键合的直形与螺旋形鞭毛丝形成超低密度玻璃
Bonded straight and helical flagellar filaments form ultra-low-density glasses
AI总结：
本文利用细菌鞭毛构建直杆、螺旋丝及杆-螺旋二嵌段共聚物，研究丝的三维形状对半稀布朗悬浮液微观动力学和宏观流变学的影响，发现杆-螺旋共聚物在极低密度下形成永久堵塞的低密度玻璃，证明丝形状可用于设计纤维悬浮液的流变性质。
摘要：
我们研究了刚性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。为了控制丝的形态，我们使用细菌鞭毛，它是由鞭毛蛋白单体组装而成的微米级螺旋结构。我们比较了直杆、螺旋丝以及由无缝连接的直形段和螺旋段组成的形状二嵌段共聚物的动力学。直杆被邻近粒子笼蔽，优先沿其长轴扩散，但旋转扩散受到显著抑制。纠缠的螺旋丝通过在其他丝形成的致密障碍物中螺旋钻行来逃离其约束管道。相比之下，杆-螺旋形状二嵌段共聚物的相邻段同时抑制了平动和螺旋钻行动力学，使得形状二嵌段共聚物在极低密度下就发生永久堵塞。我们还测量了半稀悬浮液的流变性质，并将其力学性能与组成丝的微观动力学联系起来。特别是，流变学表明，杆-螺旋共聚物形状的纠缠悬浮液形成了一种低密度玻璃，其弹性模量可以通过考虑剪切变形如何减少受约束丝的熵自由度来估算。我们的结果表明，刚性丝的三维形状可用于设计半稀纤维悬浮液的流变性质。
英文摘要：
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.
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