Many biopolymer gels generate negative normal stress, with which the polymer networks shrink in the normal of applied shear. Here we theoretically predict the sliding velocity of such a gel on a solid surface when a constant shear stress is applied to the gel. Our theory predicts that the negative normal stress drives the flow of the solvent in the gel and this produces a solvent layer between the gel and the surface. The sliding velocity of the gel is proportional to the thickness of the solvent layer and is a cubic function of the applied shear stress. With constant applied normal and shear stresses, the thickness of the solvent layer is a non-monotonic function of time with a maximum because the solvent flow from the gel to the solvent layer is dominant in the short time scale and the solvent flow from the solvent layer to the outside is dominant in a longer time scale. The maximum layer thickness depends on the ratio of the time scales of the solvent flow in the gel and in the solvent layer.

中文翻译：

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剪切引起负法向应力凝胶润滑层的形成

许多生物聚合物凝胶会产生负的法向应力，聚合物网络会在施加的剪切法线下收缩。在这里，我们从理论上预测当向凝胶施加恒定的剪切应力时，这种凝胶在固体表面上的滑动速度。我们的理论预测，负法向应力会驱动凝胶中的溶剂流动，从而在凝胶和表面之间形成溶剂层。凝胶的滑动速度与溶剂层的厚度成正比，并且是所施加剪切应力的三次函数。在法向应力和剪应力恒定的情况下，溶剂层的厚度是时间的非单调函数，具有最大值，这是因为从凝胶到溶剂层的溶剂流在短时间内占主导地位，而从溶剂层到外部的溶剂流在短时间内占主导地位。更长的时间范围。最大层厚度取决于凝胶和溶剂层中溶剂流动的时间尺度之比。