Multi-walled carbon nanotubes (MWCNTs) are promising nanomaterials for nanoelectronics due to their exceptional electrical, thermal, and mechanical properties. Heat capacity is a key parameter influencing thermal energy storage and the rate of temperature change during heat dissipation. In this study, we investigate the low-temperature specific heat of MWCNTs subjected to different grinding treatments [1]. Two modified MWCNT samples—milled and oxidized/milled—with an average outer diameter of 9.4 nm were analyzed. Grinding reduces the size of MWCNT agglomerates, resulting in an increase in heat capacity. The oxidized/milled MWCNTs were prepared via a two-step process: primary oxidation of pristine MWCNT powder followed by mechanical grinding. Oxidation effectively diminishes agglomeration, further enhancing the total heat capacity of the system. At low temperatures, the heat capacity expands in odd powers of temperature, revealing three main contributions: a defect-disorder term (C₁T), a Debye term (C₃T³), and a dispersive term (C₅T⁵). The negative value of the C₅ parameter indicates flexural phonon dispersion.

Notably, an anomalous disappearance of the characteristic “hump” in the C/T³ vs. T plot was observed, which is attributed to the combined effects of flexural phonon dispersion and disorder related to MWCNT agglomeration.

This work was supported partly by the National Research Foundation of Ukraine (Grant 2023.03/0012) and National Science Centre Poland (Grant 2022/45/B/ST3/02326).