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1.
A molecular dynamics (MD) model of the fluidic electrokinetic transport in a nano-scale channel with two bulk sinks was presented, and the process of ion transport in the nanochannel was simulated in this paper. The model consists of two water sinks at the two ends and a pump in the middle, which is different from a single pump model in previous MD simulations. Simulation results show that the charged surfaces of the nanochannel result in the depletion of co-ions and the enrichment of counterions in the nanochannel. A stable current is induced because of the motion of ions when an external electric field is applied across the nanochannel, and the current in the pump region is mainly induced by the motion of counterions. In addition, the ion number in the pump region rapidly decreases as the external electric field is applied. In the equilibrated system, the electrically neutral character in the pump region is destroyed and this region displays a certain electrical character, which depends on the surface charge. The ion distribution is greatly different from the results predicted by the continuum theory, e.g. a smaller peak value of Na+ concentration appears near the wall. The transport efficiency of counterions (coions) can be effectively increased (decreased) by increasing the surface charge density. The simulation results demonstrate that the ion distribution in the electric double layer (EDL) of a nanochannel cannot be exactly described by the classical Gouy-Chapman-Stern (GCS) theory model. The mechanism of some special experimental phenomena in a nanochannel and the effect of the surface charge density on the ion-transport efficiency were also explored to provide some theoretical insights for the design and application of nano-scale fluidic pumps. Supported by the National Basic Research Program of China (Grant No. 2006CB300404), the National Natural Science Foundation of China (Grant Nos. 50475077, 50676019, 50506008), the Natural Science Foundation of Jiangsu Province (Grant No. BK2006510), and the Foundation of Education Ministry of China (Grant No. 20050286019). The author Y. Chen also acknowledges the financial support from the Program for New Century Excellent Talents in University (NCET-04-0470).  相似文献   

2.
颗粒的双极带电与气固流化床中的静电分布   总被引:1,自引:0,他引:1  
对颗粒的双极带电现象和气固流化床中的静电分布进行了理论分析和实验研究.推导出了小颗粒上电荷量的计算公式,指出大小颗粒的带电极性由颗粒表面上的电荷载流子类型决定,若绝缘颗粒表面上的电荷载流子为电子或阴离子,则大颗粒带正电,小颗粒带负电;反之大颗粒带负电,小颗粒带正电.在150 mm的有机玻璃流化床冷模装置中,以干燥氮气为流化气体,对LLDPE、HDPE、PP1、PP2和PVC等5种聚合物粉料系统,测量了不同气速下流化床中不同床高处的静电压值.结果发现床内的静电场为非均匀电场,静电压沿床层轴向呈“Z”型或“S”型分布,且在床层稀密相分界面附近会发生极性的改变,实验验证了颗粒的双极带电理论.  相似文献   

3.
超滤过程中蛋白质带电性对水合作用的影响机制   总被引:1,自引:1,他引:0  
为解析超滤过程蛋白质带电性能对水合作用力的影响机制,在牛血清蛋白(BSA)带正电、中性及负电条件下,分别考察PVDF-BSA及BSA-BSA之间的相互作用力随离子强度的变化特征,结合相应条件下BSA的Zeta电位变化特征,探讨超滤过程蛋白质带电性能对水合作用力的影响机制.结果证实BSA带电性能是影响水合作用力的关键因素.在BSA带正电条件下,作用力随离子强度的增大而增大,主要是因为BSA带正电时无水合作用存在,静电作用力的变化是控制膜污染的主要因素.在BSA电中性及负电条件下,BSA及PVDF膜面吸附累积大量的水合阳离子,随离子强度的增大,有效触发PVDF-BSA及BSA-BSA之间的水合排斥力,进而大幅度减缓膜污染;且在BSA等电点更容易观察到水合作用现象.  相似文献   

4.
EDTA的浓度和介质PH的变化可以引起a-Fe_2O_3单分散溶胶的絮凝和再稳定。再稳定是由于带有正电荷的胶体粒子吸附了过剩的负离子,导致粒子表面电性反号引起的。C.C.C和C.S.C强烈依赖于介质的PH。该絮凝机理属于吸附凝机理,受表面化学反应所控制。  相似文献   

5.
为了研究电化学除氯对混凝土中离子分布和微观结构的影响规律,采用压汞法、SEM电子显微镜分析等方法对电化学除氯后不同水灰比混凝土试件中钢筋附近和表面层的氯离子和钾钠离子含量、孔隙结构、显微结构进行对比分析.结果显示,电化学除氯后,钢筋附近混凝土与外层混凝土相比,氯离子含量约为1/2,钾离子含量约为5~10倍,钠离子含量约为8~18倍,水化物颗粒间结合不连续、部分水化产物分解.钢筋附近区域混凝土中的氯离子含量明显低于外表层混凝土,钾、钠离子在钢筋阴极附近大量聚集.经过电化学处理后的混凝土试件钢筋附近区域的孔隙率和大孔含量增多,结构疏松;而外表层混凝土结构致密,孔隙细化,水化产物成网络状结合良好.  相似文献   

6.
The distribution of gold colloids in kaolinite and the interaction between gold and kaolinite surface were investigated by transmission electron mieroscotgy (TEM) and X-ray photoelectron spectroscopy ( XPS ). There is strong interaction between the gold particles and the edge surfaces of kaolinite, in low pH solution, the edge surface of kaolinite is positively charged and electrostutic attrcactive force between colloide gold panicles and the positive edge surface of kaolinite woald facilitate the adsorption of colloidal gold particles onto the suface. TEM observation shows that the aggregate morphology of gold particles was dominated by particle-particle interaction and gold particles were adsorbed on the edge surface of kaolinite crystals , resulting from the electrostatic attractive force between colloidal gold particles and the positice surfaces of kaolinite. XPS data show that in Au4 f electron spectra there are four energy peaks related to gold, 83.8 eV, 85.7 eV, 87.5 eV, and 89.4 eV, respectively, which suggests that in chemical states there are metallic gold and Au bonded to O, similar to the form of Au2O3 , and composite Au2O3 is formed between the edge surface of kaolinite and colloidal gold surface.  相似文献   

7.
用密度泛函理论计算研究了钠离子(Na+)在蒙脱石(MMT)内形成的水合离子的基态结构和性质。Na+受到MMT表面的影响,表现出和气相中不同的水化行为。Na+吸附水分子后,与表面的作用被削弱,逐渐被拖离表面。受Na+表面空间限制,多余的水分子之间及与表面之间形成氢键,间接地增强了Na+的水化,使Na+的水化能随水分子增加而振荡地增加。  相似文献   

8.
Reaction Activity of Kaolinite Surfaces:Quantum Chemistry Calculations   总被引:1,自引:0,他引:1  
The anion-kaolinite surface infractions and AuS - adsorption onto the surfaces of kaolinite were studied using the self-consistent-field discrete variation ( SCF - Xα - DV) method. Electronic structure and energies of the system of anion AuS- adsorbed on an atomic cluster of kaolinite were calculated. The results show that the systems with lower total energy are those AuS- adsorbed on the edge surfaces, which indicates that the systems of adsorption of AuS- on the edges are more stable relative to those adsorbed on the basal plane. On the other hand, bond order data suggest that significant shifting of atomic charge and the overlapping of electronic cloud between Au ( Ⅰ ) of the AuS- and the surface ions of kaolinite would take place in the systems with AuS - being adsorbed on the edges, especially at the she near A1 octahedra. Therqrore, it can be concluded that edge sites will dominate the complexation reactions of the surfaces of kaolinite, with negligible contributions from other fimctional groups on the basal plane, which are dominated by either siloxane sites in silica layers or aluminol sites in gibbsite layers.  相似文献   

9.
Spodumene is a silicate mineral rich in lithium. However, the gangue mineral, albite has similar crystal chemical structure and composition to spodumene. In this work, the density functional theory (DFT) calculation was taken to research the floatability from the perspective of crystal chemistry. And contact angle test and reagent adsorption test were used to support the simulation results. In addition, the weighted total density of broken bonds is proposed for the first time to judge the generation probability of cleavage surface. The DFT calculation results display that the Na and Al sites on the albite surface are the adsorption sites of water molecules. While the water molecules only bond with Al atom on the surface of spodumene and each Al site can adsorb only one water molecule. Thus, the wetting effect of water molecules on the albite surface is stronger than that of spodumene. This is consistent with the result of contact angle. In sodium oleate system, the oleic acid anion is adsorbed on the spodumene surface in form of a multicomponent ring while the albite is a single ring. Theoretically, oleic acid anion can be strongly adsorbed on the surface of spodumene and albite under vacuum. The adsorption strength of spodumene is higher than that of albite. However, on hydrated surface, the adsorption strength of oleic acid anion on mineral surface is greatly reduced due to the interaction between water molecules and metal site on mineral surface. Thus, spodumene and albite are hard to float without external activated ions in sodium oleate system.  相似文献   

10.
Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) is an aromatic polyester with molecular structure similar to that of poly(ethylene terephthalate)(PET). In this paper, the space charge storage ability and its stability in corona charged PEN were studied by measurement of surface potential decay under different storage conditions including dif- ferent temperatures and relative humidities, and analysis of open circuit thermally stimu- lated discharge (TSD) current spectra and charge TSD curves. The comparison between the charge stability of PEN and PET was carried out. The results point out that the charge stability of PEN is markedly better than that of PET under different environmental condi- tions. By means of isothermal depolarization program, the space charge lifetimes (effec- tive time constant) τ at room temperature of positively and negatively charged PEN are estimated to be 90 y. The results offer theoretical and technical support for the use of PEN as the chip of high quality electret condenser microphone due to its excellent dielectric, mechanical and thermal properties.  相似文献   

11.
The adsorption of superplasticizers in fly ash blended cement paste and its rheological effects were investigated.It is shown that the absorption of superplasticizer on portland cement particles is very different from that on fly ash particles.The fly ash particles have smooth surfaces and are negatively charged,so its adsorption capacity is weaker than the portland cement particles.The amount of adsorbed SP in the fly ash blended cement paste depends highly on the replacement proportion of portland cement with fly ash,and to a much less extent on the nature of the fly ash.However,the amount of adsorbed superplasticizer does not correspond well the ζ-potential of the solid particles,due the strong adsorbing capacities of the Portland cement particles.When fly ash replaces portland cement in the paste,the rheological behavior is radically changed,which is closely related to the fineness and density of the ash.The packing and agglomeration of the solid particles are the controlling factors on the rheological parameters of the fresh paste,instead of the amount and type of adsorbed superplasticizer.  相似文献   

12.
Polysulfone (PS) hollow-fiber ultrafiltration membrane was characterized combined with flux and streaming potential in single electrolyte solutions. The effects of trans-membrane pressure, electrolyte concentration, ion valence and pH value of electrolyte solution on the streaming potential (SP) of the membrane were investigated. The zeta potential and surface charge density of the membrane were calculated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory. The results indicate that the valence and concentration of cation have a greater influence on the SP and surface charge density of PS membrane than those of anion, and the pH value of electrolyte solution has great effects on the SP and zeta potential of the membrane surface. Both the absolute value of the streaming potential and water flux of the adsorbed membrane decrease, compared with those of the clean membrane. The streaming potential and flux of the cleaned membrane can be completely recovered by cleaning with the mass fraction of 0.8% EDTA at pH=10. Foundation item: Project(20776161) supported by the National Natural Science Foundation of China  相似文献   

13.
Pb2+ adsorption onto a soil by irrigation of sewage in the Pearl River Delta of South China was examined as a function of the reaction time, solution pH, initial lead concentration, organic matter (humic acid) and competitive ions (Cu2+). The adsorption of Pb2+ onto the soil was investigated on batch equilibrium adsorption experiments. Results show that the Pb2+ adsorption on the soil is relatively rapid in the first 30 min and reaches equilibrium at 2 h, and the kinetics of the adsorption process on the soil is well characterized by the pseudo-second order reaction rate. Langmuir, Freundlich and Temkin isothermal models are fit for the adsorption of Pb2+ onto the soil, and the maximum amount of Pb2+ adsorption (Q m) is 7.47 mg/g. The amount of Pb2+ adsorption increases with increasing the pH at the range of 1.2–4.5 and reaches a plateau at the range of 4.5–12. The presence of humic acid in soil decreases the adsorption of Pb2+ onto the soil at solution pH of 8 since the negatively charged humic acid with Pb2+ is difficult to be adsorbed on the negatively charged soil surface. The adsorption of Pb2+ onto the soil also decreases in the presence of Cu2+ due to the competition adsorption between Pb2+ and Cu2+.  相似文献   

14.
Four polyaniline-tea saponin (PTS) nanocomposites were prepared by an in-situ polymerization with tea saponin (TS) as a biosurfactant,and they were used to remove organic dyes from aqueous solution.The PTS nanocomposites were characterized by using field emission scanning electron microscopy,the Fourier transform infrared spectroscopy,the Ultraviolet-visible spectroscopy,and the thermogravimetric analysis.The adsorption performances of the PTS nanocomposites for organic dyes were studied by a st...  相似文献   

15.
The direct sulfidization of cuprite is inefficient because cuprite is a copper-oxide mineral with a strong surface hydrophilicity. In this study, oxidant was used to modify cuprite surfaces to regulate the sulfidization of cuprite. Microflotation tests showed that the flotation recovery of pre-oxidized cuprite was nearly 25% higher than that of direct sulfidization flotation, which indicates that the cuprite surface activity was enhanced after pre-oxidation by Cu(I) species (weak affinity with sulfur ions) transformation to Cu(II) species (strong affinity with sulfur ions). Zeta potential, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry results showed that pre-oxidation improved cuprite sulfidization and promoted the formation of copper-sulfide species on the cuprite surfaces. The mineral surface stability and thus, xanthate species adsorption on the cuprite surfaces were improved. The surface-adsorption measurements and infrared spectroscopy showed that a large amount of xanthate species was adsorbed onto the sulfidized cuprite surfaces after pre-oxidation, which enhanced the cuprite hydrophobicity and improved the cuprite flotation.  相似文献   

16.
本文研究了Fe离子注入Al_2O_3陶瓷的注入射程、纵向浓度分布和注入层结构,测定了注入层中的载流子浓度和迁移率,讨论了Al_2O_3陶瓷注入Fe离子其表面层的导电机理。其结论是:注入的Fe~(2-)离子进入Al_2O_3晶格,替代了Al~(3-)离子形成替位杂质。这样注入离子与原有晶格比较呈现一个有效负电荷,形成负电中心。它可以把一个空穴束缚在它的周围,在禁带引入受主能级。  相似文献   

17.
对大电流封闭母线中空间电荷引起的气体击穿进行了理论研究.对封闭母线中存在空间电荷时远离绝缘子处的电场和绝缘子周围区域的电场进行了计算.给出了不同空间电荷密度时绝缘子周围区域电场的等位线分布,得到了封闭母线中空间电行应该保持的安全密度范围.  相似文献   

18.
粉石英表面化学的表征   总被引:4,自引:0,他引:4  
分析与探讨了粉石英的表面位及其质子化反应,对粉石英的表面电化学性质作了进一步研究,以NaNO3为支持电解质,测得粉石英的表面位密度约为4.3个/nm^2,表面零和NO3^-对石英的竞争吸附能力大小为Cl^->NO3^-,粉石英表面显弱酸性。  相似文献   

19.
用数值模拟的方法,对等离子体发生器脉冲结束后,一维柱状等离子体化学反应扩散过程的时空演化规律进行了研究。对比了不同发生器半径下,电子的衰减过程,并推出了相应的等效电子寿命。发现在地面附近,发生器半径对于电子寿命的影响很小。并对不同位置的总的负离子反应扩散过程进行了研究,印证了在10~(-6)s以后,等离子体为典型的负电等离子体。给出了几种主要的负离子的反应扩散曲线,分析了负电荷的转移过程。其结果对于负离子发生器,介质阻挡放电的理论研究和实际应用都有重要意义。  相似文献   

20.
为了开发新型的深红光或红外发光材料,通过高温固相法在空气中合成了锰掺杂Ca14Zn6Al10O35∶Mn荧光粉.采用X射线衍射、反射光谱、荧光光谱、荧光衰减寿命系统研究了该材料的晶体结构及发光性能.结果表明,样品中同时存在着Mn4+和Mn5+的荧光发射,前者在深红波段,后者在近红外波段.当12.5%的Al离子被Mn离子...  相似文献   

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