当前位置: X-MOL 学术Exp. Mech. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Relaxation and Recovery in Hydrogel Friction on Smooth Surfaces
Experimental Mechanics ( IF 2.4 ) Pub Date : 2021-06-22 , DOI: 10.1007/s11340-021-00748-z
B. Wu , J. S. Méndez Harper , J. C. Burton

Background

Hydrogels are crosslinked polymer networks that can absorb and retain a large fraction of liquid. Near a critical sliding velocity, hydrogels pressed against smooth surfaces exhibit time-dependent frictional behavior occurring over multiple timescales. The origin of these dynamics is unresolved

Objective

Here, we characterize this time-dependent regime and show that it is consistent with two distinct molecular processes: sliding-induced relaxation and quiescent recovery.

Methods

Our experiments use a custom pin-on-disk tribometer to examine poly(acrylic acid) hydrogels on smooth poly(methyl methacrylate) surfaces over a variety of sliding conditions, from minutes to hours.

Results

We show that at a fixed sliding velocity, the friction coefficient decays exponentially and reaches a steady-state value. The time constant associated with this decay varies exponentially with the sliding velocity, and is sensitive to any precedent frictional shearing of the interface. This process is reversible; upon cessation of sliding, the friction coefficient recovers to its original state. We also show that the initial direction of shear can be imprinted as an observable “memory”, and is visible after 24 hrs of repeated frictional shearing.

Conclusions

We attribute this behavior to nanoscale extension and relaxation dynamics of the near-surface polymer network, leading to a model of frictional relaxation and recovery with two parallel timescales.



中文翻译:

光滑表面上水凝胶摩擦的松弛和恢复

背景

水凝胶是交联的聚合物网络,可以吸收和保留大部分液体。在接近临界滑动速度时,压在光滑表面上的水凝胶表现出在多个时间尺度上发生的与时间相关的摩擦行为。这些动态的起源尚未解决

客观的

在这里,我们表征了这种依赖于时间的机制,并表明它与两个不同的分子过程一致:滑动诱导松弛和静态恢复。

方法

我们的实验使用定制的针盘摩擦计来检查在各种滑动条件下(从几分钟到几小时)光滑聚(甲基丙烯酸甲酯)表面上的聚(丙烯酸)水凝胶。

结果

我们表明,在固定的滑动速度下,摩擦系数呈指数衰减并达到稳态值。与此衰减相关的时间常数随滑动速度呈指数变化,并且对界面的任何先前摩擦剪切敏感。这个过程是可逆的;滑动停止后,摩擦系数恢复到原来的状态。我们还表明,剪切的初始方向可以作为可观察的“记忆”印记,并且在反复摩擦剪切 24 小时后可见。

结论

我们将这种行为归因于近表面聚合物网络的纳米级扩展和弛豫动力学,从而产生了具有两个平行时间尺度的摩擦弛豫和恢复模型。

更新日期:2021-06-22
down
wechat
bug