Improvement on Surface Force Apparatus and Experimental Study of Rheological Properties of Ultra-thin Films

The previously developed surface force apparatus was reconstructed and improved with a focus on the improvement of the micro-displacement system and optical measurement system. The rheological properties of 500SN and hexadecane thin films were investigated with the improved surface force apparatus. As the results, the ultra-thin films of 500SN and hexadecane exhibited nonlinear shearing response, which was different from that of the Newtonian fluids in their bulk state. In other words, the ultra-thin films of 500SN and hexadecane were characterized by shearing thinning. Moreover, the friction force increases abruptly with increasing shearing velocity at the early stage and then decreases to a smaller value with fluctuation. The critical film thickness in the dynamic pressing test was much smaller than that in the static pressing test, indicating that the shearing movement of the ultra-thin films could lead to destruction of the structure of the adsorbed layer.