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Li et al. Soft Sci. 2025, 5, 13 https://dx.doi.org/10.20517/ss.2024.60 Page 3 of 11

EXPERIMENTAL
Materials
Cotton yarns were purchased from Jiangxi Yousheng Ribbon Co., Ltd. Ecoflex was purchased from
Smooth-On, Inc. The ionic liquid, 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide, was
purchased from Shanghai Macklin Biochemical Technology Co., Ltd.

Fabrication of the fibrous temperature sensor
In the fabrication of the fibrous temperature sensor, a dual-layered approach was employed on a scalable
production line to ensure the functional and protective layers were seamlessly integrated on the surface of
cotton yarn. The process commenced with the ionic liquid, 1-Ethyl-3-methylimidazolium bis
(trifluoromethylsulfonyl)imide, which was carefully poured into the dipping tank of the continuous
production line. Subsequently, two constituents of Ecoflex, a biocompatible and flexible polymer, were
thoroughly mixed and degassed in a vacuum oven for a duration of 5 min. This step was critical in
eliminating air bubbles, ensuring a smooth and uniform coating. The mixture was then transferred into
another dipping tank, ready for the next phase of the dip-coating process.

The cotton yarn, initially dipped into the ionic liquid, underwent a drying process through a heating tube
set at a temperature of 180 °C. This high-temperature regime was pivotal in setting the foundation for the
subsequent Ecoflex layer, ensuring the stability of the yarn during the encapsulation process. Following this,
the partially dried fiber was immersed into the well-mixed Ecoflex solution. To refine the layer and
eliminate any excess material, the fiber was guided through a micro-pinhole, precisely 0.5 mm in inner
diameter. This step was instrumental in achieving a consistent and refined layer of Ecoflex. The final stage
of the fabrication process involved curing and shaping the fiber within the heating tube at the same elevated
temperature of 180 °C. This ensured the Ecoflex layer fully adhered to the cotton yarn, completing the
encapsulation and providing the necessary protection to the sensor. Throughout this process, the fiber was
meticulously moved through the scalable production line at a controlled speed of 1 meter per minute. This
pace allowed for the uniform distribution of both the ionic liquid and Ecoflex, thereby enhancing the
sensor’s performance and longevity.

Characterization and measurement
To establish a connection during testing, a copper wire with a diameter of 50 μm and a length of
approximately 5 cm was selected to interface with the fiber core of the fibrous temperature sensor. First, the
outermost Ecoflex coating of the fiber was carefully removed using a scalpel to expose the conductive core.
The exposed section was then immersed in an ionic liquid until evenly impregnated, after which the
conductive core was securely connected to the copper wire. The interface was sealed with ultraviolet (UV)-
curing adhesive to ensure complete curing and prevent leakage of the ionic liquid. The cross-section of the
fibrous temperature sensor was characterized using an optical microscope (CX40M, Shunyu Optical
Technology Co., Ltd.). The electrical signals of the sensor were recorded by a multimeter (DMM6500, Tec
Technology Co., Ltd.). The environments for temperature-sensing performance tests were created using an
environmental test chamber (MC-800L, Min Testing Instrument and Equipment Co., Ltd). The current-
voltage (I-V) curves were recorded on a source meter (2450, Oupuda Technology Co., Ltd.). The pressing
and twisting performance of the fibrous temperature sensor was evaluated using a universal testing machine
at an ambient temperature of 25 °C.

RESULTS AND DISCUSSION
The fibrous temperature sensor was developed using cotton yarn as the substrate due to its suitability for
modification, low cost, skin-friendliness, and the ability of the ionic liquid to permeate through the gaps in
the cotton fibers by capillary action, maintaining its stability. The ionic liquid, 1-ethyl-3-methylimidazolium