TRIBOLOGICAL PROPERTIES AND MODELING OF LIQUID THIN FILM

用最新研制的纳米流变仪研究了液体弯月面桥的静态和动态行为。在直径为20μm的两个硼硅酸盐玻璃微球之间建立了液体纳米月面桥，并进行了两种实验：1)测量了八甲基环四硅氧烷(OMCTS)润湿的两个玻璃微球之间的拉力和吸力分别作为后退速度和接近速度的函数，并将拉力与理论值进行了比较；2)进行了全氟聚醚Zdo1弯月面桥玻璃球之间的法向振荡实验。每次实验的结果如下：1)在很慢的后退或接近速度下，测量的拉力或吸力几乎是恒定的。然而，当速度高于2.70μm/S时，由于粘性力可能开始工作，测定力与常值有偏差。2)在这种直径为20μm的小衬底上，液体半月面桥的弹性产生了新的动力学行为：系统的弹性分量与代表粘弹性固体特性的调制频率无关；系统在高频时以粘性分量为主，在低频时以弹性分量为主；在高频和小分离时，液体表现为常粘性的牛顿流体。另一方面，在较低的频率和较大的分离度下，体系的动态粘度增大。这与面力仪在浸没或淹没条件下的实验结果有很大不同。

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.