不同润湿性石英表面吸附页岩油的分子动力学模拟

根据吉木萨尔凹陷芦草沟组储层特征,利用分子动力学方法研究了不同润湿性石英狭缝表面吸附页岩油的特征.用甲基和羟基按照-CH₃:-OH=100:0、 75:25、 50:50、 25:75、 0:100修饰石英表面以构造不同润湿性的表面,并构建10 nm裂缝模型,以研究其对C₁₅H₃₂页岩油的吸附特性.研究结果表明,通过调节修饰官能团的比例,成功构造了润湿角为122.0°、 116.5°、 92.5°、 82.6°、 65.4°的吸附模型.由于水分子与石英表面间的相互作用能变化剧烈,水分子在修饰的石英表面的吸附是导致润湿角不断改变的主要原因.(C₁₅H₃₂在甲基改性石英表面的第一吸附层峰值是羟基改性的石英表面的1.37倍,说明润湿性会导致吸附特征发生明显改变.)通过对游离态页岩油含量的计算发现,随着羟基改性程度的增加,游离态页岩油质量占比从68%逐渐增长到83.7%,说明表面的润湿性改造有利于页岩油的解吸进而提高页岩油开发能力.     

水驱油藏中原油极性物质对吸附和润湿性影响的分子模拟

为了研究水驱油藏中原油极性物质的吸附机理及其对油藏表面润湿性的影响,构建以石英为代表的砂岩岩石骨架模型,己烷为代表的非极性物质模型和以甲苯、胶质和沥青质为代表的极性物质模型,运用分子模拟方法研究4种原油组分和水分子在砂岩油藏表面竞争吸附过程和润湿状态。结果表明：水与4种原油组分在石英矿物表面竞争吸附时,原油中的非极性物质会比极性物质更加容易脱附。极性物质会随着时间的变化逐渐吸附在矿物表面,非极性的物质会随着时间变化逐渐远离矿物表面。吸附过程中静电力起吸附作用,范德华力起排斥作用。最后结合润湿性实验结果,从机理上解释了不同原油组成对润湿性的影响,即原油组分中极性物质含量越高,胶质沥青质含量越大,岩石表面油湿性越大,且水驱过程中润湿性向亲水方向变化越难。结论对提升水驱油藏采收率影响因素的认识有重要意义。     

分子动力学模拟研究方解石表面润湿性反转机理

利用分子动力学模拟技术从分子尺度探究方解石表面润湿性反转机理.首先,研究方解石表面润湿性反转过程;而后,从原油分子-方解石表面与原油分子-原油分子/水分子相互作用两个方面系统揭示方解石表面润湿性反转机理.结果:(1)水分子能够驱离方解石表面弱吸附的非极性分子造成润湿性的改变,但不能驱离强吸附的极性分子使润湿性反转难以实现;(2)原油分子极性越强与方解石表面相互作用越强,极性分子与方解石表面之间主要为静电力,非极性分子与方解石表面之间主要为范德华力;(3)原油分子极性越相近分子之间的相互作用越强,分子极性相差越大分子之间的相互作用越弱.非极性分子之间主要是范德华力,极性分子之间主要是静电力;(4)原油分子在方解石表面和水分子的共同作用下形成乙酸-吡啶-水-甲苯-己烷的稳定吸附序列.本研究为靶向提高采收率技术的设计与应用提供理论基础.     

基于密度泛函理论的CO2吸附微观机理比较研究

为探究吸附法捕获CO₂过程中的微观机理和吸附剂材料间的作用关系,基于密度泛函理论方法,综合比较了典型吸附剂包括煤基官能团、Fe、限域离子液体、Na₂CO₃、SrTiO₃与CO₂的吸附过程和差异性.根据不同计算策略,着重分析比较了吸附能、结构优化参数、吸附构型以及原子分布等参数.结果表明,化学吸附中CO₂分子与吸附面呈平行关系时通常吸附能最大;在一种材料的同类型官能团中,吸附能大小与氧原子的数量呈正相关关系;吸附过程中C-O键的伸长活化会生成一种重要的中间产物CO₂^-.提出在探寻CO₂吸附材料时可以在含氧原子较多的官能团、活性金属表面等方面进一步探究.最后对基于密度泛函理论的CO₂的吸附机理的进一步研究方向进行了展望.     

半导体表面气体分子吸附机理的光伏研究

通过对p型和n型的同一硅单晶样品分别置于大气、氧气、氮气的不同氛围中所进行的各有关表面参量的光伏测算，分析了同一样品处于不同氛围中，以及不同导电类型的样品处于同一氛围中的测算结果的变化规律，探讨了出现这一规律的内在机理，解释了各有关的物理现象. 关键词： 半导体表面 气体分子 吸附机理 光伏方法     

CTMAB-Al复合改性蒙脱石的表征及应用

以钠基蒙脱石（Na-MMT）为原料,用十六烷基三甲基溴化铵（CTMAB）预先改性,再用羟基铝柱撑液改性,制备不同CTMAB用量的复合改性蒙脱石（CTMAB-Al-MMT）,用于同时吸附水中苯酚和镉离子.复合改性蒙脱石用X射线衍射（XRD）、傅里叶红外光谱（FTIR）表征.结果表明,CTMAB和羟基铝阳离子已有效进入蒙脱石层间,层间距随CTMAB加载量增大而增加,吸附率随CTMAB加载量增大有明显提高.当复合改性蒙脱石用量为0.1g/50mL,吸附时间2h,pH=10时,苯酚吸附率达92.1％,镉离子吸附率达98.8％.     

甘氨酸在纳米碳管中的吸附及性质的分子模拟

采用分子力学、分子动力学方法模拟研究了甘氨酸分子在单壁纳米碳管中的吸附和扩散行为 ,并对甘氨酸分子在纳米碳管中的构象和能量进行了优化 .模拟计算结果表明 ,甘氨酸在纳米碳管中的构象发生了伸缩和扭转 ,这种构象的改变将会导致氨基酸生物性能的改变 ;纳米碳管对氨基酸分子具有较强的吸附作用 ,其中纳米碳管和甘氨酸分子之间的π -π相互作用增加了纳米碳管对氨基酸的吸附能 .模拟过程中氨基酸分子和纳米碳管之间的运动会保持很强的协同效应 ,使模拟体系构型在能量上处于最稳定的状态     

页岩气在Ⅱ型干酪根有机质中吸附的分子模拟

有机质是页岩气吸附的重要场所,室内实验描述干酪根有机质的物理和结构性质和研究页岩气在其中的吸附非常困难.分子模拟软件根据干酪根的实验分析数据构建干酪根有机质模型能在分子水平上研究气体的吸附状态.通过构建三维的Ⅱ型干酪根模型,运用巨正则蒙特卡洛方法(GCMC)来研究页岩气在干酪根分子模型中的吸附,分析了干酪根类型、温度、气体组成对气体吸附的影响和吸附剂模型对CH_4,C_2H_6的选择吸附性.运用分子动力学(MD)方法分析了页岩气在干酪根模型中吸附的结构性质.结果表明:相比于Ⅱ-C,Ⅱ-D型干酪根模型有更大的吸附量;温度升高,吸附量减小;在多组份气体吸附中随着压力的上升C_2H_6吸附量呈现了先增大后减小,最后趋于稳定的现象;干酪根模型对C_2H_6具有优先吸附的性质;干酪根模型中S原子与气体分子之间的相互作用最强,H原子与气体分子之间的相互作用距离最小.     

页岩气在粗糙纳米孔中吸附和输运的分子模拟

从微观上理解固气表面的吸附和注气驱替原理,有助于完善页岩气开采理论.本文通过运用蒙特卡洛和分子动力学方法,模拟了甲烷在粗糙壁面结构孔隙中的吸附和流动行为.研究结果显示粗糙结构对甲烷的吸附量有显著影响,压力小于20 MPa时,粗糙模型中的吸附量更大.注气驱替时,粗糙模型中二氧化碳的突破时间和甲烷的采收率,相比光滑壁面模型明显增加.这是由于粗糙结构模型的页岩壁面表面积更大,在低压下气体吸附能力更强.矩形粗糙结构页岩模型的选择吸附性强于三角粗糙结构模型和光滑模型.研究阐明了甲烷吸附和驱替的微观机理,为提高页岩气采收率提供了指导.     

高温壁面润湿性对气层稳定性及其壁面滑移性能的分子动力学研究

针对流体在纳米通道的小尺度效应,采用分子动力学方法模拟了传热效应以及流体流动行为,研究在壁面温度影响下,不同润湿性壁面上方气层生成状态以及流体流动时气层的稳定特性和相应的减阻性能.结果表明:当壁面为纯疏水壁面时,不能形成气层;疏水基底+亲水组合壁面形成不规则气层;纯亲水壁面和亲水基底+疏水组合壁面能形成规则气层.当流体流动时,疏水基底+亲水组合壁面气层消失,而纯亲水壁面和亲水基底+疏水组合壁面气层较为稳定.纯疏水壁面主流区域速度较大,而纯亲水壁面主流区域最低.对于壁面滑移速度,存在气层的壁面滑移速度与纯疏水表面相对接近,甚至稍优于纯属疏水表面,而疏水基底+亲水组合壁面滑移速度最小.     

Experimental, density function theory calculations and molecular dynamics simulations to investigate the adsorption of some thiourea derivatives on iron surface in nitric acid solutions

The effects of thiourea derivatives, namely N-methyl thiourea (MTU), N-propyl thiourea (PTU) and N-allyl thiourea (ATU) on the corrosion behaviour of iron in 1.0 M solution of HNO₃ have been investigated in relation to the concentration of thiourea derivatives. The experimental data obtained using the techniques of weight loss, Tafel polarization and electrochemical impedance spectroscopy, EIS. The results showed that these compounds revealed a good corrosion inhibition, (ATU) being the most efficient and (MTU) the least. Computational studies have been used to find the most stable adsorption sites for thiourea derivatives. This information help to gain further insight about corrosion system, such as the most likely point of attack for corrosion on iron (1 1 0), the most stable site for thiourea derivatives adsorption and the binding energy of the adsorbed layer. The efficiency order of the inhibitors obtained by experimental results was verified by theoretical analysis.     

氢在碳纳米纤维中的低温吸附储存特性

利用容积法测量了77K下氢在一种碳纳米纤维上的吸附等温线。采用分子模拟的方法模拟了77K下氢分子在平板状碳纳米纤维中的吸附,碳纳米纤维的石墨层层间距分别为0.335nm、0.6nm、0.9nm以及1.5nm。模拟结果表明:石墨层层间距为0.335nm的碳纳米纤维在77K下吸附储氢密度很难达到DOE的能量密度标准;当板间距为0.9nm时,系统吸附储氢的重量密度和体积密度均能达到最大,且在77K、1MPa下,能达到DOE的能量密度标准。     

SPM analysis of fibrinogen adsorption on solid surfaces

The adsorption kinetics, adhesion and orientation of human fibrinogen on solid surfaces have been studied by surface probe microscopy (SPM) and quartz crystal microbalance techniques (QCM). CF₃-, NH₂-terminated organo-silane self-assembled monolayers (SAM) and OH-terminated silicon dioxide have been used as model surfaces. Furthermore, the interaction of fibrinogen with nanocomposite Ti/hydrocarbon plasma polymer films (Ti/ppCH) deposited by dc magnetron sputtering has also been studied.     

气体分子在类石墨烯材料负载单个金属原子表面的吸附特性

采用密度泛函理论方法研究了不同种类和数量的气体小分子在类石墨烯材料(graphenylene)衬底支撑的金属原子(M=Co, Mo和Pd, gra-M)表面的吸附特性,系统地分析了吸附不同数量的NO和CO分子的稳定构型,吸附能,电荷转移量以及引起的体系电子结构和磁性变化.研究结果表明:1) NO、CO气体小分子的稳定吸附位在金属原子顶位,吸附物与衬底间的电荷转移量表明负载不同的金属原子能够有效地调制类石墨烯材料的气敏特性;2)单个和两个气体分子吸附能够引起gra-M体系的自旋电荷密度分布发生变化,进而使得气体吸附体系表现出不同磁矩大小.     

正癸烷纳米液滴润湿特性的分子动力学研究

流体液滴在固体表面的浸润性对其润滑性能至关重要.本文利用分子动力学方法研究了正癸烷纳米液滴在铜表面上的润湿特性.结果表明：在平坦光滑表面上,壁面的厚度和分子数目对润湿效果影响不大.随着壁面能量势阱参数εs 增大,接触角线性减小.随着温度升高,液滴的接触角减小.在沟槽粗糙表面上,随着粗糙度因子增大,对于疏液表面,接触角增大到一定值后基本保持不变,符合Cassie理论;中性和亲液表面接触角则会减小,为Wenzel润湿模式.当表面分数增大时,疏液与亲液表面接触角整体呈减小的趋势,对中性表面影响不大.当温度升高时,粗糙疏液表面接触角会增大,润湿效果更差,而粗糙中性和亲液表面液滴润湿性会更好.     

Mustard gas adsorption on the pristine and BN-doped graphynes: A computational study

The electronic sensitivity and reactivity of pristine, and BN doped graphyne (BNG) are scrutinized toward mustard gas using DFT calculations. The mustard gas weakly adsorbs via its Cl atom on the graphyne with adsorption energy about -3.1 kcal/mol and has no effect on its electrical conductivity. Replacing –C≡C– linkages with isoelectronic –BN– linkages increases the HOMO-LUMO gap (E_g) and decreases the work function and reactivity of graphyne. By mustard adsorption, the E_g of BNG decreases from 2.24 to 1.12 eV, increasing the electrical conductivity. Also, the BNG work function is considerably affected, changing the field emission electron current. Finally, a short recovery time about 0.03 s at room temperature is predicted for the mustard desorption from the surface of BNG. We also showed that the electrical conductivity change relates to the mustard concentration. The results indicate that the BNG may be a promising sensor for mustard gas.     

A first-principles study of gas molecule adsorption on hydrogen-substituted graphdiyne

Hydrogen-substituted graphdiyne (HsGDY) is a novel alkynyl carbon material with a structure similar to that of graphene. In this paper, the adsorption of four gas molecules (NO, NO₂, NH₃, and N₂) on HsGDY and B-doped HsGDY (B-HsGDY) was studied using density functional theory. The results show that the adsorption of NO and NO₂ on HsGDY and B-HsGDY is characterized by a larger charge transfer, stronger interaction, and higher adsorption energy compared with that of NH₃ and N₂. Based on the doping with B atoms, the adsorption energies of the gas molecules on HsGDY significantly improve, especially that of NO and NO₂. The gas molecule adsorption on both HsGDY and B-HsGDY is physical adsorption and the adsorption selectivity is good and thus may be applied for gas-sensitive NO and NO₂ materials.     

The influence of a small amount of active sites on the adsorption kinetics of nitrogen on ruthenium

Recently, Dahl et al. [S. Dahl, A. Logadottir, R.C. Egeberg, J.H. Larsen, I. Chorkendorff, E. Törnqvist, J.K. Nørskov, Phys. Rev. Lett. 83 (1999) 1814; S. Dahl, E. Törnqvist, I. Chorkendorff, J. Catal. 192 (2000) 381] have proposed very interesting hypothesis that the rate of dissociation and adsorption of nitrogen on Ru(0 0 0 1) facet is totally dominated by the presence of a small amount of step sites on Ru(0 0 0 1) terraces. Following this idea, a kinetic model, based on applying the Statistical Rate Theory approach, was developed in order to explain if such mechanism is able to explain the observed features of the system N₂/Ru(0 0 0 1). As a result, it was stated that the activation barrier for adsorption on the active (step) sites is equal to 36 kJ/mol; in turn, the adsorption energy of nitrogen atoms on the active sites is 43 kJ/mol. It implies that the rate of adsorption via the active sites is much faster than direct adsorption on the three-fold hollow sites; moreover, the occupation of the active sites is always close to zero at the investigated temperatures, so they are not blocked and may act as an indirect channel for adsorption. Thus, the rate of nitrogen adsorption on Ru(0 0 0 1) surface is governed by the rate of diffusion of nitrogen atoms from the active sites into the three-fold hollow sites. The analysis of thermodesorption spectra revealed an important role of repulsive interactions between the N atoms adsorbed on the hollow sites, the associated interaction parameter between nearest neighbors was estimated to be 5 kJ/mol. The presence of small amount of gold on Ru(0 0 0 1), apart of blocking the active sites, seems to remove the repulsion between nitrogen atoms.