Research On The Influences Of Surface Charge On The Drag Of Liquid Flow In Micro/Nano-scale

The Micro and Nano technology has become the popular research topic amongresearchers in recent years.Compared to the macroscopic scale,in the Micro andNano dimension, there is relatively larger proportion between the channel inner wallsurface and the volume of the micro-nano tube size in the system. Therefore, themoving liquid will encounter resistance coming from the solid surface when liquidis flowing in the solid channel. Thus, it is important to conduct research in order toreduce the relative motion resistance on the solid-liquid interface and to promotevelocity of the liquid flow.In the Micro and Nano dimension, there are two salient factors, including thesurface electric charge on the solid-liquid interface and the boundary sliding, thatare considered to be affecting the relative motion resistance between solid and liquid.Using theoretical analysis as the basis and experiments analysis as the method, thispaper raise the influences that the surface electric charge has on the relative motionresistance on solid-liquid interface, systematically analyze the influence mechanismamong surface electric charge, boundary sliding, and electroviscosity, andsummarize the influences of surface charge on the solid-liquid interface of relativemotion between the resistance, also provides theoretical support for finding a way toreduce the relative motion resistance on the solid-liquid interface and to promotevelocity of the liquid flow.The boundary sliding change that is caused by the change of the surface electriccharge density has always been ignored when exploring the effect of electroviscosityin the past research. However, the model of combination influence on liquid flow isfirst built in this paper including the factors of surface electric charge density,boundary sliding, and electroviscosity, simulation analysis is conducted as well. Theresearch results show that boundary sliding is associated with the increasement ofthe velocity of flow on one hand, and the increase of electroviscosity, which furtherreduce the influences that boundary sliding has on the velocity of flow on the otherhand. Hence, reducing surface electric charge density and ion concentration of theliquid weaken electroviscosity, amplifie boundary sliding, and further increases thevelocity of liquid flow,also weaken fluid growth by the reduce of the surface chargedensity.Second, the relationship model of surface electric charge density and electricfield force is built with the introduction of a surface electric charge densitymeasurement based on AFM. Afterwards, soak the surfaces of self-made highborosilicate glass and Octadecyltrichlorosilane (OTS) into saline solution with different ion concentrations, according to the relationship model of surface electriccharge density and electrostatic force, the surface electric charge density of OTSsurface which is immersed in saline solutions with different ion concentrationscould be achieved by fitting the AFM to get electrostatic force data and calculatingthe surface charge density of common sphere. The experiment results show thatwithin the saline solutions, the surfaces of both glass and OTS are negativelycharged, and the value of electrostatic force decrease with the increasement ofseparating distance, the higher the ion concentration is, the faster the decreasinggoes. Moreover, as the surface charge density of both glass and OTS increases withthe increasement of ion concentration, it provides powerful experimental evidence sfor the impact that surface charge has on liquid flowing resistance on thesolid-liquid interface.Finally, the experiment also measures the boundary sliding change of OTSsurface in saline solutions with different ion concentrations. It is indicated that theboundary sliding length of OTS surface decreases with the increase of ionconcentration, which supports the theory that boundary sliding length decreases withthe increasement of surface charge density. Thus, it could be an effective way toreduce ion concentration for longer boundary sliding length, and further reduce therelative motion resistance of liquid on the solid-liquid interface.Synthesizing theory and experiment analysis that are stated above, with theidea that ion concentration alter the surface charge, the comprehensive influence ofsurface charge, boundary sliding, and electroviscosity is fully explored. And it isbelieved that under the Micro and Nano dimension, reducing surface charge greatlydiminishes the motion resistance of liquid on the solid-liquid interface, further raisesthe liquid flowing speed, and ultimately promotes the efficiency of micro-nanoelectro-mechanical system. This paper and the corresponding experiments offer newresearch directions and perspectives for the development of micro-nanoelectro-mechanical system.