Study On Properties Of The Confined Liquids At Solid Surface With AFM

The properties of the confined liquid near solid surfaces are different from thatof the bulk liquid. The confined liquid shows solid like behaviors induced by the solidsurface. The study of the confined liquid is of great importance for the developmentof the micro fluidic system technology and for interpreting the fluidity and lubricationproperties of the fluid.AFM is a powerful tool to study the surface and interface science. The forcecurves are measured under liquid to study the properties of the confined liquid byusing AFM. The AFM tip is modified in the experiment and the quasi solid behavioris studied by changing the approaching velocity of the tip.The study on the deionized water shows the water molecule can form anordering layered structure at the silica surface. When the tip is approaching thesurface under a relatively big velocity the deionized water performs like a solid whichshows elasticity. The experiment with the modified AFM tip shows the elasticity ofthe deionized water increases as the velocity increases. The effective viscosity of thewater near the surface shows the effective viscosity is3or4order of the bulk liquid.The sodium chloride solution with different PH value is also measured.The ordering layered structure of the hexadecane near the silica surface is alsofound. The hexadecane liquid molecule is compressed with the modified AFM tipunder different velocities. The elasticity of the hexadecane molecular layer increasesas the velocity increases. A simple bead-spring model is used to explain the solid likebehavior of the hexadecane confined near the surface.Based on the original wedge method, an improved wedge method is derived. Thecalibration is done on a FIB sample which proves the improved wedge method is aneffective AFM friction calibration method.The tip calibrated using the improved wedge method is used to measure thefriction in deionized water, hexadecane and the sodium chloride solution withdifferent PH value. The results show the way to resist the compression is different fordeionized water, hexadecane and the sodium chloride solution. It is much easier for the molecule of water and hexadecane to be squeezed out from the confined area.