Abstract: Negative Poisson's ratio materials, emerging as a novel class in recent years, exhibit a unique behavior where they expand laterally when stretched and contract laterally when compressed. These materials not only possess geometric deformation characteristics, but also demonstrate excellent shear resistance, indentation resistance, fracture toughness, shock absorption, energy absorption, moisture and air permeability, as well as surface conformability. These unconventional physical properties endow negative Poisson's ratio materials with distinct advantages, leading to their widespread application across various fields, including composites, sensors, and smart wearable devices. Among negative Poisson's ratio materials, negative Poisson's ratio yarns and fabrics constitute a significant category. First of all, negative Poisson's ratio yarns boast strong maneuverability, allowing the yarn to exhibit good negative Poisson's ratio properties through structural modifications. Secondly, these yarns and fabrics have a broad range of applications. By introducing this characteristic into yarns and designing their structure, auxetic effects can be achieved in textile materials.
In order to produce negative Poisson's ratio yarns with excellent and stable negative Poisson's ratio characteristics, this study used spandex as the core yarn and polyester filament as the wrapping yarn to prepare the composite yarn on a 16-spindle knitting machine. The wrapping yarn was spirally wrapped around the core yarn, imparting excellent negative Poisson's ratio characteristics to the composite yarn. The 10:1 ratio of polydimethylsiloxane (PDMS) rubber solution was used as the coating material. The PDMS solution was dripped onto the yarn and allowed to naturally flow down along the yarn under gravity, ensuring uniform coating. The yarn was then left to stand for 20 minutes to eliminate any bubbles. Finally, the yarn was dried and cured in an oven at 60 ℃ for 30 minutes, resulting in a PDMS-coated negative Poisson's ratio yarn with a significant negative Poisson's ratio effect and structural stability. 
The article described the preparation of a durable and stable coated negative Poisson's ratio yarn through a one-step coating process, and further investigated the mechanical properties, negative Poisson's ratio performance, stability, and hydrophilic/hydrophobic properties of the yarn before and after coating using comparative analysis. It was found that the CYc1/s2 yarn had a strength of 14.45 N and an elongation of 88.14 %, while the CYc4/s2 yarn had a strength of 24.29 N and an elongation of 108.2 %. The CYc1/s2 yarn exhibited a maximum negative Poisson's ratio effect of -2.416, which remained stable after 100 cycles of tensile testing. Additionally, the water contact angle of the coated yarn was greater than 100 °. Therefore, when the coated yarn is stretched under force, the external wrapped film provides a certain degree of protection, not only increasing the yarn's strength but also its elongation. This results in yarns with excellent and stable negative Poisson's ratio characteristics, providing reference for the preparation of more stable negative Poisson's ratio textiles.

Key words: negative Poisson's ratio yarns, coating, auxetic effect, hydrophobicity, braiding

摘要： 为了制备负泊松比特性优良且稳定的负泊松比纱线，利用16锭编织机制备了弹性芯纱外包包缠纱的复合纱，其中包缠纱呈螺旋状包缠在芯纱周围，可赋予该复合纱优良的负泊松比特性；再利用聚二甲基硅氧烷(PDMS)涂层来提高负泊松比纱线的稳定性，测试和分析了不同包缠结构及涂层对纱线负泊松比性能的影响。结果表明：在受力拉伸时，该负泊松比纱线的芯纱和包缠纱能够发生位置转换，纱线的直径变大，形成负泊松比效应。在一定范围内，当芯纱根数一定时，包缠纱的根数越多，纱线的强力与伸长率就越大，负泊松比效应越明显；当包缠纱根数一定时，芯纱根数越多，纱线的强力和伸长率就越大，负泊松比效应越明显；但当芯纱与包缠纱的直径比过大时，纱线的负泊松比效应变小。当负泊松比纱线表面涂覆PDMS时，其强力、伸长率和负泊松比效应均有所提升。研究结果可为制备结构稳定的负泊松比纱线提供参考。

关键词: 负泊松比纱线, 涂层, 拉胀效应, 疏水, 编织