| Author: | Huang, Zhenjia |
| Title: | Development of light-responsive actuators based on conjugated polymers/liquid crystal elastomers through photopolymerization |
| Advisors: | Tsui, Chi-pong (ISE) Yang, Mo (BME) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Photopolymerization Conjugated polymers Elastomers Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Industrial and Systems Engineering |
| Pages: | xx, 170 pages : color illustrations |
| Language: | English |
| Abstract: | Near-infrared (NIR) light-triggered liquid crystal elastomers (LCEs) actuators based on the photothermal effect have attracted tremendous scientific attention in biomedical devices and untethered robotics. By incorporating light-absorbing components in LCEs, the absorbed light can be converted into heat to induce the phase transition. By designing the mesogen alignment, reversible deformations from simple to complex modes can be realized. Most studies use inorganic nanoparticles as photothermal agents in LCEs; however, compatibility always complicates the LCE preparation and fabrication. This calls for developing organic photothermal agents filled LCEs, such as organic conjugated polymers (CPs)/LCEs, for addressing the material issues. There is no report on fabricating macro- and micro-actuators based on photothermal CPs for light-triggered actuation. It is highly appealing to develop new LCEs-based materials to fabricate different scales of actuators with fast response time. The microfabrication of LCE photoresists with room-temperature liquid crystal phases remains a challenge. Meanwhile, the applications of the inorganic nanoparticle-filled LCE macro-actuators are limited by relatively weaker actuation response due to the uneven distribution of nanoparticles in LCEs. Therefore, this thesis aimed to develop a method combining synthesis of photothermal CPs, photopolymerization techniques, and optimization of fabrication parameters for designing and fabricating light-triggered CPs/LCEs-based macro-actuators and micro-actuators for achieving controllable actuation. To overcome the material issue, organic CPs were proposed as photothermal materials for photoresponsive LCEs. Based on molecular design strategies and Stille cross-coupling polymerization, photothermal DPP58-TBZ12 CPs were designed and synthesized to achieve NIR light absorption ability (around 746 nm), high photothermal conversion efficiency (52.7%), and photostability. As the CPs display good solubility in tetrahydrofuran and compatibility with LCEs, they were incorporated into the LCEs homogeneously with arbitrary concentrations. This presented an effective method to prepare light-responsive CPs/LCEs for actuator manufacturing. With the CPs incorporated in the LCEs and through tailoring the mesogen alignment, 2D light-triggered macro-actuators were fabricated through one-pot UV photopolymerization for realizing various shape changes and 3D locomotion. Under NIR light irradiation, the film macro-actuators achieved multimodal shape morphing, including bending, “Swiss” rolling, and helical twisting, by controlling the alignment angles to the film's long axis. The macro-actuators had an ultrafast response time within 3 s when exposed to NIR light. With reversible and continuous helical twisting, the macro-actuators possessed locomotion ability with a high velocity of 0.47 mm/s under successive NIR light illumination. In addition to fabricating macro-actuators, micro-actuators were fabricated through direct laser writing based on two-photon polymerization (DLW-TPP) to demonstrate the applicability of the CPs/LCEs at the microscale. It is a powerful fabrication technology to achieve the sub-micrometer resolution of 3D structures with design freedom. To prepare DLW-TPP compatible LCE-based photoresists, the compositions were carefully tailored to make the photoresists maintain room-temperature liquid crystal phases. Moreover, incorporating CPs could lower the nematic-to-isotropic temperature of the photoresist, which would alleviate the crystallization occurrence during the printing process. To determine writing windows for producing the micro-structure with good structural fidelity, optimizing printing parameters was also performed. Through designing planar alignment and parameter optimization, the microactuator showed a large actuation strain (25.0%) within 5 s upon NIR light stimulation. In all, this thesis presents the work for developing novel CPs as photothermal agents for LCEs-based actuators and realizing the fabrication of CPs/LCEs actuators in different dimensions and scales through different photopolymerization technologies coupled with optimization of fabrication parameters. The diverse actuation modes and fast response speed of these actuators demonstrated the great potential of CPs/LCEs for boosting the design of light-responsive LCEs and the fabrication of LCEs-based actuators at macroscale and microscale. These CPs/LCEs actuators show great prospects in 3D dynamic cell culture platforms and soft robotics. |
| Rights: | All rights reserved |
| Access: | open access |
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