發(fā)布時(shí)間：2018-10-31 19:26

【摘要】：本文運(yùn)用分子動(dòng)力學(xué)模擬的方法,對(duì)簡(jiǎn)單分子在分子篩和碳納米管中的結(jié)構(gòu)和擴(kuò)散等動(dòng)力學(xué)行為進(jìn)行了研究。首先,基于過(guò)渡態(tài)理論模擬研究了甲烷和正丁烷的單組分以及不同比例的二元混合物在空腔結(jié)構(gòu)分子篩ITQ-3中的擴(kuò)散,分別計(jì)算了單組分分子在y、z方向孔道中的自擴(kuò)散系數(shù)和二元混合分子在各比例下的擴(kuò)散行為,并通過(guò)分子投影在ITQ-3分子篩中x-y和x-z平面上的頻率等值線圖對(duì)出現(xiàn)的現(xiàn)象進(jìn)行了解釋。研究發(fā)現(xiàn),在ITQ-3分子篩中,單組分CH_4和C_4H_(10)隨負(fù)載n的擴(kuò)散表現(xiàn)出兩種擴(kuò)散模式:在z方向孔道中,當(dāng)負(fù)載n增大時(shí),自擴(kuò)散系數(shù)也隨著增大,當(dāng)增大到一定數(shù)值時(shí)又開(kāi)始減小;而在y方向孔道中,當(dāng)負(fù)載n增大時(shí),自擴(kuò)散系數(shù)一直減小。而對(duì)CH_4和C_4H_(10)混合分子在ITQ-3分子篩中的擴(kuò)散研究表明,混合分子中CH_4的擴(kuò)散與原子總數(shù)相關(guān):當(dāng)負(fù)載n較小時(shí),CH_4的擴(kuò)散系數(shù)在z方向和y方向孔道中都表現(xiàn)為隨原子總數(shù)的增多而增大;當(dāng)負(fù)載n較大時(shí),CH_4的擴(kuò)散系數(shù)在z方向孔道中隨原子總數(shù)的增多而減小,而在y方向孔道中,使z方向孔道發(fā)生堵塞效應(yīng)而使CH_4的擴(kuò)散系數(shù)減小的原子總數(shù)在y方向孔道中依然處于過(guò)渡狀態(tài)。其次,采用分子動(dòng)力學(xué)模擬的方法,研究了水在碳納米管中的擴(kuò)散行為,闡述了水在碳納米管中擴(kuò)散的傳統(tǒng)計(jì)算的局限性并提出了水在碳納米管中擴(kuò)散的新的計(jì)算方法:根據(jù)碳納米管中水以團(tuán)簇作彈道運(yùn)動(dòng)的特點(diǎn)將其視為類(lèi)布朗運(yùn)動(dòng)提出一種直接模擬計(jì)算納米管中水的輸運(yùn)擴(kuò)散系數(shù)的方法,這對(duì)理解限制在平滑孔道中的水之外的其他極性分子的擴(kuò)散提供了一種新的視角。
[Abstract]:In this paper, the structure and diffusion behavior of simple molecules in molecular sieves and carbon nanotubes were studied by means of molecular dynamics simulation. First, based on the transition state theory, the diffusion of methane and n-butane and binary mixtures in ITQ-3 with different ratios were studied, and the single-component molecules were calculated in y. The self-diffusion coefficient in the Z channel and the diffusion behavior of binary mixed molecules in different proportions are explained. The phenomena are explained by the molecular projection on the x-y and x-z plane of ITQ-3 molecular sieve. It is found that in ITQ-3 molecular sieve, the diffusion modes of CH_4 and C4H10 show two diffusion modes with the diffusion of loading n: in the Z channel, the self-diffusion coefficient increases with the increase of loading n. When it increases to a certain value, it begins to decrease again. In the y-direction channel, the self-diffusion coefficient decreases when the load n increases. The diffusion of CH_4 and C _ 4H _ (10) in ITQ-3 molecular sieve shows that the diffusion of CH_4 in the mixed molecule is related to the total number of atoms: when the loading n is small, The diffusion coefficient of CH_4 increases with the increase of the total number of atoms in both z and y directions. When the load n is larger, the diffusion coefficient of CH_4 decreases with the increase of the total number of atoms in the Z direction, but in the y direction, the diffusion coefficient of the CH_4 decreases with the increase of the total number of atoms. The total number of atoms which make the diffusion coefficient of CH_4 decrease due to the blockage effect in the Z direction is still in the transition state in the y direction. Secondly, the diffusion behavior of water in carbon nanotubes was studied by molecular dynamics simulation. The limitation of traditional calculation of water diffusion in carbon nanotubes (CNTs) is expounded, and a new calculation method of water diffusion in CNTs is put forward: according to the characteristics of the ballistic motion of water clusters in CNTs, it is regarded as Brownian motion. A direct simulation method for calculating the transport and diffusion coefficients of water in nanotubes is presented. This provides a new perspective for understanding the diffusion of polar molecules other than water confined to smooth pores.
【學(xué)位授予單位】：中北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：O552.2

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本文編號(hào)：2303305