可编程取向液晶弹性体的4D打印

4D打印作为一种新兴的制造技术，将3D打印与智能响应材料相结合，使打印的样品“活”了起来。这种“活”是指打印的样品可以在适当的外部刺激下产生自发的形变，这种外界的刺激可以是温度、光照、湿度以及电磁场等。形变的行为能够进行预先编程设计，并在打印的过程中赋予样品。4D 打印所得的样品往往具有自驱动、高能量密度、高形变能力的优势，目前已经被应用于软体机器人、生物医疗、以及航空航天等领域。

4D打印技术的关键是打印方式和智能响应材料的选择，打印方式很大程度上决定了样品的精度、复杂程度和可设计性，智能响应材料则决定了对外部激励的响应方式以及形变能力。

本课题中综合比较各种打印技术的优缺点选择了基于光聚合打印的数字光处理打印技术。并在已被报道的智能响应材料中选取了可设计性强、能量密度高的液晶弹性体作为打印材料。使用磁场为打印的液晶弹性体进行取向以实现形变效果的预编程，使用磁场取向可以将打印过程与取向过程解耦，进一步提高了样品的可设计性。

实验中根据需求设计了适合光聚合打印的液晶弹性体材料配比与制备过程，并在理论分析的基础上着手设计完成液晶弹性体4D打印所需的各部分单元，最终搭建了一套具有三维可编程磁场取向功能的液晶弹性体4D打印系统。接着使用所搭建的系统进行了液晶弹性体3D打印与4D打印的测试，评估了系统的打印精度，初步验证了系统4D打印的效果。

As an emerging manufacturing technology, 4D printing combines 3D printing technology with smart responsive materials to make printed samples "live". This "live" means the printed sample can spontaneously deform under appropriate external stimulus, such as temperature, light, humidity, and electromagnetic fields. Altered behaviors can be pre-programmed and given to the sample during the printing technology. The samples obtained by 4D printing often have the advantages of self-actuated, high energy density and high deformability. They have been applied in soft robotics, biomedicine, aerospace and other fields.

The key to 4D printing technology is the choice of printing technology and smart response material. The printing technology largely determines the sample's accuracy, complexity and designability. While the smart response material determines the response mode to external excitation and the deformation ability.

In this study, the advantages and disadvantages of various printing technologies are compared comprehensively, and the digital light processing printing technology based on photo-aggregation printing is selected. Moreover, among the smart responsive materials that have been reported, liquid crystal elastomers with strong designability and high energy density are selected as printing materials. The magnetic field is used to align the printed liquid crystal elastomer to achieve pre-programming of the deformation effect. The printing process and alignment process can be decoupled, which further improves the designability of sample.

In the experiment, the material ratio and preparation process of liquid crystal elastomer suitable for photopolymeric printing were designed according to the requirements. Based on theoretical analysis, various parts required for liquid crystal elastomer 4D printing were designed and completed. A set of liquid crystal elastomer 4D printing system with 3D programmable magnetic field orientation function was built. Then, the built system was used to test the liquid crystal elastomer 3D printing and 4D printing, the printing accuracy of the system was evaluated, and the effect of the 4D printing of the system was preliminarily verified.

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