Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 837.0415 Santiago, Chile.
Millennium Institute for Research in Optics, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 837.0415 Santiago, Chile.
Proc Natl Acad Sci U S A. 2023 Apr 11;120(15):e2221000120. doi: 10.1073/pnas.2221000120. Epub 2023 Apr 7.
Spatial branching processes are ubiquitous in nature, yet the mechanisms that drive their growth may vary significantly from one system to another. In soft matter physics, chiral nematic liquid crystals provide a controlled setting to study the emergence and growth dynamic of disordered branching patterns. Via an appropriate forcing, a cholesteric phase may nucleate in a chiral nematic liquid crystal, which self-organizes into an extended branching pattern. It is known that branching events take place when the rounded tips of cholesteric fingers swell, become unstable, and split into two new cholesteric tips. The origin of this interfacial instability and the mechanisms that drive the large-scale spatial organization of these cholesteric patterns remain unclear. In this work, we investigate experimentally the spatial and temporal organization of thermally driven branching patterns in chiral nematic liquid crystal cells. We describe the observations through a mean-field model and find that chirality is responsible for the creation of fingers, regulates their interactions, and controls the tip-splitting process. Furthermore, we show that the complex dynamics of the cholesteric pattern behaves as a probabilistic process of branching and inhibition of chiral tips that drives the large-scale topological organization. Our theoretical findings are in good agreement with the experimental observations.
空间分支过程在自然界中无处不在，但驱动它们生长的机制可能因系统而异。在软物质物理学中，手性向列液晶提供了一个受控的环境来研究无序分支模式的出现和生长动态。通过适当的外力，可以在手性向列液晶中引发胆甾相，其自组织成扩展的分支模式。已知分支事件发生在胆甾型手指的圆形尖端膨胀、变得不稳定并分裂成两个新的胆甾型尖端时。这种界面不稳定性的起源以及驱动这些胆甾型图案的大规模空间组织的机制尚不清楚。在这项工作中，我们通过实验研究了手性向列液晶盒中热驱动分支模式的时空组织。我们通过平均场模型描述了这些观察，并发现手性负责产生手指，调节它们的相互作用，并控制尖端分裂过程。此外，我们表明，胆甾型图案的复杂动力学表现为分支和抑制手性尖端的概率过程，从而驱动大规模的拓扑组织。我们的理论发现与实验观察结果吻合较好。
