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Effect of ionic liquid on the structure and tribological properties of polycarbonate–zinc oxide nanodispersion
Materials Letters 61 (2007) 4531 – 4535 www.elsevier.com/locate/matlet
Effect of ionic liquid on the structure and tribological properties of polycarbonate–zinc oxide nanodispersion F.J. Carrión, J. Sanes, M.D. Bermúdez ⁎ Grupo de Ciencia de Materiales e Ingeniería Metalúrgica, Departamento de Ingeniería de Materiales y Fabricación, Universidad Politécnica de Cartagena, Campus de la Muralla del Mar, C/ Doctor Fleming s/n, 30202-Cartagena, Spain Received 15 February 2006; accepted 15 February 2007 Available online 28 February 2007
Abstract Room-temperature ionic liquid (IL) 1-hexyl-3-methylimidazolium hexafluorophosphate has been added to PC + 0.5 wt.%ZnO nanocomposite in a 1.5 wt.% proportion to obtain PC + 0.5%ZnO + 1.5%IL. The new PC/ZnO/IL nanocomposite shows a 80% friction reduction and a wear reduction of nearly two orders of magnitude with respect to PC + 0.5%ZnO. The influence of IL on the size, morphology and distribution of ZnO nanoparticles in the PC matrix is discussed on the basis of scanning (SEM) and transmission (TEM) electronic microscopic observations and energy dispersive X-ray (EDX) analysis. © 2007 Elsevier B.V. All rights reserved. Keywords: Polycarbonate; Zinc oxide; Nanocomposites; Ionic liquid; Wear
1. Introduction A polymer nanocomposite is defined as a composite material with a polymer matrix and filler particles that have at least one dimension less than 100 μm. A recent work by Sawyer et al. [1] includes a review of the literature on tribology of polymer nanocomposites. The role of filler components in influencing the wear behaviour of polymers is not yet fully understood, although some explanations have been provided. Nanoparticles are believed to improve the tribological performance of polymer matrices due to [2]: 1. The lower abrasiveness of nanoparticles with respect to that of microparticles due to the reduction in their angularity. 2. The formation of adhered transfer films as a result of the good blending between nanoparticles and wear debris particles. 3. The lower material removal when the fillers have a size of the order of the surrounding polymer chains.
⁎ Corresponding author. Tel.: +34 968325958; fax: +34 968326445. E-mail address: [email protected] (M.D. Bermúdez). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.02.044
Considerable experimental effort has been concentrated on the preparation and characterization of metal-containing nanoparticles embedded in polymer matrices [3–6]. However, there has been comparatively little work on the tribological study of polymer composites containing zinc oxide nanoparticles. Bahadur et al. [7] studied the effect of ZnO on the tribological behaviour of thermosetting polyester and found that Table 1 Thermal properties of the materials Thermal properties
PC
PC + 0.5%ZnO
PC + 0.5% ZnO + 1.5%IL
Tg (°C) Decomposition temperature (°C)
144.3 544.2
142.1 526.7
133.5 492.8
Table 2 Pin-on-disc tests results Disc material
Friction coefficient
Wear (mm3/Nm)
PC PC + 0.5%ZnO PC + 0.5%ZnO + 1.5%IL
1.02 0.90 0.14
2.58 × 10− 3 5.81 × 10− 3 7.54 × 10− 5
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F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Fig. 1. Friction–distance records for neat PC; PC + 0.5%ZnO and PC + 0.5% ZnO + 1.5%IL.
ZnO did not reduce the wear rate of the polymer. Li et al. [8] filled PTFE with nanoparticles of ZnO and improved wear resistance by nearly two orders of magnitude at ZnO concentrations around 15% by volume. However, the friction coef-
ficient of the nanocomposite was higher than that of the unfilled PTFE. Polycarbonate, an amorphous polymer with good moldability, is an important engineering thermoplastic which is finding applications both in structural parts and in electrooptical devices. Although there exists a great interest in developing new polycarbonate nanocomposites with improved properties [9–11], to the best of our knowledge, there is only one previous study [12] on the properties of polycarbonate–ZnO nanocomposites. Both as polymer and lubricant oil additives [13–15], inorganic nanoparticles and in particular Zn-containing nanoparticles, usually require the use of surface modifiers to achieve good dispersion of the nanoparticles. Imidazolium salts have been used as ionic surfactants to improve the dispersion of nanotubes in polymer matrices [16], and since the work by Ye et al. [17], imidazolium ILs have demonstrated their lubricating ability [18] and references therein]. We have previously [12,19] shown that the friction coefficients and wear rates of polymers against steel can be reduced by ZnO nanoparticles or by imidazolium-containing ILs, respectively.
Fig. 2. SEM micrographs of cryofracture surface: a) PC/ZnO nanocomposite; b) magnification (× 8000) and Zn elemental map.
F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Fig. 3. SEM micrograph of the cryofracture surface of PC + 0.5%ZnO + 1.5%IL.
Finally, ionic liquids have been used as reaction media to synthesize ZnO nanoparticles with different morphologies [20].
4533
Fig. 5. TEM micrograph of a thin layer of PC + 0.5%ZnO + 1.5%IL.
The aim of the present study was to determine the influence of ionic liquid addition on the tribological properties of PC/ nano-ZnO dispersions. 2. Experimental Polycarbonate (PC) was supplied by Kotec Corporation and ZnO nanopowder (average particle size 53 nm) was supplied by Aldrich. 1-hexyl-3-methylimidazolium hexafluorophosphate with purity N 97% was supplied by Fluka Chemie GmbH. PC/ZnO/IL nanocomposite was prepared by milling and injection molding as previously described [12]. The instrumentation for thermal analysis, microscopic characterization and microanalysis has also been reported [12]. Pin-on-disc tests according to ASTM G 99-05 standard were performed on 40 mm diameter, 4 mm height polymer discs sliding against AISI 316L (composition: b0.03% C; 17.55 Cr; 13% Ni; 2.5 Mo; hardness: 210 HV) stainless steel pins with 0.8 mm spherical end radius. Experimental parameters have
Fig. 4. TEM micrographs of: a) as-received ZnO nanoparticles; b) nanoparticles within the matrix of PC + 0.5%ZnO.
Fig. 6. TEM micrographs of PC + 0.5%ZnO + 1.5%IL showing the size and morphology of nanoparticles.
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F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Table 3 Element EDX analysis (%) for PC + 0.5%ZnO + 1.5%IL
Nanoparticle Matrix Interphase
abrasiveness due to their rounded morphology and their reduced tendency to agglomerate.
F
P
Zn
1.9 1.6 6.5
1.3 0.7 1.6
60.3 7.1 50.3
been previously described [12]. Friction coefficients were continuously recorded with time for each test and wear rates were calculated from wear track width measurements. 3. Results and discussion 3.1. Thermal properties Table 1 shows a significative change in chain mobility in the presence of the ZnO nanoparticles [12]. This chain mobility is further increased when IL is added. This plasticizing effect of ILs on thermoplastics has been previously described [19,21]. 3.2. Tribological properties Fig. 1 compares the friction/distance records for neat PC and for the nanocomposites PC + 0.5%ZnO and PC + 0.5%ZnO + 1.5%IL. Both PC and PC + 0.5%ZnO show low initial friction values which rapidly increase with distance to reach steady-state values after around 50 m for PC and around 150 m for PC + 0.5%ZnO. In contrast, for the IL-modified material PC + 0.5%ZnO + 1.5%IL, the initial low constant friction value is maintained up to the end of the test. Table 2 shows a 84.5% reduction in friction and a 98.7% wear reduction for PC + 0.5%ZnO + 1.5%IL with respect to the IL-free PC + 0.5%ZnO nanocomposite. The good performance obtained with the addition of IL could be related to the formation of a more homogeneous dispersion. 3.3. Structural characterization Fig. 2 shows the SEM micrographs of the cryofracture surfaces of PC + 0.5%ZnO, with large nanoparticle clusters. These agglomerates are mainly formed by ZnO nanoparticles as shown by the EDX elemental map (Fig. 2b). In contrast, PC + 0.5%ZnO + 1.5%IL (Fig. 3) shows a more ductile mode of fracture, with no large aggregates, but only rounded nanoparticles. As-received commercial ZnO nanoparticles can be observed in the TEM micrograph of Fig. 4a. Their polyhedral shape is maintained once they are embedded in the PC matrix (b) [12]. Fig. 5 shows the TEM micrograph of a thin section of PC + 0.5% ZnO + 1.5%IL where the distribution of the nanoparticles can be appreciated as black dots. The IL-modified particles have lost their sharp edges to give rise to a more rounded morphology and now appear as aggregates of entangled thin nanorods which can be more clearly seen in the outer layers of the particles (Fig. 6). EDX analysis (Table 3) shows an increase in fluorine and phosphorus content in the outer layer of the nanoparticles, at the interphase with the polymer matrix. This seems to indicate a nanoparticle–ionic liquid interaction which could explain the size and morphology changes observed in ZnO nanoparticles. The synthesis of ZnO nanoparticles with different morphologies [36] is currently being investigated [22]. The good tribological performance of the new nanocomposite PC + 0.5%ZnO + 1.5%IL could be attributed to the reduction of nanoparticle
4. Conclusions The addition of ZnO nanoparticles and a room-temperature ionic liquid to polycarbonate to obtain the new PC + 0.5%ZnO + 1.5%IL nanocomposite produces important reductions in friction and wear against AISI 316L stainless steel. The main reason for the enhanced tribological performance of the IL-modified nanocomposite could be the nanoparticle–IL interactions which modify the morphology of the nanoparticles within the polycarbonate matrix. The material described here could be the first of a new family of high performance polymer–nanoparticle–ionic liquid nanocomposites, although further research is still needed. Acknowledgements We thank MEC (Spain)/EU FEDER program (MAT200500067) and Fundación Séneca (Región de Murcia, Spain) (PI/ 00447/FS/04) for financial support. References [1] W.G. Sawyer, K.D. Freudenberg, P. Bhimaraj, L.S. Schadler, A study on the friction and wear behavior of PTFE filled with alumina nanoparticles, Wear 254 (2003) 573–580. [2] M.Q. Zhang, M.Z. Rong, S.L. Yu, B. Wetzel, K. Friedrich, Effect of particle surface treatment on the tribological performance of epoxy based nanocomposites, Wear 253 (2002) 1086–1093. [3] J. Tang, Y. Wang, H. Liu, Y. Xia, B. Schneider, Effect of processing on morphological structure of polyacrylonitrile matrix nano-ZnO composites, J. Appl. Polym. Sci. 90 (2003) 1053–1057. [4] S.P. Gubin, Metal-containing nanoparticles within polymeric matrices: preparation, structure and properties, Colloids Surf., A Physicochem. Eng. Asp. 202 (2002) 155–163. [5] L. Rapoport, O. Nepomnyashchy, A. Verdyan, R. Popovitch-Biro, Y. Volovik, B. Ittah, R. Tenne, Polymer nanocomposites with fullerene-like solid lubricant, Adv. Eng. Mater. 6 (2004) 44–48. [6] J.Q. Pham, C.A. Mitchell, J.L. Bahr, J.M. Tour, R. Krishanamoorti, P.F. Green, Glass transition of polymer/single-walled carbon nanotube composite films, J. Polym. Sci., Part B: Polym. Phys. 41 (2003) 3339–3345. [7] S. Bahadur, L. Zhang, J.W. Anderegg, The effect of zinc and copper oxides and other zinc compounds as fillers on the tribological behavior of thermosetting polyester, Wear 203/204 (1997) 464–473. [8] F. Li, K. Hu, J. Li, B. Zhao, The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene, Wear 249 (2002) 877–882. [9] B.K. Satapathy, R. Weidisch, P. Potschke, A. Janke, Crack toughness behaviour of multiwalled carbon nanotube (MWNT)/polycarbonate nanocomposites, Macromol. Rapid Commun. 26 (2005) 1246–1252. [10] P.J. Yoon, D.L. Hunter, D.R. Paul, Polycarbonate nanocomposites. Part 1. Effect of organoclay structure on morphology and properties, Polymer 44 (2003) 5323–5339. [11] P.J. Yoon, D.L. Hunter, D.R. Paul, Polycarbonate nanocomposites. Part 2: degradation and color formation, Polymer 44 (2003) 5341–5354. [12] F.J. Carrión, J. Sanes, M.D. Bermúdez, Influence of ZnO nanoparticle filler on the properties and wear resistance of polycarbonate. Wear, in press, doi: 10.1016/j.wear. 2007.01.016. [13] V.N. Bakunin, A.Y. Suslov, G.N. Kuzmina, O.P. Perenago, Synthesis and applications of inorganic nanoparticles as lubricant components—a review, J. Nanopart. Res. 6 (2004) 273–284.
F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535 [14] W. Liu, S. Chen, An investigation of the tribological behaviour of surfacemodified ZnS nanoparticles in liquid paraffin, Wear 238 (2000) 120–124. [15] A. Hernández, J.E. Fernández-Rico, A. Navas, J.L. Biseca, R. Chou, J.M. Díaz, The tribological behaviour of ZnO nanoparticles as an additive to PAO6, Wear 261 (2006) 256–263. [16] S. Bellayer, J.W. Gilman, N. Eidelman, S. Bourbigot, X. Flambard, D.M. Fox, H.C. De Long, P.C. Trulove, Preparation of homogeneously dispersed multiwalled carbon nanotube/polystyrene nanocomposites via melt extrusion using trialkyl imidazolium compatibilizer, Adv. Funct. Mater. 15 (2005) 910–916. [17] C. Ye, W. Liu, Y. Chen, L. Yu, Room-temperature ionic liquids: a novel versatile lubricant, Chem. Commun. (2001) 2244–2245. [18] A.E. Jiménez, M.D. Bermúdez, F.J. Carrión, G. Martínez-Nicolás, Room temperature ionic liquids as lubricant additives in steel–aluminium contacts. Influence of sliding velocity, normal load and temperature, Wear 261 (2006) 347–359.
4535
[19] J. Sanes, F.J. Carrión, M.D. Bermúdez, Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer–ionic liquid dispersions, Tribol. Lett. 21 (2006) 121–133. [20] J. Wang, J.M. Cao, B.Q. Fang, P. Lu, S.G. Deng, H.Y. Wang, Synthesis and characterization of multipod, flower-like, and shuttle-like, ZnO frameworks in ionic liquids, Mater. Lett. 59 (2005) 1405–1408. [21] M.P. Scott, M.G. Benton, M. Rahman, C.S. Brazel, Plasticizing effects of imidazolium salts in PMMA: high temperature stable flexible engineering materials. Ionic liquids as green solvents: progress and prospects, ACS Symp. Ser. 856 (2003) 468. [22] C. Wang, E. Shen, E. Wang, L. Gao, Z. Kang, C. Tian, Y. Lan, C. Zhang, Controllable synthesis of ZnO nanocrystals via a surfactant-assisted alcohol thermal process at a low temperature, Mater. Lett. 59 (2005) 2867–2871.
Effect of ionic liquid on the structure and tribological properties of polycarbonate–zinc oxide nanodispersion F.J. Carrión, J. Sanes, M.D. Bermúdez ⁎ Grupo de Ciencia de Materiales e Ingeniería Metalúrgica, Departamento de Ingeniería de Materiales y Fabricación, Universidad Politécnica de Cartagena, Campus de la Muralla del Mar, C/ Doctor Fleming s/n, 30202-Cartagena, Spain Received 15 February 2006; accepted 15 February 2007 Available online 28 February 2007
Abstract Room-temperature ionic liquid (IL) 1-hexyl-3-methylimidazolium hexafluorophosphate has been added to PC + 0.5 wt.%ZnO nanocomposite in a 1.5 wt.% proportion to obtain PC + 0.5%ZnO + 1.5%IL. The new PC/ZnO/IL nanocomposite shows a 80% friction reduction and a wear reduction of nearly two orders of magnitude with respect to PC + 0.5%ZnO. The influence of IL on the size, morphology and distribution of ZnO nanoparticles in the PC matrix is discussed on the basis of scanning (SEM) and transmission (TEM) electronic microscopic observations and energy dispersive X-ray (EDX) analysis. © 2007 Elsevier B.V. All rights reserved. Keywords: Polycarbonate; Zinc oxide; Nanocomposites; Ionic liquid; Wear
1. Introduction A polymer nanocomposite is defined as a composite material with a polymer matrix and filler particles that have at least one dimension less than 100 μm. A recent work by Sawyer et al. [1] includes a review of the literature on tribology of polymer nanocomposites. The role of filler components in influencing the wear behaviour of polymers is not yet fully understood, although some explanations have been provided. Nanoparticles are believed to improve the tribological performance of polymer matrices due to [2]: 1. The lower abrasiveness of nanoparticles with respect to that of microparticles due to the reduction in their angularity. 2. The formation of adhered transfer films as a result of the good blending between nanoparticles and wear debris particles. 3. The lower material removal when the fillers have a size of the order of the surrounding polymer chains.
⁎ Corresponding author. Tel.: +34 968325958; fax: +34 968326445. E-mail address: [email protected] (M.D. Bermúdez). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.02.044
Considerable experimental effort has been concentrated on the preparation and characterization of metal-containing nanoparticles embedded in polymer matrices [3–6]. However, there has been comparatively little work on the tribological study of polymer composites containing zinc oxide nanoparticles. Bahadur et al. [7] studied the effect of ZnO on the tribological behaviour of thermosetting polyester and found that Table 1 Thermal properties of the materials Thermal properties
PC
PC + 0.5%ZnO
PC + 0.5% ZnO + 1.5%IL
Tg (°C) Decomposition temperature (°C)
144.3 544.2
142.1 526.7
133.5 492.8
Table 2 Pin-on-disc tests results Disc material
Friction coefficient
Wear (mm3/Nm)
PC PC + 0.5%ZnO PC + 0.5%ZnO + 1.5%IL
1.02 0.90 0.14
2.58 × 10− 3 5.81 × 10− 3 7.54 × 10− 5
4532
F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Fig. 1. Friction–distance records for neat PC; PC + 0.5%ZnO and PC + 0.5% ZnO + 1.5%IL.
ZnO did not reduce the wear rate of the polymer. Li et al. [8] filled PTFE with nanoparticles of ZnO and improved wear resistance by nearly two orders of magnitude at ZnO concentrations around 15% by volume. However, the friction coef-
ficient of the nanocomposite was higher than that of the unfilled PTFE. Polycarbonate, an amorphous polymer with good moldability, is an important engineering thermoplastic which is finding applications both in structural parts and in electrooptical devices. Although there exists a great interest in developing new polycarbonate nanocomposites with improved properties [9–11], to the best of our knowledge, there is only one previous study [12] on the properties of polycarbonate–ZnO nanocomposites. Both as polymer and lubricant oil additives [13–15], inorganic nanoparticles and in particular Zn-containing nanoparticles, usually require the use of surface modifiers to achieve good dispersion of the nanoparticles. Imidazolium salts have been used as ionic surfactants to improve the dispersion of nanotubes in polymer matrices [16], and since the work by Ye et al. [17], imidazolium ILs have demonstrated their lubricating ability [18] and references therein]. We have previously [12,19] shown that the friction coefficients and wear rates of polymers against steel can be reduced by ZnO nanoparticles or by imidazolium-containing ILs, respectively.
Fig. 2. SEM micrographs of cryofracture surface: a) PC/ZnO nanocomposite; b) magnification (× 8000) and Zn elemental map.
F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Fig. 3. SEM micrograph of the cryofracture surface of PC + 0.5%ZnO + 1.5%IL.
Finally, ionic liquids have been used as reaction media to synthesize ZnO nanoparticles with different morphologies [20].
4533
Fig. 5. TEM micrograph of a thin layer of PC + 0.5%ZnO + 1.5%IL.
The aim of the present study was to determine the influence of ionic liquid addition on the tribological properties of PC/ nano-ZnO dispersions. 2. Experimental Polycarbonate (PC) was supplied by Kotec Corporation and ZnO nanopowder (average particle size 53 nm) was supplied by Aldrich. 1-hexyl-3-methylimidazolium hexafluorophosphate with purity N 97% was supplied by Fluka Chemie GmbH. PC/ZnO/IL nanocomposite was prepared by milling and injection molding as previously described [12]. The instrumentation for thermal analysis, microscopic characterization and microanalysis has also been reported [12]. Pin-on-disc tests according to ASTM G 99-05 standard were performed on 40 mm diameter, 4 mm height polymer discs sliding against AISI 316L (composition: b0.03% C; 17.55 Cr; 13% Ni; 2.5 Mo; hardness: 210 HV) stainless steel pins with 0.8 mm spherical end radius. Experimental parameters have
Fig. 4. TEM micrographs of: a) as-received ZnO nanoparticles; b) nanoparticles within the matrix of PC + 0.5%ZnO.
Fig. 6. TEM micrographs of PC + 0.5%ZnO + 1.5%IL showing the size and morphology of nanoparticles.
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F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535
Table 3 Element EDX analysis (%) for PC + 0.5%ZnO + 1.5%IL
Nanoparticle Matrix Interphase
abrasiveness due to their rounded morphology and their reduced tendency to agglomerate.
F
P
Zn
1.9 1.6 6.5
1.3 0.7 1.6
60.3 7.1 50.3
been previously described [12]. Friction coefficients were continuously recorded with time for each test and wear rates were calculated from wear track width measurements. 3. Results and discussion 3.1. Thermal properties Table 1 shows a significative change in chain mobility in the presence of the ZnO nanoparticles [12]. This chain mobility is further increased when IL is added. This plasticizing effect of ILs on thermoplastics has been previously described [19,21]. 3.2. Tribological properties Fig. 1 compares the friction/distance records for neat PC and for the nanocomposites PC + 0.5%ZnO and PC + 0.5%ZnO + 1.5%IL. Both PC and PC + 0.5%ZnO show low initial friction values which rapidly increase with distance to reach steady-state values after around 50 m for PC and around 150 m for PC + 0.5%ZnO. In contrast, for the IL-modified material PC + 0.5%ZnO + 1.5%IL, the initial low constant friction value is maintained up to the end of the test. Table 2 shows a 84.5% reduction in friction and a 98.7% wear reduction for PC + 0.5%ZnO + 1.5%IL with respect to the IL-free PC + 0.5%ZnO nanocomposite. The good performance obtained with the addition of IL could be related to the formation of a more homogeneous dispersion. 3.3. Structural characterization Fig. 2 shows the SEM micrographs of the cryofracture surfaces of PC + 0.5%ZnO, with large nanoparticle clusters. These agglomerates are mainly formed by ZnO nanoparticles as shown by the EDX elemental map (Fig. 2b). In contrast, PC + 0.5%ZnO + 1.5%IL (Fig. 3) shows a more ductile mode of fracture, with no large aggregates, but only rounded nanoparticles. As-received commercial ZnO nanoparticles can be observed in the TEM micrograph of Fig. 4a. Their polyhedral shape is maintained once they are embedded in the PC matrix (b) [12]. Fig. 5 shows the TEM micrograph of a thin section of PC + 0.5% ZnO + 1.5%IL where the distribution of the nanoparticles can be appreciated as black dots. The IL-modified particles have lost their sharp edges to give rise to a more rounded morphology and now appear as aggregates of entangled thin nanorods which can be more clearly seen in the outer layers of the particles (Fig. 6). EDX analysis (Table 3) shows an increase in fluorine and phosphorus content in the outer layer of the nanoparticles, at the interphase with the polymer matrix. This seems to indicate a nanoparticle–ionic liquid interaction which could explain the size and morphology changes observed in ZnO nanoparticles. The synthesis of ZnO nanoparticles with different morphologies [36] is currently being investigated [22]. The good tribological performance of the new nanocomposite PC + 0.5%ZnO + 1.5%IL could be attributed to the reduction of nanoparticle
4. Conclusions The addition of ZnO nanoparticles and a room-temperature ionic liquid to polycarbonate to obtain the new PC + 0.5%ZnO + 1.5%IL nanocomposite produces important reductions in friction and wear against AISI 316L stainless steel. The main reason for the enhanced tribological performance of the IL-modified nanocomposite could be the nanoparticle–IL interactions which modify the morphology of the nanoparticles within the polycarbonate matrix. The material described here could be the first of a new family of high performance polymer–nanoparticle–ionic liquid nanocomposites, although further research is still needed. Acknowledgements We thank MEC (Spain)/EU FEDER program (MAT200500067) and Fundación Séneca (Región de Murcia, Spain) (PI/ 00447/FS/04) for financial support. References [1] W.G. Sawyer, K.D. Freudenberg, P. Bhimaraj, L.S. Schadler, A study on the friction and wear behavior of PTFE filled with alumina nanoparticles, Wear 254 (2003) 573–580. [2] M.Q. Zhang, M.Z. Rong, S.L. Yu, B. Wetzel, K. Friedrich, Effect of particle surface treatment on the tribological performance of epoxy based nanocomposites, Wear 253 (2002) 1086–1093. [3] J. Tang, Y. Wang, H. Liu, Y. Xia, B. Schneider, Effect of processing on morphological structure of polyacrylonitrile matrix nano-ZnO composites, J. Appl. Polym. Sci. 90 (2003) 1053–1057. [4] S.P. Gubin, Metal-containing nanoparticles within polymeric matrices: preparation, structure and properties, Colloids Surf., A Physicochem. Eng. Asp. 202 (2002) 155–163. [5] L. Rapoport, O. Nepomnyashchy, A. Verdyan, R. Popovitch-Biro, Y. Volovik, B. Ittah, R. Tenne, Polymer nanocomposites with fullerene-like solid lubricant, Adv. Eng. Mater. 6 (2004) 44–48. [6] J.Q. Pham, C.A. Mitchell, J.L. Bahr, J.M. Tour, R. Krishanamoorti, P.F. Green, Glass transition of polymer/single-walled carbon nanotube composite films, J. Polym. Sci., Part B: Polym. Phys. 41 (2003) 3339–3345. [7] S. Bahadur, L. Zhang, J.W. Anderegg, The effect of zinc and copper oxides and other zinc compounds as fillers on the tribological behavior of thermosetting polyester, Wear 203/204 (1997) 464–473. [8] F. Li, K. Hu, J. Li, B. Zhao, The friction and wear characteristics of nanometer ZnO filled polytetrafluoroethylene, Wear 249 (2002) 877–882. [9] B.K. Satapathy, R. Weidisch, P. Potschke, A. Janke, Crack toughness behaviour of multiwalled carbon nanotube (MWNT)/polycarbonate nanocomposites, Macromol. Rapid Commun. 26 (2005) 1246–1252. [10] P.J. Yoon, D.L. Hunter, D.R. Paul, Polycarbonate nanocomposites. Part 1. Effect of organoclay structure on morphology and properties, Polymer 44 (2003) 5323–5339. [11] P.J. Yoon, D.L. Hunter, D.R. Paul, Polycarbonate nanocomposites. Part 2: degradation and color formation, Polymer 44 (2003) 5341–5354. [12] F.J. Carrión, J. Sanes, M.D. Bermúdez, Influence of ZnO nanoparticle filler on the properties and wear resistance of polycarbonate. Wear, in press, doi: 10.1016/j.wear. 2007.01.016. [13] V.N. Bakunin, A.Y. Suslov, G.N. Kuzmina, O.P. Perenago, Synthesis and applications of inorganic nanoparticles as lubricant components—a review, J. Nanopart. Res. 6 (2004) 273–284.
F.J. Carrión et al. / Materials Letters 61 (2007) 4531–4535 [14] W. Liu, S. Chen, An investigation of the tribological behaviour of surfacemodified ZnS nanoparticles in liquid paraffin, Wear 238 (2000) 120–124. [15] A. Hernández, J.E. Fernández-Rico, A. Navas, J.L. Biseca, R. Chou, J.M. Díaz, The tribological behaviour of ZnO nanoparticles as an additive to PAO6, Wear 261 (2006) 256–263. [16] S. Bellayer, J.W. Gilman, N. Eidelman, S. Bourbigot, X. Flambard, D.M. Fox, H.C. De Long, P.C. Trulove, Preparation of homogeneously dispersed multiwalled carbon nanotube/polystyrene nanocomposites via melt extrusion using trialkyl imidazolium compatibilizer, Adv. Funct. Mater. 15 (2005) 910–916. [17] C. Ye, W. Liu, Y. Chen, L. Yu, Room-temperature ionic liquids: a novel versatile lubricant, Chem. Commun. (2001) 2244–2245. [18] A.E. Jiménez, M.D. Bermúdez, F.J. Carrión, G. Martínez-Nicolás, Room temperature ionic liquids as lubricant additives in steel–aluminium contacts. Influence of sliding velocity, normal load and temperature, Wear 261 (2006) 347–359.
4535
[19] J. Sanes, F.J. Carrión, M.D. Bermúdez, Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer–ionic liquid dispersions, Tribol. Lett. 21 (2006) 121–133. [20] J. Wang, J.M. Cao, B.Q. Fang, P. Lu, S.G. Deng, H.Y. Wang, Synthesis and characterization of multipod, flower-like, and shuttle-like, ZnO frameworks in ionic liquids, Mater. Lett. 59 (2005) 1405–1408. [21] M.P. Scott, M.G. Benton, M. Rahman, C.S. Brazel, Plasticizing effects of imidazolium salts in PMMA: high temperature stable flexible engineering materials. Ionic liquids as green solvents: progress and prospects, ACS Symp. Ser. 856 (2003) 468. [22] C. Wang, E. Shen, E. Wang, L. Gao, Z. Kang, C. Tian, Y. Lan, C. Zhang, Controllable synthesis of ZnO nanocrystals via a surfactant-assisted alcohol thermal process at a low temperature, Mater. Lett. 59 (2005) 2867–2871.