TRIBOLOGICAL PROPERTIES AND MODELING OF LIQUID THIN FILM

用新型纳米流变仪研究了液体半月板桥的静动力特性。在两个直径为20μm的硼硅玻璃球之间建立了液体纳米板桥，并进行了两种实验：1)测量了八甲基环四硅氧烷（OMCTS）润湿的两个玻璃球之间的拉脱力和吸力分别与后退速度和接近速度的函数关系，并与理论值进行了比较；2)进行了全氟聚醚（PFPE） Zdol玻璃半月板桥球间的正振荡实验。各实验结果如下：1)在极慢的后退速度或接近速度下，所测得的牵引力或引力几乎呈恒定值。然而，当速度大于2.70μm/s时，由于粘性力的作用，测得的力偏离了恒定值。2)在直径为20μm的小基板上，产生了源于液体半月板桥弹性的新的动力行为：系统的弹性分量不受调制频率的影响，代表了固体的微弹性特性；系统在高频处以粘性分量为主，在低频处以弹性分量为主；在高频率和小间距下，液体表现为具有恒定粘度的牛顿流体。另一方面，在低频率和大分离时，系统的动态粘度增强。这与水面力仪在浸没或淹没条件下的实验结果有很大的不同。

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.