Diffusionless transformation of soft cubic superstructure from amorphous to simple cubic and body-centered cubic phases

Abstract

In a narrow temperature window in going from the isotropic to highly chiral orders, cholesteric liquid crystals exhibit so-called blue phases, consisting of different morphologies of long, space-filling double twisted cylinders. Those of cubic spatial symmetry have attracted considerable attention in recent years as templates for soft photonic materials. The latter often requires the creation of monodomains of predefined orientation and size, but their engineering is complicated by a lack of comprehensive understanding of how blue phases nucleate and transform into each other at a submicrometer length scale. In this work, we accomplish this by intercepting nucleation processes at intermediate stages with fast cross-linking of a stabilizing polymer matrix. We reveal using transmission electron microscopy, synchrotron small-angle X-ray diffraction, and angle-resolved microspectroscopy that the grid of double-twisted cylinders undergoes highly coordinated, diffusionless transformations. In light of our findings, the implementation of several applications is discussed, such as temperature-switchable QR codes, micro-area lasing, and fabrication of blue phase liquid crystals with large domain sizes.

High‐Resolution Erasable “Live” Patterns Based on Controllable Ink Diffusion on the 3D Blue‐Phase Liquid Crystal Networks

“…The reconfiguration of the 3D blue phase networks plays an important role in the reversible formation of the pattern via printing and erasing. The TEM characterization provides a realspace observation of the arrangement of the BP structure owing to the use of ultra-thin sections with controlled lattice plane orientations, [9,23] which is significant for revealing the microstructure change of the BPLC during the printing process. However, it is difficult to lock the liquid ink in the frame network during the slicing process and high-vacuum environment owing to the instability of the flowable ink.…”

“…Blue-phase liquid crystals (BPLCs) [1][2][3][4][5] are fascinating self-assembled 3D nanomaterials because of their intriguing and advantageous properties, such as fast responsiveness [1,6] and narrow photonic band gap, which greatly broadens the potential photonic applications [3] in opticelectronic switching devices, [4,[6][7][8] tuneable lasers [1,[9][10][11][12] and optic sensors. [7,11] Currently, the research on BPLCs mainly focused on broadening the temperature range [1,2,[13][14][15][16] of films, realizing the largedomain single crystals, [5,17] investigating the phase transition process [9,[18][19][20][21][22][23][24] and pursuing functional BPLCs for device applications. [25][26][27][28][29][30][31][32][33][34][35]…”

“…The development of polymer-stabilized BPLC (PS-BPLC) provided a promising approach for the unique pattern materials based on its advantages of broaden temperature windows, [1,9] and flexible, [10] stretchable, [3,10,[41][42][43] transferable properties. And the occurrence of polymer templated BPLC (PT-BPLC) facilitated an advance in free-standing device architectures for photonic applications.…”

“…Blue‐phase liquid crystals (BPLCs) [ 1–5 ] are fascinating self‐assembled 3D nanomaterials because of their intriguing and advantageous properties, such as fast responsiveness [ 1,6 ] and narrow photonic band gap, which greatly broadens the potential photonic applications [ 3 ] in optic‐electronic switching devices, [ 4,6–8 ] tuneable lasers [ 1,9–12 ] and optic sensors. [ 7,11 ] Currently, the research on BPLCs mainly focused on broadening the temperature range [ 1,2,13–16 ] of films, realizing the large‐domain single crystals, [ 5,17 ] investigating the phase transition process [ 9,18–24 ] and pursuing functional BPLCs for device applications. [ 25–42 ] BPLCs, with the unit‐cell lattice spacing on the order of the wavelength of visible light, exhibit a selective reflection as a photonic crystals and present tuneable photonic stopband/structural coloration accompanied by exterior stimuli.…”

Visualizing Invisible Phase Transitions in Blue Phase Liquid Crystals Using Early Warning Indicators

“…[24] However, a challenge arises since, for electro-optical applications of BPLCs, the Bragg peaks must be in the ultraviolet region, making all phases optically isotropic and hence transparent to visible light. Recent studies have shown that transmission electron microscopy and small-angle X-ray diffraction can be utilized to study the microscopic domain structure of different BPs; [25] however, such methods are destructive and can only provide limited information on the temporal evolution of phase transitions. Developing a non-destructive technique to observe optically isotropic samples with temporal and spatial resolution is therefore of fundamental and practical significance.In this work, we demonstrate non-destructive spatial mapping of phase transitions in featureless BPLCs using statistical indicators obtained from time-resolved optical microscopy.…”