Department of Mechanical and Aerospace Engineering , Cornell University , Ithaca , New York 14850 , United States.
Langmuir. 2018 Apr 3;34(13):3827-3837. doi: 10.1021/acs.langmuir.8b00084. Epub 2018 Mar 20.
Numerous biomimetic structures made from elastomeric materials have been developed to produce enhancement in properties such as adhesion, static friction, and sliding friction. As a property, one expects adhesion to be represented by an energy per unit area that is usually sensitive to the combination of shear and normal stresses at the crack front but is otherwise dependent only on the two elastic materials that meet at the interface. More specifically, one would expect that adhesion measured by indentation (a popular and convenient technique) could be used to predict adhesion hysteresis in the more practically important rolling geometry. Previously, a structure with a film-terminated fibrillar geometry exhibited dramatic enhancement of adhesion by a crack-trapping mechanism during indentation with a rigid sphere. Roughly isotropic structures such as the fibrillar geometry show a strong correlation between adhesion enhancement in indentation versus adhesion hysteresis in rolling. However, anisotropic structures, such as a film-terminated ridge-channel geometry, surprisingly show a dramatic divergence between adhesion measured by indentation versus rolling. We study this experimentally and theoretically, first comparing the adhesion of the anisotropic ridge-channel structure to the roughly isotropic fibrillar structure during indentation with a rigid sphere, where only the isotropic structure shows adhesion enhancement. Second, we examine in more detail the anomalous anisotropic film-terminated ridge-channel structure during indentation with a rigid sphere versus rolling to show why these structures show a dramatic adhesion enhancement for the rolling case and no adhesion enhancement for indentation.
已经开发出了许多由弹性体材料制成的仿生结构，以提高粘附、静摩擦和动摩擦等性能。作为一种特性，人们期望粘附力由单位面积的能量来表示，这种能量通常对裂纹前缘的剪切和法向应力的组合敏感，但除此之外，只取决于在界面处相遇的两种弹性材料。更具体地说，人们可能会期望通过压痕（一种流行且方便的技术）测量的粘附力可以用于预测在更实际的滚动几何形状中更重要的粘附滞后。以前，具有薄膜末端纤维状几何形状的结构在使用刚性球体进行压痕时通过裂纹捕获机制表现出明显的粘附增强。具有大致各向同性的结构，如纤维状几何形状，在压痕中的粘附增强与滚动中的粘附滞后之间存在很强的相关性。然而，各向异性结构，如薄膜末端脊槽结构，在压痕中测量的粘附与滚动之间的差异却令人惊讶地显著。我们对此进行了实验和理论研究，首先比较了各向异性脊槽结构与刚性球体压痕中的大致各向同性纤维状结构的粘附力，其中只有各向同性结构显示出粘附增强。其次，我们更详细地研究了在刚性球体压痕和滚动过程中各向异性薄膜末端脊槽结构的异常情况，以说明为什么这些结构在滚动情况下表现出明显的粘附增强，而在压痕情况下则没有粘附增强。
