Abstract: Artificial muscles can produce reversible expansion, twisting, bending, stretching, and other motions under the action of external stimuli (heat, electricity, light, magnetism, humidity, pressure, etc.), which holds potential application value in robotics, medicine, aerospace and other fields. As a class of intelligent stimulus-responsive materials, two-way shape memory polymer (2W-SMP) is an excellent substrate for preparing artificial muscles, because it can facilitate the reversible transition between its original and temporary shapes by adjusting the ambient temperature. However, 2W-SMP has shortcomings such as poor thermal conductivity, slow response speed, and single response mode. Therefore, increasing the response speed of 2W-SMP, diversifying its stimulus-response modes, and achieving precise control over reversible actuation strain are of great significance for the application and development of 2W-SMP in the field of artificial muscles.
Ethylene-vinyl acetate copolymer (EVA) is a semi-crystalline polymer. Research indicates that cross-linked EVA fibers possess excellent two-way shape memory properties, large reversible actuation strains, good flexibility, and designability. In this paper, nano hexagonal boron nitride (h-BN) was used as thermal conductive fillers, and carbon nanotubes (CNTs) as conductive fillers. BN/EVA composite fibers were prepared by melt spinning process, and CNTs/BN/EVA composite fibers with skin core structure were prepared by swelling and impregnation method. The experimental results show that the CNTs were closely combined with the fiber matrix, forming a good electrically conductive path on the surface of the fiber, and the electrical conductivity of the CNTs/BN/EVA composite fibers could reach 58.03 S/m. The CNTs/BN/EVA composite fibers have good strain sensing performance, with a detection range of up to 281%, and high sensitivity and linearity (in the range of 175%-281% strain, Gauge Factor (GF) of 35.19, R2=99.03%), with response and recovery times of 196 ms and 189 ms, respectively. The twisted CNTs/BN/EVA composite yarns could be rapidly warmed up to 111.45 ℃ in 12 s at 18 V and exhibit stable temperature rise and fall behavior under periodic electrical stimulation conditions, achieving precise regulation of the electrically induced reversible actuation strain in yarn-based artificial muscles.
In summary, the EVA-based composite fibers prepared in this thesis combine excellent two-way shape memory properties, reversible electric-driven properties and strain sensing properties, integrate actuation and sensing capabilities into one, and have potential applications in the fields of artificial muscles, wearable devices and robotics.

Key words: ethylene-vinyl acetate copolymer (EVA), functional fillers, two-way shape memory, strain sensor, electro-actuation

摘要： 为了丰富乙烯-醋酸乙烯酯共聚物(EVA)基纤维的响应方式，实现电致可逆驱动，以纳米六方氮化硼(BN)为导热填料，碳纳米管(CNTs)为导电填料，采用熔融纺丝工艺制备BN/EVA复合纤维，并通过溶胀-浸渍法在纤维表面包覆CNTs导电层，制得具有皮芯结构的CNTs/BN/EVA复合纤维。结果表明：CNTs与纤维基体结合紧密，在纤维表面形成了良好的导电通路，CNTs/BN/EVA复合纤维的电导率可达到58.03 S/m，且具有良好的应变传感性能，其检测范围高达281%，具有较高的灵敏度和线性响应度(在175%~281%应变范围，GF为35.19，R2=99.03%)，响应时间和回复时间分别为196 ms和189 ms。加捻制得的CNTs/BN/EVA复合纱线在18 V电压下可在12 s内快速升温至111.45 ℃，且该复合纱线在周期性电刺激条件下表现出稳定的升降温行为，实现了对纱线人工肌肉电致可逆驱动应变的精准调控。

关键词: 乙烯-醋酸乙烯酯共聚物(EVA), 功能填料, 双向形状记忆, 应变传感, 电致驱动