Metal-oxide-containing polysiloxane enables enhanced
10.1002/spepro.002657
Metal-oxide-containing polysiloxane enables enhanced conductivity Hyungu Im and Jooheon Kim
Newly synthesized metal/polymer composites exhibit improved electrical and thermal properties. Fabricating hybrid materials from metal/polymer combinations represents a research area of great current interest aimed at overcoming the mechanical, electrical, and thermal disadvantages associated with organic materials. In particular, metal-containing polymers are appealing targets for synthesis because of their potential uses as processable components for electronics or magnetic materials and as a framework for metallic nanostructures. However, in situ synthesis methods cannot be applied, in general, to construct such metal-containing polymers because the choice of metal species is restricted by the relatively limited range of monomers and polymerization techniques available. On the other hand, combining metallic species through physical mixing is attractive because the preparation methods are simple. A large number of studies have outlined how the magnetic and mechanical properties of metal-containing polymer composites can be improved through effective fabrication techniques.1, 2 However, it is relatively poorly known how a metal-containing polymer matrix affects these properties. Therefore, we investigated the effects of metal oxide dispersed into a polymer species as a composite matrix based on synthesis of a block-copolymer-type polysiloxane containing copper oxide (CuO) and using an ex-situ preparation method. We synthesized modified poly(methyl-dimethyl methyl vinyl) siloxane (PMDMS) using an established equilibrium polymerization method (see Figure 1).3 We added CuO to achieve coordination in the polymer chain. The PMDMS:CuO composite shows—see Figure 2(b)—that the metal particles have been dispersed uniformly in the plane throughout the composite matrix compared with the sample that did not contain CuO, shown in Figure 2(a). The differences between the surface morphologies of both composites correlate with the presence or absence of CuO. The high polarity of CuO contributes to the aggregation of Cu particles and CuO in the PMDMS matrix.
Figure 1. Synthesis of poly(methyl-dimethyl methyl vinyl) siloxane (PMDMS). TMAS: Tetramethylammonium siloxaneolate. DMAA: Dimethylacrylamide. Pt: Platinum. D4 : Octamethylcyclotetrasiloxane. D4M e;H and D4V i;M e : 1,3,5 and 1,3,5,7-tetravinyl-1,3,5,7- tetramethylcyclotetrasiloxane.
We investigated the electroconductivity of PMDMS-composite materials as a function of Cu concentration. Theoretically, we can use
Continued on next page
10.1002/spepro.002657 Page 2/4
Figure 3. Concentration dependence of the composite electrical conductivity. Symbols and lines represent our experimental results and theoretical expectations based on Equation (1), respectively. S: Siemens.
Figure 2. Scanning-electron-microscope images of polysiloxane/copper (Cu) composites. (a) PMDMS:Cu. (b) PMDMS/copper oxide (CuO):Cu.
D c C .m
c /Œ.'
'c /=.F
'c /t ;
(1)
where t is the critical exponent, 'c the critical concentration, and FD0.64 is the packing factor, to derive the expected electroconductivity, , of the metals and composites (denoted by the subscripts ‘m’ and ‘c,’ respectively).4 Following previous studies,5–7 we used tD1.7. Figure 3 shows that the electrical conductivity of a PMDMS/Cu particle exhibited typical percolation threshold behavior at the critical concentration, while the experimental conductivity value was in good agreement with theoretically predictions. The critical concentration was slightly reduced in the presence of CuO. An earlier study had indicated that well-dispersed conditions and an increased contact
Figure 4. Concentration dependence of the composite’s thermal properties.
area would enable establishment of a conductive path, leading to higher conductivity when the composite is near the percolation threshold.8 As a result, interactions between Cu and CuO disturb aggregation of Cu Continued on next page
10.1002/spepro.002657 Page 3/4
Table 1. Comparison of thermal conductivities of filled polymers. Al2 O3 : Aluminum oxide. AlN: Aluminum nitride. Fe3 O4 : Iron oxide (magnetite). PU, PS, PA: Polyurethane, polystyrene, polyamide. Filler Polymer matrix Volume % 0 10 12 12.5 16.6 20 26.6 30 34 40 50
Al2 O3 12 PU
Silica Coated AlN13 Epoxy
AlN14 PS
Fe3 O4 11 R PA Akulon F223-D
Cu PMDMS:CuO (this study)
0.29
0.29
0.27 0.3 0.4 0.633 0.45
0.67 1.149
0.6
0.66
0.9
1.11 1.95
0.79
Figure 5. Interconnectivities of Cu-filled PMDMS and other materials (from the literature) as a function of filler volume fraction, Xfiller . SCAN: Silica-coated aluminum nitride. particles and, consequently, lead to dispersity improvement of the Cu filler.
1.00 0.93
2.38
Figure 4 shows the experimentally determined dependence of the thermal diffusivity and conductivity on the copper content (by volume) for the composites we investigated. Our new composite was more conductive than the other materials (see Table 1). To explain the dispersity differences between these materials, we need additional evidence. Using Hashin-Shtrikman model conductivities,9 we can derive the interconnectivity of the conducting phase.10 Figure 5 displays the results for our new composite compared with relevant values for other composite materials.11–14 All composites show an increase in interconnectivity with filler volume fraction. The PMDMS composites exhibit the highest interconnectivity. This leads us to conclude that CuO may have contributed to dispersion of the filler, thereby enhancing the material’s conductivity. In summary, we have synthesized metal oxide with polysiloxane to improve the electrical and thermal conductivity of the metal/polymer composite. Metal fillers in composites containing metal oxide showed enhanced dispersion compared to those without metal oxide. As a result, the former were characterized by slightly lower values of the critical concentration than the latter. In addition, the thermal conductivity of the composites increased considerably with higher filler concentration. We used their thermal conductivity to calculate the associated thermal interconnectivity. As expected, composites containing metal oxide showed enhanced thermal interconnectivity. We will next investigate the effects of dispersing metal oxide into various polymer matrices to confirm the general role of metal oxide in polymer composites.
Continued on next page
10.1002/spepro.002657 Page 4/4
Author Information Hyungu Im and Jooheon Kim School of Chemical Engineering and Materials Science Chung-Ang University Seoul, South Korea Hyungu Im is a PhD student. References 1. M. Lazzari and M. A. Lopez-Quintela, Block copolymers as a tool for nanomaterial fabrication, Adv. Mater. 15 (19), pp. 1583–1594, 2003. 2. I. W. Hamley, Nanostructure fabrication using block copolymers, Nanotechnol. 14, pp. 39–54, 2003. 3. D. H. Kang and B. C. Lee, Preparation and characteristics of liquid silicone rubber using polyorganosiloxane modified with dimethylacrylamide, Polymer (Korea) 28 (2), pp. 143–148, 2004. 4. E. P. Mamunya, V. V. Davidenko, and E. V. Lebedev, Percolation conductivity of polymer composites filled with dispersed conductive filler, Polym. Compos. 16 (4), pp. 318–324, 1995. 5. J. Wu and D. S. McLachlan, Percolation exponents and thresholds obtained from the nearly ideal continuum percolation system graphite-boron nitride, Phys. Rev. B 56 (3), pp. 1236–1248, 1997. 6. E. P. Mamunya, V. V. Davydenko, P. Pissis, and E. V. Lebedev, Electrical and thermal conductivity of polymers filled with metal powders, Eur. Polym. J. 38 (9), pp. 1887– 1897, 2002. 7. F. Carmona and C. Mouney, Temperature-dependent resistivity and conduction mechanism in carbon particle-filled polymers, J. Mater. Sci. 27 (5), pp. 1322–1326, 1992. 8. H. H. Lee, K. S. Chou, and Z. W. Shih, Effect of nano-sized silver particles on the resistivity of polymeric conductive adhesives, Int’l J. Adhes. Adhes. 25 (5), pp. 437– 441, 2005. 9. Z. Hashin and A. Shtrikman, A variational approach to the theory of the effective magnetic permeability of multiphase material, J. Appl. Phys. 33, pp. 3125–3131, 1962. 10. F. R. Schilling and G. M. Partzsch, Quantifying partial melt portion in the crust beneath the central Andes and the Tibetan Plateau, Phys. Chem. Earth A 26 (4–5), pp. 239– 246, 2001. 11. B. Weidenfellera, M. Hofer, and F. Schilling, Thermal and electrical properties of magnetite filled polymers, Compos. A 33 (8), pp. 1041–1053, 2002. 12. X. Lu and G. Xu, Thermally conductive polymer composites for electronic packaging, J. Appl. Polym. Sci. 65 (13), pp. 2733–2738, 1997. 13. C. P. Wong and R. S. Bollampally, Thermally conductivity, elastic modulus, and coefficient of thermal expansion of polymer composites filled with ceramic particles for electronic packaging, J. Appl. Polym. Sci. 74 (14), pp. 3396–3403, 1999. 14. S. Yu, P. Hing, and X. Hu, Thermal conductivity of polystyrene/aluminum nitride composite, Compos. A 33 (2), pp. 289–292, 2002.
c 2010 Society of Plastics Engineers (SPE)
Metal-oxide-containing polysiloxane enables enhanced conductivity Hyungu Im and Jooheon Kim
Newly synthesized metal/polymer composites exhibit improved electrical and thermal properties. Fabricating hybrid materials from metal/polymer combinations represents a research area of great current interest aimed at overcoming the mechanical, electrical, and thermal disadvantages associated with organic materials. In particular, metal-containing polymers are appealing targets for synthesis because of their potential uses as processable components for electronics or magnetic materials and as a framework for metallic nanostructures. However, in situ synthesis methods cannot be applied, in general, to construct such metal-containing polymers because the choice of metal species is restricted by the relatively limited range of monomers and polymerization techniques available. On the other hand, combining metallic species through physical mixing is attractive because the preparation methods are simple. A large number of studies have outlined how the magnetic and mechanical properties of metal-containing polymer composites can be improved through effective fabrication techniques.1, 2 However, it is relatively poorly known how a metal-containing polymer matrix affects these properties. Therefore, we investigated the effects of metal oxide dispersed into a polymer species as a composite matrix based on synthesis of a block-copolymer-type polysiloxane containing copper oxide (CuO) and using an ex-situ preparation method. We synthesized modified poly(methyl-dimethyl methyl vinyl) siloxane (PMDMS) using an established equilibrium polymerization method (see Figure 1).3 We added CuO to achieve coordination in the polymer chain. The PMDMS:CuO composite shows—see Figure 2(b)—that the metal particles have been dispersed uniformly in the plane throughout the composite matrix compared with the sample that did not contain CuO, shown in Figure 2(a). The differences between the surface morphologies of both composites correlate with the presence or absence of CuO. The high polarity of CuO contributes to the aggregation of Cu particles and CuO in the PMDMS matrix.
Figure 1. Synthesis of poly(methyl-dimethyl methyl vinyl) siloxane (PMDMS). TMAS: Tetramethylammonium siloxaneolate. DMAA: Dimethylacrylamide. Pt: Platinum. D4 : Octamethylcyclotetrasiloxane. D4M e;H and D4V i;M e : 1,3,5 and 1,3,5,7-tetravinyl-1,3,5,7- tetramethylcyclotetrasiloxane.
We investigated the electroconductivity of PMDMS-composite materials as a function of Cu concentration. Theoretically, we can use
Continued on next page
10.1002/spepro.002657 Page 2/4
Figure 3. Concentration dependence of the composite electrical conductivity. Symbols and lines represent our experimental results and theoretical expectations based on Equation (1), respectively. S: Siemens.
Figure 2. Scanning-electron-microscope images of polysiloxane/copper (Cu) composites. (a) PMDMS:Cu. (b) PMDMS/copper oxide (CuO):Cu.
D c C .m
c /Œ.'
'c /=.F
'c /t ;
(1)
where t is the critical exponent, 'c the critical concentration, and FD0.64 is the packing factor, to derive the expected electroconductivity, , of the metals and composites (denoted by the subscripts ‘m’ and ‘c,’ respectively).4 Following previous studies,5–7 we used tD1.7. Figure 3 shows that the electrical conductivity of a PMDMS/Cu particle exhibited typical percolation threshold behavior at the critical concentration, while the experimental conductivity value was in good agreement with theoretically predictions. The critical concentration was slightly reduced in the presence of CuO. An earlier study had indicated that well-dispersed conditions and an increased contact
Figure 4. Concentration dependence of the composite’s thermal properties.
area would enable establishment of a conductive path, leading to higher conductivity when the composite is near the percolation threshold.8 As a result, interactions between Cu and CuO disturb aggregation of Cu Continued on next page
10.1002/spepro.002657 Page 3/4
Table 1. Comparison of thermal conductivities of filled polymers. Al2 O3 : Aluminum oxide. AlN: Aluminum nitride. Fe3 O4 : Iron oxide (magnetite). PU, PS, PA: Polyurethane, polystyrene, polyamide. Filler Polymer matrix Volume % 0 10 12 12.5 16.6 20 26.6 30 34 40 50
Al2 O3 12 PU
Silica Coated AlN13 Epoxy
AlN14 PS
Fe3 O4 11 R PA Akulon F223-D
Cu PMDMS:CuO (this study)
0.29
0.29
0.27 0.3 0.4 0.633 0.45
0.67 1.149
0.6
0.66
0.9
1.11 1.95
0.79
Figure 5. Interconnectivities of Cu-filled PMDMS and other materials (from the literature) as a function of filler volume fraction, Xfiller . SCAN: Silica-coated aluminum nitride. particles and, consequently, lead to dispersity improvement of the Cu filler.
1.00 0.93
2.38
Figure 4 shows the experimentally determined dependence of the thermal diffusivity and conductivity on the copper content (by volume) for the composites we investigated. Our new composite was more conductive than the other materials (see Table 1). To explain the dispersity differences between these materials, we need additional evidence. Using Hashin-Shtrikman model conductivities,9 we can derive the interconnectivity of the conducting phase.10 Figure 5 displays the results for our new composite compared with relevant values for other composite materials.11–14 All composites show an increase in interconnectivity with filler volume fraction. The PMDMS composites exhibit the highest interconnectivity. This leads us to conclude that CuO may have contributed to dispersion of the filler, thereby enhancing the material’s conductivity. In summary, we have synthesized metal oxide with polysiloxane to improve the electrical and thermal conductivity of the metal/polymer composite. Metal fillers in composites containing metal oxide showed enhanced dispersion compared to those without metal oxide. As a result, the former were characterized by slightly lower values of the critical concentration than the latter. In addition, the thermal conductivity of the composites increased considerably with higher filler concentration. We used their thermal conductivity to calculate the associated thermal interconnectivity. As expected, composites containing metal oxide showed enhanced thermal interconnectivity. We will next investigate the effects of dispersing metal oxide into various polymer matrices to confirm the general role of metal oxide in polymer composites.
Continued on next page
10.1002/spepro.002657 Page 4/4
Author Information Hyungu Im and Jooheon Kim School of Chemical Engineering and Materials Science Chung-Ang University Seoul, South Korea Hyungu Im is a PhD student. References 1. M. Lazzari and M. A. Lopez-Quintela, Block copolymers as a tool for nanomaterial fabrication, Adv. Mater. 15 (19), pp. 1583–1594, 2003. 2. I. W. Hamley, Nanostructure fabrication using block copolymers, Nanotechnol. 14, pp. 39–54, 2003. 3. D. H. Kang and B. C. Lee, Preparation and characteristics of liquid silicone rubber using polyorganosiloxane modified with dimethylacrylamide, Polymer (Korea) 28 (2), pp. 143–148, 2004. 4. E. P. Mamunya, V. V. Davidenko, and E. V. Lebedev, Percolation conductivity of polymer composites filled with dispersed conductive filler, Polym. Compos. 16 (4), pp. 318–324, 1995. 5. J. Wu and D. S. McLachlan, Percolation exponents and thresholds obtained from the nearly ideal continuum percolation system graphite-boron nitride, Phys. Rev. B 56 (3), pp. 1236–1248, 1997. 6. E. P. Mamunya, V. V. Davydenko, P. Pissis, and E. V. Lebedev, Electrical and thermal conductivity of polymers filled with metal powders, Eur. Polym. J. 38 (9), pp. 1887– 1897, 2002. 7. F. Carmona and C. Mouney, Temperature-dependent resistivity and conduction mechanism in carbon particle-filled polymers, J. Mater. Sci. 27 (5), pp. 1322–1326, 1992. 8. H. H. Lee, K. S. Chou, and Z. W. Shih, Effect of nano-sized silver particles on the resistivity of polymeric conductive adhesives, Int’l J. Adhes. Adhes. 25 (5), pp. 437– 441, 2005. 9. Z. Hashin and A. Shtrikman, A variational approach to the theory of the effective magnetic permeability of multiphase material, J. Appl. Phys. 33, pp. 3125–3131, 1962. 10. F. R. Schilling and G. M. Partzsch, Quantifying partial melt portion in the crust beneath the central Andes and the Tibetan Plateau, Phys. Chem. Earth A 26 (4–5), pp. 239– 246, 2001. 11. B. Weidenfellera, M. Hofer, and F. Schilling, Thermal and electrical properties of magnetite filled polymers, Compos. A 33 (8), pp. 1041–1053, 2002. 12. X. Lu and G. Xu, Thermally conductive polymer composites for electronic packaging, J. Appl. Polym. Sci. 65 (13), pp. 2733–2738, 1997. 13. C. P. Wong and R. S. Bollampally, Thermally conductivity, elastic modulus, and coefficient of thermal expansion of polymer composites filled with ceramic particles for electronic packaging, J. Appl. Polym. Sci. 74 (14), pp. 3396–3403, 1999. 14. S. Yu, P. Hing, and X. Hu, Thermal conductivity of polystyrene/aluminum nitride composite, Compos. A 33 (2), pp. 289–292, 2002.
c 2010 Society of Plastics Engineers (SPE)
