Large-Scale Nanofiber Manufacturing| Two-step phase-separated ANFpolyimideaerogel fibers with tunable in situ core-sheath structure for wearable heat-insulatedfabrics

Professor Chen Liming's Team (Chongqing University): Two-Step Fabrication of Wearable Polyimide Aerogel Fiber Thermal Insulation Textiles

With the global energy crisis intensifying, thermal management technologies have become crucial for reducing energy consumption in indoor temperature regulation. Traditional insulation materials struggle to balance thickness and thermal resistance, limiting comfort, space efficiency, and thermal regulation. Aerogel fibers, with ultrahigh porosity and ultralow thermal conductivity, outperform synthetic and natural fibers, making them ideal for next-generation high-performance textiles. However, developing flexible aerogel fibers with excellent insulation remains challenging.

Recently, Professor Chen Liming's team from Chongqing University published their latest research titled "Two-step phase-separated ANF/polyimide aerogel fibers with tunable in situ core-sheath structure for wearable heat-insulated fabrics" in Composites Part A: Applied Science and Manufacturing. The researchers developed a novel polyimide (PI) aerogel fiber with an in-situ core-sheath structure using an improved two-step phase separation technique (2Step) combined with aramid nanofiber (ANF) reinforcement, creating ultra-flexible and tough wearable thermal insulation fabrics.

Key findings show that both sheath thickness and pore morphology of the aerogel fibers can be precisely controlled by adjusting the phase separation steps and ethanol/water ratios in the coagulation bath. The core-sheath structure formed during 2Step phase separation, along with increased entanglement from nanofiber incorporation, significantly enhanced mechanical properties. The optimized ANF-reinforced PI aerogel fibers (ANF/PIAF) demonstrated exceptional flexibility and thermal insulation performance, with tensile modulus (748.53 MPa), tensile strength (51.94 MPa), and fracture energy (18.28 MJ/m³) improved by 2.5, 11.5, and 288.2 times respectively.The study highlights that a uniform porous core is essential for flexible aerogel fibers. 

Figure 1: SEM images and mechanical analysis of aerogel fibers with different coagulation bath compositions.

 Phase separation proves to be a cost-effective method for creating aerogel porous structures, where increasing ethanol concentration in the coagulation bath significantly improves pore uniformity (Figures 1a-e). With higher ethanol ratios, tensile strength increased from 7.55 MPa to 18.76 MPa and elongation at break improved from 5.48% to 14.13% (Figures 1f-g).The core-sheath structure formation represents another critical approach for enhancing flexibility.

Figure 2: Morphology and uniaxial tensile performance comparison before and after 2Step treatment.

After 2Step treatment, fiber diameter increased from 136.69 μm to 351.73 μm, developing a characteristic dense sheath layer that expanded from 0.53 μm to 7.69 μm (14.5× increase). The treated fibers also showed smoother surfaces. Mechanical properties improved significantly: tensile strength from 18.82 MPa to 29.07 MPa, tensile modulus from 480 MPa to 529 MPa, and fracture work from 19,488 kJ/m³ to 34,440 kJ/m³ (Figure 2).

Figure 3: Sheath formation mechanism by 2Step method and MIP analysis of three treatment methods.

The sheath formation mechanism (Figure 3a) involves using osmotic pressure differences from alternating coagulation bath compositions to collapse the outer layer of partially formed aerogel fibers, creating a compacted sheath while maintaining a uniform core in pure ethanol baths. Mercury intrusion porosimetry (MIP) data confirmed that 2Step-treated fibers maintained pore distribution similar to those treated in pure ethanol baths (EW1-0) (Figures 3b-c), demonstrating the method's effectiveness in inheriting uniform core structures while adding strength-enhancing sheath structures.

Figure 4: Aerogel fiber fabric images and Ashby plot of mechanical-thermal performance.

The ANF/PIAF woven fabrics exhibited outstanding flexibility with high tensile strength (51.94 MPa) and fracture work (18.28 MJ/m³), while maintaining ultralow thermal conductivity (0.034 W/(m·K)), showing great potential for flexible thermal insulation applications.

The research findings were published in Composites Part A: Applied Science and Manufacturing under the title "Two-step phase-separated ANF/polyimide aerogel fibers with tunable in situ core-sheath structure for wearable heat-insulated fabrics." Chen Zhilin, a master's student from the School of Aerospace Engineering at Chongqing University, served as the first author of the paper, with Professor Chen Liming and Assistant Researcher Hou Xianbo from the same institution as corresponding authors.