Molecular Dynamics Simulation Of Supercritical Carbon Dioxide Cleaning

Cleaning as a key link in high-tech innovation fields such as microelectronics and precision instruments,plays an important role in the improvement of produ ct quality.However,most traditional cleaning methods have problems such as incomplete cleaning,material damage and environmental pollution,in this case in urgent need of a highly efficient green sustainable cleaning method,so the supercritical CO₂ green efficient cleaning technology arises at the historic moment.Firstly,the physical properties of supercritical CO ₂and entrapped ethanol systems under different conditions were simulated and studied,then,the two cleaning agents were used for cleaning simulation to compare the advantages and disadvantages,finally,the temperature was changed during the simulation to explore the influence of temperature on the cleaning of supercritical CO ₂-ethanol system:The physical characteristics of the four systems and pure CO₂ were imitate under different temperature and pressure conditions,such as density,solubility parameter,diffusion coefficient and molecular aggregation morphology,wherefore the influence of temperature,pressure and ethanol content on the p hysical characteristics of the system were analyzed,and the CO₂-ethanol system had a deeper understanding from the microscopic aspect;With glycerol as the pollutant,the supercritical CO₂ system and the supercritical CO₂-ethanol system are used for cleaning simulation,supercritical CO₂-ethanol system has a higher solubility parameter and the diffusion coefficient,the molecules can be faster and more efficient diffusion into pollutant gap in the process of cleaning,,which makes glycerol swell,thereby displacing it,the supercritical CO₂-ethanol system has higher interaction energy with glycerol in terms of energy,generally speaking,the cleaning ability of the system is better than that of the supercritical CO ₂ system;In the cleaning process,with the rise of temperature,the molecular thermal motion is enhanced,which are conducive to the pervasion and contact between molecules,thereby enhancing the interaction and facilitating the cleaning.Based on the above research,a supercritical CO ₂-ethanol system with better cleaning ability was selected to simulate the cleaning of Si O ₂,single-layer graphene and Fe substrates to explore the impact of different substrates on cleaning.The heptane,cycloheptane and toluene were selected as pollutants.During the adsorption process,the pollutants exhibited double-layer distribution on the three substrates,and the types in each layer were different due to the existence of competitive adsorption.In general,the adsorption capacity of the three substrates was as follows:Fe>Graphene>Si O₂;In the process of cleaning,CO₂ and ethanol molecules come into contact with pollutants repeatedly,make pollutant volume expansion,and then step by step a displacement.In the Si O₂substrate,the adsorption energy of CO₂ molecules with the substrate is higher than that of the pollutants,which makes the adsorption of CO ₂ molecules on substrate,and effectively prevent the secondary adsorption of pollutants;In the graphene substrate,the adsorption capacity of CO₂ molecules is weaker than toluene,which leads to toluene having an advantage in competitive adsorption,which cannot prevent secondary adsorption and makes cleaning effect is poorer;The adsorption capacity of Fe substrate is up to thousands,which makes the cleaning extremely difficult,but the final simulation shows that the overall cleaning effect is still good,only the bottom pollutant molecules are difficult to be replaced,it can be considered to cooperate with other cleaning methods.The overall cleaning effe ct is:Si O₂>Graphene>Fe.