Enhanced thermal conductivity and mechanical properties of polyurethane composites with the introduction of thermally annealed carbon nanotubes

Easy, Fast Self-Heating Polyurethane Nanocomposite with the Introduction of Thermally Annealed Carbon Nanotubes Using Near-Infrared Lased Irradiation

In this study, high-crystallinity single walled carbon nanotubes (H-SWNTs) were prepared by high-temperature thermal annealing at 1800 °C and a self-heating shape memory polyurethane nanocomposite with excellent self-heating characteristics was developed within a few seconds by irradiation with near-infrared rays. With a simple method (heat treatment), impurities at the surface of H-SWNTs were removed and at the same time the amorphous structure converted into a crystalline structure, improving crystallinity. Therefore, high conductivity (electric, thermal) and interfacial affinity with PU were increased, resulting in improved mechanical, thermal and electric properties. The electrical conductivity of neat polyurethane was enhanced from ~10^-11 S/cm to 4.72 × 10^-8 S/cm, 1.07 × 10^-6 and 4.66 × 10^-6 S/cm, while the thermal conductivity was enhanced up to 60% from 0.21 W/mK, 0.265 W/mK and 0.338 W/mK for the composites of 1, 3 and 5 wt%, respectively. Further, to achieve an effective photothermal effect, H-SWNTs were selected as nanofillers to reduce energy loss while increasing light-absorption efficiency. Thereafter, near-infrared rays of 818 nm were directly irradiated onto the nanocomposite film to induce photothermal properties arising from the local surface plasmon resonance effect on the CNT surface. A self-heating shape memory composite material that rapidly heated to 270 °C within 1 min was developed, even when only 3 wt.% of H-SWNTs were added. The results of this study can be used to guide the development of heat-generating coating materials and de-icing materials for the wing and body structures of automobiles or airplanes, depending on the molding method.

High-performance transparent pressure sensors based on sea-urchin shaped metal nanoparticles and polyurethane microdome arrays for real-time monitoring

An ultra-sensitive and transparent piezoresistive pressure sensor based on a sea-urchin shaped metal nanoparticle (SSNP)-polyurethane (PU) composite with microdome arrays is successfully fabricated for the first time. The piezoresistive pressure sensor with microdome arrays was prepared using a nanoimprinting process based on an intermediate polymer substrate (IPS) replica mold. It showed a superior sensitivity (71.37 kPa^-1) and a high optical transmittance (77.7% at 550 nm) due to the effective quantum tunneling effect even at small concentrations of conductive SSNP filler (6 mg mL^-1). The high-performance characteristics of the piezoresistive pressure sensor are attributed to the geometric effects of the microdome structure, especially the stress concentration at small contact spots and the deformation of the contact area. The piezoresistive pressure sensor with microdome arrays also exhibited a fast response/relaxation time (30 ms), ultra-low pressure detection (4 Pa), and excellent long-term stability under harsh conditions. In addition, the effectiveness of the piezoresistive pressure sensors in various sensing applications including sensing mapping, human arterial pulse monitoring, and the detection of muscle movement is also successfully demonstrated. It is anticipated that this novel transparent pressure sensor based on a SSNP-PU composite with microdome arrays will be a key component in the development of integrated transparent sensing applications.

Flexible carbonized cellulose/single-walled carbon nanotube films with high conductivity

A carbonized cellulose/single-walled carbon nanotube composite film (cell/SWCNT_carbon) was prepared with well-dispersed cellulose/SWCNT doped in N-methylmorpholine N-oxide (NMMO) monohydrate. After carbonization at 400 °C, the SWCNT content at electrical threshold of the cell/SWCNT_carbon nanocomposite decreased from 2 wt% to 1 wt%, and the electrical conductivity of the cell/SWCNT(1 wt%)_carbon nanocomposite (0.6 S cm^-1) increased by more than 6 orders of magnitude compared to that of pure carbonized cellulose (1.1 × 10^-7 S cm^-1). Further, it continuously increased as the carbonization temperature increased and reached 100 S cm^-1 when the cell/SWCNT(1 wt%) nanocomposite was carbonized at 1400 °C. This drastic increase in the electrical conductivity at low carbonization temperatures (e.g. 400 °C) was due to the percolation of small carbon clusters with conducting SWCNTs. The incorporated SWCNTs improved flexibility and mechanical stability during carbonization so that the cell/SWCNT(1 wt%)_carbon nanocomposite could be bent even after carbonization at 1400 °C; however, the carbonized cellulose prepared using the same method was too brittle. This cell/SWCNT_carbon nanocomposite may render the eco-friendly production of flexible electrodes for various applications, including heat sink parts, electromagnetic interference shielding materials, and electronic devices, feasible.