Design of electrical conductive poly(lactic acid)/carbon black composites by induced particle aggregation

Scalable Thermochromic Composite Based on a Ternary Polymer Blend for Temperature-Adaptive Solar Heat Management

A scalable and durable thermochromic composite is developed for temperature-adaptive solar heat management using a carbon absorber and a thermoresponsive polymer blend consisting of an isolated polycaprolactone phase (PCL) and a continuous phase of miscible poly(methyl methacrylate) and polyvinylidene fluoride. The ternary blend exhibits reversible haze transition originating from the melting and crystallization of PCL. The refractive index matching between the molten PCL and surrounding miscible blend contributes to high-contrast haze switching in the range of 14-91% across the melting temperature of PCL (ca. 55 °C). The solar-absorption-switching properties of the composite are due to the spontaneous light-scattering switching in the polymer blend and the presence of a small amount of carbon black. Spectral measurements indicate that the solar reflectance of the composite sheet varies by 20% between 20 and 60 °C upon lamination with a Ag mirror. Solar heat management using the thermochromic composite is successfully demonstrated under natural sunlight, thereby realizing a temperature-adaptive thermal management system.

Universal assembly of liquid metal particles in polymers enables elastic printed circuit board

An elastic printed circuit board (E-PCB) is a conductive framework used for the facile assembly of system-level stretchable electronics. E-PCBs require elastic conductors that have high conductivity, high stretchability, tough adhesion to various components, and imperceptible resistance changes even under large strain. We present a liquid metal particle network (LMP Net ) assembled by applying an acoustic field to a solid-state insulating liquid metal particle composite as the elastic conductor. The LMP Net conductor satisfies all the aforementioned requirements and enables the fabrication of a multilayered high-density E-PCB, in which numerous electronic components are intimately integrated to create highly stretchable skin electronics. Furthermore, we could generate the LMP Net in various polymer matrices, including hydrogels, self-healing elastomers, and photoresists, thus showing their potential for use in soft electronics.

Fabrication of PLA/PCL/Graphene Nanoplatelet (GNP) Electrically Conductive Circuit Using the Fused Filament Fabrication (FFF) 3D Printing Technique

For the purpose of fabricating electrically conductive composites via the fused filament fabrication (FFF) technique whose properties were compared with injection-moulded properties, poly(lactic acid) (PLA) and polycaprolactone (PCL) were mixed with different contents of graphene nanoplatelets (GNP). The wettability, morphological, rheological, thermal, mechanical, and electrical properties of the 3D-printed samples were investigated. The microstructural images showed the selective localization of the GNPs in the PCL nodules that are dispersed in the PLA phase. The electrical resistivity results using the four-probes method revealed that the injection-moulded samples are insulators, whereas the 3D-printed samples featuring the same graphene content are semiconductors. Varying the printing raster angles also exerted an influence on the electrical conductivity results. The electrical percolation threshold was found to be lower than 15 wt.%, whereas the rheological percolation threshold was found to be lower than 10 wt.%. Furthermore, the 20 wt.% and 25 wt.% GNP composites were able to connect an electrical circuit. An increase in the Young’s modulus was shown with the percentage of graphene. As a result, this work exhibited the potential of the FFF technique to fabricate biodegradable electrically conductive PLA-PCL-GNP composites that can be applicable in the electronic domain.

Effect of Melt-Compounding Protocol on Self-Aggregation and Percolation in a Ternary Composite

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^-2 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 perimeter~aggregate 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.