Kim Ji Hwan, Hong Joung Sook, Ishigami Akira, Kurose Takashi, Ito Hiroshi, Ahn Kyung Hyun
School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul 08826, Korea.
Research Center for GREEN Materials & Advanced Processing, Graduate School of Organic Materials Science, Yamagata University, Yamagata 992-8510, Japan.
Polymers (Basel). 2020 Dec 18;12(12):3041. doi: 10.3390/polym12123041.
A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (4 × 10 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeteraggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G'), high Young's modulus, high dielectric loss (ε″), and negative-positive switching of dielectric constant at high frequency (of 103 Hz) of composite.
聚乳酸（PLA）、聚己内酯（PCL）和炭黑（CB）的三元复合材料显示，当作为第二相的PCL相的量与CB的量一样少时，PCL会诱导CB自聚集并形成渗流。此外，当PCL相的液滴尺寸变小时，三元复合材料会形成高阶结构的渗流，导致电导率显著提高（含4 wt.% CB时约为4×10 S/m）。为了进一步控制渗流结构，通过将典型的单步混合过程分为两步来控制复合材料的制备，重点是分别分散第二相PCL相和CB颗粒。在单步混合方案下，三元复合材料呈现出一种结构，其中CB以高纵横比和大聚集体（聚集体周长聚集体尺寸0.7）的形式有更大的聚集。同时，两步混合过程会使CB聚集体膨胀并形成更高的结构（聚集体周长聚集体尺寸0.8）。在添加CB之前的高剪切力混合条件下，第二相尺寸的减小为CB在后续混合步骤中扩散到PCL相中提供了更大的界面面积，从而导致CB聚集体在整个复合材料中进一步膨胀。这种高阶结构的颗粒渗流归因于复合材料的高储能模量（G'）、高杨氏模量、高介电损耗（ε″）以及在103 Hz高频下介电常数的正负切换。
