Interface Physics of Low-Density Polyethylene/Multi-Walled Carbon Nanotube Nanocomposites Effect on Its Dielectric Properties

Low-density polyethylene (LDPE) conductive composites are attractive for printable sensors owing to their flexibility; however, achieving desirable properties at low-conductive filler loadings remains challenging, motivating nanoparticle surface modification. In this study, unmodified (CNT), hydroxylated (CNT-OH), and carboxylated (CNT-COOH) carbon nanotubes were melt-blended with LDPE at a 1.5% volume fraction to prepare LDPE/CNT, LDPE/CNT-OH, and LDPE/CNT-COOH composites. Microscopic, rheological, thermomechanical, and impedance properties were evaluated. Microscopy revealed superior CNT dispersion in LDPE/CNT-COOH, consistent with rheological measurements showing higher storage and loss moduli. Impedance analysis showed that at low frequencies, LDPE/CNT-COOH exhibited an impedance of 800 Ω and a cutoff frequency of 67 s−1, compared to 300 Ω and 151 s−1 for the other samples. At 105 Hz, however, the resistance of LDPE/CNT-COOH dropped to 50 Ω, lower than the other composites, attributed to uniform CNT-COOH dispersion. Equivalent circuit fitting (series resistor with parallel RC) revealed capacitance increasing from 9×10−7 F (LDPE/CNT) to 1.1×10−6 F (LDPE/CNT-COOH). Calculated interaction energies of −722.09 and −580.38 kcal/mol for LDPE/CNT-COOH and LDPE/CNT, respectively, further explained the improved dispersion. This work presents a method to tune dielectric and conductivity behavior with frequency while maintaining processability at constant filler content.