Hierarchically structured PCL/CNT nanocomposites with optimized crosslinking for chemiresistive detection of acetic acid

This study reports crosslinked polycaprolactone/carbon nanotube (cPCL/CNT) nanocomposites as chemiresistive sensors for acetic acid. The composites show an exceptionally low percolation threshold (ϕc = 0.002) with conductivity spanning twelve orders of magnitude. Trimethylolpropane triacrylate (TMPTA)-induced crosslinking yields a hierarchical structure characterized by a self-limiting crosslink density with non-monotonic crystallinity, peaking at 45 % for 12.5 wt% TMPTA. The optimized sensor (2.5 wt% TMPTA) exhibits high sensitivity (134 % response/%), excellent linearity (R² = 0.98) across broad analytical range (0.004–0.418 %), and consistent cyclic performance. All sensing experiments were performed under ambient conditions (25 ± 2°C, ∼55 % RH), while humidity tolerance was confirmed by varying chamber humidity (45–95 % RH). Sensitivity progressively declined at higher crosslinking densities (>7.5 wt% TMPTA) due to reduced flexibility. The sensing mechanism involves acetic acid absorption disrupting the CNT network, with crosslinking density critically modulating the balance between matrix rigidity and analyte accessibility. Contact angle measurements reveal dramatic wettability transitions upon analyte contact (from 76.9° to 14.7°), highlighting the exceptional selectivity toward acetic acid through H-bonding with PCL carbonyl groups. Importantly, these nanocomposites address the unmet requirements of breath analyzers, maintaining robust performance under varying humidity conditions (45–95 % RH), and thus hold strong potential for industrial monitoring and breath analysis applications.