Department of Chemical and Biomolecular Engineering, Hopkins Extreme Materials Institute, Johns Hopkins University, Baltimore, MD 21218, USA.
Soft Matter. 2017 Oct 4;13(38):6718-6729. doi: 10.1039/c7sm01061c.
Elastic deformation of rigid materials with soft coatings (stratified materials) due to lubrication forces can alter the interpretation of dynamic surface forces measurements and prevent contact formation between approaching surfaces. Understanding the role of elastic deformation on the process of fluid drainage is necessary, in particular for the case where one (or both) of the interacting materials consists of a rigid substrate with a soft coating. We combine lubrication theory and solid linear elasticity to describe the dynamic of fluid drainage past a compliant stratified boundary. The analysis presented covers the full range of coating thicknesses, from an elastic foundation to a half-space for an incompressible coating. We decouple the individual contributions of the coating thickness and material properties on the elastic deformation, hydrodynamic forces, and fluid film thickness. We obtain a simple expression for the shift in contact position during force measurements that is valid for many experimental conditions. We compare directly the effect of stratification on the out-of-contact deformation to the well-known effect of stratification on indentation. We show that corrections developed for stratification in contact mechanics are not applicable to elastohydrodynamic deformation. Finally, we provide generalized contour maps that can be employed directly to estimate the elastic deformation present in most dynamic surface force measurements.
由于润滑作用力，具有软涂层（分层材料）的刚性材料的弹性变形可能会改变对动态表面力测量的解释，并防止接近表面之间的接触形成。了解弹性变形对流体排出过程的作用是必要的，特别是对于相互作用的材料之一（或两者）由具有软涂层的刚性衬底组成的情况。我们结合润滑理论和固体线性弹性来描述可变形分层边界的流体排出的动力学。所提出的分析涵盖了涂层厚度的整个范围，从弹性基础到不可压缩涂层的半空间。我们分离了涂层厚度和材料特性对弹性变形、流体动力和流体膜厚度的单独贡献。我们得到了一个在力测量期间接触位置偏移的简单表达式，该表达式在许多实验条件下都有效。我们直接比较分层对非接触变形的影响与分层对压痕的熟知影响。我们表明，在接触力学中开发的分层校正不适用于弹性流体动力变形。最后，我们提供了广义轮廓图，可以直接用于估计大多数动态表面力测量中存在的弹性变形。
