Research Of Ions Transport In Nanofluidic Channels Based On Electrical Double Layers

The microfluidic technology which developed in the past two decades has already fulfilled the fluid control in the microfluidic channels. However, as the fluid channel further shrinks to nanometer, duo to the dimension of nanometer is approximate to biologic molecule and the Debye length, a great deal of phenomena which does not exist in macroscopical world appear such as the partly overlapping of the Electrical double layers in the channel and the increasing of the Viscosity. All of these lead to the fundamental theory study about channel performance and hydrodynamics. The microfluidic technology presents a wide developing tendency and an increasing influence in the field of sample separating, chemical analysis and biomedicine as well.With the rapid development of nanofluidic chip, the application of Electroosmotic flow widen gradually, it frequently performs as the drive to control the fluid flowage and transport in the Nanofluidic Channel, Electroosmotic flow plays an important role in the microfluidic field owing to its unique advantage. This paper takes the Electrolyte solution in Nanofluidic channels as the study object, and the study focus on the ion distribution and transport characteristics in Nanofluidic channels which based on Electrical double layers principle. The paper includes the following parts:The paper briefly introduced the nanofluidic chip, explaind the origin of nanofluidic technology and the composing of nanofluidic chip, analyzed the characteristics of nanofluidic chip and application field subsequently. The nanofluidic technology is about fluid manipulation in the nanometer structure. In the recent years, the study of nanofluidic theory and experiment had been implemented overseas and had obtained some achievement, whereas domestic study is few. Presently, the orientation of nanofluidic study in China is mainly on the manufacturing of nanofluidic chip and nanofluidic channels principle which adopting molecule dynamics. The paper defined the study target based on the previous production, and presented the study content was the ion potential and concentration distribution in nanofluidic channels, as well as the ion transport characteristics.The paper analyzed the electrokinetic phenomenon in the surface between solid and liquid, and expatiated the forming mechanism of surface charge, the model of Electrical double layers and the interaction between electrical double layers. The paper also discussed the electrokinetic effect and briefly studyed the model of electroosmotic flow. The study object was the electrolyte solution in nanofluidic channels, when the electrolyte solution fill with nanofluidic channels, some interface phenomena appears which can not be ignored in the nanofluidic study. Wetting phenomena emerges when solid touches liquid, and solid will absorb solute from solution simultaneously. Moreover, the difference of structure and quality between solid and liquid results in equivalently reversed polarity charge on the both sides of the interface between solid and liquid, which makes the surface electriferous. Generally, the electriferous mechanism includes ionization, absorption, polarization as well as friction. When the solid surface is electriferous, it also absorbs reversed polarity ion in the solution and forms electrical double layers. There are four kinds of electrical double layers model:the Helmholtz, the Gouy—Chapman, the Stern and the Grahame model. The contact of solid and electrolyte solution makes the solid electriferous and produce electrical double layers, while the relative motion of solid and liquid occur to electrokinetic phenomenon. The electrokinetic phenomenon refers to the following four phenomena which produce by interaction between exterior electric field and moveable portion of electrical double layers:electroosmosis, electrophoresis, sedimentation potential and flowing potential.On the basis of the hypothesis that liquid is continuous, the paper established the nanofluidic physical model and mathematic model, and analyzed the ion environment of the solution in one-dimension nanofluidic channels by simplifying the model. According to deducing and solving by matlab, concluded the ion potential distribution and concentration distribution of the solution in nanofluidic channels, which also presentd by drawing. Via the drawing, the paper analyzed how the ion potential distribution influence by the solution concentration, surface charge density and the height of nanofluidic channels.When the solution flowing developed sufficiently, the paper calculated the transport characteristics in the nanofluidic channels in the light of balanceable ion potential and concentration distribution by revised N-S equation, it analyzed the ion transport characteristics in one-dimension nanofluidic channels which driving by electric field force. According to deducing and solving by matlab, concluded the conductance and flow velocity formula consequently.The paper verified the theory of ion environment and transport characteristics in nanofluidic channels, and discussed the method of manufacturing of nanofluidic chip, and introduced the chip structure applying in the experiment. It also introduced the two methods on studying the ion transport theory, namely, measuring ion conductance in the channel and detecting fluorescence. By the comparison between experiment results and theory calculation, the paper draw the conclusion that the deducing result in this paper accorded with the experiment result in bibliography, which further proved that the theory of the paper is correct and effective.The paper concluded the study and prospect the future work. The study in this paper further enriched the microfluid theory and will instruct partly the nanofluidic application.