page 22 of 27

Page 23 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


(29) Dang, Z. M.; Wang, L.; Yin, Y.; Zhang, Q.; Lei, Q. Q. Giant Dielectric Permittivities in Functionalized Carbon-Nanotube/Electroactive-Polymer Nanocomposites. Adv. Mater. 2007, 19, 852-857. (30) Sun, Y.; Wang, J.; Qi, S.; Tian, G.; Wu, D. Permittivity Transition from Highly Positive to Negative: Polyimide/Carbon Nanotube Composite's Dielectric Behavior around Percolation Threshold. Appl. Phys. Lett. 2015, 107, 012905. (31) Wang, B.; Liu, L.; Liang, G.; Yuan, L.; Gu, A. Boost Up Dielectric Constant and Push Down Dielectric Loss of Carbon Nanotube/Cyanate Ester Composites via Gradient and Layered Structure Design. J. Mater. Chem. A 2015, 3, 23162-23169. (32) Chen, Y.; Lin, B.; Zhang, X.; Wang, J.; Lai, C.; Sun, Y.; Liu, Y.; Yang, H. Enhanced Dielectric Properties of Amino-Modified-CNT/Polyimide Composite Films with A Sandwich Structure. J. Mater. Chem. A 2014, 2, 14118-14126. (33) Xu, W.; Ding, Y.; Jiang, S.; Zhu, J.; Ye, W.; Hou, Y. S. H. Mechanical Flexible PI/MWCNTs Nanocomposites with High Dielectric Permittivity by Electrospinning. Eur. Polym. J. 2014, 59, 129-135. (34) Xu, N.; Hu, L.; Zhang, Q.; Xiao, X.; Yang, H.; Yu, E. Significantly Enhanced Dielectric Performance of Poly(vinylidene fluoride-co-hexafluoropylene)-based Composites Filled with Hierarchical Flower-like TiO2 Particles. ACS Appl. Mater. Inter. 2015, 7, 27373-27381. (35) Pan, Z.; Yao, L.; Zhai, J.; Fu, D.; Shen, B.; Wang, H. High-Energy-Density Polymer Nanocomposites Composed of Newly Structured One-Dimensional BaTiO3@Al2O3 Nanofibers. ACS Appl. Mater. Inter. 2017, 9, 4024-4033.


23


(36) Yang, K.; Huang, X.; Zhu, M.; Xie, L.; Tanaka, T.; Jiang, P. Combining RAFT Polymerization and Thiol-Ene Click Reaction for Core-Shell Structured Polymer@BaTiO3 Nanodielectrics with High Dielectric Constant, Low Dielectric Loss, and High Energy Storage Capability. ACS Appl. Mater. Inter. 2014, 6, 1812-1822. (37) Kim, P.; Jones, S. C.; Hotchkiss, P. J.; Haddock, J. N.; Kippelen, B.; Marder,; Perry, J. W. Phosphonic Acid-Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength. Adv. Mater. 2007, 19, 1001-1005. (38) Luo, S.; Yu, S.; Sun, R.; Wong, C. P. Nano Ag-Deposited BaTiO3 Hybrid Particles as Fillers for Polymeric Dielectric Composites: Toward High Dielectric Constant and Suppressed Loss. ACS Appl. Mater. Inter. 2014, 6, 176-182. (39) Yang, Y.; Sun, H.; Yin, D.; Lu, Z.; Wei, J.; Xiong, R.; Shi, J.; Wang, Z.; Liu, Z.; Lei, Q. High Performance of Polyimide/CaCu3Ti4O12@Ag Hybrid Films with Enhanced Dielectric Permittivity and Low Dielectric Loss. J. Mater. Chem. A 2015, 3, 4916-4921. (40) Yang, Y.; Wang, Zi.; Ding, Y.; Lu, Z.; Sun, H.; Li, Y.; Wei, J.; Xiong, R.; Shi, J.; Liu, Z.; Lei, Q. Research Update: Polyimide/CaCu3Ti4O12 Nanofiber Functional Hybrid Films with Improved Dielectric Properties. APL Mater. 2013, 1, 050701. (41) Dang, Z. M.; Zhou, T.; Yao, S. H.; Yuan, J. K.; Zha, J. W.; Song, H. T.; Li, J. Y.; Chen, Q.; Yang, W. T.; Bai, J. Advanced Calcium Copper Titanate/Polyimide Functional Hybrid Films with High Dielectric Permittivity. Adv. Mater. 2009, 21, 2077-2082.


24

Page 24 of 27

Page 25 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


(42) Barber, P.; Balasubramanian, S.; Anguchamy, Y.; Gong, S.; Wibowo, A.; Gao, H.; Ploehn, H. J.; Loye, H. C. Z. Polymer Composite and Nanocomposite Dielectric Materials for Pulse Power Energy Storage. Materials 2009, 2, 1697-1733. (43) Xu, H. P.; Dang, Z. M. Electrical Property and Microstructure Analysis of Poly(vinylidene fluoride)-Based Composites with Different Conducting Fillers. Chem. Phys. Lett. 2007, 438, 196-202. (44) Kim, P.; Doss, N. M.; Tillotson, J. P.; Hotchkiss, P. J.; Pan, M. J.; Marder, S. R.; Li, J.; Calame, J. P.; Perry, J. W. High Energy Density Nanocomposites Based on Surface-Modified BaTiO3 and a Ferroelectric Polymer. ACS Nano 2009, 3, 2581-2592. (45) Polizos, G.; Tomer, V.; Manias, E.; Randall, C. Epoxy-Based Nanocomposites for Electrical Energy Storage. II: Nanocomposites with Nanofillers of Reactive Montmorillonite Covalently-Bonded with Barium Titanate. J. Appl. Phys. 2010, 108, 074117. (46) Qi, L.; Lee, I.; Chen, B. S.; Samuels, W. D.; Exarhos, G. J. High-Dielectric-Constant SilverEpoxy Composites as Embedded Dielectrics. Adv. Mater. 2005, 17, 1777-1781. (47) Chung, S. Y.; Kim, I. D.; Kang, S. J. L. Strong Nonlinear Current-Voltage Behaviour in Perovskite-Derivative Calcium Copper Titanate. Nat. Mater. 2004, 3, 774-778. (48) Yang, C.; Song, H. S.; Liu, D. B. Effect of Coupling Agents on the Dielectric Properties of CaCu3Ti4O12/PVDF composite. Composites Part B-Eng. 2013, 50, 180-186.


25


(49) Zhao, Y. L.; Pan, G. W.; Ren, Q. B.; Cao, Y. G.; Feng, L. X.; Jiao, Z. K. High Dielectric Constant in CaCu3Ti4O12 Thin Film Prepared by Pulsed Laser Deposition. Thin Solid Films 2003, 445, 7-13. (50) Hu, P.; Sun, W.; Fan, M.; Q, J.; Jiang, J.; Dan, Z.; Lin, Y.; Nan, C.; Li, M.; Shen, Y. Large Energy Density at High-temperature and Excellent Thermal Stability in Polyimide Nanocomposite Contained with Small Loading of BaTiO3 Nanofibers. Appl. Surf. Sci. 2018, 458, 743-750. (51) Zhu, T.; Qian, C.; Zheng, W.; Bei, R.; Liu, S.; Chi, Z.; Chen, X.; Zhang, Y.; Xu, J. Modified Halloysite Nanotube Filled Polyimide Composites for Film Capacitors: High Dielectric Constant, Low Dielectric Loss and Excellent Heat Resistance. RSC Adv. 2018, 8, 1052210531. (52) Amaral, F.; Rubinger, C. P. L.; Henry, F.; Costa, L. C.; Valente, M. A.; Timmons, A. B. Dielectric Properties of Polystyrene-CCTO composite. J. Non-Cryst. Solids 2008, 354, 53215322. (53) Wan, W.; Luo, J.; Huang, C.; Yang, J.; Feng, Y.; Yuan, W. X.; Ouyang, Y.; Chen, D.; Qiu, T. Calcium Copper Titanate/Polyurethane Composite Films with High Dielectric Constant, Low Dielectric Loss and Super Flexibility. Ceram. Int. 2018, 44, 5086-5092.


26

Page 26 of 27

Page 27 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


For Table of Contents Only


27

Improving Dielectric Properties and Thermostability of CaCu3Ti4O12

Recommend Documents