We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and ⁵⁷Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe₃C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe₃C as evidenced by a Curie temperature estimated at T_C = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.

We study the mechanical response of a single polymer globule in a poor solvent subjected to oscillatory stretching forces using scaling theory and coarse-grained molecular dynamics simulations. Under constant loading, increasing the applied force induces a first-order globule-stretching transition accompanied by the formation of tadpole conformations at a temperature-dependent characteristic force. Under periodic loading, the delayed response of the polymer gives rise to extension hysteresis, and the associated energy dissipation is quantified by the hysteresis area. Below the unfolding threshold, the dissipative response is controlled by the intrinsic relaxation of the compact globule, and the data collapse onto a universal master curve when the driving frequency is rescaled by the equilibrium relaxation time. At and above the unfolding threshold, a force-induced dynamic phase transition between compact and stretched states gives rise to an additional low-frequency dissipation peak associated with repeated unfolding and refolding of the globule. The crossover between the driven phase transition and the relaxation of the globular state is remarkably sharp near the force-induced globule-stretching transition, where small changes in the driving frequency can increase the dissipated energy by an order of magnitude. These results establish a physical framework for understanding the mechanics of polymer globules subjected to time-dependent forces.