Achiral symmetry breaking and positive Gaussian modulus lead to scalloped colloidal membranes
Achiral symmetry breaking and positive Gaussian modulus lead to scalloped colloidal membranes
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DOI：
10.1073/pnas.1617043114
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发表时间：
2017-04-25
影响因子：
11.1
通讯作者：
Dogic, Zvonimir
中科院分区：
文献类型：
--
作者：
Gibaud, Thomas;Kaplan, C. Nadir;Dogic, Zvonimir
在非吸附性聚合物的存在下，单分散的棒状颗粒组装成胶体膜，这是一个棒长厚的液体样单层对齐棒。与3D无边缘双层囊泡不同，胶体单层膜形成具有暴露边缘的开放结构，从而提供了研究流体片弹性的机会。由单组分手性棒组装的膜形成具有均匀边缘扭曲的扁平圆盘。相比之下，由具有相反手性的杆的混合物组成的膜可以具有任一手性的边缘扭曲。在这种极限下，盘状膜变得不稳定，而是形成具有圆齿状边缘的结构，其中具有相反旋向性的两个相邻叶被尖状点缺陷分开。这种膜采用3D构型，尖瓣缺陷交替地位于膜平面的上方和下方。在非手性制度，尖点缺陷有排斥相互作用，但远离这个限制，我们测量有效的长程吸引力结合。一个唯象模型表明，扇贝形膜的边缘能量的增加是由伴随的变形能量的减少，由于高斯曲率与扇贝形边缘相关联的补偿，表明胶体膜具有正的高斯模量。一个简单的排除体积参数预测的高斯曲率模量，这是在与实验测量一致的符号和幅度。我们的研究结果提供了深入了解如何膜弹性，几何挫折，和非手性对称性破缺之间的相互作用可以用来折叠成3D形状的胶体膜。
In the presence of a nonadsorbing polymer, monodisperse rod-like particles assemble into colloidal membranes, which are one-rod-length-thick liquid-like monolayers of aligned rods. Unlike 3D edgeless bilayer vesicles, colloidal monolayer membranes form open structures with an exposed edge, thus presenting an opportunity to study elasticity of fluid sheets. Membranes assembled from single-component chiral rods form flat disks with uniform edge twist. In comparison, membranes composed of a mixture of rods with opposite chiralities can have the edge twist of either handedness. In this limit, disk-shaped membranes become unstable, instead forming structures with scalloped edges, where two adjacent lobes with opposite handedness are separated by a cusp-shaped point defect. Such membranes adopt a 3D configuration, with cusp defects alternatively located above and below the membrane plane. In the achiral regime, the cusp defects have repulsive interactions, but away from this limit we measure effective long-ranged attractive binding. A phenomenological model shows that the increase in the edge energy of scalloped membranes is compensated by concomitant decrease in the deformation energy due to Gaussian curvature associated with scalloped edges, demonstrating that colloidal membranes have positive Gaussian modulus. A simple excluded volume argument predicts the sign and magnitude of the Gaussian curvature modulus that is in agreement with experimental measurements. Our results provide insight into how the interplay between membrane elasticity, geometrical frustration, and achiral symmetry breaking can be used to fold colloidal membranes into 3D shapes.