Realization Of Self-Motion Of A Liquid Microdroplet On Self-ASSEMBLY Monolayers

In recent years, with the rapid development of MEMS and its applications in themechanical and electrical, the research of the gradient surface energy materials hasattracted more and more attentions. And the surface-tension-driven technology playsan critical role in the microfluidic devices. In this dissertation, the gradient surfaceenergy materials with single or double self-assembled monolayers (SAMs) wereprepared. The self-motion behavior of the micro-droplets on such surfaces were alsostudied. In addition, the self-motion mechanism was theoretically discussed. Theresults are:(1) Base on the light-responsive effect on octadecyltrimethoxysilane(ODS),(heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane(FAS), hexadecyltrimeth-oxysilane(HDS),(3-Aminopropyl)-triethoxysilane(APTS), single (i. e. ODS-SAMs,HDS-SAMs, APTS-SAMs) and double (i. e. ODS-FAS-SAMs、ODS-HDS-SAMs和HDS-ODS-SAMs) gradient surface energy surfaces were successively prepared alongwith illumination time increasing. And the movement of a microdroplet can beself-driven from low energy area to high energy area on these energy-gradient surfaces.(2) Among the three single SAMs gradient surfaces, the microdroplet on theHDS-SAMs gradient surfaces moved with a longest distance and a highest velocity.On the APTS-SAMs, the microdroplet moved with a shortest distance and a lowestvelocity. In addition, the movement of microdroplet can be controlled by adjusting thegap between the baffle and the substance. This indicate that the energy gradientsurfaces with single SAMs can be used in different occasions by controlling differentparameters.(3) The energy gradient of the double SAMs gradient surfaces was less than thesingle SAMs gradient surfaces. Therefore, the average velocity of a microdroplet onthe single FAS gradient surfaces can reach to20.49mm/s, and the moving distance is8mm. But on the double ODS-FAS-SAMs gradient surfaces, the average velocity isonly1.796mm/s, and the moving distance is only4.36mm. (4) On the ODS SAMs, the velocity and the moving distance can reach up to5.5mm/s and4.7mm after FAS-SAMs modification, however, the velocity and movingdistance are only0.29mm/s and2.7mm after HDS-SAMs modification. Thisdemonstrate that the different SAMs modification on the same SAMs will result indifferent behavior of the self-motion of a microdroplet. Additionally, the differentbehavior of self-motion also results from the different sequence of SAMs modification.(5) By research on the microdroplet’s self motion behavior on different gradientsurfaces under different experimental parameters, it is revealed that the movingvelocity changed with a same trend of the surface free energy. And the changing trendsbetween the droplets velocity and the surface tension is inconsistent. Therefore, thechanging of the surface free energy may be the main driving mechanism that causedmicro-droplets spontaneous movement.