应变控制对形状记忆聚氨酯表面微纳结构的影响

Effects of strain-control on the surface micro-nano structures of shape memory polyurethane

目的探讨应变控制对形状记忆聚氨酯表面微纳结构的影响。方法将拉伸率为200%的聚氨酯薄膜,以夹具将两端固定的应变控制方式在32°C的空气中静置24 h;随后去除固定装置,让薄膜在41℃的空气环境中进行形状回复。计算薄膜形状回复率,采用原子力显微镜和扫描电镜观测和分析不同形态下(原始形状、应变控制后形状、回复后形状)聚氨酯薄膜表面微纳结构的变化与差异。结果应变控制降低了薄膜的形状回复率。原子力显微镜和扫描电镜观测结果显示:原始形状中聚氨酯分子链段中的硬段与软段发生相分离,硬段聚集形成无序的微区结构,并进一步组装成纳米纤维。拉伸引起微区结构沿拉伸方向有序排列,其结果是纳米纤维在拉伸薄膜表面沿拉伸方向延伸。应变控制对拉伸薄膜表面微纳结构无显著影响;经应变控制处理后薄膜表面微纳结构的排列仍处于有序状态,形状回复仅改变纳米纤维排列方向。结论应变控制可调节聚氨酯形状回复性能及表面微纳结构,研究结果对该材料在生物医学领域的应用具有重要参考价值。

Objective The aim of this work was to investigate the effects of strain-control on the surface micro-nanostructures of shape memory polyurethane.Methods Polyurethane films were stretched at stretching ratio of 200%.Then,the stretched films were strain-controlled by clamping the two ends of films and incubated at 32°C for 24h in air.Thereafter,the films were un-fixed and allowed to recover at 41°C in air.The shape recovery ratio of SMPU films was calculated.The surface micro-nanostructures in different morphologies including original shape,strain-controlled shape,as well as shape recovered shape were observed using atom force microscope(AFM)and scanning electron microscope(SEM).Results Strain-control reduced the shape recovery ratio of SMPU films.AFM and SEM results showed that the phase separation between hard and soft segments of SMPU led to sequential aggregation of hard segments into domains and nano-fibers,which arrayed disorderly on original shape of SMPU films.After stretching,the domains packed along the stretching direction.Consequently,nano-fibers extending along the stretching direction were observed on the stretched SMPU films.During strain control period,significant changes in the nanostructures were not observed.For films with treatment of straincontrolled,however,the subsequently shape recovery process could only alter the arrangement direction of nano-fibers,the arrangement of micro-nano structures on the surface of the film was still in an orderly state.Conclusion Strain-control could regulate shape recovery properties and micro-nano structures of SMPU films,which had a significant effect on the biomedical application of SMPU.