We use a new method based on the Electrostatic Force Microscopy (EFM) to perform quantitative measurements of the dielectric constants of individual electrospun nanofibers of poly(L-lactic acid) (PLLA), as well as composite fibers of PLLA with embedded multiwall carbon nanotubes (MWCNT-PLLA). The EFM data record the oscillation phase of an atomic force microscope (AFM) cantilever as a function of the AFM tip position. In our experiments the relative dielectric constants of the sample are measured from the EFM phase shifts vs. the tip-surface separation, according to a simple analytical model describing the tip-surface interactions. We perform a comprehensive study of how the dielectric constant depends on the fiber diameter for both electrospun PLLA and MWCNT/PLLA fiber composites. Our measurements show that EFM can distinguish between dielectric properties of PLLA fibers and fiber composites with different diameters. Dielectric constants of both PLLA and MWCNT-PLLA composite fibers decrease with increasing fiber diameter. In the limit of large fiber diameters (D > 100 nm), we measure dielectric constants in the range:  = 3.4-3.8, similar to the values obtained for unoriented PLLA films:film = 2.4-3.8. Moreover, the dielectric constants of the small diameter MWCNT-PLLA composites are significantly larger than the corresponding values obtained for PLLA fibers. For MWCNT-PLLA nanofiber composites of small diameters (D < 50 nm),  approaches the values measured for neat MWCNT:CN = 12 ± 2. These results are consistent with a simple fiber structural model that shows higher polarizability of thinner fibers, and composites that contain MWCNTs. The experimental method has a high-resolution for measuring the dielectric constant of soft materials, and is simple to implement on standard atomic force microscopes. This non-invasive technique can be applied to measure the electrical properties of polymers, interphases, and polymer nanocomposites.

中文翻译：

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使用静电力显微镜定量表征聚合物纤维和聚合物复合材料的介电性能

我们使用基于静电力显微镜 (EFM) 的新方法对聚 (L-乳酸) (PLLA) 的单个电纺纳米纤维以及嵌入多壁碳纳米管的 PLLA 复合纤维的介电常数进行定量测量(MWCNT-PLLA)。EFM 数据将原子力显微镜 (AFM) 悬臂的振荡相位记录为 AFM 尖端位置的函数。在我们的实验中，根据描述尖端-表面相互作用的简单分析模型，从 EFM 相移与尖端-表面分离测量样品的相对介电常数 。我们对电纺 PLLA 和 MWCNT/PLLA 纤维复合材料的介电常数如何取决于纤维直径进行了全面研究。我们的测量表明，EFM 可以区分不同直径的 PLLA 纤维和纤维复合材料的介电性能。PLLA 和 MWCNT-PLLA 复合纤维的介电常数随着纤维直径的增加而降低。在大纤维直径（D > 100 nm）的限制下，我们测量范围内的介电常数： = 3.4-3.8，类似于未取向的 PLLA 薄膜获得的值：film = 2.4-3.8。此外，小直径 MWCNT-PLLA 复合材料的介电常数明显大于 PLLA 纤维的相应值。对于小直径 (D < 50 nm) 的 MWCNT-PLLA 纳米纤维复合材料， 接近于纯 MWCNT 的测量值：CN = 12 ± 2。这些结果与一个简单的纤维结构模型一致，该模型显示更细的纤维具有更高的极化率, 和含有 MWCNTs 的复合材料。该实验方法具有测量软材料介电常数的高分辨率，并且在标准原子力显微镜上易于实现。这种非侵入性技术可用于测量聚合物、界面相和聚合物纳米复合材料的电性能。