Molecular simulation of hydrogen permeation behavior of polyamide 6 liner material for type IV hydrogen storage cylinder
In this work,the permeability of hydrogen in the polymer polyamide 6(PA6)was studied by molecular simula-tion methods at different temperatures(30,40,60 and 80℃)and pressures(82,87.5,98 and 103 MPa).Meanwhile,the permeability mechanism of hydrogen was analyzed.The results indicated that as the temperature increases,the ad-sorption heat and free volume fraction gradually increases,the thermal motion intensifies and the molecular motion space increases.And the solubility,diffusion and permeability coefficient of hydrogen in PA6 all increase.At a pressure of 103 MPa,increasing the temperature has the greatest impact on the permeability coefficient,which increases by 88.3%.With the increase of pressure,the interaction between hydrogen and PA6 molecular chains decreases and the free volume fraction decreases,so the solubility,diffusion and permeability coefficient of hydrogen in PA6 all show a downward trend.When the temperature was 60℃,the pressure had the most significant influence on the permeability coefficient,which de-creased by 38.6%.The permeation mechanism of hydrogen in PA6 includes the aggregation adsorption process in the low potential energy region and the diffusion process of intra-cavity vibration-inter-cavity transition formed in the free vol-ume.With the increase of temperature,the movement of hydrogen molecules becomes active and there are more inter-cavity jumps.When the pressure increases,the change is opposite.
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