The adsorption of rubber adsorbate models on the sulfide surfaces generally show weak interactions via the saturated hydrocarbons while carbon-carbon double bonds and thiol groups of rubbers lead to stronger interactions. However, with the inclusion of different dopant atoms on both sulfide surfaces, the adsorption strength of the rubber adsorbate models can either be enhanced or reduced. Therefore, the use of different transition metals as dopant atoms on ZnS(110) and Cu2S(111) surfaces has been studied to determine their interaction with rubber adsorbate models, and the promotional impacts are presented in Figure 14 and Figure 15, respectively.
Figure 14. The effect of doping on interaction of the rubber adsorbate models and the doped ZnS(110) surfaces. Saturated and unsaturated hydrocarbons present an average effect on the adsorption of methane, ethane, and propane, and ethene and methyl-substituted ethene, respectively.
Figure 15. The effect of doping on the interaction of the rubber adsorbate models and the doped Cu2S(111) surfaces. Saturated and unsaturated hydrocarbons present an average effect on the adsorption of methane, ethane, and propane, and ethene and methyl-substituted ethene, respectively.
In the case of the ZnS(110) surface (Figure 14), the copper dopant notably weakens the adsorption strength of all the functional groups of rubber. On the other hand, the iron and nickel dopants on the ZnS(110) surface display little or no effect on the adhesion. Manganese and cobalt doping not only enhance the adsorption strength of the carbon-carbon double bonds and thiol groups of the rubber adsorbate but also trigger the saturated hydrocarbon groups, leading to higher adsorption energies. These positive effects are more significant in the case of cobalt doping than when manganese is used for doping.
The enhancement of the adsorption strength of all the functional groups of rubber by cobalt and manganese doping on the ZnS(110) surface is not shown on the doped Cu2S(111) surfaces.
Only the adsorption involving the carbon-carbon double bonds of rubber is initiated on all the doped Cu2S(111) surfaces. Even so, the effect is significantly stronger, as shown in the case of manganese and iron doping when compared to the doped ZnS(110) surfaces (Figure 15). While the highest promotional effect is shown through cobalt doping on the ZnS(110) surface, this is not in the case on the Cu2S(111) surface, since the manganese and iron doping on the Cu2S(111) surfaces have a higher promotional effect than the cobalt doping. On the other hand, while the nickel dopant does not show a promotional effect on the ZnS(110) surface, the adsorption strength of rubber to Cu2S(111) surface is also increased through carbon-carbon double bond when the nickel dopant is used.
5 Adsorption of rubber adsorbate models on zinc oxide surfaces
The calculated adsorption energies on both the ZnO(110) and ZnO(001) surfaces are tabulated in Table 8. Even though the most stable polymorph of ZnO and ZnS are different, the results obtained from the adsorption of rubber adsorbate models on the ZnS(110) surface is being used as a reference. The adsorption trend between functional group models and the ZnO(110) surface follow the same trend seen on the ZnS(110) surface, in which saturated hydrocarbons exhibit the weakest interaction, followed by ethene while hydrogen sulfide had a slightly stronger interaction than ethene. Even so, the adsorption energies are slightly enhanced, by approximately 4-7 kJ mol-1 through the saturated hydrocarbons and ethene but are reduced by 20 kJ mol-1 when interacting with hydrogen sulfide. The adsorption strength for larger adsorbate models is also shown to be similar to that on the ZnS(110) surface, where thiol-substituted ethene shows a stronger interaction than methyl-thiol-substituted ethene, but the adsorption energies are lower compare to ZnS(110) surface.
On the other hand, the adsorption is noticeably stronger on the ZnO(110) surface than on the ZnO(001) surface. The adsorption strength for ethene and hydrogen sulfide on the ZnO(110) surface is approximately 30 kJ mol-1 higher than on the ZnO(001) surface. A similar observation can also applied to larger models, where the ZnO(110) surface exhibits higher adsorption strength than the ZnO(001) surface.
Table 8 The calculated adsorption energies on the ZnO surfaces. Calculated adsorption energies on the ZnS(110) surface are included as a reference (in kJ mol–1).
Adsorbate ZnS(110)55 ZnO(110) ZnO(001)
Methane –3.0 –7.6 –1.1
Ethane –4.3 –8.6 –0.4
Propane –3.0 –5.2 –1.4
Ethene –29.8 –37.2 –2.9
Hydrogen sulfide –61.4 –41.7 –9.8
Methyl-substituted ethene –39.8 –26.3 –5.0
Thiol-substituted ethene –50.5 –39.3 –13.1
As on the ZnS(110) surface, saturated hydrocarbons only exhibit weak physisorption on the ZnO(110) surface, while ethene interacts via the carbon-carbon double bond and hydrogen sulfide through the donation of the lone pair electrons of sulfur. On the other hand, for the adsorption on the ZnO(001) surface, all the functional group models exhibit weak physisorption as they display low adsorption strength. Even so, as predicted via adsorption on the ZnS(110) surface, the preferred binding mechanism is through the sulfur containing models, since hydrogen sulfide exhibits a stronger interaction than ethene. The optimized structures of the rubber adsorbate models on the ZnO(110) and ZnO(001) surfaces are presented in Figure 16 and Figure 17, respectively. The outward relaxation of the interacting zinc atom on the zinc oxide surfaces caused by rubber adsorbate models having carbon-carbon double bond and sulfur containing models is smaller than in zinc and copper sulfide surfaces cases. Similar
relative observations can be seen in the adsorption of larger adsorbate models on both ZnO surfaces.
Figure 16. Side view of the optimized configurations on the ZnO(110) surface interacting with (a) methane, (b) ethane, (c) propane, (d) ethene, (e) hydrogen sulfide, (f) methyl-substituted ethene, and (g) thiol-substituted ethene.
Figure 17. Side view of the optimized configurations on the ZnO(001) surface interacting with (a) methane, (b) ethane, (c) propane, (d) ethene, (e) hydrogen sulfide, (f) methyl-substituted ethene, and (g) thiol-substituted ethene.
The role of the functional groups of the rubber structure in rubber–brass adhesion was explored on copper and zinc sulfide and on zinc oxide surfaces at the atomic level, finding distinct differences in the preferential binding between the rubber adsorbate models and the surfaces involved. In general, carbon-carbon double bonds and the thiol groups of rubber are responsible for the interaction with the surface metal atoms. However, zinc and copper sulfide surfaces display contradicting binding preferences. Zinc sulfide surface prefer to bond with sulfur containing functional groups, while copper sulfide preferentially bonds with the carbon-carbon double bond. The preferential binding of the sulfur containing functional groups also shown on the zinc oxide surfaces, but the adsorption strengths are lower compared to zinc sulfide surface.
The bonding via the carbon-carbon double bond occurs in the adsorption mode, where a π-donation from the adsorbate containing the carbon-carbon double bond into the empty orbitals of the metal occurs together with a back-donation from the metal into the empty π*-orbital of the adsorbate. This is the Dewar-Chatt-Duncanson adsorption model.58 On the other hand, the bonding that occurs through the sulfur-containing adsorbate is due to lone pair electron donation from the sulfur in the sulfur-containing adsorbate to the metal atom of the surface and occurs together with the back-donation of the surface electrons to the sulfur-containing adsorbates.59
Additives play an important role in rubber–brass adhesion, as they enhance the interaction.
Hence, the promotional effect of additives towards the rubber–brass adhesion has also been studied. Cobalt is widely used as additive especially in tire manufacturing since it assists in the formation of an essential amount of the copper sulfide layer and affects the durability of rubber–metal bonds.35 From our findings, only the adsorption involving carbon-carbon double bonds is enhanced by the cobalt doping on the copper sulfide surface. However, a notable promotional effect is achieved on all the functional groups of rubber, including saturated hydrocarbons, on the cobalt doped zinc sulfide surface. The dissociation of methane is known to occur on transition metal surfaces, and for a cobalt surface the activation barrier is 120 kJ mol–1.60,61 This could be the reason why a stronger interaction is observed, as the cobalt dopant on the zinc sulfide moderately activates the carbon-hydrogen bond of the saturated hydrocarbons.
Despite its advantages, the limitations of cobalt usage as an additive, which include the cost, have increased the demand for finding an alternative to substitute for cobalt as an additive.
Therefore, we substituted cobalt with manganese, iron, and nickel. The results were compared with those of cobalt doped substances. In the case of zinc sulfide, the promotional effect from cobalt is still the strongest. On the other hand, manganese and iron doping on the coper sulfide surface show a greater promotional effect than cobalt due to the enhancement in the interaction via the carbon-carbon double bond. This finding is important for the interaction between rubber and brass at the adhesive interlayer, since copper sulfide is speculated to be responsible for the interfacial adhesion.12
The rubber–brass adhesion process has been investigated using DFT involving the adsorption of rubber adsorbate models on copper and zinc sulfide and on zinc oxide surfaces at the adhesive interlayer. It was found that the functional groups of the rubber structure that are responsible for the interfacial interaction with metal are olefinic and sulfidic. The obtained adsorption energies reveal that preferential binding on copper sulfide is via the double bond, while sulfur containing functional groups are preferable for zinc sulfide and zinc oxide. Both copper and zinc sulfide exhibit a stronger interaction with the rubber structure than zinc oxide does. The different behavior of the functional groups of the rubber structure and the different preferential binding on the copper and zinc sulfide at the adhesive interlayer can play an important role in rubber–brass adhesion.
The doping of zinc and copper sulfides is a useful tool in the optimization of the interfacial interaction. Cobalt as an additive is found to be important in rubber–brass adhesion, as it enhances the rubber adhesion on both sulfide surfaces, with a greater promotional effect shown through the interaction with zinc sulfide. Cobalt even activates carbon-hydrogen bonds, which can be useful in enhancing rubber–brass adhesion. However, the search for more economical and effective additives has been carried out. Considering the promotional effect on both copper and zinc sulfide, out of manganese, iron, and nickel additives, manganese seems to be a good substitute. Compared to cobalt, manganese displays a lower effect on the zinc sulfide but a notable effect on copper sulfide. Therefore, from our findings, the best method for achieving optimum enhancement of the rubber–brass adhesion in practical applications is by using a combination of dopants.
1. Lewis, P.M. Rubber to metal bonding. In: Packham, D.E. Handbook of adhesion. 2nd. West Sussex, England: John Wiley & Sons. 2005, 417.
2. Mark, J.E.; Erman, B.; Eirich, F.R. The science and technology of rubber third edition.
Academic Press. 2005.
3. Subramaniam, A. Immunol Allergy Clin. North America. 1995, 15, 1.
4. van Ooij, W.J.; Harakuni, P.B; Buytaert, G. Rubber Chem. Technol. 2009, 82, 315.
5. Buchan, S. Rubber to metal bonding (2nd revised Ed.). Crosby Lockwood & Son, London.
6. Tanaka, Y. Rubber Chem. Technol. 1991, 64, 325.
7. Ting, R.Y. A study on elastomer/metal bonds applicable in underwater sonar systems. In:
Mittal, K.L. (Ed.): Adhesive joints: Formation, characteristics, and testing. Plenum Press:
New York and London. 1984, 555.
8. van Ooij, W.J. Rubber Chem. Technol. 1984, 57, 421.
9. Barr, T.L. Surf. Interface Anal. 1982, 4, 185.
10.Hotaka, T.; Ishikawa, Y.; Mori, K. Rubber Chem. Technol. 2007, 80, 61.
11.Ozawa, K.; Kakubo, T.; Shimizu, K.; Amino, N.; Mase, K.; Komatsu, T. Appl. Surf. Sci.
2013, 264, 297.
12.van Ooij, W.J. Surf. Sci. 1977, 68, 1.
13.van Ooji, W.J. Rubber Chem. Technol. 1978, 51, 52.
14.Chandra, A.K.; Mukhopadhyay, R.; Konar, J.; Ghosh, T.B.; Bhowmick, A.K. J. Mater. Sci.
1996, 31, 2667.
15.Buytaert, G.; Coornaert, F.; Dekeyser, W. Rubber Chem. Technol. 2009, 82, 430.
16.Persoone, P.; De Volder, P.; De Gryse, R. Solid State Commun. 1994, 92, 675.
17.Hammer, G.E. J. Vac. Sci. Technol. 2001, 19, 2846.
18.van Ooji, W.J. Rubber-brass bonding. In: Crowther, B.G (Ed.): The handbook of rubber bonding. Rapra Technology Ltd., Shawbury, UK. 2001, 163.
19.Haemers, G. Rubber World. 1980, 182, 26.
20.McBain, J.W.; Hopkins, D.G. J. Phys. Chem. 1925, 29, 199.
21.Gent, A.N.; Schultz, J. J. Adhes. 1972, 3, 281.
22.Sharpe, L.H.; Schonhorn, H. Chem. Eng. News. 1963, 15, 67.
23.Patil, P.Y.; van Ooij, W.J. J. Adhes. Sci. Technol. 2004, 18, 1367.
24.Kurbatov, G.G.; Beshenkov, V.G.; Zaporozchenko, V.I. Surf. Interface Anal. 1991, 17, 779.
25.Jeon, G.S.; Han, M.H.; Seo, G. Korean J. Chem. Eng. 1998, 15, 317.
26.Jeon, G.S.; Han, M.H.; Seo, G. J. Adhesion. 1999, 69, 39.
27.Jeon, G.S.; Han, M.H.; Seo, G. J. Adhesion Sci. Technol. 1999, 13, 153.
28.van Ooij, W.J. Rubber Chem. Technol. 1979, 52, 605.
29.Haemers, G.; Mollet, J. J. Elastom Plast. 1978, 10, 241.
30.Fulton, W.S.; Sykes, D.E.; Smith, G.C. Appl. Surf. Sci. 2006, 252, 7074.
31.van Ooij, W.J.; Biemond, M.E.F. Rubber Chem. Technol. 1984, 57, 686.
32.Hotaka, T.; Ishikawa, Y.; Mori, K. Journal-Society of Rubber Industry Japan. 2002, 75, 488.
33.Fulton, W.S. Rubber Chem. Technol. 2005, 78, 426.
34.Chandra, A.K.; Biswas, A.; Mukhopadhyay, R.; Bhowmick, A.K. J. Adhes. Sci. Technol.
1996, 10, 431.
35.Ball, J.J.; Gibbs, H.W.; Tate, P.E.R. J. Adhes. 1990, 32, 29.
36.Jeon, G.S.; Kim, Y.M.; Seo, G. Korean Chemical Engineering Research. 1998, 36, 179.
37.Isac, L.A.; Duta, A.; Kriza, A.; Nanu, M.; Schoonman, J. J. Optoelectron. Adv. M. 2007, 9, 1265.
38.Wright, K.; Gale, J.D. Phys. Rev. B. 2004, 70, 035211.
39.Özgür, Ü.; Alivov, Y.I.; Liu, C.; Teke, A.; Reshchikov, M.A.; Doğan, S.; Avrutin, V.; Cho, S.J.; Morkoç, H. J. Appl. Phys. 2005, 98, 041301.
40.Dubrovin, I.V.; Budennaya, L.D.; Mizetskaya, I.B.; Sharkina, E.V. Inorg. Mater. 1983, 19 1603.
41.Oliveria, M.; McMullan, R.K.; Wuensch, B.J. Solid State Ionics. 1988, 28, 1332.
42.Gotsis, H.J.; Barnes, A.C.; Strange, P. J. Phys.: Condens. Mat. 1992, 4, 10461.
43.Jaffe, J.E.; Zunger, A. Phys. Rev. B. 2001, 64, 241304.
44.Wright, K.; Watson, G.W.; Parker, S.C.; Vaughan, D.J. Am. Mineral. 1998, 83, 141.
45.Korzhavyi, P.A.; Abrikosov, I.A.; Johansson, B. Mater. Res. Soc. Symp. P. 2000, 608, 115.
46.Rosso, K.M.; Hochella, Jr.M.F. Surf. Sci. 1999, 423, 364.
47.Èvarestov, R.A. Springer. 2015, 56.
48.Zhao, J.H.; Han, E.J.; Liu, T.M.; Zeng, W. Asian Journal of Chemistry. 2012, 24, 2903.
49.Dovesi, R.; Saunders, V.R.; Roetti, C.; Orlando, R.; Zicovich-Wilson, C.M.; Pascale, F.;
Civalleri, B.; Doll, K.; Harrison, N.M.; Bush, I.J.; D’Arco, P.; Llunell, M. Crystal09 User’s Manual. University of Torino: Torino, 2009.
50.Perdew, J.P.; Ernzerhof, M.; Burke, K. J. Chem. Phys. 1996, 105, 9982.
51.Ernzerhof, M.; Scuseria, G.E. J. Chem. Phys. 1999, 110, 5029.
52.Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158.
53.Rodriguez, J.A.; Chaturvedi, S.; Kuhn, M.; Hrbek, J. The Journal of Physical Chemistry B.
1998, 102, 5511.
54.Schäfer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829.
55.Ling, C.Y.; Hirvi, J.T.; Suvanto, M.; Bazhenov, A.S.; Ajoviita, T.; Markkula, K.; Pakkanen.
T.A. Chem. Phys. 2015, 453-454, 7.
56.Ling, C.Y.; Hirvi, J.T.; Suvanto, M.; Bazhenov, A.S.; Markkula, K.; Hillman, L.; Pakkanen, T.A. Theor. Chem. Acc. 2017, 136, 24.
57.Boys, S.F.; Bernardi, F. Mol. Phys. 1970, 19, 553.
58.Shriver, D.F.; Atkins, P.W. Inorganic chemistry, third ed. Oxford University Press: United Kingdom and Other Countries. 1999, 561.
59.Yin, G.Y.; Ding, K.N.; Li, J.Q. Chin. J. Struct. Chem. 2010, 29, 1139.
60.Zuo, Z.J.; Huang, W.; Han, P.D.; Li, Z.H. Appl. Surf. Sci. 2010, 256, 5929.
61.Hao, X.B.; Wang, Q.; Li, D.B.; Zhang, R.G.; Wang, B.J. RSC Adv. 2014, 4, 43004.
THE UNIVERSITY OF EASTERN FINLAND Dissertations in Forestry and Natural Sciences
ISBN 978-952-61-3366-9 ISSN 1798-5668
Dissertations in Forestry and Natural Sciences
DISSERTATIONS | CHIAN YE LING | ATOMIC-LEVEL UNDERSTANDING OF THE RUBBER–BRASS ADHESION... | No 376
CHIAN YE LING
ATOMIC-LEVEL UNDERSTANDING OF THE RUBBER–BRASS ADHESION AND
THE EFFECT OF ADDITIVESPUBLICATIONS OF
THE UNIVERSITY OF EASTERN FINLAND
Rubber–brass adhesion has high importance in practical applications like tire production.
A detailed understanding of the adhesion is essential to enhance the rubber–brass interaction for better performance. The thesis focuses on the adsorption of rubber adsorbate models on ZnS, CuxS and ZnO surfaces to study the role of rubber functional groups and effect of different dopants at atomic level. The results can be used in practical applications for optimum
enhancement of the rubber–brass adhesion.