Controlling Terahertz Dielectric Responses in Polymer Composites by Engineering α-Al2O3 Whisker Filler Distribution

As the communication band gradually approaches the terahertz (THz) range, there is an urgent need to explore materials with ideal dielectric properties for THz communication devices. Nevertheless, most polymers present a low dielectric constant (Dk), and the regulation of their dielectric properties in the THz range has rarely been reported. In this work, the isotactic polypropylene (iPP)/α-Al2O3 whisker composites were synthesized and their THz dielectric parameters were optimized. The Dk values increased from 2.23 to 3.13 with filler (α-Al2O3 whisker) concentration, ranging from 0 to 20 vol%, but were almost independent of the test frequency. The loss tangent (Df) values presented an increasing tendency along with both filler concentrations and test frequency. All composites exhibited Df values of less than 4.0 × 10−3. Particularly, the dielectric properties of composites can be further regulated by adjusting the orientation direction of the whisker fillers. The orientation of the whisker fillers was adjusted via the injection molding method. Along the direction of the whisker orientation distribution, the composites exhibit higher Dk values and lower Df values. This work presented a schematic to design polymer composites with higher Dk but controlled Df in the THz range and is significant for the development of advanced materials-based THz devices.