Liquid-assisted approaches in thermal fiber drawing techniques to develop conductive polymer fibers

Abstract

Flexible electronic fibers that combine scalable manufacturability with multimodal physiological sensing remain challenging due to the conflicting requirements of conductivity, porosity, mechanical compliance, and environmental robustness. Here, an in situ thermally induced phase separation (TIPS) strategy integrated into thermal fiber drawing (TFD) is proposed to produce continuous porous graphene–polymer nanocomposite fibers with independently tunable pore architecture and electrical properties. Starting from a solvent-borne graphene/polyvinylidene fluoride (PVDF) slurry encapsulated within an elastomeric cladding, tens-of-meters-long fibers are produced from a compact preform, while high graphene loadings are accommodated, enabling the formation of a percolated conductive network embedded within a phase-separated polymeric matrix. The resulting fiber exhibits an electrical conductivity of (1.35 ± 0.96) × 10−3 Sm−1, indicative of a moderately percolated network that balances electrical transport and structural porosity. The fabricated fibers are operated as multimodal wearable sensors, including: (i) a temperature sensor exhibiting a stable output and high temperature sensitivity with a negative temperature coefficient of resistance (TCR = 0.558 ◦C−1); (ii) a pressure sensor demonstrating a reliable cyclic response; and (iii) a dry-electrode cardiovascular monitoring interface, for which impedance magnitude and phase behavior are observed to closely match those of commercial electrodes at low frequencies, while the fundamental features of signals recorded from human skin are captured. The removable elastomeric cladding, imparting water resistance, is shown to support textile integration and stable operation under humid conditions. In the second part of this thesis, the fabrication and characterization of highly conductive polymer fibers incorporating carbon nanotubes (CNTs) were systematically investigated. A liquid-assisted thermal drawing approach was employed, in which a homogeneous carbon nanotube/propylene carbonate (CNT/PC) slurry was introduced into the fiber preform to enable continuous material feeding during the thermal drawing process. This methodology facilitated uniform nanoscale dispersion of CNTs within the polymer matrix and promoted the formation of interconnected conductive pathways along the fiber axis during drawing. As a result of this optimized liquid-assisted process, the fabricated fibers exhibited an electrical conductivity as high as 95 Sm−1, which is more than two orders of magnitude higher than that of conventional conductive polymer films. This significant enhancement is attributed to the effective CNT dispersion, alignment, and percolation achieved under continuous thermal elongation, highlighting the advantages of fiber-based architectures over planar film counterparts for efficient electrical transport. Overall, this thesis establishes scalable thermal drawing–based strategies for engineering highly conductive and porous conductive polymer fibers, providing a unified framework that bridges fundamental conductive network formation with multifunctional fiber-based sensing platforms for wearable and textile-integrated applications.