• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Enhancing surface adhesion of polytetrafluoroethylene induced by two-step in-situ treatment with radiofrequency capacitively coupled Ar/Ar+CH4+NH3 plasma

    2023-11-16 05:38:08MantingLU盧曼婷YiHE何弈XueLIU劉學(xué)JiaminHUANG黃嘉敏JiaweiZHANG張佳偉XiaopingMA馬曉萍andYuXIN辛煜
    Plasma Science and Technology 2023年10期

    Manting LU (盧曼婷), Yi HE (何弈), Xue LIU (劉學(xué)), Jiamin HUANG (黃嘉敏),Jiawei ZHANG (張佳偉), Xiaoping MA (馬曉萍) and Yu XIN (辛煜)

    Jiangsu Key Laboratory of Thin Films,School of Physical Science and Technology, Soochow University,Suzhou 215006, People’s Republic of China

    Abstract

    Keywords: adhesion property, surface modification, capacitively coupled plasma,polytetrafluoroethylene

    1.Introduction

    Polytetrafluoroethylene (PTFE) has been used in various applications due to its excellent properties, such as wear resistance, acid and alkali resistance and thermal stability[1-4].The hydrophobicity and low surface tension of PTFE make it very difficult to bond with other materials, seriously limiting its scope of application [5, 6].Hence, various techniques have been used to modify PTFE to improve its surface activity and adhesion strength, such as chemical etching[7, 8], radiation-induced grafting [9], plasma treatment [10]and so on.Chemical etching,by destroying the C-F bonds of PTFE and connecting the functional groups using a sodium naphthalene solution, has become the most representative method.However, this causes environmental pollution and human injury.In comparison, the low-temperature plasma treatment is a good candidate and one of the most promising methods [11].

    When electrons with enough energy obtained from the electric field collide with other particles in plasma, decomposition, adsorption, ionization, excitation and other reaction processes occur [12].Thus, the resultant active species in plasma not only have high chemical activity but also appropriate ion bombardment energy.The chemical structure and surface morphology of PTFE can be controlled by changing the discharge parameters of plasma.

    Lee et al [13] treated PTFE with an Ar+ion beam andion beam, respectively.They found that the roughness and adhesion of PTFE treated with the Ar+ion beam in O2atmosphere were better than those with only theion beam.Generally, charges will always be accumulated on the insulating PTFE surface, and the formed potential due to the accumulated charges will decrease the ability of ion bombardment.Therefore, it is necessary for tungsten wire to emit electrons to neutralize the ion beam, which limits its application.Pachchigar et al [14] obtained a superhydrophobic structure when treating PTFE with Ar capacitively coupled plasma (CCP).Low-pressure O2plasma was used to treat PTFE to form a surface with a spherical structure,which was explained by the different etching rates, influenced by the orientation and size of the crystallites in the polymer substrates [10].Atmospheric pressure plasma treatment did not produce a textured structure on the PTFE surface due to the lack of effective ion bombardment[15].However,the surface etching could be improved with thermal assistance [16, 17].

    Generally,the low surface tension of PTFE is determined by its surface nonpolar structure.Destroying the C-F bonds or grafting other non-fluorine groups on the surface may improve the surface tension[18,19].In the plasma discharge process, highly active H produced by H-containing gas can scavenge fluorine at the PTFE surface, thus enhancing the surface defluorination.Chen et al [20] used Ar, O2, He, H2and NH3plasmas to treat PTFE samples, respectively, and showed that the F/C ratio of the PTFE surface treated with H-containing plasma was always smaller than that with hydrogen-free plasma under the same conditions.Hai et al[21] reported that H-containing inductively coupled plasma can not only reduce the F/C ratio but also combine some active groups, such as -OH and -NH2, on the PTFE surface.The introduction of these polar groups contributes to the enhancement of the wettability of PTFE, beneficial to the improvement of the adhesion.Inagaki et al[22]treated PTFE with NH3plasma at high temperatures.The F/C was reduced to 0.29 at 150°C, and the adhesion strength with rubber reached 8.1 × 103N m?1.

    Although the surface can be defluorinated and combined with certain polar groups to improve the surface hydrophilicity,its service life cannot be maintained for a long time[23, 24].Zanini et al [10] studied the aging effect of PTFE under the treatment of O2plasma.Due to the rotation and migration of the polymer chain,the density of polar groups on the surface decreased over time, and the water contact angle of the sample gradually recovered to 150° after 30 days.For the sake of the service life of the treated samples, grafting acrylic acid, acrylamide and other organics on the PTFE surface was widely considered because the presence of an acrylic coating not only protects the PTFE surface from oxidation but also effectively prevents the rotation and migration of polymer chains.Additionally, the adhesion of PTFE can be improved by adding an acrylic coating with a large number of -COOH radicals, since a covalent bond is formed between these radicals and the epoxy group in epoxy resin [11, 25-31].Meanwhile, Hegemann et al found that using C2H4+CO2plasma to deposit a cross-linked layer on the surface of PTFE can also reduce the water contact angle and suppress the aging effect [32].

    Figure 1.Schematic of the CCP apparatus equipped with Langmuir probe.

    Inspired by the considerations mentioned above, we proposed a two-step in-situ strategy to form a PTFE surface with a hill-shaped microstructure and high surface free energy.The hill-shaped microstructure on the PTFE with a high specific surface area was prepared by controlling the parameters of Ar CCP, and subsequently, an a-CNx:H crosslinking layer was used to cover the hill-shaped microstructure of the PTFE by Ar+CH4+NH3CCP treatment.The crosslinking layer showed high surface free energy and possessed good adhesion to the PTFE substrate.Our two-step in-situ strategy not only lessens the processing procedure and time of treatment, but also greatly improves the stability and the adhesion ability of samples.

    2.Experiment

    In this experiment,PTFE with a thickness of 0.2 mm was cut into pieces of 50 × 50 mm2, cleaned with absolute alcohol,and dried at 60°C.

    As shown in figure 1, the discharge chamber, made of stainless steel, is 300 mm in height and 350 mm in diameter.The distance between the two electrodes was set to 45 mm.The PTFE samples were placed on the bottom electrode,which was connected by a power supply (RSG-500) with a frequency of 13.56 MHz via an automatic matcher (SP-Ⅱ).The bias voltage was measured by a DC voltmeter,which was connected to the powered electrode via a 9 MΩ resistor.The Ar plasma was diagnosed by a compensated Langmuir probe(Hiden Analytical).Details can be found in other articles[33].

    Before each experiment, the chamber was pumped to a background pressure lower than 5 × 10?3Pa.The total gas flow rate was set to be 80 sccm, the discharge power was set between 50 W and 150 W, and the pressure was set between 5.0 Pa and 12.0 Pa.In the two-step in-situ treatment, Ar plasma was used for the PTFE treatment for 8 min, and then the plasma was switched to Ar+NH3+CH4treatment for 5 min.During the plasma treatment, the chamber cannot be exposed to the air.The reason for choosing CH4and NH3can be attributed to the following points.Carbon atoms contain four unpaired electrons, while nitrogen atoms have three unpaired electrons, which can generate more cross-linked structures via the interaction of plasma and surface and thus improve the molecular bonding ability [34].Most importantly, rich H-containing plasma enhances defluorination,which is beneficial for surface hydrophilicity [20].

    The adhesion strength tests were conducted with a tensile testing machine.After a special adhesive with a thickness of about 10 μm was brushed on an iron plate with 100 mesh sandblasting, the plasma-treated PTFE was covered on the iron plate and pressed with a pressure of 10 MPa at 150°C for an hour.After that, the machine peeled it away to obtain the adhesion strength.

    The surface morphologies of the treated samples were examined using scanning electron microscopy(SEM,SU8100,Regulus) and atomic force microscopy (AFM, MFP-3D, Asylum Research), respectively.X-ray photoelectron spectroscopy(XPS,ESCALAB 250 XI,Thermo Fisher Scientific)was used to analyze the surface chemical composition of the treated samples.The water and diiodomethane contact angles of the treated samples were measured with a contact angle tester(JC2000DM) to calculate their surface free energy.

    3.Results and discussion

    3.1.Plasma diagnosis

    In capacitively coupled discharges, electrons gain energy from the oscillating radiofrequency electric field and lose energy through collisions with background atoms, accompanied by reactions such as excitation, ionization, decomposition and so on.Due to the difference between electrons and ions in mass, a sheath with a certain thickness and negative bias forms between the bulk plasma and electrode.Under the influence of negative bias,ions entering the sheath will bombard the electrode.The negative bias can be expressed by the following equation [12]:

    Figure 2.Electron density and bias voltage of Ar CCP with different(a) input powers and (b) gas pressures.

    where Vrf, Te, m and M are the amplitude of the discharge voltage, the electron temperature, the electron mass and the ion mass, respectively.As shown in the equation, the bias depends on both Vrfand Te.Additionally,with the increasing discharge pressure, ions passing through the sheath will experience collisions and scatter with the background gas molecules and thus decrease its bombardment ability.Figure 2 shows the power and discharge pressure dependence of the electron density and bias voltage in Ar plasma.It can be found that the bias voltage increases linearly with the discharge power from 185 to 500 V, while the electron density goes from 2.0 × 109to 10.0 × 109cm?3at a pressure of 5.0 Pa.Furthermore, figure 2(b) also shows that the electron density increases with the pressure, while the bias voltage decreases slightly due to ion scattering with background gas molecules for the power of 150 W.

    3.2.Surface morphology of Ar-treated PTFE

    Figure 3.Surface morphology of PTFE treated by Ar CCP at 5.0 Pa with different powers: (a) 50 W, (b) 70 W, (c) 90 W, (d) 120 W,(e) 150 W.

    Figure 4.Surface morphology of PTFE treated by Ar CCP at 150 W with different gas pressures: (a) 5.0 Pa, (b) 6.0 Pa, (c) 7.0 Pa, (d)9.0 Pa, (e) 10.0 Pa, (f) 12.0 Pa.

    Figure 3 shows the evolution of the surface morphology of PTFE with the input power ranging from 50 to 150 W at the pressure of 5.0 Pa.As is known,the ion energy increases with the input power.From figure 3,it can be found that the greater the input power, the clearer the microstructure on the PTFE surface.This indicates that the formed hill-shaped structure is actually induced by the ion bombardment, which is in accordance with a report from Pachchigar et al [14].This is also evidenced by figure 4 showing the dependence of the microstructure of PTFE on the discharge pressure.From figure 4, we see that with a discharge pressure larger than 5.0 Pa, the surface hill-shaped structure almost disappears.When the pressure is set to be 6.0 Pa,the treated surface looks like a net.The reason for this is attributed to the enhanced ion scattering with background gases with the increasing pressure, while the lateral ion energy will almost smooth out the formed microstructure but with a few holes on the surface,as seen in figures 4(c)-(f).

    AFM was used to characterize the depth information of the PTFE surface microstructure treated by Ar CCP,including the specific surface area.As shown in figures 5(a)-(e), the measurement results agree with those of SEM.From the AFM measurements, we also find that the specific surface area and roughness of samples rise linearly with the discharge power,as shown in figure 5(f).The roughness changes from 17.65 to 105.6 nm with the discharge power,while the specific surface area increases from 1.07 to 2.18.For the discharge pressure influence,the roughness decreased dramatically from 105.6 to 55.92 nm,while the specific surface area decreased from 2.18 to 1.28,as shown in figure 6.This further indicates the role of ion bombardment on the surface microstructure formation.It is noteworthy that a high surface roughness and high specific surface area are helpful to the mechanical interlocking between bonding surfaces [35].

    Figure 5.AFM images of samples treated by Ar plasma with gas pressure of 5.0 Pa and input powers of: (a)50 W,(b)70 W,(c)90 W,(d)120 W, (e) 150 W.(f) Power dependence of specific surface area and roughness of samples.

    Figure 6.AFM images of samples treated by Ar plasma with input power of 150 W and gas pressures of(a)5.0 Pa,(b)7.0 Pa,(c)9.0 Pa,(d)10.0 Pa, (e) 12.0 Pa.(f) Pressure dependence of specific surface area and roughness of samples.

    Table 1.Surface adhesion strength of PTFE treated by plasmas with different discharge gases.

    3.3.Comparison of single-step method and two-step in-situ method

    The adhesion of the PTFE surface not only depends on the mechanical interlocking between bonding surfaces but also on the molecular bonding ability between the PTFE surface and adhesive [36].Therefore, three typical CCP-treated samples were fabricated for comparison.The three groups of experimental conditions are as follows:

    (1) PTFE with single-step treatment in Ar CCP for 8 min,marked as PA.This step confirms that a high roughness and specific surface area of the PTFE surface can improve the mechanical interlocking between bonding surfaces.

    (2) PTFE with single-step treatment of Ar+CH4+NH3CCP for 8 min, marked as PACN.This step confirms that a-CNx:H cross-linking film can improve the molecular bonding ability between bonding surfaces.

    (3) PTFE with two-step in-situ treatment,firstly treated in Ar CCP for 8 min, then in Ar+CH4+NH3CCP for 5 min,marked as PA2CN.This step confirms the role of the combination of mechanical interlocking and molecular bonding between surfaces.

    The detailed experimental parameters and results are shown in table 1.The adhesion strength of PA, which represents the mechanical interlocking effect, is 49.3 N·10 mm?1, which is much better than that of the raw sample (20 N·10 mm?1).Meanwhile, the adhesion strength of PACN, which represents molecular bonding ability,is 58.5 N·10 mm?1.It is worth noting that the PA2CN sample shows obvious improvement in adhesion strength (77.1 N·10 mm?1), which is 56% higher than PA and 32% higher than PACN.

    Figure 7.SEM and AFM images of PTFE treated with single-step plasma and two-step in-situ plasma methods: (a) untreated, (b) PA, (c)PACN, (d) PA2CN.

    Figure 8.High-resolution C 1 s and N 1 s XPS spectra of untreated PTFE and samples treated by plasma with single-step or two-step in-situ methods.

    Figure 7 shows SEM and AFM images of the three samples and the untreated sample.As can be seen,the surface of the untreated sample is extremely smooth, while those of PA and PA2CN with Ar plasma treatment present a textured microstructure with specific surface area greater than 2.0.However, for PACN, although ion bombardment also exists with a bias voltage of about ?500 V, seen from the DC voltmeter, the electronegative plasma takes on a deposition nature.The ion bombardment only strengthens the film deposition, but the role of ion bombardment in the formation of its surface microstructure is limited,which is different from the Ar electropositive plasma.As a result, the surface morphology of the a-CNx:H cross-linking layer grown in the deposited plasma is significantly different from that of the other two.

    XPS was used to investigate the chemical state and element content of untreated and plasma-treated PTFE.Compared with the raw PTFE sample, whose F/C ratio is about 2.0,the F/C ratio of PA is significantly reduced to 1.24 due to the argon ion bombardment.Due to the coverage of the a-CNx:H cross-linking film, the F/C ratio of PACN is only about 0.002,while that of PA2CN is 0.32.The XPS spectra of C 1 s and N 1 s are shown in figure 8.The C 1s-XPS spectra of the untreated sample are fitted into two peaks.The peaks located at 284.8 eV and 292.0 eV are assigned to C-C and CF2, respectively.After Ar plasma treatment, CF3,CF,C=O and N-C=O bonds appear on the PA surface because many unsaturated bonds caused by ion bombardment react with O2,N2and water in the air[15,37,38].For the C 1s-XPS spectra of PACN,the CF2peak almost disappears and is replaced by C-C and C-NH2bonds [39].The chemical structure of PA2CN is similar to that of PACN.

    The intermolecular force on the surface of the material is proportional to the surface free energy[16,20],and the higher surface free energy indicates better adhesion properties.In order to characterize the surface free energy of the samples with plasma treatment, the contact angles of deionized water and diiodomethane on the PTFE samples were measured to calculate the surface free energy.The formula for the calculation is as follows [40]:

    where the subscripts L and S denote liquid and solid surfaces,respectively.The superscripts d and h represent the energies of the dispersion force and the hydrogen bonding force components, respectively.θ is the measured contact angle.The surface free energy of PTFE is the sum ofγSdandγ.Sh

    Figure 9 shows the surface free energy of samples treated by the single-step and two-step in-situ methods.The surface free energy of PA is less than that of the untreated sample(21.0 mN m?1).After aging six days, the surface free energy decreases by nearly 35%, and the surface of PA shows superhydrophobic property because of the surface microstructure and molecular chain migration [32, 41-44].The surface free energy of both PACN and PA2CN increases significantly.The surface free energy of PACN is almost 2.5 times that of the original sample, and that of PA2CN reaches 74.0 mN m?1,which is mainly attributed to the combination of both the microstructure of the PA2CN surface and the a-CNx:H film.After aging six days,the surface free energy of PACN is about 50 mN m?1, while that of PA2CN decreases to a certain extent but is still higher than that of PACN.

    Figure 9.Surface free energy of samples treated by plasma with single-step or two-step in-situ methods.

    Figure 10.Aging time dependence of water contact angles for samples treated by plasma with single-step or two-step in-situ methods.

    Figure 10 shows the changes in the water contact angle of the three samples with aging time.According to Wenzel’s equation [41, 45],

    where r, θrand θsare the surface roughness ratio, contact angle of the rough surface and contact angle of the smooth surface, respectively.

    When the roughness of a surface increases, hydrophobic substances will be more hydrophobic, and hydrophilic substances will be more hydrophilic[46].That is why the surface of PA with high roughness showed hydrophobic characteristics.The decrease in the water contact angle of PACN is due to the existence of the cross-linking layer on its surface.The water contact angle of the sample treated by two-step in-situ plasma remains low at the initial stage, but with the increase in aging time, the angle rises to 60° and tends to be stable.

    4.Conclusions

    Ar/Ar+CH4+NH3CCPs were used to treat PTFE.The treatment of Ar CCP caused a hill-shaped microstructure on the PTFE surface with a specific surface area of up to 2.18,while the treatment of Ar+CH4+NH3plasma formed an a-CNx:H cross-linking layer on the surface.After the two-step in-situ plasma treatment, a surface with high specific surface area and extremely low F/C ratio was obtained.XPS analysis showed that the F/C ratio of the surface after the two-step insitu treatment decreased to 0.32, and that polar groups were connected on the surface, improving the molecular bonding ability.In our work, an adhesion strength of PTFE of up to 77.1 N·10 mm?1was achieved after the two-step in-situ plasma treatment, which was 56% higher than PA and 32%higher than PACN.Our results provide a reliable experimental direction for the application of PTFE in the industry.

    一进一出抽搐gif免费好疼| 一本久久中文字幕| АⅤ资源中文在线天堂| 18禁国产床啪视频网站| 2021天堂中文幕一二区在线观| 12—13女人毛片做爰片一| 精品无人区乱码1区二区| 国产97色在线日韩免费| 99久国产av精品| 最近在线观看免费完整版| 国产精品av久久久久免费| 免费电影在线观看免费观看| 久久99热这里只有精品18| 日韩 欧美 亚洲 中文字幕| 国产三级在线视频| 婷婷精品国产亚洲av在线| 此物有八面人人有两片| 嫩草影视91久久| 日韩精品青青久久久久久| 午夜福利高清视频| www日本在线高清视频| 国产伦在线观看视频一区| 99国产精品99久久久久| 91老司机精品| 国产精品一区二区免费欧美| 真实男女啪啪啪动态图| 久久久久精品国产欧美久久久| 99久久成人亚洲精品观看| 亚洲国产精品久久男人天堂| 99久久成人亚洲精品观看| 两个人看的免费小视频| 在线看三级毛片| 国产日本99.免费观看| 夜夜夜夜夜久久久久| xxxwww97欧美| 国产麻豆成人av免费视频| cao死你这个sao货| 成人午夜高清在线视频| 成人特级av手机在线观看| 俄罗斯特黄特色一大片| 成在线人永久免费视频| 最近视频中文字幕2019在线8| 国产精品精品国产色婷婷| 日韩欧美免费精品| 国内毛片毛片毛片毛片毛片| 国产成人精品久久二区二区91| 免费人成视频x8x8入口观看| 91在线精品国自产拍蜜月 | 国产男靠女视频免费网站| 我的老师免费观看完整版| 亚洲一区二区三区色噜噜| 国产午夜福利久久久久久| 精品国产超薄肉色丝袜足j| 国产一级毛片七仙女欲春2| 又粗又爽又猛毛片免费看| 日韩精品青青久久久久久| 丁香欧美五月| 日韩三级视频一区二区三区| 美女大奶头视频| 一二三四社区在线视频社区8| 90打野战视频偷拍视频| 91久久精品国产一区二区成人 | 97超视频在线观看视频| 日韩三级视频一区二区三区| 亚洲欧美一区二区三区黑人| 精品久久久久久久末码| 一级作爱视频免费观看| 热99re8久久精品国产| 三级毛片av免费| 女人被狂操c到高潮| 99热这里只有精品一区 | 女同久久另类99精品国产91| 国产一区二区三区视频了| 国产精品影院久久| 在线视频色国产色| 精品人妻1区二区| av国产免费在线观看| 美女大奶头视频| 国产91精品成人一区二区三区| 国产精品一区二区三区四区久久| 99久久精品热视频| 亚洲精品美女久久久久99蜜臀| 久久久久久国产a免费观看| 观看美女的网站| 在线观看午夜福利视频| 国产真实乱freesex| 亚洲成av人片免费观看| 在线免费观看不下载黄p国产 | 国产综合懂色| 丁香六月欧美| 亚洲中文日韩欧美视频| 亚洲国产欧美网| 国产熟女xx| 亚洲精品一卡2卡三卡4卡5卡| 身体一侧抽搐| 一进一出抽搐gif免费好疼| 99国产极品粉嫩在线观看| 天天躁狠狠躁夜夜躁狠狠躁| 巨乳人妻的诱惑在线观看| 国产精品久久久久久精品电影| 国产精品日韩av在线免费观看| 日韩欧美免费精品| 中国美女看黄片| 亚洲欧美一区二区三区黑人| 欧美在线一区亚洲| 午夜精品在线福利| 很黄的视频免费| 久久伊人香网站| 啦啦啦韩国在线观看视频| 国产亚洲精品av在线| 婷婷亚洲欧美| 国产午夜福利久久久久久| 男人舔奶头视频| 亚洲国产精品999在线| 久久精品夜夜夜夜夜久久蜜豆| 一进一出好大好爽视频| 19禁男女啪啪无遮挡网站| 视频区欧美日本亚洲| а√天堂www在线а√下载| 夜夜爽天天搞| 成人性生交大片免费视频hd| 久久久国产成人精品二区| 午夜成年电影在线免费观看| 99热这里只有是精品50| 国产亚洲精品综合一区在线观看| 99久久99久久久精品蜜桃| 蜜桃久久精品国产亚洲av| 色av中文字幕| 日本黄色片子视频| 精品国产乱子伦一区二区三区| 国产精品99久久久久久久久| 日韩精品中文字幕看吧| 网址你懂的国产日韩在线| 国产视频一区二区在线看| 老熟妇仑乱视频hdxx| 亚洲成人中文字幕在线播放| 亚洲av免费在线观看| 两个人视频免费观看高清| 久久午夜亚洲精品久久| 欧美3d第一页| 精品久久久久久成人av| 99热精品在线国产| 婷婷亚洲欧美| 18禁观看日本| 国产精品久久久人人做人人爽| 国产精品免费一区二区三区在线| 久久久久久国产a免费观看| 亚洲黑人精品在线| 久99久视频精品免费| 熟女少妇亚洲综合色aaa.| 久久久精品大字幕| 久久精品亚洲精品国产色婷小说| 久久久久国产精品人妻aⅴ院| 黄色日韩在线| 999精品在线视频| 日本五十路高清| 亚洲国产欧洲综合997久久,| 在线观看美女被高潮喷水网站 | 精品国产乱子伦一区二区三区| 天堂av国产一区二区熟女人妻| 免费看光身美女| 免费在线观看影片大全网站| 国产真人三级小视频在线观看| 亚洲精品粉嫩美女一区| 精品免费久久久久久久清纯| 麻豆av在线久日| 热99re8久久精品国产| 色尼玛亚洲综合影院| 久久久久久久久中文| 麻豆成人av在线观看| 久久久久亚洲av毛片大全| 精品乱码久久久久久99久播| 国产精品爽爽va在线观看网站| 在线观看午夜福利视频| 国产亚洲欧美98| 一本精品99久久精品77| netflix在线观看网站| 一个人看的www免费观看视频| 欧美三级亚洲精品| 成人三级黄色视频| 亚洲18禁久久av| 欧美激情在线99| 久久久国产成人精品二区| 丁香六月欧美| 中文亚洲av片在线观看爽| 五月伊人婷婷丁香| 国产午夜精品久久久久久| 十八禁人妻一区二区| 午夜成年电影在线免费观看| 99国产精品一区二区三区| 日本黄大片高清| 99久久精品热视频| 午夜亚洲福利在线播放| 一进一出抽搐动态| 黑人欧美特级aaaaaa片| 日韩欧美在线乱码| 熟女电影av网| 国内少妇人妻偷人精品xxx网站 | 美女高潮的动态| 亚洲av片天天在线观看| 国产亚洲精品久久久久久毛片| av国产免费在线观看| 欧美日韩中文字幕国产精品一区二区三区| 麻豆av在线久日| 午夜激情福利司机影院| 国产综合懂色| 国产伦一二天堂av在线观看| 两个人的视频大全免费| 国产免费av片在线观看野外av| 两个人视频免费观看高清| 国产97色在线日韩免费| 亚洲 欧美一区二区三区| 亚洲专区国产一区二区| 免费看a级黄色片| www.999成人在线观看| 欧美成人一区二区免费高清观看 | 女人高潮潮喷娇喘18禁视频| 波多野结衣高清作品| 99国产精品一区二区蜜桃av| 麻豆成人午夜福利视频| 99热这里只有是精品50| 精品不卡国产一区二区三区| 97人妻精品一区二区三区麻豆| 午夜福利免费观看在线| 午夜福利视频1000在线观看| 午夜福利成人在线免费观看| 在线国产一区二区在线| 日韩免费av在线播放| 亚洲,欧美精品.| 日韩av在线大香蕉| 夜夜夜夜夜久久久久| 看片在线看免费视频| 亚洲 欧美 日韩 在线 免费| 欧美午夜高清在线| 免费人成视频x8x8入口观看| 美女 人体艺术 gogo| 成人一区二区视频在线观看| 亚洲人成网站在线播放欧美日韩| 亚洲国产精品999在线| 国产又色又爽无遮挡免费看| 叶爱在线成人免费视频播放| 国产精品美女特级片免费视频播放器 | 国产成人精品久久二区二区免费| 亚洲成人免费电影在线观看| 国产主播在线观看一区二区| 欧美激情在线99| 久久精品国产99精品国产亚洲性色| 亚洲欧洲精品一区二区精品久久久| 搞女人的毛片| 国产男靠女视频免费网站| 国产av不卡久久| 国产亚洲av嫩草精品影院| 亚洲天堂国产精品一区在线| 手机成人av网站| 美女免费视频网站| 一个人免费在线观看的高清视频| 操出白浆在线播放| 国产激情欧美一区二区| 亚洲 欧美 日韩 在线 免费| 热99在线观看视频| 亚洲av熟女| 欧美中文日本在线观看视频| 中文字幕av在线有码专区| 波多野结衣高清无吗| 成人特级av手机在线观看| 无人区码免费观看不卡| 夜夜躁狠狠躁天天躁| 成年女人看的毛片在线观看| 亚洲av成人av| 亚洲欧美日韩高清专用| 淫妇啪啪啪对白视频| 日本黄色视频三级网站网址| 黄色女人牲交| 久久精品影院6| 99久久无色码亚洲精品果冻| 最近最新免费中文字幕在线| 91麻豆av在线| 国产黄片美女视频| 日韩欧美国产一区二区入口| 亚洲乱码一区二区免费版| 久久精品aⅴ一区二区三区四区| 精品国产三级普通话版| 精品国产美女av久久久久小说| 久久香蕉国产精品| 免费看十八禁软件| 亚洲欧美精品综合久久99| 亚洲国产欧美网| 午夜福利高清视频| 国产主播在线观看一区二区| 男女之事视频高清在线观看| 国产精品亚洲av一区麻豆| 亚洲最大成人中文| 97人妻精品一区二区三区麻豆| 天天添夜夜摸| 国产视频内射| www日本在线高清视频| 97人妻精品一区二区三区麻豆| 女生性感内裤真人,穿戴方法视频| 亚洲成人久久爱视频| 国产成+人综合+亚洲专区| 亚洲国产精品999在线| а√天堂www在线а√下载| 婷婷丁香在线五月| 岛国在线观看网站| 一进一出好大好爽视频| 午夜福利在线观看吧| 中文字幕最新亚洲高清| 三级男女做爰猛烈吃奶摸视频| 亚洲激情在线av| 日韩高清综合在线| 淫妇啪啪啪对白视频| 1000部很黄的大片| 国产黄a三级三级三级人| 在线观看日韩欧美| 天堂av国产一区二区熟女人妻| 老熟妇仑乱视频hdxx| 最近视频中文字幕2019在线8| 少妇的丰满在线观看| 两性午夜刺激爽爽歪歪视频在线观看| 亚洲欧美日韩无卡精品| 精品国产乱码久久久久久男人| 成年女人毛片免费观看观看9| 国产精品国产高清国产av| 久久婷婷人人爽人人干人人爱| 亚洲精华国产精华精| 午夜精品一区二区三区免费看| 我的老师免费观看完整版| 国产午夜精品久久久久久| av片东京热男人的天堂| 熟妇人妻久久中文字幕3abv| 久久久国产欧美日韩av| 久久久精品欧美日韩精品| 国产97色在线日韩免费| 国产伦一二天堂av在线观看| 美女大奶头视频| 综合色av麻豆| 亚洲人成电影免费在线| 成人永久免费在线观看视频| 色在线成人网| 国产精品一区二区三区四区久久| 午夜精品在线福利| av黄色大香蕉| 在线观看免费视频日本深夜| 久久久久久久久久黄片| 久久九九热精品免费| 免费在线观看日本一区| 神马国产精品三级电影在线观看| 亚洲国产欧美人成| 国产成人aa在线观看| 亚洲国产日韩欧美精品在线观看 | 亚洲精品在线观看二区| 亚洲精品中文字幕一二三四区| 成人亚洲精品av一区二区| 亚洲欧美精品综合一区二区三区| 日本 av在线| 1024手机看黄色片| 脱女人内裤的视频| 男女午夜视频在线观看| 欧美zozozo另类| 久久午夜综合久久蜜桃| 在线观看免费视频日本深夜| 精品乱码久久久久久99久播| 亚洲色图 男人天堂 中文字幕| 可以在线观看毛片的网站| 伊人久久大香线蕉亚洲五| 黄色视频,在线免费观看| 免费看日本二区| 国产精品一区二区精品视频观看| 无遮挡黄片免费观看| 色播亚洲综合网| 国产人伦9x9x在线观看| 黄色 视频免费看| or卡值多少钱| 欧美成人免费av一区二区三区| 亚洲午夜精品一区,二区,三区| 免费电影在线观看免费观看| 国产成人影院久久av| 窝窝影院91人妻| www日本黄色视频网| 俺也久久电影网| 亚洲av片天天在线观看| www日本黄色视频网| 国产亚洲精品久久久com| 久久久久久久久中文| 美女免费视频网站| 性色avwww在线观看| 亚洲中文日韩欧美视频| av国产免费在线观看| 桃红色精品国产亚洲av| 国产1区2区3区精品| 美女午夜性视频免费| a在线观看视频网站| 国产精品电影一区二区三区| 在线视频色国产色| 天天躁日日操中文字幕| 两个人看的免费小视频| 伊人久久大香线蕉亚洲五| 国产成人精品久久二区二区91| 两个人看的免费小视频| 99国产极品粉嫩在线观看| 狠狠狠狠99中文字幕| 精品一区二区三区av网在线观看| 日韩欧美国产一区二区入口| 亚洲黑人精品在线| 久久久久久久久免费视频了| 欧美又色又爽又黄视频| 亚洲九九香蕉| 最近最新中文字幕大全电影3| 男人舔女人的私密视频| 国产成人精品无人区| 日日夜夜操网爽| 婷婷精品国产亚洲av在线| 亚洲午夜理论影院| 久久精品人妻少妇| 亚洲aⅴ乱码一区二区在线播放| 亚洲欧洲精品一区二区精品久久久| 此物有八面人人有两片| 嫩草影院入口| 中文字幕av在线有码专区| 日本与韩国留学比较| 色播亚洲综合网| 亚洲av中文字字幕乱码综合| 九九久久精品国产亚洲av麻豆 | 亚洲成a人片在线一区二区| 国产精品久久久久久久电影 | 亚洲av日韩精品久久久久久密| 色尼玛亚洲综合影院| 亚洲av成人不卡在线观看播放网| 久久亚洲真实| 精品国内亚洲2022精品成人| 啦啦啦免费观看视频1| 一边摸一边抽搐一进一小说| 亚洲国产欧美网| 精品国产美女av久久久久小说| 久久久国产成人免费| 老司机深夜福利视频在线观看| 他把我摸到了高潮在线观看| aaaaa片日本免费| 欧美日韩综合久久久久久 | 日韩欧美国产一区二区入口| 丁香欧美五月| 久9热在线精品视频| 亚洲av五月六月丁香网| 国产午夜精品久久久久久| 丰满人妻熟妇乱又伦精品不卡| 日本五十路高清| 俺也久久电影网| 99久久99久久久精品蜜桃| 香蕉av资源在线| 国产成人欧美在线观看| 亚洲一区二区三区色噜噜| 国产高清有码在线观看视频| 久久人妻av系列| 午夜福利18| 一级作爱视频免费观看| 国产精品99久久99久久久不卡| or卡值多少钱| 看免费av毛片| 亚洲国产精品999在线| 麻豆成人午夜福利视频| 精品福利观看| 香蕉丝袜av| 成人欧美大片| 国产精品av视频在线免费观看| 欧美色欧美亚洲另类二区| 亚洲 欧美 日韩 在线 免费| 久久久久久久精品吃奶| 日日摸夜夜添夜夜添小说| 久久中文看片网| 欧美日韩亚洲国产一区二区在线观看| 成人国产一区最新在线观看| 日本一二三区视频观看| 亚洲自偷自拍图片 自拍| 国产三级黄色录像| 男女那种视频在线观看| 久久精品aⅴ一区二区三区四区| 中文字幕精品亚洲无线码一区| 国语自产精品视频在线第100页| 国产精品自产拍在线观看55亚洲| 99久久成人亚洲精品观看| 成人三级黄色视频| 午夜福利视频1000在线观看| 亚洲午夜精品一区,二区,三区| 亚洲狠狠婷婷综合久久图片| 窝窝影院91人妻| 美女黄网站色视频| 亚洲avbb在线观看| 男女午夜视频在线观看| 在线观看日韩欧美| 动漫黄色视频在线观看| 母亲3免费完整高清在线观看| 香蕉久久夜色| 久久久国产精品麻豆| 国内精品久久久久精免费| 免费av毛片视频| 亚洲精品456在线播放app | 1000部很黄的大片| 国产亚洲精品久久久com| 一级黄色大片毛片| 色播亚洲综合网| 国产精品乱码一区二三区的特点| 极品教师在线免费播放| 怎么达到女性高潮| 久久天堂一区二区三区四区| 一卡2卡三卡四卡精品乱码亚洲| 亚洲自拍偷在线| 成人av在线播放网站| 老汉色∧v一级毛片| 成年人黄色毛片网站| 九九在线视频观看精品| 母亲3免费完整高清在线观看| 亚洲欧美日韩东京热| 欧美性猛交黑人性爽| 精品国内亚洲2022精品成人| 丰满人妻一区二区三区视频av | 91久久精品国产一区二区成人 | 国产成人欧美在线观看| 又粗又爽又猛毛片免费看| 欧美成狂野欧美在线观看| 老熟妇乱子伦视频在线观看| 欧美日韩乱码在线| 亚洲无线观看免费| 国产一区二区三区在线臀色熟女| 可以在线观看毛片的网站| 一二三四社区在线视频社区8| 蜜桃久久精品国产亚洲av| 91av网一区二区| 桃色一区二区三区在线观看| 伊人久久大香线蕉亚洲五| 99精品久久久久人妻精品| 亚洲精品在线美女| 欧美xxxx黑人xx丫x性爽| 亚洲午夜精品一区,二区,三区| 欧美激情在线99| 日韩精品中文字幕看吧| 国产黄色小视频在线观看| 国产伦精品一区二区三区四那| 国产av不卡久久| 中文字幕久久专区| 国产免费av片在线观看野外av| 亚洲avbb在线观看| 国产一区在线观看成人免费| www国产在线视频色| 日本与韩国留学比较| 日本撒尿小便嘘嘘汇集6| 嫩草影视91久久| 精品一区二区三区视频在线 | 精品国产亚洲在线| 久久久久九九精品影院| 麻豆成人av在线观看| 成人无遮挡网站| 在线a可以看的网站| 国产精品久久久久久人妻精品电影| 熟妇人妻久久中文字幕3abv| 90打野战视频偷拍视频| 欧美高清成人免费视频www| 欧美性猛交黑人性爽| 国产伦精品一区二区三区四那| 亚洲国产欧美人成| 中文字幕高清在线视频| 久久久久久大精品| 黑人操中国人逼视频| 免费大片18禁| 日韩国内少妇激情av| а√天堂www在线а√下载| 亚洲va日本ⅴa欧美va伊人久久| 两个人视频免费观看高清| 两性午夜刺激爽爽歪歪视频在线观看| 一夜夜www| 国产精品一区二区三区四区免费观看 | 一二三四社区在线视频社区8| 久久久久久大精品| 亚洲一区二区三区不卡视频| 久久久久久国产a免费观看| 亚洲中文日韩欧美视频| 亚洲av电影在线进入| 久久精品亚洲精品国产色婷小说| 欧美性猛交╳xxx乱大交人| 亚洲专区字幕在线| 免费看美女性在线毛片视频| 国产成+人综合+亚洲专区| 国模一区二区三区四区视频 | 啪啪无遮挡十八禁网站| 亚洲精品在线美女| 精品无人区乱码1区二区| 日韩免费av在线播放| tocl精华| 97碰自拍视频| 亚洲男人的天堂狠狠| 88av欧美| 国产成人精品久久二区二区免费| 日本免费a在线| 黄色日韩在线| 给我免费播放毛片高清在线观看| 又粗又爽又猛毛片免费看| 两人在一起打扑克的视频| 午夜a级毛片| 国产成人av激情在线播放| 亚洲av电影在线进入| 色老头精品视频在线观看| 一本久久中文字幕| 亚洲 国产 在线| 少妇的丰满在线观看| 午夜免费观看网址| 天堂av国产一区二区熟女人妻| 欧美性猛交╳xxx乱大交人| 免费无遮挡裸体视频| 亚洲色图 男人天堂 中文字幕| 日韩精品青青久久久久久| 欧美成人免费av一区二区三区| 丰满人妻一区二区三区视频av | 一卡2卡三卡四卡精品乱码亚洲| 日韩欧美三级三区| 亚洲av成人一区二区三| 99久久无色码亚洲精品果冻|