CERAMICS
INTERNATIONAL
Available online at www.sciencedirect
Ceramics International 41(2015)1595–
1601
Fabrication of high infrared re flective ceramic films on polyester fabrics
by RF magnetron sputtering
Dagang Miao a ,Hongmei Zhao b ,Qingxin Peng a ,Songmin Shang a ,Shouxiang Jiang a ,n
a
Institute of Textiles and Clothing,The Hong Kong Polytechnic University,Kowloon,Hong Kong,China
b
Department of Prosthodontics,The Af filiated Hospital of Qingdao University,Qingdao,China Received 18July 2014;received in revised form 16September 2014;accepted 17September 2014
Available online 28September 2014
Abstract
In this project,AZO/Ag/AZO and AZO/Cu/AZO multilayer films were deposited on polyester fabrics with radio frequency (RF)magnetron sputtering technology.The prepared samples were systematically investigated with X-ray diffraction (XRD),Scanning Electron Microscope (SEM)and Fourier Transform Infrared Spectroscopy.Physical properties of the coated fabrics were evaluated by infrared re flection rate,contact angle (CA),air permeability and UPF value.The results indicated that the AZO/Ag/AZO coated polyester fabrics presented a high infrared re flection rate of 95–96%and CA of about 92.51/93.51,air permeability of 17.1/15.4ml/s/cm 2at 100Pa and UPF values of 40.64/46.67.The AZO/Cu/AZO coated polyester fabrics exhibited an infrared re flection rate of 50–60
%,CA of about 881/88.51,air permeability of 18.1/17.5ml/s/cm 2at 100Pa and UPF values of 41.96/48.437.
&2014Elsevier Ltd and Techna l.All rights reserved.
Keywords:AZO/Ag/AZO;AZO/Cu/AZO;Polyester fabric;Infrared re flection;RF magnetron sputtering
1.Introduction
In recent years,researches on near-infrared (NIR)re flective thin films have attracted considerable attention and interest,particularly the ones related to highly visible transparent films.Such films have found a broad range of usages.For example,when coated on glass,they help to substantially reduce energy consumption of buildings.Transparent conductive oxides (TCOs)are promising materials for energy conservation films due to their high transparency level and high concentration of free electrons [1–4].Of them,Al-doped ZnO (AZO)is an emerging TCO material and has been extensively investigated,because of its ability to substitute the widely used but expensive Indium Tin Oxide (ITO),and its rich reserve on the earth,non-toxic nature,reduction stability to hydrogen plasmas,and the relative easiness of its synthesis and processing [5].However,the best NIR re flectance of AZO films can only be obtained when heating treatments are employed during or after the deposition proc
ess,which increases the overall cost of solar
materials fabrication.Recently,TCO/Metal/TCO multilayer film has received a renewed interest as a highly promising route in fabricating solar materials [6–9].It has been reported that the infrared re flective property of the TCO/Metal/TCO multilayer films is proportional to the metal's electrical conductivity [10–12].Of all the metals,Ag and Cu have the highest electrical conductivity,thus AZO/Ag/AZO and AZO/Cu/AZO multilayer films have been intensively investigated,and a considerable amount of results have been reported.
Miao [10–12]has investigated the high infrared properties of AZO/Ag/AZO trilayers deposited on polyester film and glass substrate.Sahu [13]has prepared AZO/Ag/AZO trilayers by electron beam evaporation.Zhu [14]has studied the infrared emissivity of AZO thin films.Wu [15]and Crupi [16]have investigated the optimization of AZO/Ag/AZO structures.Lin [17]has studied the optoelectronics and microstructures of AZO/nano-layer metals/AZO.Jung [18]has characterized the AZO/Cu/AZO films prepared on polyethersulfone substrate.Wang [19]investigated the transparent,conductive and NIR re flective pro-perties of Cu-based Al-doped ZnO multilayer films.However,most of infrared re flective thin films are deposited on rigid glass
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0272-8842/&2014Elsevier Ltd and Techna l.All rights reserved.
n
Corresponding author.Tel.:þ852********;fax:þ852********.E-mail address:kinor.j@polyu.edu.hk (S.Jiang).
or polyester films to fabricate heat shielding glasses and window-films.These studies have enriched and deepened our under-standing of these films.However,most of the infrared re flective thin films studied are deposited on rigid materials such as glass or polyester films to form heat shielding glasses and window-films.Textiles possess unique properties,such as flexibility and permeability.Traditional heat shielding textiles are developed by coating a layer or layers of substance on the surface,and are widely used in various products such as curtains,tents,and umbrellas.However,these products have some limitations,such as low transparency,high visible light re flection,low air permeability and stiff hand feeling.To solve these problems,radio frequency (RF)magnetron sputtering technology was used in this project to deposit AZO/Ag/AZO and AZO/Cu/AZO multilayer films on polyester fabrics to form innovative heat shielding textiles.It has bee
n proved that the nanostructure has a profound effect on the hydrophobic properties of the materials,that hydrophobic materials can be obtained by depositing nanostructured materials and the hydrophobic properties can be evaluated by the measurement of contact angle (CA)[20–22].
The surface morphology of the multilayer films coated polyester fabric was analyzed by a Scanning Electron Microscope (SEM).X-ray diffractometer (XRD)analysis was conducted to analyze the crystal structure of the multilayer films.In addition,the ultraviolet (UV)protection,contact angle,air permeability and infrared rad-iation properties of the coated polyester fabrics were also evaluated.2.Experimental
AZO/Ag/AZO and AZO/Cu/AZO multilayer films were deposited on polyester fabrics (75D/180T 90n 90,64.50g/m 2)by a RF magnetron sputtering apparatus.Prior to deposition,the fabric substrates were ultrasonically cleaned in a detergent bath first and washed in acetone solution later,and then dried in nitrogen.The polyester samples were cut into 6cm by 6cm pieces and conditioned in accordance to ASTM D1776-08before sputtering.Deposition parameters are shown in Table 1.Film thickness was controlled by an online mea-surement system which was calibrated by post-deposition measurements in a surface pro file system (Alpha-Step 500)and film cross section measurement by Scanning Electron Microscope (JEOL-7100F).The accuracy of the film thickness was better than 75
%.Both of the bottom and the top AZO layers were fixed at 30nm,while the Ag and Cu inner layers were deposited at 15and 20nm,respectively.
The surface morphology of the coated fabrics was investigated by using a Scanning Electron Microscope (JEOL-7100F).Surface morphology was obtained by Atomic Force Microscopy (Bruker Nanoscope 8).Crystal structure of the AZO/Ag/AZO and AZO/Cu/AZO coated fabrics was characterized by θ/2θX-ray diffract-ometer (Rigaku SmartLab)using Cu K αradiation (λ¼0.154nm)(45kV at 200mA)at X'celerator normal mode.The XRD spectra were obtained at 2θangles range of 30–701with a scanning increment of 0.021/step and the scanning speed was 51/min.Contact angle measurements were conducted by using a contact angle meter (Model CAM-Moric;Tantec Inc.).Samples (2.0Â2.0cm 2)were taken from the coated fabrics and placed on the observation platform.A water drop of 5μl was placed on the tested sample and the CA was taken by manual manipulation of the protractor on the apparatus.The measurements were taken on side of the water droplet 1min after its placement.Air permeability measurements were taken by using an air permeability tester (SDL international,M021S)according to ISO 9237:1995.The testing area was 5cm 2and pressure drop across the testing area was 100Pa.UV radiation penetration of the coated fabrics was evaluated with a UV –visible spectrophotometer (Varian,Cary 300Conc)over wavelengths rangin
g from 280to 400nm.The ultraviolet protection factor (UPF)results were calculated by using the methods described in AATCC 183-2004.Infrared radiation properties of the coated samples were evaluated by Perkin Elmer Spectrum 100Spectrophotometer ranging from 1.5to 20μm.3.Results and discussion
3.1.XRD analysis
XRD spectra of the AZO/Ag/AZO and AZO/Cu/AZO coated polyester fabrics are shown in Fig.1.In the AZO/Ag/AZO coated samples,both ZnO (002)and Ag (111)peaks can be observed in the XRD spectra.These results proved the well de fined wurtzite ZnO structure and the crystallization of Ag inner layer in the multilayer films.Intensity of Ag (111)peaks increased with the increase of Ag layer thickness as expected.In the AZO/Cu/AZO coated samples,only ZnO (002)peak can be detected,which also proved that the wurtzite ZnO structure was formed in the AZO/Cu/AZO multilayer film.However,no obvious Cu peak was present in the XRD spectra,which may indicate that either the Cu particles were deposited in amorphous form in the multilayer film or the weak Cu peak diffraction was covered by the diffraction from the top AZO layer.The result is similar to that in other report [23]that Ag film presented higher intensity than that of Cu film under the
Table 1
Deposition parameters.
AZO layers
Ag layer
Cu layer
Target
AZO (ZnO:Al 2O 3¼98wt%:2wt%)99.99%;Φ9cm Ag 99.99%;Φ9cm Cu 99.99%;Φ9cm Base Pressure (Pa)5Â10–45Â10–45Â10–4RF power (W)
1503050Ar flow rate (sccm)402530Working pressure (Pa)
0.50.250.3Target-substrate distance (cm)
10
10
10
D.Miao et al./Ceramics International 41(2015)1595–1601
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same situation.By comparing the two groups of samples,it is also found that the intensity of ZnO (002)peaks of the AZO/Cu/AZO coated samples was lower than that of AZO/Ag/AZO coated samples.This may indicate that the crystallization of metal inner layer also helped increase the crystallization of the top layer.3.2.Surface morphology analysis
SEM images of the AZO/Ag/AZO and AZO/Cu/AZO coated polyester fabrics are presented in Fig.2.As shown in the images,
nano-particles were well deposited and the sizes of the particles ranged from about 40to 80nm,according to the bar in SEM images.The deposited nano-particles would endow the deposited polyester fabrics with nanomaterials'unique properties.It can also be observed that the particles of the film with 20nm inner layer were slightly bigger than that of the film with 15nm inner layer.This result is in accordance with those reported by other rese-archers [24,25].In addition,fluctuant surface and groove of the polyester fiber affected the flatness of deposited films.The deposited multilayer films were not as flat as the films deposited on glass substrate.
AFM images of the AZO/Ag/AZO and AZO/Cu/AZO coated polyester fabrics are presented in Fig.3.Surface roughness of the AZO/Ag/AZO coated polyester fabrics were 1.74nm (Ag 15nm)and 5.56nm (Ag 20nm)respectively;and roughness of the AZO/Cu/AZO coated polyester fabrics were 1.63nm (Cu 15nm)and 5.00nm (Cu 20nm)respectively.It can be obtained that surface roughness of the AZO/Ag/AZO coated polyester fabrics was a little bigger than that of AZO/Cu/AZO coated fabrics,and thicker metal inner layer would cause rougher surface.3.3.Contact angle (CA)analysis
Wettability of the coated samples was evaluated by the water CA measurement of the uncoated and coated polyester fabrics.CA of the bare polyester fabric was about 501due to the hydrophobic property of the fabric (presented in Fig.4
(a)).
Fig.1.XRD spectra of the AZO/Ag/AZO and AZO/Cu/AZO coated
samples.
Fig.2.SEM images of the AZO/Ag/AZO and AZO/Cu/AZO coated samples.
D.Miao et al./Ceramics International 41(2015)1595–16011597
CAs of the AZO/Ag/AZO coated polyester fabrics were about 92.51(Ag 15nm)and 93.51(Ag 20nm)respectively,and CAs of the AZO/Cu/AZO coated polyester fabrics were about 881(Cu 15nm)and 88.51(Cu 20nm)respectively.The selected representative CA images of the prepared samples are shown in Fig.4.These results demonstrated that water repellency of the coated fabrics increased by about 70–80%compared with the bare polyester fabric.The water repellency property of the coated fabrics was caused by the novel function of nano-materials.As stated by other researchers [22],CA of the coated fabric was affected by the thickness of the coated films.In this study,film thickness only varied little in each group,therefore,CA of the coated fabrics only changed slightly.Additionally,CAs of the AZO/Cu/AZO coated polyester fabrics was lower than that of AZO/Ag/AZO coated polyester fabrics,which may
be caused by the better crystallization of the top AZO layers of the AZO/Ag/AZO multilayer film.This is consistent with the XRD results presented in Fig.1.It may also be caused by the differences in natu
re of Cu and Ag,which has been reported in other study [26].
3.4.Air permeability analysis
Air permeability values of AZO/Ag/AZO coated polyester fabrics were 17.1(Ag 15nm)and 15.4(Ag 20nm)ml/s/cm 2at 100Pa respectively;and the values of AZO/Cu/AZO coated polyester fabrics were 18.1(Cu 15nm)and 17.5(Cu 20nm)ml/s/cm 2at 100Pa respectively.On the other hand,air per-meability of the uncoated polyester fabric was 20ml/s/cm 2at 100Pa.Fabric air permeability is largely determined by
the
Fig.3.AFM images of the AZO/Ag/AZO and AZO/Cu/AZO coated samples.
D.Miao et al./Ceramics International 41(2015)1595–1601
1598
spaces between the fabric yarns [27];deposited nano-particles reduce the spaces thus causing the decrease of air permeability.However,the deposited particles are nano-sized;blocking only a fraction of the spaces,and thus only reduce air permeability of the coated fabric slightly.Actually the largest reduction of air permeability of the coated fabrics as compared with that of the bare fabric in this project was about 23%.It can also be observed that air permeability decreased with the increase of the deposited films thickness.Air permeability of the AZO/Cu/AZO coated polyester fabrics was higher than that of the AZO/Ag/AZO coated polyester fabrics.This indicates that the AZO/Cu/AZO coated polyester fabrics had more yarn spaces than the AZO/Ag/AZO coated polyester fabrics.This may be cau-sed by the differences between the amorphous Cu inner layer and crystallized Ag inner layer;the amorphous layer was not as compact as the crystallized layer.
3.5.Ultraviolet radiation penetration analysis
UV transmittance through a fabric is the crucial factor to determine the UV protection properties of textiles.Ultraviolet protection factor (UPF)is the scienti fic term used to indicate the degree of UV protection provided to the skin of a wearer by the fabric.UPF is de fined as the ratio of the average effective UV irradiance unprotected skin to the irradiance protected by the test fabric.The higher the value,the better the UV protection properties of the fabric will be.
UPF values of AZO/Ag/AZO coated polyester fabrics were 40.64(Ag 15nm)and 46.67(Ag 20nm)respectively,and UPF
values of AZO/Cu/AZO coated polyester fabrics were 41.96(Cu 15nm)and 48.437(Cu 20nm)respectively.UPF value of the uncoated polyester fabric was only 20.09.Hence UPF values of the coated polyester fabrics increased by 102–141%.AZO/Cu/AZO coated fabrics presented higher UPF values than AZO/Ag/AZO coated fabrics with the same film thickness,probably because of the darker color of the AZO/Cu/AZO coated fabrics.Usually,darker colored materials provide better UV protection,as reported by other researchers [28,29].
According to AATCC 183-2004,fabrics with UPF values between 15and 24are classi fied as having “Good Protection ”;those between 25and 39are “Very Good Protection ”and those of 40or above are
“Excellent UV Protection ”.The results of this study indicate that AZO/Ag/AZO and AZO/Cu/AZO coated polyester fabrics are generally able to provide “Excellent UV Protection ”.3.6.Infrared properties analysis
Infrared properties of AZO/Ag/AZO coated polyester fabrics are shown in Fig.5.In Fig.5(a),the coated fabrics exhibited much higher infrared re flection rate than the bare polyester fabric,and the re flection rate was about 95–96%in the FIR region.The infrared re flection is caused by the interactions between the infrared elec-tromagnetic wave and free electrons in the multilayer film,where when the free electrons re flect the infrared photons [7,30].Infrared re flection rate is largely determined by the concentration of the free electrons;actually it is proportional to the number of free electrons in the multilayer film.Because free electrons affect electrical conductivity directly,the IR re flection rate also has a
similar
Fig.4.CA images of the samples:(a)bare polyester fabric (501);(b)AZO/Ag/AZO coated polyester fabric (93.51);and (c)AZO/Cu/AZO coated polyester fabric (881).
D.Miao et al./Ceramics International 41(2015)1595–16011599
curtains

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