Cellular Core/Sheath Filaments with Thermoresponsive Vacuum Cavities for Prolonged Passive Temperature-Adaptive Thermoregulation

Abstract

Acting as the interface between the human body and its environment, clothing is indispensable in human thermoregulation and even survival under extreme environmental conditions. Development of clothing textiles with prolonged passive temperature-adaptive thermoregulation without external energy consumption is much needed for protection from thermal stress and energy saving, but very challenging. Here, a temperature-adaptive thermoregulation filament (TATF) consisting of thermoresponsive vacuum cavities formed by the temperature-responsive volume change of the material confined in the cellular cores of the filament is proposed. Using a droplet-based microfluidic system, the cellular core/sheath filament using octadecane (OD) as a temperature-responsive volume-changing material to form droplet cellular cores within the thermoplastic polyurethane (TPU) sheath is fabricated. It is found that the fabric made of TATF has a remarkable temperature adaptive thermal conductivity, which increases by 83% as the mean fabric temperature increases from 20 °C to 35 °C, due to the volume change of vacuum cavities in the cellular cores of the filament in response to temperature. TATF fabrics have no problem associated with undesirable appearance changes or leakage of encapsulated molten materials as some existing thermoregulatory textiles do, and can therefore have wide applications in functional clothing for prolonged passive personal thermal management.

Keywords: droplet‐based microfluidics; passive thermoregulation filament; phase change materials; temperature‐adaptive thermal conductivity; vacuum cavity.

Figure 1

a) A schematic diagram of the droplet‐based microfluidic system for the fabrication of the TATFs, b) the coaxial needles for cellular microfluidic spinning, c) TATFs collected on a continuously automatic roller (scale bar = 5 mm), d) embroidered pattern of “RCTFF” (scale bar = 5 mm) using TATF, e) woven fabrics (scale bar = 2 mm) using the TATFs, f) temperature‐adaptive heat transfer through TATF fabric.

Figure 2

a) Photographs of OD/TPU filaments fabricated upon different flow ratios (scale bar = 500 µm). (i) The cellular OD/TPU filaments (TATFs) contained uniformly distributed OD particles; (ii) uneven OD/TPU filaments contained nonuniform OD particles; (iii) core–sheath OD/TPU filaments consist of continuous OD core and TPU sheath layer; (iv) TPU filaments are the ones in which no OD component can be encapsulated in the continuous phase of TPU solution; (v) deformed bumps mean OD and TPU components cannot form filament morphology. b) Phase diagram of OD/TPU filament morphologies with respect to Ca and We. c) Influence of We (We = 1.36, 2.12, 3.05, 4.15, 5.42×10⁻³) on the diameter of OD cells and the distance between adjacent capsules in the filament at Ca = 3.39. d) Photographs of TATFs with 32.4% (TATF_low‐OD), 41.5% (TATF_medium‐OD), and 52.3% (TATF_high‐OD) OD loading ratios generated at We = 1.36, 3.05, 5.42 ×10⁻³ when Ca = 3.39. The OD core cells were marked by white boxes (scale bar = 500 µm).

Figure 3

ESEM images of TATF_high‐OD: a) filament surface, b) top, c) middle and d) bottom cross sections of cellular OD cells; higher magnification ESEM of e) outer surface, f) cross section, g) inter wall and h) inner cavity of the filament.

Figure 4

a) Photographs of the high stretchability of TATF with high OD content in (i) solid OD state at about 22 °C and (ii) melting OD state at about 30 °C under a weight loading of 50 g. b) Stress–strain curves of TATFs in solid OD state. c) Cyclic stress‐strain curves of TATF_high‐OD at a fixed strain of 150% for 10 cycles in a solid OD state. d) Elastic modulus and critical diameter of filaments with different OD content. e) Bending stiffness of filaments with different OD content.

Figure 5

a) DSC curves of pure OD and TATFs. b) Comparison of the melting enthalpy of the proposed TATF_high‐OD with that of previously reported core–sheath PCM filaments in refs. [28, 30, 31, 32, 33, 34, 35] c) XRD spectra of OD, TPU filament‐woven fabric (Fabric_TPU) and TATF_high‐OD‐woven fabric (Fabric_high‐OD). d) TGA curves for the decomposition of OD, TPU filament and TATF_high‐OD. e) The testing photo of a sample with a surface density of 284 g m⁻² and the thermal conductivities of polyester fabric, Fabric_TPU, and the fabrics woven by TATF_low‐OD (Fabric_low‐OD), TATF_medium‐OD (Fabric_medium‐OD) and TATF_high‐OD (Fabric_high‐OD), respectively.

Figure 6

a) Time‐sequential infrared images and b) transient average temperature of different fabrics in the cooling process, and c) time‐sequential infrared images and d) transient average temperature of different fabrics in the heating process.