TRIBOLOGICAL PROPERTIES AND MODELING OF LIQUID THIN FILM

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Static and dynamic behavior of liquid meniscus bridges have been investigated with newly developed nanorheometer. The liquid nanomeniscus bridges were established between two borosilicate glass spheres of 20μm in diameter and two kinds of experiment were performed : 1) The pull-off and attracting forces between two glass spheres wetted by OMCTS (Octamethylcyclotetrasiloxane) were measured as a function of receding and approaching velocity respectively and the pull-off force is compared with the theoretical value ; 2) Normal oscillatory experiment between two glass spheres with meniscus bridge of PFPE (Perfluoropolyether) Zdol was conducted. Results of each experiment are as follows : 1) The measured pull-off or attracting forces show almost constant value at very slow receding or approaching velocity. Whereas, the measured forces deviate from the constant value at higher velocity than 2.70μm/s because the viscous force may begin to operate. 2) With such small substrates of 20μm in diameter, new dynamic behavior originated from the elasticity of the liquid meniscus bridge emerges : The elastic components of the system are independent of the modulation frequency representing the characteristic of vicoelastic solid ; The system is dominated by the viscous component at high frequency and the elastic component at low frequency ; At high frequencies and small separations, the liquid behaves as a Newtonian fluid with a constant viscosity. On the other hand, at low frequencies and large separations, the dynamic viscosity of the system is enhanced. These are quite different from the experimental results of the surface forces apparatus in immersed or submerged condition.