Department of Materials Physics, Nagoya University, Furocho, Chikusa-ku, Nagoya, 464-8603, Japan.
Soft Matter. 2017 Sep 27;13(37):6515-6520. doi: 10.1039/c7sm01316g.
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.
许多生物聚合物凝胶会产生负法向应力，聚合物网络会在法向剪切力的作用下收缩。本文中，我们从理论上预测了在对凝胶施加恒定剪切应力时，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溶剂的流动，从而在凝胶和表面之间产生一层溶剂。凝胶的滑动速度与溶剂层的厚度成正比，并且与施加的剪切应力的立方成正比。在恒定的法向和剪切应力下，溶剂层的厚度随时间呈非单调函数变化，在短时间尺度上，溶剂从凝胶流向溶剂层占主导地位，而在较长时间尺度上，溶剂从溶剂层流向外部占主导地位，因此会出现一个最大值。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。
