This paper describes a novel method to produce poly(lactic acid) (PLA) stereocomplex (SC) crystallites directly from high molecular weight PLLA by incorporation of small quantities of choline dihydrogen phosphate ([Ch][DHP]), at room temperature. Combined results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirm the formation of the PLA SC crystals. ¹H NMR spectroscopy indicates a modification of the short range structural environment of choline in the blend with PLA in good agreement with the major long-range structural changes suggested by XRD, both suggesting a direct role of the choline in the PLA stereocomplexation. The electrical conductivity of these membranes measured using impedance spectroscopy is in the 6 × 10⁻⁷–4 × 10⁻⁶ S cm⁻¹ range, which increases with increasing choline content and with increasing relative humidity (RH). The dependence on RH is weaker than for pure PLA, thus suggesting that the SC enhances the hydrophobic character of PLA, in agreement with contact angle measurements. Atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) reveal a new phase with piezoelectric properties at the microsphere interfaces, with d₃₃ corresponding to ∼60% of d₃₃ of a periodically poled lithium niobate reference, which is directly related to the formation of SC crystalline domains. This first report of intrinsic piezoelectricity in PLA stereocomplexes opens the possibility for the development of new types of bio-based piezoactive polymers.

中文翻译：

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压电聚丙交酯立体配合物与胆碱有机离子塑料晶体

本文介绍了一种在室温下通过掺入少量磷酸胆碱二氢（[Ch] [DHP]）直接从高分子量PLLA生产聚乳酸（PLA）立构复合物（SC）微晶的新方法。X射线衍射（XRD），傅立叶变换红外光谱（FTIR）和差示扫描量热法（DSC）的综合结果证实了PLA SC晶体的形成。¹ H NMR谱表明与PLA共混物中胆碱的短程结构环境发生了变化，与XRD所建议的主要的长程结构变化很好地吻合，均表明胆碱在PLA立体络合中具有直接作用。使用阻抗光谱法测量的这些膜的电导率为6×10⁻⁷ –4×10 ^-6 S cm ^-1范围，随着胆碱含量的增加和相对湿度（RH）的增加而增加。对RH的依赖性比纯PLA弱，因此表明SC与接触角测量结果一致，可增强PLA的疏水性。原子力显微镜（AFM）和压电响应力显微镜（PFM）揭示了在微球界面处具有压电特性的新相， d ₃₃对应于d _33的约60％周期性极化的铌酸锂参考文献的名称，它直接与SC晶畴的形成有关。有关PLA立体复合物中固有压电性的第一份报道为开发新型生物基压电活性聚合物开辟了可能性。