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Page 6 of 15 Zhao et al. Soft Sci. 2026, 6, 4

process [Figure 1C]. Copper wires, respectively coated with epoxy resin and PVDF, form the triboelectric
pair [Supplementary Figure 1] To enhance the sensitivity of the triboelectric sensor , we employ a plasma
[40]
surface treatment using a 1:1 argon-oxygen gas mixture under low pressure [Supplementary Note 1], which
modifies the fiber surface by creating nanoscale roughness and surface modification [41,42] . These wires are
then helically twisted into flexible yarns and woven into textiles [Supplementary Figure 2]. The macroscopic
and scanning electron microscopy images of the resulting textiles reveal a uniform fiber arrangement with
consistent coating [Figure 1D]. These images confirm the micro- and nanoscale surface features introduced
by plasma treatment and the uniformity of the coatings, which together underpin consistent sensor
performance. When positioned above the mouth-nose airflow channel of a fighter-pilot oxygen mask [Figure
1E], cyclic inhaled and exhaled airflow deforms the textile, generating periodic triboelectric voltage
signals [43-45] . These voltage signals are subsequently acquired and processed by a machine learning-assisted
monitoring system, including feature extraction, respiratory patterns classification, and real-time breathing
metrics display to support adaptive oxygen delivery [Figure 1F].

Characterization of surface-modified triboelectric fibers
During the plasma treatment, high-energy ions bombard the polymer surface, causing surface roughness to
increase the frictional contact area between fibers for enhanced signal output intensity from small
deformations [Figure 2A] [42,46] . To establish a clear link between processing parameters and sensor
performance, we systematically characterized both morphology and chemistry of the fibers after different
plasma exposure durations. Figure 2B and C shows the surface-treated epoxy-coated and PVDF-coated
copper wires. These macroscopic images provide preliminary visual confirmation of the surface coating on
the copper wires. Figure 2D and E confirms significant morphological changes after 60-minute plasma
treatment. The untreated fibers exhibit relatively smooth surfaces [Figure 2D , 2D , 2E , and 2E ], while the
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plasma-treated fibers develop pronounced nanoscale roughness with characteristic etching patterns [Figure
2D , 2D , 2E , and 2E ]. The contrast between untreated and treated surfaces indicates that plasma
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processing effectively creates new topographical features that are expected to increase effective contact area
during mechanical deformation. Moreover, EDS mappings [Supplementary Figures 3-5] show the
compositional changes of carbon, oxygen, and fluorine elements on the surfaces of epoxy resin and PVDF
fibers. Progressive surface modifications are observed with increasing plasma treatment duration
[Supplementary Figures 6 and 7]. Three-dimensional AFM further confirms the enhancement in surface
roughness after plasma treatment [Figure 2F and Supplementary Figure 8]. Quantitative analysis of surface
roughness parameters, including R and R demonstrates a significant increase with plasma treatment
q
a
duration [Figure 2G].
Chemical changes are characterized using FTIR spectroscopy. Figure 2H presents the FTIR spectra of epoxy
and PVDF fibers before and after 60-minute plasma treatment, respectively. For epoxy fibers [Figure 2H ],
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the plasma treatment introduced oxygen-containing groups. These modifications are evidenced by the
enhanced absorption around 1,200 cm , where the C-O stretching vibrations become more pronounced.
-1
Additionally, the characteristic C-H stretching vibration at 2,900 cm shows reduced intensity after
-1
treatment, indicating that the introduced oxide leads to the removal or oxidation of C-H groups. For epoxy
fibers [Figure 2H ], plasma treatment resulted in the disappearance of minor absorption peaks in the
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1,500-1,600 cm region, which correspond to the stretching vibration of C=C bonds in the aromatic ring and
-1
the bending vibration of C–H bonds. Besides, the weakened C-H stretching vibrations around 2,900 cm -1
corresponding to non-polar aliphatic groups (methyl and methylene) manifest as a notable reduction in
absorption intensity. This can also be attributed to surface damage and coverage of oxygen-containing
functional groups. XPS analysis of the C 1s spectra further confirmed the plasma-induced surface chemical
modifications of PVDF and epoxy fibers [Supplementary Figure 9]. For PVDF, the C–C, CH , and CF/C–C–F
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components shift from 284.0, 285.3, and 288.0 eV to 284.2, 286.4, and 291.3 eV, respectively. The binding