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Article

Synergistic Integration of Drop-Casting with Sonication and Thermal Treatment for Fabrication of MWCNT-Coated Conductive Cotton Fabrics

by
Muhammad Shahbaz
1 and
Hiroshi Furuta
1,2,*
1
Graduate School of Engineering, Kochi University of Technology, Kochi 782-8502, Japan
2
Research Institute, Kochi University of Technology, Kochi 782-8502, Japan
*
Author to whom correspondence should be addressed.
Crystals 2026, 16(1), 60; https://doi.org/10.3390/cryst16010060
Submission received: 15 December 2025 / Revised: 8 January 2026 / Accepted: 10 January 2026 / Published: 14 January 2026
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Abstract

This study introduces a synergistic drop-casting, sonication, and thermal treatment (DSTT) method for fabricating multi-walled carbon nanotube (MWCNT)-coated conductive cotton fabrics. The process produced uniform MWCNT networks with a minimum sheet resistance of 0.072 ± 0.004 kΩ/sq. at ~30 wt.% loading. Scanning electron microscopy confirmed an improved MWCNT network. Reproducibility was demonstrated for different fabric sizes, with resistance values remaining consistent within experimental errors. Stability tests showed only minor changes in sheet resistance after 16 weeks of ambient storage and periodic manual bending. Compared to conventional methods such as room-temperature drying, vacuum drying, and sonication alone, DSTT consistently performed better, yielding fabrics with lower resistance and more reliable conductivity. These results highlight DSTT as a reproducible and scalable method for producing conductive cotton fabrics suitable for smart textiles and wearable electronics.

1. Introduction

Conductive fabrics represent a transformative class of materials at the intersection of traditional textiles and advanced electronics. These hybrid materials are designed to exhibit electrical conductivity while retaining the fundamental properties of fabrics, such as flexibility, breathability, comfort, and durability. The integration of conductivity into conventional textiles enables the development of next-generation applications that extend far beyond clothing, encompassing fields such as electronic skin [1], strain sensors [1,2], wearable antennas [3,4], military applications [5,6] and energy storage devices such as textile-based supercapacitors [4,7,8,9,10]. Therefore, the rapid progress of wearable electronics has created strong demand for reliable, lightweight, and mechanically robust conductive fabrics.
Different strategies have been developed to introduce conductivity into fabrics, which are broadly categorized into polymerization-based processes [11], surface coating [12,13,14] and advanced printing methods [11,15,16,17]. Among these, surface coating techniques are particularly attractive because they allow versatile control over the loading, layering, and patterning of conductive materials without changing the inherent textile structure. Within this category, drop-casting has emerged as one of the simplest and most widely used deposition methods in material research [12,14,18]. This technique has been successfully adapted to integrate conductive elements into textile substrates [19,20,21].
Cotton is considered one of the most promising substrates for conductive textiles. As an abundant, natural, and biodegradable fibre, it offers advantages that extend beyond comfort and mechanical durability [12]. Cotton has a high surface area due to its porous microstructure and twisted ribbon morphology, which facilitates penetration and anchoring of nanomaterials. Furthermore, its intrinsic softness, and biocompatibility make cotton particularly suitable for applications that require direct and prolonged skin contact [22].
Materials such as silver, copper, and nickel offer high electrical conductivity, making them suitable for applications that require robust electrical performance. However, metals can add weight, reduce flexibility and are prone to corrosion, thus limiting their use in flexible and washable textiles [23,24]. On the other hand, polymers, such as polyaniline and poly(3,4-ethylenedioxythiophene) (PEDOT), are lightweight, flexible, and ideal for wearable applications. However, their conductivity is generally lower than that of metals or carbon materials and may degrade over time [25,26]. In contrast, carbon-based materials such as graphene and CNTs offer a balance of high conductivity, low density, chemical stability, and excellent mechanical strength [27,28,29]. Multiwalled carbon nanotubes (MWCNTs) are particularly attractive because of their exceptional electrical and thermal conductivities, robust mechanical reinforcement properties, and resilience against environmental degradation, making them ideal candidates for functionalizing textiles. CNT-based inks and dispersions have attracted significant attention as solution-processable conductive materials for thin-film deposition, printing, and coating on both rigid and flexible substrates [30,31,32,33,34,35]. In particular, MWCNT dispersions have been widely employed to form percolative conductive networks with high mechanical robustness and electrical stability, allowing applications ranging from transparent and flexible thin films to conductive and wearable fabrics [32,36,37]. A recent comprehensive review [38] highlighted that CNT-polymer composites exhibit significant advancements in mechanical, electrical, and thermal properties, and emphasized that the dispersion of CNTs within various manufacturing techniques, such as melt mixing, solution mixing, and in situ polymerization, significantly impacts the properties of the composite material. Previous studies have demonstrated that properly dispersed MWCNT inks, including alcohol-based systems, allow low-temperature processing and good substrate compatibility, which are critical for textile electronics and flexible devices [33,34,35].
Conductive textiles can be realized either by assembling free-standing CNT nonwoven structures or by coating CNTs onto conventional textile substrates such as cotton. While CNT nonwoven fabrics can provide high intrinsic conductivity, they differ from conventional garments in terms of textile handling, flexibility, and breathability. In contrast, CNT-coated cotton fabrics retain the mechanical compliance and comfort of the base textile while introducing electrical functionality, which motivates the focus of the present study.
Several studies have reported MWCNT-coated cotton fabrics prepared by different methods. Alamer et al. [39] achieved conductivity through drop-casting of MWCNT dispersions. Xu et al. [40] used functionalized CNTs in an impregnation–drying process to improve stability. Dyeing techniques have also been applied, providing uniform deposition of CNT at higher resistances [41]. Rahman et al. [42] employed a dip and dry technique, demonstrating the progress made in incorporating CNTs into cotton fabrics and highlighting the versatility of coating-based approaches.
Building on these advances, this study introduces a novel method that integrates drop casting, sonication, and thermal treatment into a single process, called DSTT. Each of these steps has been studied separately or partially combined [12,39], but their combination in a workflow for MWCNT-coated cotton fabrics has not been reported. Drop-casting provides a straightforward yet controlled route for depositing MWCNTs on textile substrates [39]. Sonication is commonly employed in the solution phase to de-bundle CNTs and improve dispersion uniformity prior to deposition [43]. Conventional dip-coating or impregnation–drying approaches rely on passive uptake of CNT dispersions by textile substrates and often require multiple coating cycles or chemical functionalization to achieve sufficient conductivity [40,41,42]. Plasma or chemical surface treatments have also been reported to enhance CNT adhesion by modifying fibre surface chemistry, but these methods typically involve additional processing steps and specialized equipment [40,42]. In contrast, the DSTT method introduced here applies sonication during deposition, actively assisting the penetration of CNT and network formation within the cotton fibres. Finally, mild thermal treatment at 100 °C promotes physical consolidation of the CNT network by removing residual solvent and enabling closer CNT–CNT contact through van der Waals interactions and network densification. This process does not involve chemical bonding or curing, but instead acts as a low-temperature thermal treatment step commonly used to stabilize CNT networks in cotton-based textiles [42,44,45]. The integration of these steps is expected to yield a more homogeneous coverage, consistent conductivity, and reliable stability.
To evaluate this approach, four fabrication conditions were investigated: drop-casting at room temperature, drop-casting with vacuum drying, drop-casting with sonication, and the integrated DSTT process. All samples were prepared using cotton fabric as the substrate. Since electrical conductivity is a vital factor in the advancement of smart textiles for wearable electronic applications [46], a direct comparison of these fabrication methods was carried out. The results demonstrate the effectiveness of DSTT in producing highly conductive fabrics. Reproducibility across fabric sizes and stability were evaluated over a 16-week period for DSTT samples, confirming its potential as a scalable and practical method for smart textiles and wearable electronic devices. The conductive MWCNT cotton fabrics were analyzed using scanning electron microscopy (SEM), and their electrical properties were evaluated on the basis of MWCNT concentration.

2. Materials and Methods

2.1. Materials

Commercial cotton fabric was used as the substrate and cut into square pieces of 2.5 × 2.5 cm2. Cotton was chosen for its abundance, porous structure, and suitability for wearable applications. A commercial dispersion of multi-walled carbon nanotubes (MWCNT) in ethanol (5 wt.%, product name: MW-I) was obtained from Meijo Nanocarbon Co., Ltd. (Nagoya, Japan). The MWCNTs had diameters ranging from 10 to 40 nm [47]. Acetone was used as received for cleaning and processing. All materials were handled under ambient laboratory conditions without further purification.

2.2. Fabrication of MWCNT-Coated Conductive Cotton Fabrics

2.2.1. DSTT Method

The Pristine Cotton fabric (2.5 × 2.5 cm2) was first cleaned in acetone for 1 min, dried at room temperature for 10 min and weighed. The dried cotton fabric was then placed in a Petri dish, which was placed on a stainless-steel support bar inside a laboratory ultrasonic cleaner operating at 38 kHz. The cleaner tank was filled with water and ultrasonic waves were transmitted through the support to the Petri dish, providing indirect sonication during processing (Figure 1). The experimental setup corresponding to the schematic shown in Figure 1 is presented in Figure 2.
For coating, 500 ± 10 μL of the MWCNT dispersion was dropped immediately onto the fabric surface. To increase the CNT content, the coating was repeated in successive cycles, with an additional 500 μL of dispersion applied in each cycle. After each drop-casting step, sonication was maintained for 30 min, during which the bath temperature rose to approximately 50 °C due to oscillation.
After deposition, the coated samples were transferred to a vacuum heater and heated at 100 °C for 1 h. After treatment, the samples were weighed again and the MWCNT loading was calculated using the following equation [39]:
C w t . % =   C 2 − C 1 C 2   × 100  
where C2 is the weight of the conductive MWCNT coated cotton and C1 is the weight of the pristine cotton. After coating and final weighing, the samples were stored under ambient laboratory conditions until further testing.

2.2.2. Comparative Fabrication Conditions

For comparison, three additional fabrication routes were investigated using the same fabric size and CNT dispersion volume per coating cycle (500 ± 10 μL). In each method, the coating was repeated in successive cycles to increase the CNT content, consistent with the DSTT process. The procedures were as follows:
  • Drop-casting at room temperature: CNT dispersion was drop-cast onto the cotton fabric, which was then dried naturally under ambient conditions.
  • Drop-casting with vacuum drying: After drop casting, the coated fabric was placed in a vacuum heater at 100 °C for 1 h.
  • Drop-casting with sonication: The CNT dispersion was drop-cast onto the fabric placed in a Petri dish on a stainless steel support inside the ultrasonic cleaner (38 kHz). Following deposition, sonication was maintained for 30 min, and the fabric was subsequently dried at room temperature.
These three conditions served as reference methods to assess the relative effectiveness of the integrated DSTT approach.

2.3. Characterization Techniques

The sheet resistance of the MWCNT-coated cotton fabrics was measured using a four-point probe method (Loresta GP, MCP-T610, Mitsubishi Chemical Corporation, Tokyo, Japan) at room temperature. At each measurement position, the sheet resistance was recorded three times. Measurements were performed at nine different positions across the sample surface, and the average value was reported. This procedure was adopted to validate measurement consistency and minimize operator-related variability. Scanning electron microscopy (SU8020, Hitachi High-Tech Corporation, Tokyo, Japan) was used to investigate the surface morphology of the pristine and MWCNT-coated cotton fabrics.

3. Results and Discussion

3.1. Electrical Performance of MWCNT-Coated Fabrics

Electrical performance of the MWCNT-coated cotton fabrics was systematically evaluated as a function of the fabrication route and the coating cycle. The results are summarized in Figure 3, which presents both the complete resistance range and a magnified view of the low resistance region for clarity.
For simple drop-casting at room temperature, the fabrics exhibited very high sheet resistances. After the first coating, the resistance was 9.590 ± 1.690 kΩ/sq. at approximately 12 wt.%, and although additional coatings increased the CNT loading, the values remained in the kiloohm range. After six cycles (36.5 wt.%), the resistance decreased only to 4.690 ± 0.540 kΩ/sq. This poor performance indicates discontinuous CNT coverage and limited infiltration into the cotton fibre network.
Introducing vacuum drying after drop-casting produced only moderate improvement. Resistance decreased from 8.200 ± 1.090 kΩ/sq. after one coating (11.5 wt.%) to 4.810 ± 0.720 kΩ/sq. after six coatings (35.2 wt.%), but overall values were still too high after thermal treatment alone.
On the contrary, sonication during deposition greatly enhanced the conductivity. After one coating, the resistance dropped to 1.902 ± 0.150 kΩ/sq. at 8.2 wt.%. With additional coatings, the sheet resistance decreased rapidly, reaching 0.259 ± 0.016 kΩ/sq. after five cycles (26.8 wt.%) and 0.143 ± 0.008 kΩ/sq. after six cycles (31.4 wt.%). Sonication was therefore essential for uniformly dispersing CNTs within the porous cotton structure and forming interconnected conductive networks.
The DSTT process, which combines drop-casting, sonication, and mild thermal treatment, yielded the lowest sheet resistances among all routes. After one cycle, the resistance was 1.196 ± 0.047 kΩ/sq. at 7.8 wt.%. With successive coatings, the values decreased to 0.534 ± 0.040 kΩ/sq. after three cycles (16.3 wt.%), 0.171 ± 0.007 kΩ/sq. after five cycles (25.3 wt.%), and 0.072 ± 0.004 kΩ/sq. after six cycles (30.1 wt.%). The improvement compared to sonication alone, particularly at higher loadings, reflects the additional benefit of mild thermal consolidation, which stabilizes the CNT network through solvent removal and densification, thereby reducing resistance without inducing chemical bonding.
In summary, the comparison establishes a clear performance order: Room-temperature < Vacuum drying < Sonication < DSTT.
Although sonication is crucial for CNT dispersion and penetration into the fibre matrix, its combination with mild thermal treatment produces denser and more uniform networks that yield the highest electrical conductivity. Therefore, the DSTT route represents the most effective fabrication strategy for wearable and flexible electronic textile applications.

3.2. Morphological Analysis

Figure 4 presents optical photographs of pristine cotton and DSTT-coated cotton fabrics of two different sizes. The coated samples exhibit a visually uniform macroscopic CNT distribution across the full fabric area for both 2.5 × 2.5 cm2 and 3.0 × 3.0 cm2 sizes, with no obvious center-to-edge contrast related to the initial drop-casting location. This macroscopic uniformity is attributed to the porous structure of cotton combined with sonication-assisted deposition, which promotes redistribution of the CNT dispersion beyond the initially wetted region.
The surface morphology of pristine and MWCNT-coated cotton fabrics was examined using SEM, as shown in Figure 5. The pristine cotton fibre (Figure 5a) exhibits a smooth surface without any noticeable nanostructure.
For fabrics prepared by drop-casting at room temperature, the MWCNT network appeared to be discontinuous and uneven (Figure 5b). The nanotubes formed localized separated regions on the fibre surface with minimal penetration into the cotton fabric, resulting in weak inter-fibre connections. This irregular morphology is consistent with the high sheet resistance measured for these samples.
The addition of vacuum drying after drop-casting led to a slight improvement in the uniformity of the coating (Figure 5c). Partial adhesion of MWCNTs to the fibre surface was observed; however, separated regions were still present, indicating incomplete network formation. This explains the moderate reduction in sheet resistance achieved by this method.
On the contrary, sonication-assisted deposition resulted in a more uniform distribution of MWCNTs on cotton fibres (Figure 5d). The nanotubes aligned along the cotton fibres, forming a more continuous coating with fewer agglomerates. This improved uniformity and surface coverage correspond to a significant reduction in the sheet resistance, suggesting the formation of an effective conductive network.
The most homogeneous and interconnected coating was obtained using the DSTT method, which combines sonication with thermal treatment (Figure 5e). In this case, the MWCNTs were firmly attached to the fibre surface, forming a compact, and continuous conductive layer. This morphology provides efficient charge transport pathways, resulting in the lowest sheet resistance among all fabrication methods.
Cross-sectional SEM analyses are shown in Figure 6a,b for conductive fabrics prepared by drop-casting at room temperature and by the DSTT method, respectively. These images highlight the difference in MWCNT penetration, coating uniformity and network connectivity between the two fabrication approaches. Figure 6a shows that drop-casting at room temperature forms a limited and uneven nanotube layer, with most MWCNTs remaining on the surface and weak inter-fibre contact. Figure 6b shows that the DSTT method produces a more compact, continuous and deeply penetrated MWCNT network across the fibre cross sections.
Additional cross-sectional SEM images of the pristine cotton fabric and the samples prepared using all four methods (drop-casting at room temperature, drop-casting followed by thermal treatment, sonication-assisted coating and DSTT) are provided in the Supplementary Data (Figures S1–S5).
In addition to microscopic observations, the macroscale appearance of the DSTT-coated 3.0 × 3.0 cm2 cotton fabric was visually examined under manual bending. As shown in Figure 7, no obvious surface cracking or delamination was observed by naked-eye inspection during bending, indicating that the MWCNT coating remains visually intact under moderate deformation. A video of the manual bending procedure is provided in the Supplementary Information (Video S1).
In summary, the DSTT method forms a uniform and stable MWCNT network with strong inter-fibre bonding and deep penetration into the cotton structure. This continuous and well-integrated layer supports reliable electrical pathways and contributes to the improved performance of the DSTT-coated conductive fabric.

3.3. Size Consistency of Electrical Performance in DSTT-Coated Fabrics

Since the DSTT process produced the lowest sheet resistances among all coating methods tested, we investigated whether this performance is maintained when the coated area is increased. Cotton fabrics of 3.0 × 3.0 cm2 were coated using the same six-cycle DSTT protocol as the original 2.5 × 2.5 cm2 samples. The mean sheet resistances and their standard deviations for each coating cycle are summarized in Table 1 and plotted in Figure 8.
Both fabric sizes show a monotonic decline in sheet resistance with increasing coating cycles. For 2.5 × 2.5 cm2 samples the resistance falls from 1.196 ± 0.047 kΩ/sq. after cycle 1 to 0.072 ± 0.004 kΩ/sq. after cycle 6. The 3.0 × 3.0 cm2 samples exhibit a similar trend, decreasing from 1.250 ± 0.069 kΩ/sq. to 0.078 ± 0.005 kΩ/sq. across the same range of cycles. These values are very close despite the 44% increase in sample area, suggesting that the CNT coating is sufficiently uniform at both scales.
To determine whether the small differences between the two sizes are meaningful, we compared the absolute difference between the mean resistances at each cycle with the combined measurement uncertainty, calculated as the square root of the sum of the individual variances. As illustrated in Figure 9a,b, the difference for each cycle is well below this combined uncertainty, which means the resistance values for the two fabric sizes are statistically indistinguishable. This analysis indicates that the DSTT coating retains its electrical performance when the area is scaled up. A more detailed uncertainty analysis, including the propagation of uncertainties and the calculation of combined standard deviations, is provided in Supplementary Table S1a,b.

3.4. Stability of Sheet Resistance in MWCNT-Coated Cotton Fabrics

To assess the combined effects of environmental aging and mechanical deformation on electrical stability, the sheet resistance was re-measured after 16 weeks of ambient storage during which the fabrics were also subjected to periodic manual bending. Measurements were made for both 2.5 × 2.5 cm2 and 3.0 × 3.0 cm2 samples prepared under identical coating cycles.
For 2.5 × 2.5 cm2 fabrics, the sheet resistance increased slightly from 1.196 ± 0.047 kΩ/sq. to 1.340 ± 0.100 kΩ/sq. at the lowest MWCNT loading (~7.8 wt.%) and from 0.072 ± 0.004 kΩ/sq. to 0.084 ± 0.006 kΩ/sq. at the highest loading (~30.1 wt.%), as shown in Figure 10a. The gradual change across all coating cycles suggests minor environmental or interfacial effects, such as weak oxidation or contact ageing, rather than any structural degradation of the conductive network.
A similar trend was observed for the 3.0 × 3.0 cm2 fabrics. The sheet resistance rose from 1.250 ± 0.069 kΩ/sq. to 1.390 ± 0.112 kΩ/sq. at the lowest MWCNT content (~6.9 wt.%) and from 0.078 ± 0.005 kΩ/sq. to 0.092 ± 0.008 kΩ/sq. at the highest loading (~29.3 wt.%), as shown in Figure 10b. These small increases are within the range of expected fluctuations due to atmospheric exposure and handling, and the value remains well below 0.200 kΩ/sq., indicating reliable electrical functionality.
The maintained low standard-deviation percentages confirm that the DSTT-coated networks preserve high uniformity and minimal variation between measurements. The results collectively demonstrate that the DSTT process provides stable, well-connected MWCNT films whose sheet resistance remains consistent even after extended environmental exposure and manual bending. Such stability verifies the suitability of this coating method for wearable and flexible electronic textiles. The complete numerical data set for both initial and 16-week measurements are summarized in Supplementary Tables S2 and S3.

3.5. Discussion

Table 2 provides a comparison of the sheet resistance values for MWCNT-coated cotton fabrics prepared using different fabrication methods. These studies show a wide variation in electrical performance depending on the dispersion medium, the deposition route, and the post-treatment conditions. In this context, the DSTT method used in the present work combines sonication with mild thermal treatment at 100 °C, providing a straightforward and scalable route. This approach achieves a practical balance between conductivity, consistency, and textile compatibility without the need for harsh conditions, high CNT loadings, or additional hybrid materials.
Conventional CNT coating techniques for textiles, including dip-coating, spray-coating, and plasma-assisted treatments, are widely used due to their compatibility with large-area and continuous processing. However, these methods often require repeated coating cycles, chemical functionalization, or additional surface treatments to obtain stable electrical performance. The DSTT process is currently implemented as a batch-based method, and its limitations are mainly related to process configuration rather than fundamental constraints. Adaptation of the ultrasonic-assisted coating concept to controlled coating or flow-based systems may provide possible routes toward improved scalability.
The MWCNT-coated cotton fabric developed in this study is intended for strain sensing applications and is not designed for direct contact with human skin. In practical wearable systems, the conductive fabric would be incorporated within a multilayer structure that includes a protective or insulating layer to ensure user safety and comfort. Compared with CNT nonwoven or buckypaper structures, CNT-coated cotton fabrics retain the flexibility and handling characteristics of conventional textiles, which motivated the material choice in this work.
In addition to electrical conductivity, CNT-coated cotton fabrics reported in the literature have been associated with other functional characteristics such as thermal conductivity, flame resistance, mechanical strength, and modified wettability. These properties were not evaluated in the present study, as the focus is on the fabrication strategy and electrical performance relevant to strain sensing applications. However, the conductive cotton fabric developed here may serve as a general conductive textile platform, and its potential for multipurpose applications could be explored in future work. Repeated coating cycles in the DSTT process were used as a controlled means to adjust CNT loading and electrical percolation without introducing additional materials or changes in processing chemistry. Long-term stability was verified through ambient storage for up to 16 weeks and mechanical deformation, but the washing test was not conducted, as this evaluation depends on the intended application and will be addressed in future work.
The DSTT approach demonstrated here is optimized for cotton substrates, whose porous and hydrophilic structure facilitates CNT ink penetration and network formation. Extension of this method to other textile substrates with different fibre chemistry or morphology may require substrate-specific optimization and remains open for future studies.

4. Conclusions

The synergistic method of drop-casting, sonication, and thermal treatment (DSTT) proved to be an effective approach for producing highly conductive MWCNT-coated cotton fabrics. Compared to conventional fabrication routes, DSTT consistently produced lower sheet resistance, reaching 0.072 ± 0.004 kΩ/sq. at ~30 wt.% loading, and demonstrated consistent performance across different fabric sizes. Statistical validation confirmed that the observed trends were robust, while long-term stability tests showed only minor changes in conductivity after 16 weeks under ambient conditions and manual bending. Together, these results highlight DSTT as a reproducible and scalable process that combines high conductivity with durability. The method provides a reliable platform for advancing smart textiles and wearable electronics, and future efforts can build on this foundation by tailoring process parameters for specific device applications such as strain sensing, electrothermal fabrics, or energy storage.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/cryst16010060/s1, Figures S1–S5: Cross-sectional SEM analysis of pristine and MWCNT-coated cotton fabrics prepared using different fabrication methods; Table S1a,b: Combined measurement uncertainty analysis of sheet resistance values for different fabric sizes (initial and after 16 weeks); Tables S2 and S3: Sheet resistance values of 2.5 × 2.5 cm2 and 3 × 3 cm2 MWCNT-coated cotton fabrics (initial and after 16 weeks); Video S1: Macroscale visual inspection of DSTT-coated 3.0 × 3.0 cm2 cotton fabric under manual bending deformation.

Author Contributions

Conceptualization, M.S. and H.F.; methodology, M.S. and H.F.; validation, H.F.; investigation, M.S. and H.F.; writing—original draft preparation, M.S.; writing—review and editing, H.F.; visualization, M.S. and H.F.; supervision, H.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data generated or analyzed during this study are included in this published article as well as available in supplementary data.

Acknowledgments

The authors would like to thank Saiful Islam (Kochi University of Technology, Japan) for providing technical support.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DSTTDrop-casting, Sonication, and Thermal Treatment
MWCNTMulti-Walled Carbon Nanotube
CNTCarbon Nanotube
SEMScanning Electron Microscopy
PEDOTPoly(3,4-ethylenedioxythiophene)
DMFN,N-Dimethylformamide
SDSSodium dodecyl sulfate

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Figure 1. Schematic representation of the DSTT method (drop-casting, sonication, and thermal treatment) for fabricating MWCNT-coated conductive cotton fabrics.
Figure 1. Schematic representation of the DSTT method (drop-casting, sonication, and thermal treatment) for fabricating MWCNT-coated conductive cotton fabrics.
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Figure 2. Photograph of the experimental setup used for the DSTT process.
Figure 2. Photograph of the experimental setup used for the DSTT process.
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Figure 3. Variation in sheet resistance (kΩ/sq.) with MWCNT loading for fabrics prepared by four fabrication methods: (a) full resistance range (0–15 kΩ/sq.), and (b) magnified low-resistance region (0–3 kΩ/sq.).
Figure 3. Variation in sheet resistance (kΩ/sq.) with MWCNT loading for fabrics prepared by four fabrication methods: (a) full resistance range (0–15 kΩ/sq.), and (b) magnified low-resistance region (0–3 kΩ/sq.).
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Figure 4. Optical photographs of pristine cotton fabric and MWCNT-coated cotton fabrics prepared by the DSTT method.
Figure 4. Optical photographs of pristine cotton fabric and MWCNT-coated cotton fabrics prepared by the DSTT method.
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Figure 5. SEM images of pristine and MWCNT-coated cotton fabrics prepared by different methods: (a) pristine cotton, (b) drop-casting at room temperature, (c) drop-casting at room temperature with post thermal vacuum heating, (d) drop-casting at room temperature with sonication, and (e) DSTT method.
Figure 5. SEM images of pristine and MWCNT-coated cotton fabrics prepared by different methods: (a) pristine cotton, (b) drop-casting at room temperature, (c) drop-casting at room temperature with post thermal vacuum heating, (d) drop-casting at room temperature with sonication, and (e) DSTT method.
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Figure 6. Cross-sectional SEM images of MWCNT-coated cotton fabrics prepared by two fabrication methods: (a) drop-casting at room temperature and (b) DSTT method.
Figure 6. Cross-sectional SEM images of MWCNT-coated cotton fabrics prepared by two fabrication methods: (a) drop-casting at room temperature and (b) DSTT method.
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Figure 7. Photographs of DSTT-coated cotton fabric subjected to manual bending deformation, showing the macroscale appearance of the MWCNT coated 3.0 × 3.0 cm2 cotton fabric during bending (Video S1).
Figure 7. Photographs of DSTT-coated cotton fabric subjected to manual bending deformation, showing the macroscale appearance of the MWCNT coated 3.0 × 3.0 cm2 cotton fabric during bending (Video S1).
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Figure 8. Comparison of sheet-resistance values for 2.5 × 2.5 cm2 and 3 × 3 cm2 cotton fabrics coated using the DSTT method over six coating cycles.
Figure 8. Comparison of sheet-resistance values for 2.5 × 2.5 cm2 and 3 × 3 cm2 cotton fabrics coated using the DSTT method over six coating cycles.
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Figure 9. Comparison of the absolute difference (|Δ|) and combined uncertainty (U_comb) in sheet-resistance measurements for 2.5 × 2.5 cm2 and 3 × 3 cm2 DSTT-coated fabrics across coating cycles (a) initial and (b) after 16 weeks.
Figure 9. Comparison of the absolute difference (|Δ|) and combined uncertainty (U_comb) in sheet-resistance measurements for 2.5 × 2.5 cm2 and 3 × 3 cm2 DSTT-coated fabrics across coating cycles (a) initial and (b) after 16 weeks.
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Figure 10. Stability of sheet resistance in MWCNT-coated cotton fabrics as a function of MWCNT loading, measured initially and after 16 weeks of ambient storage with periodic manual bending: (a) 2.5 × 2.5 cm2 MWCNT-coated fabrics and (b) 3.0 × 3.0 cm2 MWCNT-coated fabrics.
Figure 10. Stability of sheet resistance in MWCNT-coated cotton fabrics as a function of MWCNT loading, measured initially and after 16 weeks of ambient storage with periodic manual bending: (a) 2.5 × 2.5 cm2 MWCNT-coated fabrics and (b) 3.0 × 3.0 cm2 MWCNT-coated fabrics.
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Table 1. Comparison of sheet resistance (kΩ/sq.) between 2.5 × 2.5 cm2 and 3 × 3 cm2 cotton fabrics fabricated using the DSTT process at identical coating cycles (1–6).
Table 1. Comparison of sheet resistance (kΩ/sq.) between 2.5 × 2.5 cm2 and 3 × 3 cm2 cotton fabrics fabricated using the DSTT process at identical coating cycles (1–6).
Coating CycleMWCNT (wt.%)
2.5 × 2.5 cm2		Sheet Resistance (kΩ/sq.)
2.5 × 2.5 cm2		MWCNT (wt.%)
3.0 × 3.0 cm2		Sheet Resistance (kΩ/sq.)
3.0 × 3.0 cm2
17.8%1.196 ± 0.0476.9%1.25 ± 0.069
211.0%1.007 ± 0.04911.9%1.08 ± 0.059
316.3%0.534 ± 0.0417.0%0.56 ± 0.04
420.7%0.394 ± 0.02219.6%0.423 ± 0.025
525.3%0.171 ± 0.00724.1%0.18 ± 0.01
630.1%0.072 ± 0.00429.3%0.078 ± 0.005
Table 2. Comparative analysis of CNT-coated cotton fabrics: methods and electrical performance.
Table 2. Comparative analysis of CNT-coated cotton fabrics: methods and electrical performance.
YearSubstrateMethod/Dispersion
(CNT wt.% in Solution; Solution Type)		CNT LoadingSample SizeElectrical Performance (as Reported)Measurement MethodReference
2015CottonDip-dry coating (repeated cycles) using functionalized MWCNTs (citric-acid-assisted plasma treatment) in water
(0.25–1.0 wt.% f-MWCNTs in solution)		~18.5 wt.%
(on fabric)		5 × 5 cm2~9.65 kΩ/sq.
(sheet resistance)		Two-point probe
(Ni mesh electrodes)		[42]
2015CottonDip-coating (20 cycles) with SDS-dispersed MWCNTs + HNO3 treatment (5%, 3 h)
(1.2 wt./vol% MWCNTs with 0.1% SDS in water; 3.5 mol/L)		Not reported1 × 1 cm22.5–1.5 kΩ·cm−2
(area-normalized resistance)		Two-point probe
(digital multimeter)		[45]
2019CottonConventional dyeing with reactive vinyl sulphone dye + MWCNTs in aqueous solution
(1% dye; 1–5 mg/mL MWCNTs; varied: 1.0, 2.0, 3.0, 4.0, 5.0 mg/mL)		Varied
(reported as mg/cm2; wt.% not reported)		Not reported5486–0.433 MΩ/sq.
(5,486,000–433 kΩ/sq.)
(sheet resistance)		Two-electrode system[41]
2020CottonImpregnation-drying (3 cycles) using chemically functionalized MWCNTs (dimethyl phosphite + perfluorohexyl iodine) in hexafluoroisopropanol
(~28.6 mg/mL; ~1.8 wt.% in solution)		11.9 wt.%
(on fabric)		2 × 8 cm2225.6 kΩ/sq.
(sheet resistance)		Four-probe tester[40]
2022CottonDip-coating: GPTMS-stabilized MWCNTs + tannic acid (concentration not specified; 1-methylimidazol catalyst)Not reportedNot reported115 Ω/cm
(linear resistance; best: tannic acid/GPTMS/MWCNTs)		Multimeter[48]
2024CottonLayer-by-layer assembly: PSS-wrapped CNTs + chitosan (3 mg/mL CNTs; 0.3 wt.% equivalent)Not reported50 × 20 × 0.6 mm3 (fabric)34.57 S/m
(conductivity; 4 LBL cycles)		Four-probe[49]
2025CottonInkjet printing: CNT ink (1 wt.%) + reactive silver ink (34 wt.% Ag) with PLL coatingNot reportedNot reported1.25 × 105 S/m
(conductivity)		Four-probe meter[50]
This workCottonDSTT (drop-casting, sonication, thermal treatment)
(CNT 5 wt.% in ethanol dispersion)		~7.8–~30 wt.%
(on fabric)		2.5 × 2.5 cm21.196–0.072 kΩ/sq.
(sheet resistance; 1–6 coating cycles)		Four-point probeThis work
Note: CNT loading reported as wt.% on fabric where available. Electrical performance is reported with the measurement type indicated in parentheses. Sheet resistance (kΩ/sq.) allows direct comparison between studies; area-normalized resistance, linear resistance, and conductivity depend on sample geometry or thickness and are not directly comparable. All studies used cotton fabric substrate. “Not reported” indicates data not available in the original source.
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Shahbaz, M.; Furuta, H. Synergistic Integration of Drop-Casting with Sonication and Thermal Treatment for Fabrication of MWCNT-Coated Conductive Cotton Fabrics. Crystals 2026, 16, 60. https://doi.org/10.3390/cryst16010060

AMA Style

Shahbaz M, Furuta H. Synergistic Integration of Drop-Casting with Sonication and Thermal Treatment for Fabrication of MWCNT-Coated Conductive Cotton Fabrics. Crystals. 2026; 16(1):60. https://doi.org/10.3390/cryst16010060

Chicago/Turabian Style

Shahbaz, Muhammad, and Hiroshi Furuta. 2026. "Synergistic Integration of Drop-Casting with Sonication and Thermal Treatment for Fabrication of MWCNT-Coated Conductive Cotton Fabrics" Crystals 16, no. 1: 60. https://doi.org/10.3390/cryst16010060

APA Style

Shahbaz, M., & Furuta, H. (2026). Synergistic Integration of Drop-Casting with Sonication and Thermal Treatment for Fabrication of MWCNT-Coated Conductive Cotton Fabrics. Crystals, 16(1), 60. https://doi.org/10.3390/cryst16010060

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