Nanolayer on Polyester

Article pubs.acs.org/IECR

Electroless Plating of Silver Nanoparticles/Nanolayer on Polyester Fabric Using AgNO3/NaOH and Ammonia Majid Montazer* and Vida Allahyarzadeh Textile Engineering Department, Center of Excellence in Textile, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran, Iran ABSTRACT: A new method of producing conductive polyester fabric by using a novel electroless plating of silver nanoparticles on the fabric is introduced. The fabric was first treated with silver nitrate and sodium hydroxide at 130 °C for 1 h and then with ammonia at boil for 1 h. This treatment enhanced the fabric surface activity, created surface roughness, improved nanoparticle absorption, and produced ethylene as a reducing agent. This led to the formation of silver nanoparticles condensed into a nanolayer on the fabric surface after post-treatment with ammonia. X-ray diffraction patterns confirmed the presence of pure silver metal with a crystal size of 14 nm. Field-emission scanning electron microscopy images and energy-dispersive X-ray patterns also showed the presence of a silver nanolayer comprising silver nanoparticles on the fabric surface. The fabric treated under optimized conditions exhibited a low electrical resistivity of around 1.3 Ω/square. activation, electroless plating, rinsing, and drying.6,13,14 The pretreatments of sensitization and activation are the most important steps for enhancing the rate of reduction of the plating metal ions and improving the stability of the metal plating. However, these pretreatment processes are very expensive because they require the application of noble metal ions such as Au and Pd.6,18,21−23 The cost of electroless plating can be reduced by introducing organic functional groups such as amino, carboxyl, thiol, and silane groups onto the polymer surface by other methods.24−27 Then, the metal ions can bind to these functional groups by coordination and ionic bonding, forming a metal layer on the polymer surface by chemical reduction of the metal ions to elementary metal.27 Because the metal ions are absorbed on the polymer surface by weak van der Waals forces through electroless plating without activation and polymer surface modification,24 the metal layer on the polymer surface is not sufficiently stable. Therefore, introducing functional groups onto the polyester fabric surface is the best choice for chemical electroless plating.13,17,28 Lu13 and Lili et al.17 modified polyester fabric with 3-mercaptopropyltriethoxysilane and then deposited Cu and Ag, respectively, onto the fabric by chemical electroless plating. They produced Cu- and Ag-coated polyester fabrics with good stability and high electric conductivity. In these previous works, different steps including alkali hydrolysis under hard conditions, surface modification with complex chemicals such as 3-mercaptopropyltriethoxysilane, and electroless metal (Cu and Ag) plating were carried out. In another work, Lu et al. formed a silica-like layer on polyester fabric by using an acetone solution of (3aminopropyl)trimethoxysilane followed by an anhydrous toluene solution containing 3-mercaptopropyltriethoxysilane and finally produced silver-plated polyester fabric with good

1. INTRODUCTION Smart functional textiles with metallic layers on their surfaces that exhibit new properties such as electrical conductivity have received a great deal of attention during recent years. Conductive fabrics with high electrical conductivity and desirable properties, such as light weight, fineness, and flexibility, have been applied in electromagnetic interference (EMI) shielding, electronic sensors, microwave absorption, and heat generation1−4 and are also the focus of research attention. Among different textile fibers, synthetic fibers are of interest in the production of conductive fibers, and polyester is foremost in terms of fiber production and consumption, although its high electrical resistance makes it difficult for use in various applications requiring low electrical conductivity.4 Diverse methods have been employed to improve the conductivity of synthetic fabrics, including using conductive fillers such as carbon nanotubes, carbon black, carbon fiber, metalized fiber, and metal powder;5−7 applying coatings of conductive polymers such as poly(3-methylthiophene), polyaniline, and polypyrrole;8−12 and producing metallic layers on the fabric surface using sputtering, electric plating, chemical electroless plating, physical vapor deposition (PVD), and chemical vapor deposition (CVD).5,6 The electroplating process requires a conductive substrate and is not an appropriate method for textile substrates, whereas nonconductive substrates can be coated by chemical electroless plating, sputtering, PVD, and CVD.6 Moreover, sputtering and CVD processes require high-temperature treatments, which are not suitable for textiles,13 and PVD processes require high vacuum and huge energy supply systems, which are very expensive.6 Among the different processes for metallic coating of textiles, chemical electroless plating is a useful process that has been used for a long time and has attracted much attention because of its low cost and uniform metallic plating. The electroless depositions of Ag, Cu, Ni, and Fe on polyester fabric surfaces and other substrates have been reported.6,14−20 Generally, the chemical electroless plating process requires several steps including scouring, etching, sensitization, © XXXX American Chemical Society

Received: March 12, 2013 Revised: May 21, 2013 Accepted: May 29, 2013

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dx.doi.org/10.1021/ie400804n | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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Table 1. Production of a Silver Layer on a Polyester Fabric Surface by Various Researchers material(s) used

electroless bath

advantages

polydopamine

AgNO3 and glucose

NaOH, 3-mercaptopropyltriethoxysilane

AgNO3, NaOH, NH4OH, C6H12O6, tartaric acid, and CH3CH2OH AgNO3, C4H4O6, NaK, and NH3·H2O

acetone solution of (3-aminopropyl) trimethoxysilane; anhydrous toluene containing 3-mercaptopropyltriethoxysilane, toluene, and ethanol

ref

fast, simple, efficient, nontoxic, controllable procedure, good electrical conductivity, and strong adherence good electrical conductivity and electromagnetic shielding property

28

conductivity and strong adherence

16

17

2.2. Simultaneous Alkali Hydrolysis of Polyester and Electroless Plating of Silver. The polyester fabrics were washed with 1 g/L anionic detergent for 20 min and then rinsed with distilled water and dried at room temperature. The polyester fabric samples were cut to 5 cm × 3 cm; weighed; and immersed in a prepared bath containing silver nitrate, sodium hydroxide, and distilled water with a liquor-to-goods (L/G) ratio of 40:1 for 1 h at 130 °C (Table 2). The remaining

conductivity and strong adherence using ultrasonic-assisted electroless plating.16 Moreover, Wang et al. functionalized polyester fabric with polydopamine (PDA) and then used electroless plating of silver to produce poly(ethylene terephthalate)−PDA/Ag fibers with good electrical conductivity and high stability.28 The materials used in the mentioned methods and their advantages for producing a silver layer on the surface of polyester fabric are summarized in Table 1. All of the methods used to produce conductive polyester fabric require several steps and high-cost materials. They also cannot introduce a metallic layer onto the fabric surface directly and instead must cover the polyester surface with intermediate materials that assist metal-particle absorbance. The new method introduced in this article is capable of producing conductive polyester fabric in reduced time and cost by using a low-cost material. This method also introduces the silver nanoparticle/ nanolayer onto the polyester surface directly without using any chemicals as intermediates. In this work, a compact nanolayer of silver nanoparticles was introduced onto the polyester surface to produce a highly conductive polyester fabric with reasonable stability. The silver was plated onto the polyester fabric directly using simple, lowcost, and easily available materials in a conventional exhaustion process without the need for sensitization and activation processes. The polyester fabric was hydrolyzed with sodium hydroxide to introduce carboxyl and hydroxyl functional groups onto the polyester fabric surface and also to produce terephthalic acid and ethylene glycol and other forms of water-soluble low-molecular-weight polyester structures as reducing agents, as a result of polyester alkali hydrolysis. Silver ions were then absorbed onto the polyester fabric surface through binding to the carboxyl and hydroxyl functional groups and then reduced to elementary silver by various reducing agents including ethylene glycol, terephthalic acid, and other water-soluble low-molecular-weight polyester structures. This step was followed by the formation of a condensed nanolayer of silver nanoparticles on the polyester fabric surface by posttreatment with ammonia. The conditions of the electroless silver plating were optimized, and the surface morphology and mechanical and electrical properties of the treated polyester fabrics were investigated. The results are thoroughly discussed in this article.

Table 2. Effect of Electroless Silver Plating on the Weight Changes of Treated Samples electroless plating bath AgNO3 (g/L)

sample raw alkalihydrolyzed treated treated treated treated treated

NaOH (%, w/v)

weight change (%)

electrical resistance (Ω/square)

− −

− 0.5

− +9.7

6.8 × 109 4.1 × 109

1.25 7.5 12.5 17.5 25

0.5 0.5 0.5 0.5 0.5

+5.5 −8.5 −10 −17.5 −24

2.5 × 109 58 × 106 49 × 106 37 × 106 25 × 106

solution along with the treated polyester fabric was then treated with ammonia solution at boil for 1 h. The fabric was rinsed with distilled water and then dried at room temperature for 48 h. 2.3. Characterization. Field-emission scanning electron microscopy (FESEM) (Hitachi S4160) was used to observe the surface morphology of the treated fabrics. Also, energydispersive X-ray (EDX) analysis was used to analyze the elemental composition. A gold layer was deposited on the fabric surfaces before the analysis. X-ray diffraction (XRD; model EQuniox3000, INEL, Artenay,France) with nickel-filtered Cu Kα radiation was used to study the crystalline structure and presence of the absorbed nanoparticles on the fabric surface and also to estimate the size of the crystalline structure. The crystalline size was calculated according to the Scherrer equation D=

Kλ Bcor cos θB

(1)

with

2. EXPERIMENTAL DETAILS 2.1. Materials. Plain white polyester fabric with a weight of 188.5 g/m2 (Nafis Yarn Co., Qazvin, Iran), silver nitrate (AgNO3, extra-pure >99.8%, Merck, Darmstadt, Germany), sodium hydroxide (Merck, Darmstadt, Germany), aqueous ammonia (25%; Merck, Darmstadt, Germany), and anionic detergent (Ultravon GPN, Ciba Co., Basel, Switzerland) were used.

Bcor = (Bsample 2 − Bref 2 )1/2

where D, K, λ, and θ are the average crystal size, Scherrer coefficient (0.9), X-ray wavelength (λ = 1.540560 Å), and Bragg’s angle, respectively. Also, Bcor, Bsample, and Bref are the corrected full width at half-maximum (FWHM) in radians and the values of the fwhm of the reference and sample peaks, respectively.29 B



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The weight loss (WL) percentages of various samples were calculated as WL (%) =

W1 − W2 × 100 W1

A possible mechanism of the in situ synthesis of silver nanoparticles under alkali conditions of the hydrolysis of polyester fabric is shown in eqs 3−8.50,51 The addition of silver nitrate to the alkali solution leads to the formation of a hydrated form of Ag+ as [Ag(H2O)4]+, which then becomes silver oxide (Ag2O) sediment through the reaction of OH− ions with Ag+ ions. A dark cream solution is produced as a result of the formation of a large amount of silver oxide (Ag2O) sediment (eq 3).50 Increasing the temperature to 130 °C in strong alkali solution (pH 13) leads to the dissociation of Ag2O into Ag+ ions bonded to the hydroxyl (−OH) and carboxylate (−COO−) end groups on the fiber surfaces through an ionic interaction (eq 4).52 In addition, alkali hydrolysis of polyester fabrics leads to the formation of ethylene glycol, which is oxidized to aldehyde, producing electrons. This leads to the reduction of the silver ions to silver nanoparticles, resulting in a transparent clear solution (eqs 5−8).49,50

(2)

where W1 and W2 are the weights of the sample before and after treatment, respectively. The electrical resistance of different treated samples was measured using a precision impedance analyzer (6500 B series, Wayne Kerr Electronics, Chichester, U.K.) at 100 Hz and 1 V. Additionally, an atomic absorption spectrophotometer (Unicam 939, Cambridge, U.K.) was used to determine the percentage of silver metal on the treated fabrics. This was done by dissolving the silver plated on the fabric in nitric acid solution. Moreover, the stability of the silver nanolayer/nanoparticles on the polyester fabric surface was assessed by repeated washing with ammonia at 60 °C for 20 min for two cycles. The electrical conductivity of the washed samples was examined by the same method as described previously, and the stability of the silver nanolayer/nanoparticles on the surface of polyester fabric was assessed. To study the stability of the silver nanolayer/nanoparticles on the polyester fabric surface, a rubbing fastness test was also carried out. Rubbing fastness is a useful test for determining the resistance of color to transfer from a treated sample onto other surfaces by rubbing under dry or damp conditions and refers to the property of a treated textile to resist color loss or fading resulting from various conditions of use. The test was performed according to American Association of Textile Chemists and Colorists (AATCC) standard method AATCC 8-2007 using an AATCC crock meter. Specifically, a piece of white cotton fabric was attached at the end of the finger of the crock meter and moved against the dry test sample surface for 10 cycles under dry conditions. The color transferred by rubbing was evaluated for staining using gray scales.

2AgNO3 + 2NaOH → Ag 2O(s) + 2NaNO3 + H 2O(l) (3) +

2−

Ag 2O(s) → 2Ag + O

(4)

H−[−O−CH 2CH 2−O−CO−(C6H4)−CO−]n −OH + 2NaOH → HOCH 2CH 2OH + H 2O + H−[−O−CH 2CH 2−O−CO−(C6H4)−CO−]n − 1 −OH + NaO−CO−(C6H4)−CO−ONa

(5)

HOCH 2CH 2OH → CH3CHO + H 2O −

−

CH3CHO(aq) + 3OH → CH3COO + 2H 2O + 2e

(6) −

(7) +

−

Ag + e → Ag

0

(8)

Also, the produced silver nanoparticles are adhered on the polyester fabric surface through physical interlocking because of the rough surface produced by the alkali hydrolysis of polyester. Finally, a nanolayer of silver nanoparticles was formed on the polyester fabric surface upon treatment of the alkali-treated polyester fabric in ammonia solution. The mechanism of formation of a silver nanolayer on the polyester fabric is given by the equations53

3. RESULTS AND DISCUSSION 3.1. Alkaline Hydrolysis of Polyester Fabric and Synthesis of Silver Nanoparticles to Form Silver Nanolayer. The alkaline hydrolysis reaction of polyester with sodium hydroxide is topochemical degradation that takes place on the fiber surface. In this reaction, the hydroxide ions attack the electron-deficient carbonyl groups, causing polyester chain cleavage, removing terephthalate anions and ethylene glycol, producing hydroxyl (−OH) and carboxylate (−COO−) end groups on the fiber surfaces, and also decreasing the fiber weight and diameter. This reaction also removes the lowmolecular-weight segments of the chains, generating pits and holes on the fiber surfaces.30 The effects of alkaline hydrolysis on the polyester fiber surface and its physical properties were explained in our previous works.31,32 Silver nanoparticles have been widely investigated because of their good conductivity, catalytic properties, and high stability. Moreover, several methods have been used to synthesize silver nanoparticles such as chemical reduction; Tollen’s reagent; photoreduction; and biochemical, sol−gel, and polyol approaches.33−46 Ethylene glycol is a commonly used reducing agent in the polyol method for synthesizing silver nanoparticles47,48 through the reduction of silver ions by the oxidation of hydroxyl groups of poly(ethylene glycol) to aldehyde groups.49

Ag 2O(s) + 4NH3(aq) + 2NaNO3(aq) + H 2O → 2Ag (NH3)2 NO3(aq) + 2NaOH(aq)

(9)

2Ag(NH3)2 NO3(aq) + CH3CHO → 2Ag 0 + CH3COOH + 4NH3 + HNO3

(10)

Silver nitrate in alkali solution oxidizes to Ag2O, leading to the formation of Ag+ ions, some of which are reduced to Ag0 and others of which remain in solution. Addition of ammonia to the solution leads to the formation of diamminesilver(I) ([Ag(NH3)2]+) complex (eq 9) with positive charge53 that is known as Tollen’s reagent. The diamminesilver(I) complex usually oxidizes the aldehyde groups to carboxylate ions and then reduces the silver complex to elemental silver that is widely used to synthesize silver nanoparticles.51 [Ag(NH3)2]+ can be absorbed onto the polyester fabric surface through bonding to −COO− and −O− functional groups through ionic C



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interactions and then reduced to Ag0 by ethylene glycol (eq 10). Many functional groups and more pits can be formed on the polyester fabric surface as a result of the high level of alkali hydrolysis; consequently, the number of silver nanoparticles on the polyester fabric surface that absorbed by physical interlocking and chemical bonding is increased. The silver nanoparticles with a high surface activity are connected to each other; therefore, the growth of silver seeds occurs on the fabric surface, leading to the formation of a continuous silver nanolayer on the polyester fabric surface. This mechanism is proposed in Scheme 1.

fabrics treated with 0.5% (v/w) NaOH solution was about 10% (Table 2). Surface modification of polyester fibers with an alkali solution leads to a reduction of the fabric weight. A weight reduction of at least 10% can be the best modification for activating the surface of polyester fibers to increase the resulting plated metal coating and enhance the stability of the metal coating on the polyester fiber surface. The reason for this phenomenon is not clear completely; however, it appears that the functional end groups and pits introduced onto the surface of the polyester fibers by alkali hydrolysis play an important role in the higher absorption and adherence of the metallic layer on the surface of the fabric.19,30 The electroless plating of silver was performed with five different concentrations of silver nitrate (1.25−25 g/L) without ammonia post-treatment. The results showed that the weight loss percentages of the treated polyester fabrics decreased from +5% to −24% as the silver ion concentration was increased from 1.25 to 25 g/L, and the color of the treated fabrics changed from dark gray to dark cream. This indicates successful loading of the silver ions onto the surface of the polyester fabrics, confirming the reduction of silver ions to silver metal (Ag0) particles attached on the polyester fabrics. However, an increase in the AgNO3 concentration led to a higher fabric weight. Also, the electrical resistance of the treated polyester fabrics decreased from 4.1 GΩ/square to 25 MΩ/square because of the increase in Ag0 particles loaded on the polyester fabric surface as the AgNO3 concentration was increased from 1.25 to 25 g/L. However, because of the high level of electrical resistance of the treated polyester fabric with a low concentration of silver nitrate, the electroless plating of polyester fabric with low concentration of silver ions was not considered for further study. 3.3. Influence of Ammonia Post-Treatment on the Electrical Resistance of Treated Polyester Fabrics. The effect of ammonia post-treatment on the lowering of the electrical resistance of the polyester fabric is reported in Table 3. A marked difference was obtained in the electrical resistance

Scheme 1. Mechanism of Silver Nanolayer Formation on Polyester Fabric Surface

Table 3. Influence of Ammonia on the Electrical Resistance of Polyester Fabric electroless plating bath

It is worth noting that the production of a silver layer on polyester has been reported by others using methods requiring several processing steps, including alkali hydrolysis, surface modification, and electroless silver plating using different materials. In contrast, in the method applied in this research, all of these separate steps are combined in one single step employing simple materials including AgNO3 and NaOH. This introduces a silver nanoparticle onto the surface of polyester directly with strong adherence to the polyester fabric surface because of the alkali hydrolysis of the fabric with NaOH, which produces ethylene glycol as a reducing agent for the synthesis of silver nanoparticles. This approach reduces the time and processing cost significantly. Further, post-treatment with ammonia solution is a simple and inexpensive process with distinctive influences on the formation of a condensed nanolayer of silver nanoparticles on polyester fabric. 3.2. Effect of Electroless Silver Plating on the Treated Polyester Fabrics. The weight loss percentage of polyester


sample

AgNO3 (g/ L)

NaOH (%, w/v)

without ammonia

with ammonia (80 mL)

S1 S2

12.5 25

0.5 0.5

49 × 106 25 × 106

28.6 120

of samples S1 and S2 before and after ammonia post-treatment. Although silver electroless plating without ammonia posttreatment reduced the electrical resistance of the fabrics by more than a factor of 1000, the treated polyester fabrics exhibited a high level of electrical resistance. This could be due to the low silver nanoparticle absorption or scattered distribution of silver nanoparticles on the polyester fabric surface. Ammonia post-treatment of the silver electroless-plated polyester fabric led to formation of [Ag(NH3)2]+ complexes and the absorption of more silver ions onto the polyester fabric surface, which were then reduced to Ag0 nanoparticles. The Ag0 nanoparticles attached to each other as a result of high surface activity, forming a continuous silver nanolayer on the polyester fabric. Therefore, the electrical resistance on the polyester fabric was significantly reduced, and a reasonable conductivity was obtained. D



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Increasing the volume of ammonia solution from 80 to 150 mL (Table 4) led to greater reductions in the electrical

Table 5. Atomic Absorption Spectroscopy of Samples BS1 and BS2

Table 4. Influence of Ammonia Volume on the Electrical Resistance of the Fabric sample

NH3 (mL)


weight change (%)

S1

80 150 80 150

28.6 1.3 120.0 6.8

−16 −28 −21 −26

S2

sample

silver (%)

BS1 BS2

20.3 18.3

(treated with 25 g/L AgNO3 and 150 mL of aqueous ammonia), in agreement with the weight loss results. Further, more silver nanoparticles were loaded on the surface of sample BS1 compared to sample BS2, suggesting a better connection between the silver nanoparticles producing the condensed silver nanolayer on sample BS1. Increasing the AgNO3 concentration from 12.5 to 25 g/L possibly led to the synthesis of larger silver nanoparticles in solution, which decreased the tendency of the nanoparticles toward the fabric surface of sample BS2; therefore, a lower amount of silver nanoparticles absorbed on the surface of sample BS2. Thus, a condensed silver nanolayer was not formed on the surface of sample BS2, and consequently, its electrical resistance was higher than that of sample BS1. However, through the electroless silver plating of sample BS1, a higher concentration of AgNO3 led to a higher synthesis of silver nanoparticles on the sample surface, and their growth on the sample surface produced a condensed silver layer on the surface of sample BS1. These results were also confirmed by FESEM images (Figures 2 and 3). 3.5. XRD, FESEM, and EDX Analyses. The XRD pattern of sample BS1 (Figure 2e) includes five obvious peaks at 37.6°, 43.5°, 63.6°, 76.1°, and 80.6° corresponding to the (111), (200), (220), (311), and (222) planes, which are reflections of face-centered cubic (fcc) silver (JCPDS, silver file 4-0783). No characteristic peaks to indicate impurities such as Ag2O were found in this sample. Thus, pure silver metal with fcc symmetry was synthesized on all of the fabric samples. An average crystalline size of 14 nm was obtained according to the Scherrer equation and the full width at half-maximum (fwhm) for silver particles. Meanwhile, Figures 2 and 3 present micrographs of samples BS1 and BS2, respectively. A uniform and condensed silver nanolayer coated on the polyester fabric can be seen in Figure 2a,b, and the connection of silver seeds to each other can be observed in Figure 2c,d. Silver nanoparticles with diverse particle sizes ranging from 200 to 400 nm can be seen in the

resistance of the fabric from 28.6 to 1.3 Ω/square and from 120 to 6.8 Ω/square for samples S1 and S2, respectively. Further, introducing more ammonia into the solution led to increases in the fabric weight from 16% to 28% and from 21% to 26% for samples S1 and S2, respectively. This possibly led to the formation of more Ag[(NH3)2]+ complexes that adsorbed on the polyester fabric surface and formed a denser silver nanolayer on the fabric surface. Therefore, a heavier fabric with higher conductivity was obtained when the polyester fabrics were treated with more ammonia solution. Thus, samples S1 and S2 treated with 150 mL of ammonia were denoted as BS1 and BS2, respectively, considered as the best conductive polyester fabrics. The influence of ammonia posttreatment on the formation of a silver nanolayer on sample BS1 was confirmed by FESEM images. The FESEM images of the treated polyester fiber without ammonia post-treatment (S1) and with ammonia post-treatment (BS1) (Figure 1) confirm that the ammonia post-treatment led to more connection between the silver nanoparticles and, consequently, the formation of a condensed silver layer on the treated polyester fibers. The presence of silver nanolayer on samples BS1 and BS2 was also confirmed by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) analysis. 3.4. Atomic Absorption Spectroscopy (AAS). The silver contents of 2 g of samples BS1 and BS2 were calculated by AAS, and the results are reported in Table 5. The silver content of sample BS1 (treated with 12.5 g/L AgNO3 and 150 mL of aqueous ammonia) was greater than that of sample BS2

Figure 1. FESEM images of alkali-treated polyester fibers (a) without ammonia post-treatment (S1) and (b) with ammonia post-treatment (BS1). E



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Figure 2. FESEM images of sample BS1: (a) 1000×, (b) 2000×, (c) 30000×, and (d) 70000×. (e) XRD pattern. (f) EDX spectrum.

between 3 keV and 3.5 keV, pertaining to the silver characteristic lines Lα and Lβ. These results confirm those obtained by the other analysis methods. 3.6. Stability of Silver Nanoparticles/Nanolayer on the Surface of Polyester Fabric. 3.6.1. Stability of Silver Nanoparticles/Nanolayer against Washing. The stability of the silver nanoparticles/nanolayer on sample BS1 was studied by washing it twice with ammonia under the conditions described previously. The washed samples exhibited resistances of 120 Ω/square after two cycles of washings. Thus, the silver nanoparticles/nanolayer remained firmly adhered to the polyester surface, indicating good durability. Further, the surface hydrolysis of polyester fabric under alkali conditions assisted in the chemical and physical bonding of the silver nanoparticles/nanolayers on the polyester fabric by the creation of hydroxyl and carboxylate anions and also pits on the fabric surface. 3.6.2. Stability of Silver Nanoparticles/Nanolayer against Rubbing. The rubbing fastness test is designed to determine the color transferred from the surface of a colored textile to another surface by rubbing, whereas the strong bonding

nanolayer coated on sample BS1. Although it is difficult to determine the silver layer thickness on the fiber surface from the FESEM images, it can be estimated that the thickness of the silver layer on sample BS1 is less than 1 μm, confirming the formation of a silver nanolayer on the polyester fabric (Figure 2c,d). The silver nanolayer on sample BS2 is thin and not condensed, including silver nanoparticles with different sizes ranging from 30 to 250 nm, as can be seen in Figure 3. The silver seeds were not connected to each other instantly in sample BS2, forming a thin silver nanolayer on the sample surface because of the low and scattered absorption of silver nanoparticles. Overall, the sample coated with a condensed silver nanolayer (sample BS1) exhibited a lower electrical resistance than the sample coated with an uncondensed thin silver nanolayer (sample BS2). This can be clearly seen in the FESEM images of samples BS1 and BS2, confirming the results of electrical conductivity measurements. The silver plating on sample BS1 was also confirmed by EDX patterns (Figure 2f). The characteristic peaks related to the silver are located between 2 and 4 keV.29 In Figure 2f, the intense peaks attributed to elemental silver are observed F



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Figure 3. FESEM images of sample BS2: (a) 1000×, (b) 2000×, (c) 8000×, and (d) 70000×.

between the color and the surface of the fiber plays the main role in determining the transfer of color. This test has been used to evaluate the stability of silver nanolayer/nanoparticles on the surface of sample BS1. The bonding between the silver nanolayer/nanoparticles and the polyester fabric surface and also the bonding among the nanoparticles themselves are strong, as the number of particles transferred from the surface of sample BS1 was very low. The color transferred from the surface of sample BS1 (as indicator of nanoparticles transferred) to white cotton during the test was evaluated by gray scale for staining, and grade 4 was obtained. Because grade 5 means negligible or no color transfer, the obtained grade 4 shows that very few particles were transferred from the surface of sample BS1. This confirms the strong bonding between the silver nanolayer/nanoparticles and the polyester fibers of sample BS1, confirming the effect of alkaline hydrolysis in introducing many functional groups onto the surface of the polyester fibers and indicating the role of ammonia in adhering the silver nanoparticles to each other to form a silver nanolayer. The very small color change, namely, grade 4.5, obtained for sample BS1 after rubbing confirms the same results.

silver nanoplating on the polyester fabric surface led to a higher fabric weight with lower electrical resistance. Ammonia posttreatment of the silver electroless-plated polyester fabric also led to the formation of a condensed silver nanolayer on the polyester fabric surface, as confirmed by electric resistance and FESEM images. The concentration of ammonia was a crucial point, as increasing the amount of ammonia from 80 to 150 mL led to a lower electrical resistivity of 1.3 Ω/square. XRD and EDX patterns of the conductive polyester fabric confirmed the synthesis of pure silver metal with face-centered cubic symmetry on the fabric surface. The washing and rubbing fastness tests also confirmed the good stability of the silver nanolayer on the polyester fabric surface. Overall, a uniform silver nanolayer was plated on the polyester fabric surface to produce a conductive fabric through the application of the conventional alkali hydrolysis of polyester as a simple and lowcost processing method.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +982164542657. Fax: +982166400245.

4. CONCLUSIONS In this research, electroless plating of silver and surface modification of polyester fabric were performed in a single processing without surface sensitization and activation. The

Notes

The authors declare no competing financial interest. G



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