1. Percolative dielectric behavior of titanium carbide MXene/cellulose nanofibrils composite filmsVida Jurečič, Subramanian Lakshmanan, Nikola Novak, Vanja Kokol, Vid Bobnar, 2024, izvirni znanstveni članek Opis: Cellulose-based nanomaterials are fascinating renewable biosystems, yet low thermal conductivity and dielectric permittivity often limit their potential applications in flexible electronics. We report dielectric properties of composite films prepared by vacuum filtration or solvent casting method from the native (CNF) or carboxylated (TCNF) cellulose nanofibrils and high electrically and thermally conductive 2D titanium carbide (Ti3C2Tx) MXenes. Measurements over broad frequency and temperature ranges revealed the influence of preparation method and type of nanofibrils matrix on the overall dielectric response, as well as a notable impact of absorbed water, particularly on the cellulose’s secondary β and γ relaxations. A detailed investigation of material with the lowest amount of impurities, vacuum-filtered MXene/CNF composites, confirmed that the dielectric response follows the predictions of the percolation theory. The resulting strong enhancement of the dielectric permittivity on increasing MXene content demonstrates the potential of developed composites for applications in eco-friendly dielectric and piezoelectric devices.
Ključne besede: percolation theory, piezoelectric devices, dielectric properties, nanomaterials, carbides, biological systems, biological models, carbohydrates
Objavljeno v DKUM: 08.09.2025; Ogledov: 0; Prenosov: 3
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2. Electrochemical capacitance of CNF–Ti3C2Tx MXene-based composite cryogels in different electrolyte solutions for an eco-friendly supercapacitorVanja Kokol, Subramanian Lakshmanan, Vera Vivod, 2025, izvirni znanstveni članek Opis: Cellulose nanofibrils (CNFs) are promising materials for flexible and green supercapacitor electrodes, while Ti3C2Tx MXene exhibits high specific capacitance. However, the diffusion limitation of ions and chemical instability in the generally used highly basic (KOH, MXene oxidation) or acidic (H2SO4, CNF degradation) electrolytes limits their performance and durability. Herein, freestanding CNF/MXene cryogel membranes were prepared by deep freeze-casting (at −50 and −80 ◦C), using different weight percentages of components (10, 50, 90), and evaluated for their structural and physico-chemical stability in other less aggressive aqueous electrolyte solutions (Na2/Mg/Mn/K2-SO4, Na2CO3), to examine the influence of the ions transport on their pseudocapacitive properties. While the membrane prepared with 50 wt% (2.5 mg/cm2 ) of MXene loading at −80 ◦C shrank in a basic Na2CO3 electrolyte, the capacitance was performed via the forming of an electroactive layer on its interface, giving it high stability (90% after 3 days of cycling) but lower capacitance (8 F/g at 2 mV/s) than in H2SO4 (25 F/g). On the contrary, slightly acidic electrolytes extended the cations’ transport path due to excessive but still size-limited diffusion of the hydrated ions (SO4 2− > Na+ > Mn2+ > Mg2+) during membrane swelling, which blocked it, reducing the electroactive surface area and lowering conductivities (<3 F/g).
Ključne besede: cellulose nanofibrils, Ti3C2Tx MXene, freeze-casting, aqueous electrolytes, physico-chemical properties, electric double layer, pseudocapacitance
Objavljeno v DKUM: 07.04.2025; Ogledov: 0; Prenosov: 6
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3. Dielectric and thermal conductive properties of differently structured ▫$Ti_3C_2T_x$▫ MXene-integrated nanofibrillated cellulose filmsSubramanian Lakshmanan, Vida Jurečič, Vid Bobnar, Vanja Kokol, 2024, izvirni znanstveni članek Opis: The fabrication of nanocellulose-based substrates with high dielectric permittivity and anisotropic thermal conductivity to replace synthetic thermoplastics in flexible organic electronics remains a big challenge. Herein, films were prepared from native (CNF) and carboxylated (TCNF) cellulose nanofibrils, with and without the addition of thermally conductive multi-layered Ti3C2Tx MXene, to examine the impact of polar (− OH, − COOH) surface groups on the film morphological, moisturizing, dielectric, and thermal dissipation properties. The electrostatic repulsion and hydrogen bonding interaction between the hydrophilic surface/terminal groups on CNF/TCNF and MXene was shown to render their self-assembly distribution and organization into morphologically differently structured films, and, consequently, different properties. The pristine CNF film achieved high intrinsic dielectric permittivity (ε' ~ 9), which was further increased to almost ε' ~ 14 by increasing (50 wt%) the MXene content. The well-packed and aligned structure of thinner TCNF films enables the tuning of both the composite’s dielectric permittivity (ε' ~ 6) and through-plane thermal conductivity (K ~ 2.9 W/mK), which increased strongly (ε' ~ 17) at higher MXene loading giving in-plane thermal conductivity of ~ 6.3 W/mK. The air-absorbed moisture ability of the films contributes to heat dissipation by releasing it. The dielectric losses remained below 0.1 in all the composite films, showing their potential for application in electronics.
Ključne besede: nanofibrillated cellulose, Ti3C2T, Mxene, film preparation, moisture content, thermal conductivity
Objavljeno v DKUM: 03.09.2024; Ogledov: 36; Prenosov: 19
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