Poly(L-lactic acid) crystallization in a confined space containing graphene oxide nanosheets.
Poly(L-lactic acid) crystallization in a confined space containing graphene oxide nanosheets.
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DOI：
10.1021/jp4055796
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发表时间：
2013-09
期刊：
影响因子：
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通讯作者：
Hua-Dong Huang;Jia‐Zhuang Xu;Ying Fan;Ling Xu;Zhong‐Ming Li
中科院分区：
文献类型：
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作者：
Hua-Dong Huang;Jia‐Zhuang Xu;Ying Fan;Ling Xu;Zhong‐Ming Li
掺入纳米填料的半晶聚合物往往表现出复杂的结晶行为，这可能与纳米填料构成的复杂结晶环境，特别是密闭空间有关。在本工作中，为了深入了解可生物降解的聚l -乳酸（PLLA）结晶行为对氧化石墨烯纳米片（GONS）负载的依赖，特别是相对较高的GONS负载，采用差示扫描量热法和时间分辨傅里叶变换红外光谱技术，研究了一组GONS/PLLA纳米复合材料在0 ~ 4.0 wt %的不同GONS负载下的等温结晶行为。结果表明，GONSs不仅是PLLA结晶的非均相成核剂，而且还限制了PLLA链的迁移率和扩散。在低浓度（0.25 wt %和0.5 wt %）下，由于具有极高的比表面积，GONSs充当PLLA链的“圣殿”，从而促进构象有序，降低成核屏障。GONSs的成核作用是实现加速整体结晶动力学的主要因素。当GONS浓度上升到1.0 wt %时，在PLLA基体中形成了GONS网络，在流变学测量中得到了低频类固体流变行为的验证。纳米填充物网络显著地限制了PLLA链的迁移和扩散，抵消了GONSs的成核效应，导致结晶速率从促进到限制的转折点。此外，在更高的GONS浓度（4.0% wt %）下，更拥挤、更密集的GONS网络构建了一个严重受限的空间，迫使PLLA片层以二维模式生长。四区模型还对PLLA从促进到限制的异常结晶行为进行了理解，并提供了半定量的结晶环境描述。这些结果为进一步揭示高纳米填料负载下聚合物的结晶行为提供了有效途径。
The semicrystalline polymer incorporated with nanofillers frequently exhibits complicated crystallization behavior, which is probably attributed to the nanofiller-constructed complex crystalline circumstance, especially a confined space. In the present work, in order to have a thorough understanding of biodegradable poly(L-lactic acid) (PLLA) crystallization behavior on the dependence of graphene oxide nanosheet (GONS) loadings, in particular the relatively high GONS loading, a set of GONS/PLLA nanocomposites with different GONS loadings ranging from 0 to 4.0 wt % were investigated in terms of isothermal crystallization behavior by differential scanning calorimetry and time-resolved Fourier-transform infrared spectroscopy techniques. The results indicated that GONSs not only served as heterogeneous nucleating agents for PLLA crystallization but also restricted the mobility and diffusion of PLLA chains. At low GONS concentrations of 0.25 and 0.5 wt %, GONSs acted as a temple for PLLA chains to land on due to extremely high specific surface area, thus promoting the conformational ordering and reducing the nucleating barrier. The nucleation effect of GONSs was dominant to achieve accelerated overall crystallization kinetics. As the GONS concentration rose up to 1.0 wt %, the GONS network was formed in the PLLA matrix, which was verified by solid-like rheological behavior at low frequencies in rheological measurement. The nanofiller network significantly constrained the mobility and diffusion of PLLA chains and offset the nucleation effect of GONSs, giving rise to a turning point in crystallization rate from promotion to restriction. Furthermore, a severely confined space was constructed by the more crowded and denser GONS networks at a higher GONS concentration of 4.0 wt %, compelling PLLA lamellae to grow in a two-dimensional mode. The unusual crystallization behavior of PLLA from promotion to restriction was also understood by the four-region model, in which the semiquantitative description of crystalline circumstance was provided. These results pave an effective way to further reveal the crystallization behavior of polymer at a relatively high nanofiller loading.