Tribological Characterization of Gradient-density Polyacrylamide Hydrogel Surfaces
Tribological Characterization of Gradient-density Polyacrylamide Hydrogel Surfaces
复制标题
DOI：
10.1007/s11340-021-00704-x
复制
发表时间：
2021-03
影响因子：
2.4
通讯作者：
C. L. Johnson;A. C. Dunn
中科院分区：
文献类型：
--
作者：
C. L. Johnson;A. C. Dunn
背景水凝胶的接触和摩擦响应取决于凝胶表面的聚合物结构。最近的工作表明，聚合过程中与凝胶接触的不同模具材料会影响所得聚合物的密度。 目的具有“刷状”密度较低的聚合物表面的凝胶的摩擦学响应尚未得到彻底研究。我们的目标是进行一系列摩擦学实验，以更好地了解密度较小层的响应。方法在这项工作中，我们使用各种负载、速度和探针材料进行压痕、蠕变和滑动实验，以确定密度较小层对聚丙烯酰胺水凝胶的接触和摩擦行为的影响。我们还使用微荧光颗粒排除来测量每个实验中的接触面积。结果压痕揭示了第一次接触后前 13-29 µm 的非赫兹状态，对于给定的压痕深度，其力响应较弱。蠕变实验表明，尽管接触压力较低，但表面层会发生多孔弹性松弛，梯度层内会发生水渗出。摩擦力高度依赖于速度，较快的滑动速度会将摩擦力降低至低至 0.01 的值；大多数实验都没有观察到瞬态行为，这表明表面层在脱离接触时能够快速重新吸收水。结论我们对这种梯度密度表面层的接触和摩擦响应有了更深入的了解，这对于动态应用中需要超低摩擦的水凝胶设计将是有用的。
BackgroundThe contact and frictional response of a hydrogel is dependent on the polymer structure at the gel surface. Recent work has shown that different mold materials in contact with the gel during polymerization will affect the resulting polymer density.ObjectiveThe tribological response of a gel with a ‘brushy’ less-dense polymer surface has not been thoroughly studied. Our goal was to perform a suite of tribological experiments to better understand the response of the less-dense layer.MethodsIn this work, we conducted indentation, creep, and sliding experiments with various loads, speeds, and probe materials to determine the impact of the less-dense layer on the contact and frictional behavior of polyacrylamide hydrogels. We additionally used micro-fluorescent particle exclusion to measure the contact areas throughout each experiment.ResultsIndentation revealed a non-Hertzian regime for the first 13–29 µm after first contact that has a weaker force response for a given indentation depth. Creep experiments showed that the surface layer relaxes poroelastically, with water exudation occurring within the gradient layer despite the low contact pressures. Friction was highly speed-dependent, with faster sliding speeds decreasing friction to values as low as 0.01; transient behavior was not seen for most of the experiments, suggesting that the surface layer is capable of quick water re-uptake when out of contact.ConclusionsWe have provided a deeper understanding of the contact and frictional response of this gradient-density surface layer, which will prove useful for hydrogel designs requiring ultra-low friction in a dynamic application.