本文關(guān)鍵詞： 二維受限水 石墨烯納米通道 壓縮極限 側(cè)向壓強 方形冰 過熱熔化 相變 相圖 分子動力學(xué)模擬　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：水是地球上最常見也是最普通的物質(zhì)之一,被譽為是生命之源。地球上的水絕大部分是以體相水的形式存在,主要為氣態(tài)、液態(tài)和固態(tài)(冰)。然而水卻更多地以界面或受限水的形式參與各種物理、化學(xué)和生物過程,因此研究微納米結(jié)構(gòu)中受限水的成鍵構(gòu)型、物理化學(xué)性質(zhì)以及流動行為等,進(jìn)而面向材料科學(xué)、水資源、環(huán)境和能源利用等領(lǐng)域的實際需求系統(tǒng)地開展受限水的應(yīng)用研究,成為當(dāng)前水科學(xué)研究的重要領(lǐng)域和國際前沿?zé)狳c。近年來,石墨烯以其獨特的力學(xué)、電磁學(xué)與物理等特性而備受關(guān)注。氧化石墨烯薄膜不同尋常的滲透行為和離子海綿效應(yīng)不僅使得其在海水淡化和物質(zhì)輸運等領(lǐng)域具有廣闊的應(yīng)用前景,而且相應(yīng)的機理研究也是學(xué)術(shù)界關(guān)注的前沿科學(xué)問題。實驗和模擬發(fā)現(xiàn),氧化石墨烯薄膜的限域效應(yīng)使得水分子能夠進(jìn)入間隙只有0.35納米左右的石墨烯納米通道中,而且自發(fā)形成二維的晶體狀類固體結(jié)構(gòu)。Algara-Siller等在實驗中觀察到納米水滴在兩片石墨烯之間形成單層方形冰,這種二維方形結(jié)構(gòu)是常溫下水的一種全新存在形式,突破了長久以來人們對冰的已有認(rèn)識。模擬表明這種特殊的晶體相主要是由于石墨烯受限空間內(nèi)高達(dá)GPa量級的vanderWaals壓強(類毛細(xì)壓)作用,即納尺度限域效應(yīng)。納尺度限域效應(yīng)會明顯影響受限水的結(jié)構(gòu)形態(tài)、動力學(xué)行為以及熱力學(xué)特性等,相關(guān)的內(nèi)在機理還未得到全面的認(rèn)識。從力學(xué)的角度來看,水在兩片石墨烯之間由液態(tài)到固態(tài)的相變具有二維液體的亞穩(wěn)態(tài)極限(壓縮極限)的特征�；诖�,本文通過經(jīng)典分子動力學(xué)模擬研究二維受限水在石墨烯納米通道內(nèi)的相態(tài)和相變。第一次系統(tǒng)地研究了二維受限水的壓縮穩(wěn)定極限,發(fā)現(xiàn)多種新的二維冰相和相變過程,首次得到了側(cè)向壓強作用下二維材料的壓縮極限相圖,同時發(fā)現(xiàn)了側(cè)向壓強主導(dǎo)的兩階段過熱熔化現(xiàn)象。本文首先研究了兩片石墨烯包裹形成的單層方形冰,從結(jié)構(gòu)特征與動力學(xué)特性的角度來揭示兩片石墨烯包裹的單層方形冰的形成,用統(tǒng)計平均的方法證明單層方形冰固有的方形特征。根據(jù)單元特點對模擬中得到的單層方形冰的結(jié)構(gòu)給出定義,具體分析了有限溫度作用下單層方形冰中水分子自發(fā)翻轉(zhuǎn)行為和翻轉(zhuǎn)引發(fā)的結(jié)構(gòu)演化,結(jié)合幾何平均和時間平均概念,使用統(tǒng)計平均的方法研究單層方形冰的方形特征。隨后,本文對石墨烯納米通道內(nèi)二維受限水的壓縮相變和過熱熔化相變進(jìn)行了詳細(xì)的研究。分子動力學(xué)模擬研究發(fā)現(xiàn),在不同的納米通道寬度或溫度條件下,側(cè)向壓強作為一個可控因素,能夠?qū)崿F(xiàn)二維受限水的一階相變和連續(xù)型相變,得到新的不同結(jié)構(gòu)的冰相。在模擬中共觀察到12種不同的二維冰相,分別是:平的單層方形冰(fMSI)、之字形褶皺的單層方形冰(pMSI)、單層三角形非晶態(tài)冰(ML-T)、AB堆垛結(jié)構(gòu)雙層方形冰(BL-ABI)、AB堆垛結(jié)構(gòu)雙層方形非晶態(tài)冰(BL-AB2)、AB堆垛結(jié)構(gòu)雙層菱形冰(BL-AB1)、AA堆垛結(jié)構(gòu)雙層正六邊形冰(BL-iceI)、AA堆垛結(jié)構(gòu)雙層方形管狀冰(BL-VHDI)、AA堆垛結(jié)構(gòu)雙層三角形冰(BL-AAI)、ABA堆垛結(jié)構(gòu)三層方形冰(TL-ABAI)、ABA堆垛結(jié)構(gòu)三層菱形冰(TL-ABA)和AAA堆垛結(jié)構(gòu)三層三角形冰(TL-AAAI)。根據(jù)一系列的熱力學(xué)平衡狀態(tài)和Clapeyron方程,在通道寬度-側(cè)向壓強(h-P)平面內(nèi)得到了二維受限水的壓縮極限相圖,壓縮極限曲線具有多個局部極大值。從雙層液態(tài)水到BL-VHDI和BL-AA1的相變分別是一階相變和連續(xù)型相變,這兩種不同相變的溫度閾值是～275 K。從BL-VHDI到BL-AAI的結(jié)構(gòu)轉(zhuǎn)變可以看作是方形冰納米管的屈曲失穩(wěn)。ABA堆垛結(jié)構(gòu)的三層冰結(jié)構(gòu)類似于雙層籠形水合物,其中間層水分子被當(dāng)作客體分子。對于AAA堆垛結(jié)構(gòu)的三層冰,與石墨烯壁面相鄰的兩層水分子比中間層的擴散更快。在單層方形冰的過熱熔化過程中,共有四種不同的熔化相變情形,其中在較高的側(cè)向壓強條件下,發(fā)現(xiàn)兩種不同的兩階段熔化現(xiàn)象以及單層冰和液相的共存狀態(tài),并給出了單層方形冰的與側(cè)向壓強相關(guān)的過熱熔化相圖。"What is the structure of water"是Scienc雜志公布的125個最具挑戰(zhàn)性的科學(xué)前沿問題之一。研究受限水的相態(tài)行為是水科學(xué)研究領(lǐng)域的重要分支,對受限水的物質(zhì)形態(tài)、固液界面多種物理機制耦合以及納尺度限域傳質(zhì)等基礎(chǔ)科學(xué)研究和海水淡化、物質(zhì)輸運、生物科學(xué)、材料科學(xué)以及傳統(tǒng)產(chǎn)業(yè)轉(zhuǎn)型升級等實際應(yīng)用需求具有重要的學(xué)術(shù)價值。
[Abstract]:Water is the most common one of the material is the most common, is known as the source of life. Most of the water on the earth is in the form of bulk water, mainly for gaseous, liquid and solid (ice). However, the water is more limited to interface or water in the form of a variety of physical and chemical and biological processes, therefore limited water research on micro nano structure in the bonding configuration, physical and chemical properties and flow behavior, and for materials science, water resources, research and application of the system to carry out the actual needs of the field of confined water environment and energy utilization, as an important field of water science research and international frontier in recent years, graphene with its unique mechanics, electromagnetics and physical characteristics have attracted much attention. The ion permeation behavior and sponge effect of graphene oxide film is unusual not only makes the transport in desalination of sea water and material etc. Has broad application prospects, and the corresponding mechanism is also concern the academic frontier scientific issues. Experimental and simulation show that the confinement effect of graphene oxide film which water molecules can enter the gap is only 0.35 nm graphene nano channel, and the spontaneous formation of two-dimensional crystalline solid structure.Algara-Siller to observe the nano water forming a layer of ice in the square between two sheets of graphene in the experiment, the two dimensional structure is a new form of water at normal temperature, break the people long ice has been understanding. Simulation shows that this special crystal phase is mainly due to the pressure of vanderWaals graphene in confined space of up to GPa the order (type of capillary pressure), namely the nanoscale confinement effect. Nano scale limit structure domain effect can significantly affect the dynamic behavior of confined water, and heat The mechanical properties, mechanism of correlation has not been fully understood. From the mechanical point of view, the metastable limit of water between two sheets of graphene from liquid to solid phase transition with two-dimensional liquid (compression limit) characteristics. Based on this, the phase and phase transition through classical molecular dynamics simulation of 2D the limited water in graphene nano channel. The first systematic study of the two-dimensional water confined compression stability limit, found a variety of new two-dimensional ice phase and phase transformation, obtained two-dimensional material under the action of lateral pressure limit of compression phase diagram, and found two stage overheating melting phenomenon. Firstly, lateral pressure leading research two pieces of graphene wrapped to form single-layer square ice, forming a layer of ice to reveal two square pieces of graphene package from the characteristics and dynamic characteristics of the structure of the angle, with the statistical average Method that features a square single square ice. According to the definition of the inherent characteristics of the single unit structure are square ice obtained in simulation, detailed analysis of the structural evolution of the finite temperature under the action of single square ice water molecules in spontaneous behavior and triggered flip flip, combined with the geometric mean and the average time of conception, characteristics of single square square ice use the statistical average. Subsequently, the graphene nano channel in two-dimensional confined water compression phase and overheating melting phase transition is studied in detail. The molecular dynamics simulation study found that in different nano channel width or temperature conditions, the lateral pressure as a controllable factor, a first-order phase transition and continuous phase can the realization of two-dimensional confined water, different structures of the new ice phase. In the simulation were observed in 12 kinds of two-dimensional ice phase, are: single layer flat. The shape of ice (fMSI), single square ice zigzag fold (pMSI), triangular amorphous ice (ML-T), AB stacking structure double square ice (BL-ABI), AB square double stacking structure of amorphous ice (BL-AB2), AB stacking structure of double diamond ice (BL-AB1), AA double hexagonal stacking structure ice (BL-iceI), AA stacking structure double square tubular ice (BL-VHDI), AA stacking structure (BL-AAI), double triangle ice ABA stacking structure of three layers of ice, ABA square (TL-ABAI) stacking structure of three layers of diamond ice (TL-ABA) and AAA stacking structure of three layers of triangular ice (TL-AAAI). According to the state equation and Clapeyron equation a series of thermodynamic equilibrium, the channel width of lateral pressure (h-P) in the plane of the two-dimensional water confined compression limit diagram, compression limit curve has multiple local maxima. The double liquid water phase transition to the BL-VHDI and BL-AA1 are the first order phase transition and continuous phase, the two Different kinds of transformation temperature threshold is 275 ~ K. from BL-VHDI to BL-AAI transition can be seen as buckling of square ice nanotubes lost three layer of ice structure stability.ABA stacking structure similar to the double clathrate hydrate, the interlayer water molecules are as guest molecules. The three layer of ice AAA stacking structure, diffusion and two water layer graphene wall adjacent to the intermediate layer faster. In hot melting process of ice in the single square, a total of four different melting transition, in which the high lateral pressure conditions, found two different two stages of melting phenomenon and monolayer ice and liquid phase coexistence. And gives a single square ice associated with the lateral pressure of melt. "What is the structure phase of water 125" is one of the most challenging scientific frontier issues of Scienc magazine published. The phase study of confined water for Water is an important branch of scientific research in the field of confined water, physical form, physical mechanism and variety of solid-liquid interface coupling nanoscale confinement and mass transfer of basic scientific research and desalination, material transport, biological science, material science and the practical needs of the transformation and upgrading of traditional industries has an important academic value.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O613.71;TB383.1
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本文編號：1474202