![]() For material near the surface of the filament (shell), its temperature drops shortly. Reorientation of mesogen takes certain period of time, which is temperature dependent. Before crosslinking, liquid crystal mesogens in the filament can rotate and tend to form a macroscopically unaligned state. Subsequently, the hot viscous filament cools down gradually to room temperature, accompanied with a marked increase of its viscosity ( Fig. Photo credit: Zijun Wang, UCSD.Īs reported in previous studies, liquid crystal mesogens align under shear and extensional flow along the printing path ( 10– 14). ( E) Polarized optical microscope (POM) images of LCE filaments printed at different temperatures. ( D) Viscosity of the ink as a function of shear rate at different temperatures. ( C) DSC traces of LCE ink and cured LCE. ( B) Molecular structure of uncrosslinked liquid crystal oligomer in the printing ink. As a result, well-aligned liquid crystal mesogens in the outer shell are temporarily fixed by high viscosity of the material, while the mesogens have enough time to reorientate to a polydomain state in the inner core. The outer shell of the filament cools down much faster than the inner core. ![]() ![]() After certain period of time, the extruded LCE filament gradually cools down to room temperature and a core-shell structure forms in the filament. Because of the shear stress generated through the extrusion process, liquid crystal mesogens are initially aligned along the printing path. The nozzle tip moves at a speed of V during the printing, and the distance between the nozzle tip and build plate is h. The LCE ink is heated up to the temperature T and extruded out of the nozzle with an inner diameter d. ( A) Schematic illustration of the setup of DIW printing of LCE. However, soft responsive structures with both functionally graded mechanical properties and actuation performance have been seldom reported because of limited option of materials and underlying fabrication challenges. Graded hip prostheses have been developed to enhance the bonding strength between implants and bones ( 22). ( 21) constructed a functionally graded soft robot powered by combustion and used modulus gradient to reduce local deformation in the robot legs. Structures with graded mechanical properties have been fabricated to minimize stress concentration and to realize combined high compliance and high resilience ( 20). For example, mechanical properties and microstructure of the tissue in tendon-to-bone insertion (enthesis) change gradually for enhancing structural durability ( 19). In contrast, functionally graded materials are ubiquitous both in biology and in engineering applications ( 18). ![]() In the previous studies of 3D printing LCEs, filaments may follow various paths in one structure, but they often have identical properties, which are mainly determined by printing parameters such as printing temperature and nozzle size ( 10, 12, 14, 17). The strategy developed here will facilitate potential applications of LCEs in different fields. We further demonstrate mitigation of stress concentration near the interface between an actuatable LCE tube and a rigid glass plate through gradient printing. On the basis of the comprehensive processing-structure-property relationship, we propose a simple strategy to print functionally graded LCEs, which greatly increases the design space for creating active morphing structures. Here, we report a facile method to tailor both the actuation behavior and mechanical properties of printed LCE filaments by varying printing parameters. Despite the advancement in printing LCE, it remains challenging to print three-dimensional (3D) LCE structures with graded properties. Recently, direct ink writing technique has been developed to print LCE structures with various geometries and actuation behaviors. As a promising actuating material, liquid crystal elastomer (LCE) has been intensively explored in building diverse active structures and devices.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |