纳米粒子改性高分子材料是一种有效的改进方式。纳米粒子由于具备尺寸小、比表面积高的特点，可作为成核剂在聚合物中诱导晶体生成，提高材料性能。Qian等^[2]将氨基改性片层氧化铝加入PA612中，同时提高了PA612的强度和韧性，并且降低了磨损率。RuSu等^[17]将经过表面处理的TiO₂加入PA612中制备纳米复合材料，发现TiO₂的加入提高了PA612的熔点，高配比的TiO₂能有诱导γ晶的生成。纳米SiO₂是一种重要的改性材料，加入SiO₂后对提高聚合物拉伸强度和冲击强有重要的作用。Hu等^[18]研究了SiO2对PA66晶体结构和结晶性能的影响，SiO2对PA66具有成核能力，降低了PA66的熔点，延长了PA66的结晶时间，并提高了PA66的拉伸强度和储能模量。Xu等^[19]采用原位聚合法制备了PA6/SiO₂复合材料，研究表明SiO₂能诱导γ晶的生成，提高PA6的结晶度，降低PA6的晶粒尺寸。Rusu等^[20]发现在PA6中SiO₂添加含量为3%在以内时可提高PA6的冲击强度和弯曲强度。目前SiO₂加到PA612里面没有研究，对于球形纳米粒子在拉伸过程中的形貌变化和对基体材料结构的影响相关机理缺乏系统性的研究，本文主要研究在拉伸条件下，SiO₂对PA612的结晶行为的影响，进一步探究SiO₂对材料结构和性能的影响。
    

Nanoparticle modification is an effective modification approach for polymers. In virtue of their small sizes and high specific areas, nanoparticles can be used as nucleators to induce crystallization of polymers, thereby enhancing their performance. Qian et al. added amino-modified lamellar Al₂O₃ into PA612 ^[2]to improve its strength and toughness, while reduce its wear rate. RuSu et al. reported PA612/TiO₂ nano-composite by adding surface treated TiO₂ into PA612 ^[17]. The PA612/TiO₂ nano-composite had a melting point higher than that of PA612 and TiO₂ in high content can induce generation of γ crystals. Nano SiO₂ is a key modification material that has a significant effect on stretching strength and impact strength of polymers. Hu et al. studied the effects of SiO₂ on crystal structure and crystallization performance of PA66 ^[18]. Serving as a nucleator in PA66, SiO₂ can reduce the melting point of PA66, extending the crystallization time of PA66 and enhancing its stretching strength and energy storage modulus. Xu et al. prepared PA6/SiO₂ composite using in situ polymerization ^[19]. This study demonstrated that SiO₂ can induce generation of γ crystals, thus enhancing the crystallinity of PA6, while reducing its grain size. Rusu et al. reported that SiO₂ can improve impact and bending strengths of PA6 if its content was within 3% ^[20]. To date, addition of SiO₂ into PA612 has not been investigated and morphological changes of spherical nanoparticles during stretching, as well as their effects on matrix material structure, have not been systematically investigated. In this study, the effects of SiO₂ on crystallization of PA612 under stretching were investigated to further explore the effects of SiO₂ on structure and performance of PA612.