Nonequilibrium molecular dynamics (MD) method was used to study the dielectrophoresis (DEP) mo-tion of nanocolloids in non-uniform electric field. By changing the electric field strength and system temperature, aggregation phenomena of nanocolloids was analyzed. Simulation results showed that at normal temperature, though the Brownian force can affect the motion of colloids, the attractive force will increase quickly with the distance between colloids down to 12σ, which makes colloids aggregate. When the Brownian force is weak to colloid's motion, for the enhancement of electric field strength, the DEP force of colloid will increase and so did the attractive force, which finally quickens the aggregate speed. Simulation results also showed that the temperature' enhancement will increase the Brownian force of colloids, hence disturbing the colloids aggregation. Moreover, the DLVO theory was used to study the motion of a pair of interactional colloids, both the potential energy and the attractive force versus distance of colloids were presented, then the latter graph was used to compare with another graph elicited by MD method. Results showed that the two graphs were nearly the same, indicating the MD model accorded with the theory.

On the basis of the research on the status and problems of micro/nano bio-particles manipulation using dielectrophoresis, the theoretical basis and the model simulation of micro/nano bio-particles manipu-lation using light-induced dielectrophoresis were discussed. The space distribution of electric field and dielectrophoresis forces in different heights were also obtained. On this basis, the core component of the micro manipulation system, that is, photoconductive layer of the chip, was completed in the mate-rial selection, fabricating process and performance analysis testing. Then the voltage drop of the sus-pension and the effective voltage frequency spectrum were obtained. Finally, by combining the ma-chine vision detection with real-time tracking system, the micro/nano bio-particles manipulation plat-form based on the light-induced dielectrophoreisis was established, and then the manipulations for micro/nano bio-particles, such as quick collection, transport, separation, were implemented. This pro-vided a basis for rapid, accurate, and low-cost detection of serious diseases based on the micro-fluidic biochip and early diagnosis.

The ion distribution and electroosmotic flow of sodium chlorine solutions confined in cylindrical nanotubes with high surface charge densities are studied with molecular dynamics (MD). To obtain a more practical physical model for electroosmotic driven flow in a nanoscale tube, the MD simulation process consists of two steps. The first step is used to equilibrate the system and to obtain a more realistic ion distribution in the solution under different surface charge densities. Then, an external electric field is acted to drive the liquids. The simulation results indicate that with the increase of the surface charge density, both the thickness of the electric double layer and the peak height of the counterion density increase. However, the phenomenon of charge inversion does not occur even as the surface charge density increases to -0.34 C/m2, which is rather difficult to reach for real materials in practical situations. This simulation result confirms the recent experimental observation that monovalent ions of sufficiently high concentrations can reduce or even cancel the charge inversion occurred in the case of multivalent ions

The dependence of superlattice thermal conductivity on period length is investigated by molecular dynamicssimulation. For perfectly lattice matched superlattices, a minimum is observed when the period length is of the order of the effective phonon mean free path. As temperature decreases and interatomic potential strength increases, the position of the minimum shifts to larger period lengths. The depth of the minimum is strongly enhanced as mass and interatomic potential ratios of the constituent materials increase. The simulation results are consistent with phonon transmission coefficient calculations, which indicate increased stop bandwidth and thus strongly enhanced Bragg scattering for the same conditions under which strong reductions in thermal conductivity are found. When nonideal interfaces are created by introducing a 4% lattice mismatch, the minimum disappears and thermal conductivity increases monotonically with period length. This result may explain why minimum thermal conductivity has not been observed in a large number of experimental studies.

采用非平衡态分子动力学方法模拟可极化纳米胶体在非均匀电场下的介电泳情况，通过改变电场强度和系统温度，分析纳米胶体的团聚现象。常温状态下的仿真结果表明，虽然布朗力能影响纳米胶体的介电泳状况，但当纳米胶体之间的距离小于12σ时，其相互吸引力迅速增大，从而克服布朗力影响，使胶体产生团聚。当布朗力对胶体运动影响较小时，电场强度增大使得胶体所受的介电泳力增大，相应地胶体所受的吸引力也增大，最终导致胶体的聚集速度变快。仿真结果也显示系统温度的升高使得胶体所受的布朗力增大，从而影响纳米胶体的团聚。最后，采用DLVO理论对相互作用的胶体运动状态进行研究，得出胶体的位能曲线图和胶体间吸引力随胶体中心距变化的曲线图，并将后者与分子动力学方法得出的结论进行对比，发现这两条曲线的变化趋势基本相同，这说明本文的仿真模型是符合理论的。