We study how the three-dimensional shape of rigid filaments determines the microscopic dynamics and macroscopic rheology of entangled semi-dilute Brownian suspensions. To control the filament shape we use bacterial flagella, which are micron-long helices assembled from flagellin monomers. We compare the dynamics of straight rods, helical filaments, and shape diblock copolymers composed of seamlessly joined straight and helical segments. Caged by their neighbors, straight rods preferentially diffuse along their long axis, but exhibit significantly suppressed rotational diffusion. Entangled helical filaments escape their confining tube by corkscrewing through the dense obstacles created by other filaments. By comparison, the adjoining segments of the rod-helix shape-diblocks suppress both the translation and the corkscrewing dynamics, so that shape-diblocks become permanently jammed at exceedingly low densities. We also measure the rheological properties of semi-dilute suspensions and relate their mechanical properties to the microscopic dynamics of constituent filaments. In particular, rheology shows that an entangled suspension of shape rod-helix copolymers forms a low-density glass whose elastic modulus can be estimated by accounting for how shear deformations reduce the entropic degrees of freedom of constrained filaments. Our results demonstrate that the three-dimensional shape of rigid filaments can be used to design rheological properties of semi-dilute fibrous suspensions.

中文翻译：

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粘合的直螺旋鞭毛丝形成超低密度玻璃

我们研究了刚性细丝的三维形状如何决定纠缠半稀布朗悬浮液的微观动力学和宏观流变学。为了控制细丝形状，我们使用细菌鞭毛，这是由鞭毛蛋白单体组装而成的微米长螺旋。我们比较了由无缝连接的直链段和螺旋链段组成的直棒、螺旋长丝和形状二嵌段共聚物的动力学。被它们的邻居笼罩，直杆优先沿它们的长轴扩散，但表现出显着抑制的旋转扩散。纠缠的螺旋细丝通过开瓶器穿过其他细丝产生的密集障碍物而逃离它们的限制管。相比之下，杆螺旋形状二嵌段的相邻部分抑制了平移和开瓶器动力学，因此，形状二嵌段在极低的密度下会永久堵塞。我们还测量了半稀释悬浮液的流变特性，并将它们的机械特性与组成细丝的微观动力学联系起来。特别是，流变学表明，形状棒-螺旋共聚物的纠缠悬浮液形成低密度玻璃，其弹性模量可以通过考虑剪切变形如何降低约束细丝的熵自由度来估计。我们的研究结果表明，刚性细丝的三维形状可用于设计半稀纤维悬浮液的流变特性。我们还测量了半稀释悬浮液的流变特性，并将它们的机械特性与组成细丝的微观动力学联系起来。特别是，流变学表明，形状棒-螺旋共聚物的纠缠悬浮液形成低密度玻璃，其弹性模量可以通过考虑剪切变形如何降低约束细丝的熵自由度来估计。我们的研究结果表明，刚性细丝的三维形状可用于设计半稀纤维悬浮液的流变特性。我们还测量了半稀释悬浮液的流变特性，并将它们的机械特性与组成细丝的微观动力学联系起来。特别是，流变学表明，形状棒-螺旋共聚物的纠缠悬浮液形成低密度玻璃，其弹性模量可以通过考虑剪切变形如何降低约束细丝的熵自由度来估计。我们的研究结果表明，刚性细丝的三维形状可用于设计半稀纤维悬浮液的流变特性。流变学表明，形状棒螺旋共聚物的缠结悬浮液形成低密度玻璃，其弹性模量可以通过考虑剪切变形如何降低受约束细丝的熵自由度来估计。我们的研究结果表明，刚性细丝的三维形状可用于设计半稀纤维悬浮液的流变特性。流变学表明，形状棒螺旋共聚物的缠结悬浮液形成低密度玻璃，其弹性模量可以通过考虑剪切变形如何降低受约束细丝的熵自由度来估计。我们的研究结果表明，刚性细丝的三维形状可用于设计半稀纤维悬浮液的流变特性。