大气压He/O_(2)等离子体活性粒子在水溶液中传质的氧含量效应

Oxygen Concentration Effect on the Mass Transfer of Reactive Species of the Atmospheric-Pressure He/O_(2) Plasma in Aqueous Solution

大气压低温等离子体作用于生物组织要穿过其表面几十到几百微米厚的水溶液,将会涉及等离子体中活性粒子在水溶液中的传质,而活性粒子的生成与放电气体的氧含量密切相关。该文基于一维流体模型,研究了在放电气体中不同的氧含量下(体积分数为0.1%~5%)大气压He/O_(2)等离子体中五种主要活性粒子H_(2)O_(2)、O_(2)^(-)、HO_(2)、O_(3)及OH在水溶液中的渗透深度分布,并阐释了相关机理。研究表明,氧含量对活性粒子的生成与消耗反应产生较大影响,进而影响到活性粒子在水溶液中的渗透深度。随着氧含量的增加,H_(2)O_(2)、O_(2)^(-)和HO_(2)的渗透深度减小,但仍维持在数百微米以上的可观量值,而O_(3)和OH的渗透深度增加,并可达20μm以上,这一深度使得两种粒子可以直接作用到某些生物组织,因而对于等离子体的生物医学应用具有重要意义。

Cold-temperature atmospheric plasma(CAP)has been successfully applied in biological engineering,such as sterilization,surgery and even cancer treatment.However,the biological tissue to be treated is usually covered with a layer of aqueous solution with a thickness of tens to hundreds of microns.Plasma action on the surface of biological tissues necessarily involves the mass transfer process of the active species generated by the plasma in aqueous solution.There are lots of experimental measurement techniques have been used to analyze the mass transfer process between plasma and water.However,due to the limited detection technology,it is difficult to obtain the concentration distribution of species in aqueous solution.Thus,we used numerical simulations to quantify the mass transfer of active species in aqueous solutions.Based on the one-dimensional diffusion-reaction model,the mass transfer process of active species produced in plasma from the gas phase region to the gas-liquid interface region and finally into the liquid phase region is investigated in this work by establishing the control equations and boundary conditions of liquid phase region.The generation of active species in the plasma is closely related to the oxygen volume in the discharge gas,so we analyzed the generation and consumption reactions of active species in aqueous solution by simulating 19 reactive oxygen species(ROS)and 84 main chemical reactions in the liquid phase region with the change of the oxygen volume fraction in the discharge gas(the range is 0.1%~5%),in order to study the penetration depth distribution of the five main ROSs(H_(2)O_(2),O_(2)^(−),HO_(2),O_(3),and OH)in liquid phase region under different conditions.According to the simulation,the change of oxygen volume in the discharge gas has an impact on the flux of active species generated by the plasma into the liquid phase region,which also affects the generation and consumption of the five main ROS in the aqueous solution.For H_(2)O_(2),O_(2)^(−),and HO_(2),all the generation,consumption,and net generation decrease with the increase of oxygen content,while for the OH and O_(3),all the generation,consumption,and net generation increase with increase of oxygen content.These processes finally results in the change of the species number density and penetration depth of the ROS.The following conclusions can be drawn from the simulation analysis:(1)The change of the oxygen content volume in the discharge gas affects the flux of related oxygen species and electrons into the liquid surface,and then affects the species number density concentration and penetration of the five ROSs in the aqueous solution depth.(2)The penetration depth of OH and O_(3) increases with the increase of oxygen volume,from a fewμm to more than 20μm within the range of oxygen volume considered,this depth makes it possible for these two species to act directly on some biological tissue.(3)The species number density of H_(2)O_(2),O_(2)^(−),and HO_(2) in aqueous solution decreases with the increase of oxygen volume,so their penetration depth also decreases,but they still remains above a considerable value of hundreds of microns.Therefore,the reduction of the penetration depth of the three particles has little effect on their biomedical applications.