Kim Minkyu, Jeon Jisoo, Pierce Kellina, Bukharina Daria, Choi Woosung, Choi Jinyoung, Nepal Dhriti, McConney Michael E, Bunning Timothy J, Tsukruk Vladimir V
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Department of Chemical Engineering, Dankook University, Yongin 16890, Republic of Korea.
ACS Nano. 2024 Sep 17;18(37):25512-25521. doi: 10.1021/acsnano.4c05320. Epub 2024 Sep 5.
Magnetic fields have been used to uniformly align the lyotropic chiral nematic (cholesteric) liquid crystalline (LC) phase of biopolymers to a global orientation and optical appearance. Here, we demonstrate that, in contrast, weak and patterned magnetic field gradients can create a complex optical appearance with the variable spatial local organization of needle-like magnetically decorated cellulose nanocrystals. The formation of optically patterned thin films with left- and right-handed chiral and achiral regions is observed and related to local magnetic gradient-driven vortices during LC suspension flow. We trace the localized flow directions of the magnetically decorated nanocrystals during evaporation-induced assembly, demonstrating how competing evaporation and field-induced localized flow affect the twisted organization within magnetically induced vortices. The simulations suggested that localized twisting inversion originates from the interplay between the direction and strength of the local-depth-related magnetic gradients and the receding front through peripheral magnetic gaps. We propose that this finding will lead to magnetically patterned photonic films.
磁场已被用于使生物聚合物的溶致手性向列（胆甾相）液晶（LC）相均匀排列成全局取向和光学外观。相比之下，本文我们证明了弱且有图案的磁场梯度可以通过针状磁性修饰纤维素纳米晶体的可变空间局部组织创造出复杂的光学外观。观察到具有左旋和右旋手性以及非手性区域的光学图案化薄膜的形成，并将其与LC悬浮液流动过程中局部磁场梯度驱动的涡旋相关联。我们追踪了蒸发诱导组装过程中磁性修饰纳米晶体的局部流动方向，展示了竞争的蒸发和场诱导局部流动如何影响磁诱导涡旋内的扭曲组织。模拟结果表明，局部扭曲反转源于与局部深度相关的磁场梯度的方向和强度与通过外围磁隙的后退前沿之间的相互作用。我们认为这一发现将导致磁性图案化光子薄膜的产生。
