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Communication

Influence of MWCNT Concentration on Performance of Nylon/MWCNT Nanocomposite-Based Triboelectric Nanogenerators Fabricated via Spin Coating Method

by
Talia Tene
1,
Orkhan Gulahmadov
2,*,
Lala Gahramanli
2,3,
Mustafa Muradov
2,
Jadranka Blazhevska Gilev
4,
Telli Hamzayeva
5,
Shafag Bayramova
5,
Stefano Bellucci
6 and
Cristian Vacacela Gomez
3
1
Department of Chemistry, Universidad Técnica Particular de Loja, Loja 110160, Ecuador
2
Nano Research Laboratory, Excellent Center, Baku State University, Academic Zahid Khalilov St. 23, Baku AZ1148, Azerbaijan
3
INFN—Laboratori Nazionali di Frascati, Via E. Fermi 54, 00044 Frascati, RM, Italy
4
Faculty of Technology and Metallurgy, Ss. Cyril and Methodius University in Skopje, Rugjer Boskovic 16, 1000 Skopje, North Macedonia
5
Institute of Geology and Geophysics, Ministry of Science and Education of the Republic of Azerbaijan, H. Javid Ave., 119, Baku AZ1143, Azerbaijan
6
National Institute of Materials Physics, Atomistilor str. 405 A, 077125 Magurele, Romania
*
Author to whom correspondence should be addressed.
Nanoenergy Adv. 2025, 5(3), 9; https://doi.org/10.3390/nanoenergyadv5030009
Submission received: 8 May 2025 / Revised: 21 June 2025 / Accepted: 3 July 2025 / Published: 7 July 2025
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Versions Notes

Abstract

This work reports the fabrication and optimization of nylon/multi-walled carbon nanotube (MWCNT) nanocomposite-based triboelectric nanogenerators (TENGs) using a spin coating method. By carefully tuning the MWCNT concentration, the device achieved a substantial enhancement in electrical output, with open-circuit voltage and short-circuit current peaking at 29.7 V and 3.0 μA, respectively, at 0.05 wt% MWCNT loading on the surface of nylon. The corresponding power density reached approximately 13.9 mW/m2, representing a significant improvement over pure nylon-based TENGs. The enhanced performance is attributed to improved charge trapping and dielectric properties due to well-dispersed MWCNTs on the surface of nylon, while excessive loading caused agglomeration, reducing efficiency. This lightweight, flexible nanocomposite TENG offers a promising solution for efficient, sustainable energy harvesting in wearable electronics and self-powered sensor systems, highlighting its potential for practical energy applications.

1. Introduction

The increasing demand for renewable and sustainable energy sources has intensified research into energy harvesting technologies [1,2]. Among these, triboelectric nanogenerators (TENGs) have garnered considerable attention due to their ability to convert mechanical energy into electrical output with relatively low material costs and structural simplicity [3,4]. TENGs operate through the coupling of triboelectrification and electrostatic induction [5], making them suitable for a wide range of applications [6,7], including wearable electronics [8,9], self-powered sensors [10,11,12,13], and portable devices [14,15]. Recently, TENGs fabricated from waste-derived materials such as coffee powder [16], nopal powder [17], and banana leaf have attracted interest because of their environmental friendliness and resource recyclability [18]. However, these natural materials often suffer from inconsistent surface properties, poor mechanical durability, and limited electrical performance, which restrict their practical use and device longevity [19]. Conversely, synthetic polymer nanocomposites, exemplified by nylon matrices reinforced with multi-walled carbon nanotubes (MWCNTs), demonstrate enhanced mechanical robustness, well-controlled surface morphology, and superior dielectric properties, thereby facilitating improved and more stable triboelectric outputs [20].
Advancements in TENG technology have increasingly emphasized material selection and device architecture optimization [21,22]. Nanocomposites integrating carbon-based fillers, such as carbon nanotubes (CNTs), have demonstrated considerable potential to augment electrical output through improved charge transport, mechanical stability, and interfacial interactions [23,24]. These nanocomposites comprise a flexible polymer matrix combined with nanoscale fillers, where the matrix imparts mechanical flexibility while the fillers enhance electrical conductivity, thermal stability, and interfacial charge transfer efficiency [25,26,27,28,29]. Within the triboelectric layer, CNT incorporation notably strengthens charge transfer processes and mechanical integrity, thereby sustaining consistent electrical output under cyclic loading conditions [27].
Multi-walled carbon nanotubes (MWCNTs) are of significant interest due to their exceptional electrical conductivity, large specific surface area, and superior mechanical strength, which collectively enhance charge transfer and storage capabilities within triboelectric layers [27,30]. Achieving uniform dispersion of MWCNTs within the polymer matrix is critical to preserving interfacial homogeneity and optimizing contact area, thereby increasing the overall charge density [31,32]. Previous studies have demonstrated that nylon/f-MWCNT nanocomposite-based TENGs fabricated through varying spray deposition cycles exhibit electrical output improvements dependent on the number of deposition passes [27]. These findings suggest that fabrication parameters, such as deposition cycles, play a crucial role in modulating triboelectric performance.
Among the various material options for developing flexible TENGs, CNTs stand out due to their exceptional electrical conductivity, mechanical robustness, and thermal stability. In this work, we have leveraged MWCNTs in combination with nylon and polysiloxane to develop a composite TENG with enhanced performance metrics suitable for wearable electronics and energy harvesting applications. Similarly to findings reported in the literature and summarized in Table 1, both single-walled (SWCNTs) and MWCNTs have been shown to boost output voltage and power density, while also imparting mechanical flexibility, an essential property for dynamic environments such as biomedical and environmental sensing [33,34,35,36,37,38,39].
As demonstrated in Table 1, our Nylon/MWCNT/polysiloxane-based TENG achieves competitive electrical outputs while maintaining ease of fabrication and good nanofiller dispersion. This aligns with existing trends in CNT-based TENG development, where polymers serve not only as triboelectric layers but also as effective mechanical support structures. The composite formulation developed here benefits from the dielectric enhancement of nylon and the conductivity of well-dispersed MWCNTs, offering a promising balance between electrical performance and mechanical resilience.
However, despite these advancements, significant challenges persist in the field of CNT-based nanogenerators, many of which are also relevant to our current system. One of the primary obstacles is the tendency of CNTs—particularly at higher loadings—to agglomerate due to strong van der Waals forces, which disrupts uniform dispersion and reduces device performance. While surfactants or dispersing agents have been employed to mitigate this, they can undesirably alter the physical structure or electrical conductivity of CNTs, introducing variability into device performance and complicating large-scale fabrication. Moreover, the integration of CNTs within polymer matrices presents a trade-off: enhancing mechanical flexibility often comes at the expense of reducing the intrinsic conductivity of the nanofillers. This interplay poses additional barriers to achieving standardized, scalable TENG devices with consistent performance metrics. When CNTs are hybridized with other functional nanomaterials to further enhance triboelectric response, careful design is required to prevent the suppression of individual material properties—an issue that continues to limit material selection strategies.
This study aims to overcome key limitations associated with waste-derived TENGs by developing a nylon/MWCNT nanocomposite-based device with an optimized filler concentration that delivers significantly enhanced energy harvesting capabilities and mechanical durability. Unlike natural waste materials, which often suffer from variability in surface morphology, limited dielectric strength, and unstable electrical output, the engineered nanocomposite presented here offers precise control over both surface structure and charge distribution through the uniform dispersion of MWCNTs. The adoption of a spin coating technique facilitates the fabrication of thin, homogeneous films with high reproducibility and scalability, contributing to consistent triboelectric performance. A systematic investigation of electrical output across varying MWCNT loadings underscores the critical influence of filler concentration on dielectric properties and charge-trapping efficiency. This work not only achieves substantial improvements in output performance and structural integrity compared to previously reported waste-based and polymer-based TENGs but also establishes a robust, scalable pathway for the development of high-performance energy harvesting devices. The proposed TENG is particularly well-suited for real-world applications in wearable electronics, environmental sensing, and self-powered systems.

2. Materials and Methods

2.1. Materials

Multi-walled carbon nanotubes (MWCNTs) were obtained from SouthWest NanoTechnologies (SWeNT, Norman, OK, USA). Ethanol (≥95.0% ethyl alcohol) was purchased from Merck (Darmstadt, Germany). Nylon was sourced from commercial nylon socks composed of 90% nylon and 10% other polymers, with a thread diameter of 43 μm, and used as the triboelectric pair. Polysiloxane (RTV2 silicone rubber), commonly employed in mold-casting applications, was selected as the negative triboelectric material based on its electron affinity. This property enhances charge transfer when paired with nylon, significantly improving the triboelectric performance of the nanogenerator. Polysiloxane was selected in part due to its commercial availability and low material cost, which supports its use in TENG fabrication. Aluminum foil (Pratikon, 16 μm thick) served as the metal electrode for electrical output measurement.

2.2. Functionalization of MWCNTs and Preparation of Ethanol/MWCNT Mixtures with Varying Concentrations

2.2.1. Functionalization Process

MWCNTs were purified using 30% nitric acid (HNO3) (Carlo Erba, Milan, Italy) and deionized (DI) water. After purification, 100 mg of MWCNTs were treated with 4 mL of 65% HNO3 and 12 mL of 93.6–95.6% sulfuric acid (H2SO4) (AO Бaзa №1 Xимpeaтивoв, Moscow, Russia). The mixture was placed in a glass container and subjected to ultrasonication at 68 kHz while maintained at 50 °C for 3 h. Following the reaction, 500 mL of DI water was added, and the suspension was left to stabilize for 12 h. The product was then washed with DI water by vacuum filtration and dried in an oven at 40 °C for 24 h. Fourier-transform infrared (FTIR) spectroscopy (IR Affinity-1, Shimadzu, Kyoto, Japan) was employed to verify the presence of oxygen-containing functional groups [27].

2.2.2. Preparation of Ethanol/MWCNT Mixtures

Ethanol/MWCNT solutions at varying concentrations were prepared by dispersing precise quantities of MWCNTs in ethanol. Masses of 0.001 g, 0.003 g, 0.005 g, and 0.01 g were each added to 10 mL of ethanol to obtain 0.01%, 0.03%, 0.05%, and 0.1% solutions, respectively. To promote uniform dispersion and reduce agglomeration, the mixtures were subjected to ultrasonication using a UP200Ht ultrasonic (Hielscher Ultrasonics GmbH, Teltow, Germany) processor operating at 50% amplitude for 45 min. The treated suspensions were used in subsequent steps for the preparation of nylon-based nanocomposite layers.

2.3. Fabrication of Nylon/MWCNT Nanocomposites by Using Spin Coating Method

Nylon/MWCNT nanocomposite films were fabricated using the spin coating method (Spin Coater, Ossila). As shown in Figure 1, 1 mL of each ethanol-based MWCNT solution was deposited onto nylon substrates during the coating process. The procedure was carried out in two stages: an initial spin at 300 rpm for 20 s to distribute the solution, followed by a second spin at 1200 rpm for 20 s to enhance film uniformity and reduce solvent content. This method produced four nylon/MWCNT films corresponding to different MWCNT concentrations. Spin coating was selected for its capability to produce uniform coatings with controlled film thickness [40,41]. The technique supports reproducibility and consistent layer formation and is commonly used for nanostructured thin films where dimensional precision is required. The process was selected in part due to its capacity to reduce material loss and control film coverage across the substrate [42].
The incorporation of MWCNTs into nylon matrices has been used to enhance mechanical, electrical, and triboelectric characteristics. These improvements are attributed to increased charge trapping and conductivity, which contribute to the material’s function in triboelectric nanogenerator (TENG) applications. Nylon’s flexibility, chemical resistance, and low density support its integration into energy harvesting structures and devices intended for wearable electronics.

2.4. Fabrication of Triboelectric Films for TENG

The fabrication process of the triboelectric films used in the TENG is illustrated in Figure 2. As shown in Figure 1, nanocomposite films consisting of multi-walled carbon nanotubes (MWCNTs) uniformly dispersed within a nylon polymer matrix were prepared via a spin coating technique, ensuring controlled film thickness and homogeneity. For the preparation of nylon films, nylon pieces—sourced from nylon socks due to their favorable mechanical strength and intrinsic electron transfer properties—were carefully cut and affixed onto pre-cleaned aluminum foil substrates using double-sided adhesive tape. The aluminum foil, serving as the conductive electrode, was thoroughly cleaned with ethanol to remove surface contaminants and then dried before assembly, as depicted in Figure 2a. The thickness of the nylon films was precisely measured to be approximately 110 μm, an optimal dimension for effective triboelectric interaction. To enhance device stability and prevent environmental interference, one side of the nylon film attached to the aluminum electrode was insulated with a carton paper as a substrate layer.
Polysiloxane was selected as the complementary triboelectric material in this study due to its advantageous combination of high electronegativity, mechanical flexibility, chemical inertness, and ease of processing [5]. While polytetrafluoroethylene (PTFE) and polydimethylsiloxane (PDMS) are widely recognized triboelectric materials and frequently used in nanogenerator applications, each presents inherent limitations. PTFE, despite its strong electron-accepting ability and high negative position in the triboelectric series, suffers from poor film-forming capability due to its high melting point and insolubility in common solvents, which hinders its application in scalable and uniform device fabrication [25]. PDMS, although valued for its elastomeric nature and processability, exhibits relatively low surface charge density and limited dielectric tunability, which can constrain triboelectric output when used without further modification.
In contrast, polysiloxane offers a balanced set of properties suitable for triboelectric energy harvesting, including excellent mechanical compliance, environmental stability, and superior compatibility with nanofillers such as carbon-based or metal oxide nanoparticles. These characteristics facilitate the formation of nanocomposite systems with enhanced dielectric properties and improved interfacial charge trapping, which are critical for boosting the output performance of TENGs [5].
For the fabrication of the polysiloxane layer, equal parts by weight (5.5 g each) of precursor components Part 5A and Part 5B were mixed using a mechanical mixer for 15 min to obtain a homogeneous solution, as illustrated in Figure 2b. The mixture was then uniformly deposited onto a pre-treated aluminum foil substrate via a drop-casting method. The coated films were allowed to cure under ambient conditions (~25 °C) for 24 h to ensure complete cross-linking and solvent evaporation. The final polysiloxane film exhibited a uniform thickness of approximately 215 μm. This straightforward and scalable approach supports reproducibility and is conducive to large-area fabrication of flexible triboelectric layers for energy harvesting applications.
After drying, 4 cm × 4 cm sections were precisely cut from both the polysiloxane and nylon nanocomposite films to serve as the triboelectric layers in the TENG assembly. These layers were arranged in a contact–separation configuration, separated by a 10 mm thick, soft sponge spacer to maintain a consistent gap distance during operation. This assembly ensured reliable mechanical contact and separation cycles necessary for efficient triboelectric charge generation.

2.5. Characterization Methods

Structural analysis of the samples was conducted using BRUKER D2-PHASER and D8-ADVANCE diffractometers (Bruker AXS GmbH, Karlsruhe, Germany). Elemental composition and distribution were analyzed using energy-dispersive X-ray spectroscopy (EDS) with an X-Max detector (Oxford Instruments, Abingdon, UK). FTIR measurements were obtained using a Fourier-transform infrared spectrometer (IR Affinity-1, Shimadzu, Kyoto, Japan) over the wavenumber range of 400–4000 cm−1. Dielectric properties of the nylon/MWCNT nanocomposite films were evaluated using an Immittance Meter E7-20 (MNIPI, Minsk, Belarus) over a frequency range of 60 Hz to 1 MHz. Electrical output of the TENG devices was measured with a digital multimeter (DMM6500 6-1/2, Keithley, Keithley Instruments, Cleveland, OH, USA).

2.6. Measurement of the Performance of the TENG

To investigate the effect of MWCNT concentration on the TENG output, pristine nylon and MWCNT-reinforced nylon nanocomposite films were utilized as triboelectric layers. Polysiloxane served as the complementary triboelectric material. Square samples measuring 4 cm × 4 cm were cut from each film and assembled by placing the nylon-based layer in direct contact with the polysiloxane surface. A fixed separation distance of 10 mm was maintained between the two layers during operation. Electrical characterization was performed using a digital multimeter (Keithley DMM6500, 6½-digit resolution, Keithley Instruments, Cleveland, OH, USA) under controlled environmental conditions. The contact–separation motion was applied at a frequency of 2 Hz, with all tests conducted at a temperature of 29 °C and relative humidity of 58%. The performance of the proposed nylon/MWCNT-based triboelectric nanogenerator is influenced by environmental factors, such as humidity and temperature, as well as device structural parameters, including the gap distance between the triboelectric layers and electrodes. Increased humidity introduces moisture on the triboelectric surfaces, potentially forming a conductive layer that facilitates charge leakage and reduces surface charge density, thereby diminishing the output voltage and current. Typically, relative humidity levels above 70% significantly impair triboelectric charge generation, while moderate humidity (40–60% RH) maintains more stable performance [5,43]. Temperature variations affect the dielectric properties and mechanical compliance of the polymer matrix. Moderate temperature increases may enhance charge mobility and improve output, but excessive heat can degrade material integrity and increase leakage currents, ultimately leading to performance deterioration. Additionally, the gap distance between the triboelectric layers and electrodes critically impacts electrical output. A larger gap increases the potential difference by enhancing charge separation, thereby boosting open-circuit voltage; however, excessive separation can reduce effective electrostatic induction and lower current output. Conversely, a smaller gap improves charge transfer efficiency but risks electrical breakdown or short-circuiting. In this work, an optimized spacer thickness was employed to balance these effects, ensuring consistent and enhanced energy harvesting. Understanding and controlling these factors is essential for achieving reliable and efficient TENG operation under practical environmental conditions.

3. Results and Discussion

3.1. XRD Analysis

The structural properties of the samples were analyzed using X-ray diffraction (XRD) to confirm the formation of the composite materials. This method was used to assess the phase composition and verify material integration. Diffraction patterns were collected for the nylon base material and nylon 6/MWCNT composites at different MWCNT loadings (0.01%, 0.03%, 0.05%, and 0.1%). Figure 3a shows the XRD pattern of unmodified nylon 6, while Figure 3b presents the patterns of the composite samples.
In the pattern of nylon 6 (Figure 3a), diffraction peaks appear at 20.50° and 23.00°, corresponding to the α1 and α2 phases, associated with the (100) and (010) Miller indices [44,45]. Aluminum foil, used as the substrate, contributes additional peaks at approximately 44°, 65°, and 78°, indexed to the (200), (220), and (311) Miller indices of crystalline aluminum [46].
For the nylon/MWCNT composites, diffraction features attributed to MWCNTs were observed at 26.29° across all concentrations. Additional peaks at 44.52°, 44.55°, and 44.58° correspond to the (002) and (100) Miller indices of MWCNTs at concentrations of 0.01%, 0.03%, 0.05%, and 0.1% [47]. As MWCNT loading increased, diffraction features not present in the nylon reference became visible. Overlapping signals in the 44° region, shared with the aluminum substrate, indicate the emergence of a secondary peak. The intensity of this peak increased proportionally with MWCNT content, which is consistent with the incorporation of carbon-based material into the nylon matrix, as indicated by the diffraction patterns.

3.2. SEM and EDS Analysis

SEM and EDS analysis were performed to determine the deposition of different percentages of MWCNT on the nylon surface, the morphology of the samples, as well as their elemental analysis. Figure 4 presents both their SEM images and EDS analyses.
As can be seen from the results, in the SEM image of pure nylon 6 (Figure 4a), the surface of the nylon tubes is smooth and there is no residual substance on it. Its elemental analysis shows that the atomic percentage of C is 82.91% and the atomic percentage of O is 17.09. When 0.01 wt% MWCNT is formed on the surface of nylon, we can see the accumulation of wires on it in certain parts (Figure 4c). From the elemental analysis of nylon 6/0.01 wt% MWCNT, it is determined that the atomic percentage of C is 83.89% and the atomic percentage of O is 16.11% (Figure 4d). From the SEM image of nylon 6/0.03 wt% MWCNT (Figure 4e), it is seen that the amount of these tubes increases and a larger precipitate is formed on the surface of nylon. Elemental analysis (Figure 4f) also determined that the atomic percentage of C was 84.77% and that of O was 15.23%. In the SEM image of the nylon 6/0.05 wt% MWCNT composite (Figure 4g), it is clearly visible that MWCNTs were deposited on the surface of nylon in the form of an agglomerate and that MWCNTs were combined in this agglomerate. As can be seen from the elemental analysis (Figure 4h), the atomic percentage of C was 85.68% and the atomic percentage of O was 14.32%. Finally, from the SEM images of the highest concentration—nylon 6/0.1 wt% MWCNT (Figure 4i)—it is clearly visible that in addition to the deposition of MWCNTs on the surface of nylon, small-sized MWCNTs on the side walls joined them and deposited on it as a thin surface. In the elemental analysis (Figure 4j), the atomic percentage of C was determined as 89.26 and the atomic percentage of O was determined as 10.74%. In general, the atomic percentage of C increased with the increase in the concentration of MWCNT, and at the same time, it was observed from SEM images that MWCNT deposited on the surface of nylon in the form of agglomerates with the increase in concentration. At the same time, the surfaces of nylon tubes were covered with a thin layer of MWCNT at the highest concentration of 0.1 wt%. From SEM images, it is seen that MWCNTs are in physical contact with nylon. That is, it is assumed that there are van der Waals interactions between nylon and MWCNT. Thus, with the increase in concentration, van der Waals forces also increase between MWCNTs, which leads to the formation of agglomerates.

3.3. FTIR Spectroscopy Analysis

Fourier-transform infrared spectroscopy (FTIR) was used to analyze chemical bonding and to evaluate the functionalization of the nanocomposite materials. Figure 5 presents the transmittance spectra of nylon 6, f-MWCNTs, and nylon/f-MWCNTs in the range of 4000–400 cm−1. In the spectrum of nylon 6, a peak at 934 cm−1 is attributed to amide axial deformation (C–C=O). This peak shows reduced intensity in the nylon/f-MWCNTs spectrum. An absorption band at 1620 cm−1, attributed to C=C stretching in the graphitic domains of CNTs, appears with reduced intensity in the spectrum of nylon/f-MWCNTs [48]. The peak corresponding to sp2-hybridized carbon atoms, which form the CNT backbone, exhibits lower intensity due to the limited proportion of functionalized CNTs in the sample. A band near 1720 cm−1, associated with the functionalization of CNTs, becomes more prominent when f-CNTs are combined with nylon. This feature is attributed to stretching vibrations of C=O, C–O, and C–H bonds in carboxyl (–COOH) groups [49]. The carboxyl groups introduced during functionalization can form chemical bonds with amine (–NH) or carbonyl (–C=O) groups in nylon, enhancing vibrational activity in the carbonyl region and increasing peak intensity.
The intensity of the peak at 3471 cm−1, corresponding to O–H stretching vibrations of hydroxyl groups, appears with comparable intensity in both the nylon/f-MWCNTs nanocomposite and the f-MWCNTs spectrum. Peaks located at 2863 cm−1 and 2938 cm−1 are attributed to C–H stretching vibrations from alkane groups [50]. These stretching vibrations are from the methylene (–CH2) groups in the aliphatic chains of the polymer, typical of the carbonaceous nylon structure. The absence of these peaks in the f-MWCNT spectrum suggests that functionalized CNTs do not contribute to these specific vibrational modes [27].
A peak at 3064 cm−1 for the pure nylon spectrum of CH2 stretching and N–H axial deformation is associated with aromatic segments or unsaturated C–H groups in the polymer. In the nylon/f-MWCNTs spectrum, this peak shifts to 3085 cm−1, indicating changes in molecular interactions and the local chemical environment. The shift in vibrational frequency reflects structural modifications in the composite, consistent with the presence of functionalized carbon nanotubes within the polymer matrix. The peak shifts to 3085 cm−1 due to molecular interaction and environmental change in the composite material. These changes in the spectra provide valuable insight into the structural characteristics of the nanocomposite, which implies that carbon nanotubes have been effectively incorporated into the polymer matrix.

3.4. Dielectric Measurements of the Films

As can be seen from the graph of dielectric permittivity versus frequency, the dielectric permittivity at low frequencies is the smallest (1.78) in nylon, and when MWCNT is added to the nylon surface in different percentages—0.01 wt% (2.56), 0.03 wt% (2.85), 0.05 wt% (3.81), 0.1 wt% (4.75)—the dielectric permittivity value increases as a rule (Figure 6). This is due to the interfacial polarization of dipoles in the relaxation mode [25,51,52,53,54]. In other words, concerning Maxwell–Wagner polarization, polarization is due to the formation of dipoles because of the accumulation of charges at their boundary due to the interaction between two different materials—nylon and MWCNT—at the boundary due to the electrical mismatch [27]. With increasing frequency, the dielectric permittivity of the composite material decreased to lg ω = 5.5, increased at lg ω = 5.79, and then decreased again. Orientational dipolar polarization is observed here, in which the dipoles orient in the direction of the field under the influence of an external electric field. At lg ω = 5.5, the polarization was maximum at medium frequency, and with increasing frequency, since the dipoles needed time to rotate in the direction of the field and responded to the field late with increasing frequency, the polarization decreased, and the dielectric permittivity value also decreased. With increasing MWCNT concentration at both low and high frequencies, the dielectric permittivity value generally increased. This is due to the enhancement of charge accumulation and dipole orientation at the boundary interfaces due to the high conductivity and large surface area of MWCNTs. As a result, the addition of MWCNTs increases the dielectric properties of nylon through polarization mechanisms occurring at the interface.

3.5. Output Parameters of TENG

As shown in Figure 7, the TENG is composed of a nylon/f-MWCNT nanocomposite film and a polysiloxane film as the triboelectric layers, with aluminum foil functioning as the electrode and carton paper used as the structural substrate. To evaluate device performance, five TENG samples were fabricated using both unmodified nylon films and nylon/f-MWCNT nanocomposites.
The operating principle is illustrated in four stages (Figure 7). In Stage I, mechanical separation between the two triboelectric layers leads to the accumulation of positive surface charges on the nylon/MWCNT layer and negative charges on the polysiloxane surface. In Stage II, this charge distribution induces an opposite potential on the aluminum electrodes through electrostatic induction, causing electron flow between the upper and lower electrodes. In Stage III, as the separation distance increases, surface charge density rises, reaching a maximum at full separation, which corresponds to the peak current output. In Stage IV, when the layers return to contact, charge recombination occurs at the interface, reversing the direction of charge flow in the electrodes and interrupting the external current. This contact–separation cycle forms the basis of the TENG’s energy conversion process.
In Stage III, the incorporation of MWCNTs increases the local charge storage capacity of the nanocomposite, supporting a higher surface charge density at the contact interface. According to the capacitor-based model of TENGs, this increase in charge density improves electrical output by enhancing interfacial charge retention.
Output parameters of triboelectric nanogenerators (TENGs) fabricated with unmodified nylon and nylon/f-MWCNT nanocomposites at various concentrations are shown in Figure 8. The open-circuit voltage (Voc) values are presented in Figure 8a, and the short-circuit current (Isc) values appear in Figure 8b.
The open-circuit voltage values recorded were 17.5 V for unmodified nylon (i), 17.8 V for the 0.01 wt% nylon/f-MWCNT nanocomposite (ii), 22.4 V for 0.03 wt% (iii), and a maximum of 29.7 V for 0.05 wt% (iv). At 0.1 wt%, the voltage decreased to 20.3 V (v). A similar trend was observed for the short-circuit current: 1.8 μA for unmodified nylon (i), increasing to 3.0 μA at 0.05 wt% (iv), followed by a decrease to 2.2 μA at 0.1 wt% (v).
The increase in electrical output is attributed to the rise in dielectric permittivity introduced by the incorporation of MWCNTs, consistent with previous reports on CNT-based nanocomposite TENGs [24,27,52,53,54]. The presence of MWCNTs introduces additional polar groups and dipoles, which increase the dielectric constant and the effective capacitance of the system, as described by the capacitor model of triboelectric energy generation [52,53]. A higher dielectric constant supports greater surface charge storage and transfer at the interface between the nylon and polysiloxane layers.
At 0.1 wt% concentration, the decrease in output suggests that excess MWCNT content may lead to agglomeration of the nanoparticles, reducing the effective contact area between the triboelectric layers [5,27,51]. This phenomenon has been previously described in nanocomposite-based TENGs, where high filler concentrations were associated with diminished charge transfer efficiency due to percolation limits on dielectric enhancement. Furthermore, elevated MWCNT content beyond the optimal threshold may introduce conductive pathways within the dielectric layer, resulting in charge dissipation and lower triboelectric output.
This trend aligns with findings from prior work on CNT-reinforced polymer-based TENGs, where an optimal nanoparticle loading was identified, beyond which performance declined due to reduced interfacial interaction and increased aggregation [54,55]. Comparable behavior has been observed in polymer-based TENGs incorporating graphene and other carbon-based nanomaterials, where excessive filler loading led to reduced triboelectric charge density [24].
Figure 9 illustrates the influence of MWCNT concentration on the open-circuit voltage (Voc) and short-circuit current (Isc) of the fabricated nylon/MWCNT-based TENGs. The electrical output shows a distinct concentration-dependent trend: both Voc and Isc gradually increase with MWCNT loading up to 0.05 wt%, followed by a decline at 0.1 wt%. Specifically, the Voc rises from 17.5 V for the pure nylon film to a peak value of 29.7 V at 0.05 wt%, while the Isc increases from 1.8 μA to 3.0 μA. Beyond this optimum, at 0.1 wt% MWCNT, both parameters drop to 22.3 V and 2.2 μA, respectively.
These results demonstrate the critical role of filler concentration in tailoring the performance of nanocomposite-based TENGs. At lower concentrations, MWCNTs are well-dispersed within the nylon matrix, leading to an enhanced dielectric constant and increased interfacial polarization. This improved dielectric environment enables better charge storage and transfer efficiency, resulting in higher triboelectric output. The formation of a homogeneous network of conductive pathways facilitates effective charge trapping without causing electrical shorting.
However, at concentrations exceeding 0.05 wt%, agglomeration of MWCNTs becomes prominent. These aggregates disrupt the uniformity of the composite and introduce localized conductive regions, which can lead to charge leakage and a reduction in triboelectric efficiency. The trend observed here aligns with previous findings, such as those by Gulahmadov et al. (2025) [27], who reported that increasing MWCNT content in polymer matrices enhances triboelectric output up to a percolation threshold, beyond which performance deteriorates due to structural non-uniformity and leakage paths.
Figure 10 presents the variation in maximum power output and corresponding power density as a function of MWCNT concentration for the fabricated TENG samples. The maximum power output and power density of the TENGs with different MWCNT concentrations were estimated using the measured open-circuit voltage and short-circuit current. The power density was calculated by dividing the maximum power by the active contact area of the TENG films (0.0016 m2). The results show a clear dependence of power density on MWCNT content. The pure nylon TENG exhibited a power density of approximately 4.9 mW/m2, which gradually increased with MWCNT concentration, reaching a maximum power density of about 13.9 mW/m2 at 0.05 wt% MWCNT.
This enhancement is attributed to improved charge trapping and better dielectric properties provided by well-dispersed MWCNTs, which promote more effective triboelectric charge generation and transfer. When the MWCNT concentration increased beyond 0.05 wt%, the power density decreased to around 7.7 mW/m2 at 0.1 wt%. This reduction likely results from MWCNT agglomeration, which reduces the effective contact area and increases charge leakage, thereby lowering the output power. These findings underscore the importance of optimizing MWCNT loading to maximize the power density and overall performance of nylon-based TENGs. The significant increase in power density at 0.05 wt% MWCNT demonstrates the potential of nanocomposite engineering to enhance energy harvesting capabilities in triboelectric devices [56].
The increase in power density at 0.05 wt% is attributed to improved charge trapping and enhanced dielectric properties due to well-dispersed MWCNTs, promoting more effective triboelectric charge generation and transfer. The decrease at higher concentrations results from MWCNT agglomeration, which reduces the effective contact area and increases charge leakage, thereby lowering output power.
Mechanical durability and wear resistance of the triboelectric layer are essential for practical TENG applications. Although wear testing was not conducted here, the incorporation of MWCNTs into nylon is expected to enhance mechanical robustness and wear resistance relative to pure polymer films. Recent studies confirm that adding MWCNTs to polymer matrices significantly improves wear resistance up to an optimal concentration, beyond which agglomeration negatively impacts performance [57,58,59]. Thus, controlling the dispersion and loading of MWCNTs is key to balancing mechanical stability with triboelectric efficiency.
These findings emphasize the importance of optimizing filler content to balance dielectric enhancement and material stability, maximizing the triboelectric energy harvesting performance of nylon/MWCNT nanocomposite TENGs.

4. Conclusions

This study investigated the impact of MWCNT concentration on the dielectric properties and output performance of nylon-based TENGs fabricated via the spin coating method. The results demonstrate a clear correlation between MWCNT loading, dielectric enhancement, and energy conversion efficiency. Dielectric characterization revealed that the incorporation of f-MWCNTs significantly increased the dielectric permittivity of the nylon matrix, primarily due to interfacial polarization effects and enhanced dipole orientation. The maximum dielectric constant was observed at 0.1 wt% f-MWCNT; however, the optimal triboelectric performance was recorded at 0.05 wt%. This concentration provided the highest open-circuit voltage (29.7 V), short-circuit current (3.0 μA), and power density (13.9 mW/m2), confirming it as the most effective loading level for energy harvesting applications.
At higher concentrations (0.1 wt%), electrical output declined due to nanoparticle agglomeration, which reduced effective interfacial contact, introduced conductive leakage paths, and impaired charge retention. These findings underscore the critical importance of controlling nanofiller dispersion and avoiding excessive filler content to prevent the formation of non-uniform conductive domains that compromise TENG efficiency.
Moreover, the study affirms the validity of the capacitor-based model for interpreting triboelectric performance in nanocomposite systems, linking dielectric enhancement with surface charge density and energy output. The spin coating technique proved effective for achieving homogeneous film formation, enabling reliable control over material morphology and functional properties. These results are valuable for guiding the design of next-generation TENGs with optimized nanocomposite compositions for wearable electronics, low-power sensing systems, and sustainable energy harvesting technologies.

Author Contributions

O.G. contributed to the conceptualization and drafting of the original manuscript. L.G. assisted in conducting the XRD analysis of the samples, reviewed the manuscript, and contributed to interpretation of the results. T.H. and S.B. (Shafag Bayramova) assisted in conducting the SEM and EDS analysis of the samples. M.M. contributed to the conceptualization and provided supervision. J.B.G. supported sample acquisition and analysis. T.T., S.B. (Stefano Bellucci), and C.V.G. supervised the study, reviewed the manuscript, and contributed to editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially funded and supported by the Universidad Técnica Particular de Loja under grant No.: POA_VIN-56. This work was partially funded by the European Cooperation in Science and Technology (COST) under Action CA19118—High-Performance Carbon-Based Composites with Smart Properties for Advanced Sensing Applications (EsSENce). This work is also supported in part by a project funded by Romania’s National Recovery a Resilience Plan (PNRR), component C9. Support for the private sector, research, development and innovation “I8. Development of a program to attract highly specialised human resources from abroad in research, development and innovation activities”, entitled “Composite materials for the applications in the water management field”, ID-11/26.07.2023, contract number 760270/26.03.2024.

Data Availability Statement

All data used in this study are available upon request from the corresponding author.

Acknowledgments

The authors would like to thank the members of the NanoResearch Laboratory at Baku State University for their technical support and collaborative discussions throughout the study.

Conflicts of Interest

The corresponding author, on behalf of all authors, declares that there are no conflicts of interest related to this work.

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Figure 1. Fabrication of Nylon/MWCNT-based nanocomposite thin films via spin coating method.
Figure 1. Fabrication of Nylon/MWCNT-based nanocomposite thin films via spin coating method.
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Figure 2. Fabrication of nylon (a) and polysiloxane (b) thin films for TENG.
Figure 2. Fabrication of nylon (a) and polysiloxane (b) thin films for TENG.
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Figure 3. XRD pattern of (a) pure nylon 6 and different percentage nylon 6/MWCNT composite materials: (b) 0.01%, (c) 0.03%, (d) 0.05%, (e) 0.1%.
Figure 3. XRD pattern of (a) pure nylon 6 and different percentage nylon 6/MWCNT composite materials: (b) 0.01%, (c) 0.03%, (d) 0.05%, (e) 0.1%.
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Figure 4. SEM images and EDS analysis of samples: SEM images: (a) pure nylon 6; (c) nylon 6/0.01 wt% MWCNT; (e) nylon 6/0.03 wt% MWCNT; (g) nylon 6/0.05 wt% MWCNT; (i) nylon 6/0.1 wt% MWCNT. EDS analysis: (b) pure nylon 6; (d) nylon 6/0.01 wt% MWCNT; (f) nylon 6/0.03 wt% MWCNT; (h) nylon 6/0.05 wt% MWCNT; (j) nylon 6/0.1 wt% MWCNT.
Figure 4. SEM images and EDS analysis of samples: SEM images: (a) pure nylon 6; (c) nylon 6/0.01 wt% MWCNT; (e) nylon 6/0.03 wt% MWCNT; (g) nylon 6/0.05 wt% MWCNT; (i) nylon 6/0.1 wt% MWCNT. EDS analysis: (b) pure nylon 6; (d) nylon 6/0.01 wt% MWCNT; (f) nylon 6/0.03 wt% MWCNT; (h) nylon 6/0.05 wt% MWCNT; (j) nylon 6/0.1 wt% MWCNT.
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Figure 5. FTIR spectrum of (a) nylon, (b) f-MWCNTs, and (c) nylon/f-MWCNTs.
Figure 5. FTIR spectrum of (a) nylon, (b) f-MWCNTs, and (c) nylon/f-MWCNTs.
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Figure 6. Frequency dependence of dielectric constant at different concentrated MWCNT loadings in nylon matrix.
Figure 6. Frequency dependence of dielectric constant at different concentrated MWCNT loadings in nylon matrix.
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Figure 7. The working mechanism of the TENG with the nylon/f-MWCNTs films.
Figure 7. The working mechanism of the TENG with the nylon/f-MWCNTs films.
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Figure 8. Output performance of TENGs based on different concentrated f-MWCNT in nylon/f-MWCNT nanocomposites: (a) open-circuit voltage and (b) short-circuit current.
Figure 8. Output performance of TENGs based on different concentrated f-MWCNT in nylon/f-MWCNT nanocomposites: (a) open-circuit voltage and (b) short-circuit current.
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Figure 9. Dependence maximum value of UOC and ISC of different concentrated f-MWCNT in nylon/f-MWCNT nanocomposites for TENGs.
Figure 9. Dependence maximum value of UOC and ISC of different concentrated f-MWCNT in nylon/f-MWCNT nanocomposites for TENGs.
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Figure 10. Maximum power output and power density of fabricated TENGs.
Figure 10. Maximum power output and power density of fabricated TENGs.
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Table 1. Review: main parameters, advantages, and limitations of TENGs based on CNT composite materials.
Table 1. Review: main parameters, advantages, and limitations of TENGs based on CNT composite materials.
MaterialsOutput (Voc/Isc)Power/Power DensityAdvantagesLimitationsReference
SWCNTs, PI, PDMS170 nA-High sensitivity, flexible design, self-powered, simple fabricationLimited resolution, durability, scalability issues[33]
SWCNTs, MWCNTs, PDMS, Ag NWs 760 V,
51 µA		19.2 mW
0.77 mW/cm2 		High output, charge retention, simple fabrication, wearable designDurability, scalability[34]
MWCNTs, Silk fibroin, PET/ITO 184 V,
6.13 µA 		317.4 μW/cm2Durable, flexible, and straightforwardEnvironmental durability, long-term stability[35]
MWCNTs, PDMS, Kapton6.6 V,
25.7 µA 		1.98 mW
3.29 W/m2		Enhanced output, flexible designDurability untested, stability unknown[36]
MWCNTs, PDMS, Ag435 V3.7 mW/cm2High output, flexible, hydrophobicStability issues, scalability, no storage integration[37]
PAN, MWCNTs, Al, PET24 V48 mW/m2Improved power density, enhanced charge mobility, wearable sensing potentialLimited environmental stability, scale-up complexity, lacks storage integration[38]
PDMS, MWCNTs, Al, PET249 V, 28.03 µA2.81 W/m2High output, flexible design, haptic potentialLimited durability, scalability issues, no energy storage[39]
Nylon, MWCNT, Polysiloxane29.7 V,
3.0 μA		13.9 mW/m2High dielectric permittivity, good dispersion, easy processingAgglomeration at >0.05 wt% reduces performanceThis work
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Tene, T.; Gulahmadov, O.; Gahramanli, L.; Muradov, M.; Gilev, J.B.; Hamzayeva, T.; Bayramova, S.; Bellucci, S.; Vacacela Gomez, C. Influence of MWCNT Concentration on Performance of Nylon/MWCNT Nanocomposite-Based Triboelectric Nanogenerators Fabricated via Spin Coating Method. Nanoenergy Adv. 2025, 5, 9. https://doi.org/10.3390/nanoenergyadv5030009

AMA Style

Tene T, Gulahmadov O, Gahramanli L, Muradov M, Gilev JB, Hamzayeva T, Bayramova S, Bellucci S, Vacacela Gomez C. Influence of MWCNT Concentration on Performance of Nylon/MWCNT Nanocomposite-Based Triboelectric Nanogenerators Fabricated via Spin Coating Method. Nanoenergy Advances. 2025; 5(3):9. https://doi.org/10.3390/nanoenergyadv5030009

Chicago/Turabian Style

Tene, Talia, Orkhan Gulahmadov, Lala Gahramanli, Mustafa Muradov, Jadranka Blazhevska Gilev, Telli Hamzayeva, Shafag Bayramova, Stefano Bellucci, and Cristian Vacacela Gomez. 2025. "Influence of MWCNT Concentration on Performance of Nylon/MWCNT Nanocomposite-Based Triboelectric Nanogenerators Fabricated via Spin Coating Method" Nanoenergy Advances 5, no. 3: 9. https://doi.org/10.3390/nanoenergyadv5030009

APA Style

Tene, T., Gulahmadov, O., Gahramanli, L., Muradov, M., Gilev, J. B., Hamzayeva, T., Bayramova, S., Bellucci, S., & Vacacela Gomez, C. (2025). Influence of MWCNT Concentration on Performance of Nylon/MWCNT Nanocomposite-Based Triboelectric Nanogenerators Fabricated via Spin Coating Method. Nanoenergy Advances, 5(3), 9. https://doi.org/10.3390/nanoenergyadv5030009

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