Institute of Multidisciplinary Research for Advanced Material, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, Japan.
J Chem Phys. 2018 Oct 28;149(16):163327. doi: 10.1063/1.5037326.
The deformation of the interfaces between a soft material and hard material in contact plays an important role in the friction and lubrication between them. We recently reported that the elastic property of the contact interface dominated the friction of the interface between a flat polymer hydrogel [double network (DN) gel of 2-acrylamide-2-methylpropanesulfonic acid and ,-dimethylacrylamide] and a silica sphere [Ren , Soft Matter , 6192-6200 (2015)]. In this study, in order to quantitatively describe the dependence of the elastic response on the geometrical parameters of the deformed interfaces, we employed the resonance shear measurement (RSM) and investigated the deformation of the interfaces between a flat DN gel and silica spheres by varying the curvature radius ( = 18.3, 13.8, 9.2, 6.9 mm). Resonance curves were analyzed using a mechanical model consisting of the elastic ( ) and viscous ( ) parameters of the contact interface. The obtained elastic parameter ( ) increases at higher loads and for smaller silica spheres, while the viscous parameter ( ) was negligibly low for all the conditions. The relations between the elastic parameter ( ), geometric parameters of the deformed contact interface, and the applied normal load were investigated. The elastic parameter ( ) was found to be proportional to the arc length () (radius of contact area, ), i.e., ∝ or ∝ . We introduced the term "elastic modulus of the contact interface, " as a proportionality constant to describe the elastic parameter of the deformed interfaces ( ): (N/m) = (m) × (Pa). Thus, the friction () between the DN gel and the silica sphere can be described by the following equation: = = (m) × (N/m) × Δ (m) (Δ: shear deformation of the contact interface between the DN gel and silica sphere). The value determined from the slope vs was 493 ± 18 kPa. The RSM measurement and the analysis presented here can be a unique method for characterizing the specific properties of the deformed interfaces between soft and hard materials.
软材料和硬材料接触界面的变形在它们之间的摩擦和润滑中起着重要作用。我们最近报道，接触界面的弹性性质主导了平面聚合物水凝胶（2-丙烯酰胺-2-甲基丙磺酸和，-二甲基丙烯酰胺的双网络凝胶）和二氧化硅球之间界面的摩擦[Ren，Soft Matter，6192-6200（2015）]。在这项研究中，为了定量描述弹性响应对变形界面几何参数的依赖性，我们采用共振剪切测量（RSM）并通过改变曲率半径（= 18.3、13.8、9.2、6.9 mm）来研究平面 DN 凝胶和二氧化硅球之间界面的变形。通过使用由接触界面的弹性（）和粘性（）参数组成的机械模型来分析共振曲线。得到的弹性参数（）在较高的载荷和较小的二氧化硅球下增加，而所有条件下的粘性参数（）都可以忽略不计。研究了弹性参数（）与变形接触界面的几何参数和施加的法向载荷之间的关系。发现弹性参数（）与变形接触界面的弧长（）（接触面积的半径，）成正比，即 ∝ 或 ∝ 。我们引入了术语“接触界面的弹性模量，”作为描述变形界面弹性参数的比例常数（）： （N/m）= （m）× （Pa）。因此，DN 凝胶和二氧化硅球之间的摩擦力（）可以用以下方程描述： = = （m）× （N/m）×Δ（m）（Δ：DN 凝胶和二氧化硅球之间接触界面的剪切变形）。从斜率 vs 确定的 值为 493 ± 18 kPa。这里提出的 RSM 测量和分析可以成为表征软材料和硬材料之间变形界面特定性质的独特方法。
