Structure And Properties Of Coordination Bond Between Nitrile-butadiene Rubber And Metal Ions

With the increasing attention to the ecological environment,people pay more attention to recycling and self-healing.As a controllable reversible non-covalent interaction,the metal coordination bond has attracted attention.There were many articles on coordination repair,but a few theoretical studies on metal coordination bonds.In this paper,coordination NBR composites were prepared.XPS and FT-IR were used to characterize the composites.The bonding ability and bond energy of the coordination bonds were calculated by the Arrhenius equation and bond valence-bond length theory.Combined with mechanical property and molecular orbital theory,we analyzed the affection of coordination bonds on the self-healing of materials.Details are as follows:1.The starting temperature of the coordination reaction was determined to be100°C by observing the changes in vulcanization curves.XPS N1s spectra indicated that different coordination bonds were formed at different temperatures.Quantitative analysis of N1s spectra showed that the linear coordination bond[Cu²⁺-N_L]was mainly existed in tri-coordinated[Cu²⁺-3N_L],and the copper ions in the bending coordination bond[Cu³⁺-N_B]were coordinated in the form of ion clusters.The binding energies of XNBR/Zn Cl₂-15 at 400.5 e V and 401.5 e V corresponded to N atoms participating in linear and bending coordination,respectively.The binding energies of XNBR/Cu Cl₂-15at 401.2 e V and 402.6 e V corresponded to N atoms participating in linear and bending coordination,respectively.It indicated that the binding ability of Cu²⁺to the solitary electrons was stronger than Zn²⁺.The Cu LM2 spectra of the XNBR/Cu Cl₂-10 indicated that the electrons of copper ions were dissociation at 190°C.Therefore,the oxidation state of Cu increased from 2 to 3.The orbital hybridization forms were different.At100°C,the 4s and 4p orbitals of Cu²⁺were hybridized to form an’outer-orbital coordination compound’,which has weak bonding ability and low strength.At 190°C,the 3d,4s,and 4p orbitals of Cu³⁺were hybridized to form an’infra-orbital coordination compound’,which had strong bonding ability and high strength.2.Infrared spectra showed that the stretching vibration absorption peak of the C=N group appeared at 1654 cm^-1 at 190°C,while the intensity of the C≡N absorption peak decreased at 2237 cm^-1,indicating that C≡N changed into C=N at high temperature.The changes of central ions and ligands were the main reasons for the transformation of coordination bonds from linear to bend.At the same time,the addition of copper ions effectively promoted the fracture of C=C and the formation of C=N.Arrhenius equation and bond valence-bond length theory were used to calculate the apparent activation energy of coordination reaction and the bond energy and strength of coordination bonds.The results showed that the apparent activation energy,bond energy,and strength of linear coordination bond were lower than bending coordination bond.The apparent activation energy was affected by the type,coordination number,and content of the coordination bond.By comparing the bond energy and strength of different coordination bonds,it was found that the bond energy and strength of[Zn²⁺-N_L]was higher than[Cu²⁺-3N_L]and[Cu²⁺-2N_L],so[Cu²⁺-3N_L]and[Cu²⁺-2N_L]were preferentially formed.The bond energy and strength of[Zn²⁺-N_B]were lower than[Cu³⁺-N_B],so the formation of[Zn²⁺-N_B]was easier than[Cu³⁺-N_B].3.The tensile strength of the XNBR/Cu Cl₂-n-100°C sample was higher than XNBR/Cu Cl₂-n-190°C,the elongation at break was much higher than XNBR/Cu Cl₂-n-190°C.It was because the reversibility of[Cu²⁺-N_L]was stronger than[Cu³⁺-N_B].The bending coordination bond had high strength.Therefore,[Zn²⁺-N_B]and[Cu³⁺-N_B]have little effect on the repair process of the material due to the low reversibility,so the repair of the material mainly depended on the flow diffusion of the molecular chain.Due to the strength of the linear coordination bond being low,the elongation at the break of the composite was significantly higher than the tensile strength.At this time,the repair of the material mainly depended on the re-formation of the reversible coordination bond.When the fracture surface was quenched,the repairability of the material was reduced.