Molecular Dynamics Simulation Of Corrosion Inhibitor Diffusion Behavior In VCI Packaging Film

Through the diffusion and volatilization of Volatile Corrosion Inhibitor(VCI)in the film,uniform protective layer can be formed on the metal surface,and then the reaction between corrosive medium and metal can be prevented and non-contact metal rust prevention can be realized.However,most of the VCI formulations used for gas phase anticorrosive films are based on the selection of gas phase corrosion inhibitor based on experience,and the theoretical guidance is limited.Therefore,it is of great engineering value to study the diffusion behavior of gas phase corrosion inhibitors in polymers,analyze the interaction of multi-component corrosion inhibitors during diffusion,and reveal the diffusion mechanism of gas phase corrosion inhibitors in polymers.Based on the molecular dynamics simulation method,this topic studies the diffusion behavior of sodium benzoate(SB),Benzotriazole(BTA),sodium nitrite(NIT)and benzoic acid(BE)in polyethylene(PE)film after the combination of one component and multiple components,analyzes and compares the possible interaction of VCI multi-component diffusion,and summarizes the diffusion law.According to the simulation conditions,the gas phase anticorrosive film was prepared,and the basic properties of the film were characterized.The diffusion and migration of BTA were detected by ethanol leaching and ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry,and the diffusion coefficient was calculated to verify the validity of the simulation analysis results.The main research contents and conclusions are as follows:(1)In the single-component diffusion system of VCI,the diffusion modes of the four VCI molecules in PE are mainly peristaltic diffusion;The diffusion coefficients of the four VCI molecules under different temperature conditions are NIT > BE > SB > BTA.The VCI molecules with larger diffusion coefficients have larger diffusion trajectories and less overlap.When VCI molecular structure is flexible,it is easier to diffuse,and the corresponding diffusion coefficient is larger.The interaction between VCI molecules and diffusion system will hinder its diffusion process.With the increase of temperature,the fluidity of PE chain segment increases,the change frequency of free volume distribution is accelerated,and the diffusion coefficients of the four VCI molecules increase accordingly.(2)In the VCI multicomponent diffusion system,the addition of SB and BE inhibitor will hinder the diffusion of BTA in PE,and the obstruction effect of SB is more significant,while NIT has no obvious effect on its diffusion.Compared with the single-component VCI diffusion system,the diffusion coefficients of each VCI in the four-component VCI co-diffusion system are reduced,but the law of their magnitude is consistent with that of single-component VCI diffusion system.In VCI two-component and four-component co-diffusion systems,the diffusion mode of VCI molecules is still peristaltic diffusion,and the distribution of diffusion trajectory corresponds to the variation law of diffusion coefficient.With the increase of the number of PE chains,the diffusion constraints of VCI molecules become more and the diffusion coefficient decreases further.The free volume fraction of multicomponent VCI diffusion system,the interaction energy between VCI molecules and diffusion system,and the self-diffusion of PE chain all affect the diffusion behavior of VCI in PE.(3)LDPE anti-rust films of single component BTA,two component BTA and SB,and four component VCI were prepared according to the simulation conditions.The BTA migration amount in the films was measured by ethanol leaching and triple quadrupole composite linear ion trap liquid-mass combination method.The surface of the films was observed by atomic force microscope to verify the validity of the BTA migration test method.The experimental value of BTA diffusion coefficient is calculated and compared with the simulation results under corresponding conditions.It is found that the experimental value of BTA diffusion coefficient is one order of magnitude different from the simulated value,but the regularity of the two diffusion coefficients is consistent,which verifies the feasibility of the molecular dynamics simulation method.