An Asymmetric Layer Structure Enables Robust Multifunctional Wearable Bacterial Cellulose Composite Film with Excellent Electrothermal/Photothermal and EMI Shielding Performance.

Highly robust flexible multifunctional film with excellent electromagnetic interference shielding and electrothermal/photothermal characteristics are highly desirable for aerospace, military, and wearable devices. Herein, an asymmetric gradient multilayer structured bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx (BC@Fe3O4/CNT/Ti3C2Tx) multifunctional composite film is fabricated with simultaneously demonstrating fast Joule response, excellent EMI shielding effectiveness (EMI SE) and photothermal conversion properties. The asymmetric gradient 6-layer composite film with 40% of Ti3C2Tx possesses excellent mechanical performance with exceptional tensile strength (76.1 MPa), large strain (14.7%), and good flexibility. This is attributed to the asymmetric gradient multilayer structure designed based on the hydrogen bonding self-assembly strategy between Ti3C2Tx and BC. It achieved an EMI SE of up to 71.3 dB, which is attributed to the gradient "absorption-reflection-reabsorption" mechanism. Furthermore, this composite film also exhibits excellent low-voltage-driven Joule heating (up to 80.3 °C at 2.5 V within 15 s) and fast-response photothermal performance (up to 101.5 °C at 1.0 W cm-2 within 10 s), which is attributed to the synergistic effect of heterostructure. This work demonstrates the fabrication of multifunctional bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx composite film has promising potentials for next-generation wearable electronic devices in energy conversion, aerospace, and artificial intelligence.

Multifunctional MoSe2 @MXene Heterostructure-Decorated Cellulose Fabric for Wearable Thermal Therapy.

A booming demand for wearable electronic devices urges the development of multifunctional smart fabrics. However, it is still facing a challenge to fabricate multifunctional smart fabrics with satisfactory mechanical property, excellent Joule heating performance, highly efficient photothermal conversion, outstanding electromagnetic shielding effectiveness, and superior anti-bacterial capability. Here, a MoSe2 @MXene heterostructure-based multifunctional cellulose fabric is fabricated by depositing MXene nanosheets onto cellulose fabric followed by a facile hydrothermal method to grow MoSe2 nanoflakes on MXene layers. A low-voltage Joule heating therapy platform with rapid Joule heating response (up to 230 °C in 25 s at a supplied voltage of 4 V) and stable performance under repeated bending cycles (up to 1000 cycles) is realized. Besides, the multifunctional fabric also exhibits excellent photothermal performance (up to 130 °C upon irradiation for 25 s with a light intensity of 400 mW cm-2 ), outstanding electromagnetic interference shielding effectiveness (37 dB), and excellent antibacterial performances (>90% anti-bacterial rate toward Escherichia coli, Bacillus subtilis, and Staphylococcus aureus). This work offers an efficient avenue to fabricate multifunctional wearable thermal therapy devices for mobile healthcare and personal thermal management.

Electrothermal enrichment of submicron particles in an insulator-based dielectrophoretic microdevice.

Insulator-based dielectrophoresis (iDEP) exploits in-channel hurdles and posts etc. to create electric field gradients for various particle manipulations. However, the presence of such insulating structures also amplifies the Joule heating in the fluid around themselves, leading to both temperature gradients and electrothermal flow. These Joule heating effects have been previously demonstrated to weaken the dielectrophoretic focusing and trapping of microscale and nanoscale particles. We find that the electrothermal flow vortices are able to entrain submicron particles for a localized enrichment near the insulating tips of a ratchet microchannel. This increase in particle concentration is reasonably predicted by a full-scale numerical simulation of the mass transport along with the coupled charge, heat and fluid transport. Our model also predicts the electric current and flow pattern in the fluid with a good agreement with the experimental observations.

Hydrated alginate polysaccharide fabrics grafted with sliver nanocrystals for wearable thermal and health management.

The creation of functional components with precise chemistries on carbohydrate polymers is of great significance for future wearable biomedicine and health management. Among various carbohydrate polymers, marine polysaccharide featured with antimicrobial, biodegradable and biocompatible properties is an ideal platform while the water-swelling nature makes it difficult to form stable interface. Here, well-dispersed silver nanoparticles have been in-situ assembled on hydrated alginate fabric (AF), involving chemical absorption of Ag ions and in-situ reduction of conductive Ag layer. Owing to the stable complex formed between Ag ions and carboxyl groups, the Ag-grafted AF exhibits superior Joule heating capability, including low operating voltage (1-3 V), high saturation temperature (63 °C), rapid response time (25 s) and outstanding durability against harsh conditions. Furthermore, the Ag-grafted AF demonstrates noticeable inhibition against E. coli and S. aureus as compared with the pristine AF. This work provides a rational strategy for the functionalization of hydrated polysaccharide and enables wearable thermotherapy devices for human health management.

Zwitterionic surfactant as an additive for efficient electrophoretic separation of easily absorbed rhodamine dyes on plastic microchips.

Plastic microchips possess the advantages of easy fabrication and low-cost, but their surface properties are frequently incompatible with electrophoretic separation without proper surface modification. Meanwhile, the separation microchannels on typical microchips are usually only a few centimeters long, the pressurized flow may significantly affect the electrophoretic separation if their inner diameters (id) are relatively larger (approximately > 50 µm), viscous separation medium is therefore required for efficient separation. Herein, a zwitterionic surfactant, N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate (HDAPS), was used as a multifunctional additive to inhibit the analyte adsorption, improve the surface status, control Joule heating and modulate the resolution on cyclic olefin copolymer microchips with 80 µm id, 5 cm long separation microchannels, eliminating the necessity of viscous polymeric additives. The effectiveness of HDAPS was compared with an ionic polymeric additive, poly(diallydimethylammonium chloride). The streaming potential and electroosmotic flow measurements indicated an effective inhibition of the adsorption of rhodamine B and a stable negative surface charge with zwitterionic HDAPS. Using 15 mmol/L HDAPS, 40% (v/v) methanol, and 10 mmol/L boric acid (pH 3.2) as the running buffer, rapid separation of four rhodamines was achieved within 90 s under a separation electric field of 520 V/cm. The theoretical plate numbers were in a range of 5.0×105-6.9×105/m. The relative standard deviations were no more than 0.9% for retention time and 1.5% for peak area. The proposed system was verified by the determination of rhodamines in eyeshadow and wolfberry, with standard recoveries in a range of 98.2%-101.4%.

Recycle and Reuse of Continuous Carbon Fibers from Thermoset Composites Using Joule Heating.

This study demonstrates a new and sustainable methodology for recycling continuous carbon fibers from end-of-life thermoset composite parts using Joule heating. This process addresses the longstanding challenge of efficiently recovering carbon fibers from composite scrap and reusing them to make fresh composites. The conductive carbon fibers volumetrically heat up when an electric current is passed through them, which in turn rapidly heats up the surrounding matrix sufficiently to degrade it. Fibers can be easily separated from the degraded matrix after the direct current (DC) heating process. Fibers reclaimed using this method were characterized to determine their tensile properties and surface chemistry, and compared against both as-received fibers and fibers recycled using conventional oven pyrolysis. The DC- and oven-recycled fibers yielded similar elastic modulus when compared against as-received fibers; however, an around 10-15 % drop was observed in the tensile strength of fibers recycled using either method. Surface characterization showed that DC-recycled fibers and as-received fibers had similar types of functional groups. To demonstrate the reusability of recycled fibers, composites were fabricated by impregnation with epoxy resin and curing. The mechanical properties of these recycled carbon fiber composites (rCFRCs) were compared against conventional recycling methods, and similar modulus and tensile strength values were obtained. This study establishes DC heating as a scalable out-of-oven approach for recycling carbon fibers.

Ultralow loading mussel-inspired conductive hybrid as highly effective modifier for function-engineered poly(lactic acid) composites.

It remains a great challenge to prepare polylactic acid (PLA) composites with excellent mechanical properties, superior anti-bacteria, and highly effective electromagnetic interference (EMI) shielding using ultralow loading of functional fillers. Herein, lignin particles were uniformly nano-sized as the matrix reinforcement and the fillers carrier via green mechanochemistry for improved thermal properties of polymer matrix. Through one-pot approach to a multitasking engineered agent, hybridized ZnO/Ag particles were synthesized for multi-functionalities. Inspired by mussels, the bio-derived dopamine cross-linker was introduced to in-situ synthesize the polypyrrole (PPy-PDa) glutinous nanofibrils as an interfacial modifier and a particles dispersant to regulate surface free energy of nanoparticles and improve filler-matrix interactions. With effective constructed 3D conductive networks by glutinous nanofibrils and hybridized particles, the dramatic improvement in EMI shielding and electrical conductivity was accomplished using an ultralow content of the conductive particles modifier (0.29 vol% Ag). The resulted biobased composites presented outstanding anti-dripping properties, mechanical properties, electrical conductivity (104.2 S/cm), anti-bacteria, joule heating, photothermal conversion ability and EMI shielding effectiveness (48.6 dB at X-band), which are superior to those reported. This work will broaden the application prospects of PLA composites in the fields of wearable electronics, food packaging and medical devices.

Ti3C2Tx MXene-Decorated Nanoporous Polyethylene Textile for Passive and Active Personal Precision Heating.

Heating the human body to maintain a relatively constant temperature is pivotal for various human functions. However, most of the current heating strategies are energy-consuming and energy-wasting and cannot cope with the complex and changing environment. Developing materials and systems that can heat the human body precisely via an efficient energy-saving approach no matter indoors/outdoors, day/night, and sunny/cloudy is highly anticipated for mitigating the growing energy crisis and global warming but is still a great challenge. Here, we demonstrate the low mid-infrared radiative (mid-IR) emissivity characteristic of Ti3C2Tx MXene and then apply it for energy-free passive radiative heating (PRH) on the human body. Our strategy is realized by simply decorating the cheap nanoporous polyethylene (nanoPE) textile with MXene. Impressively, the as-obtained 12 µm thick MXene/nanoPE textile shows a low mid-IR emissivity of 0.176 at 7-14 µm and outstanding indoor PRH performance on the human body, which enhances by 4.9 °C compared with that of traditional 576 µm thick cotton textile. Meanwhile, the MXene/nanoPE textile exhibits excellent active outdoor solar heating and indoor/outdoor Joule heating capability. The three heating modes integrated in this wearable MXene/nanoPE heating system can be switched easily or combined arbitrarily, making this thin heating system able to heat the human body precisely in various scenarios like indoors/outdoors, day/night, and sunny/cloudy, providing multiple promising and energy-saving solutions for future all-day personal precision thermal management.

Electrically conductive membranes for anti-biofouling in membrane distillation with two novel operation modes: Capacitor mode and resistor mode.

This study evaluated the anti-biofouling efficacy of capacitor mode and resistor mode in membrane distillation (MD). Polytetrafluoroethylene (PTFE) membrane coated with carbon nanotube (CNT) was adopted as the electrically conductive membrane. The biofouling formation on the pre-treatment membrane was systematically analyzed, and the results showed that both operation modes had obvious inhabitation on bacteria, especially the capacitor mode exhibited stronger prevention capability on biomass accumulation than resistor mode. NMDs analysis of microbial communities further revealed that the anti-biofouling effect mainly occurred on the membrane surface, and gram-positive biomarkers which can survive better in external electric field was distinctively found in capacitor mode through LEfSE analysis. Hypothesis was introduced to explain the anti-fouling function of two modes that in the capacitor mode, the competitive electrostatic repulsion of bacteria cells on negative electrode associated by the cell-disruption effect of electro-catalyzed reactive oxygen species (ROS) generation, while the anti-fouling function of resistor mode was a result of temperature increment on membrane surface caused by Joule heating effects. This article attempts to provide an insight of anti-fouling mechanism of electric field applied in MD and to prove the feasibility of above-mentioned operation modes as non-chemical methods for optimization of membrane-based water treatment process.

Transforming Commercial Textiles and Threads into Sewable and Weavable Electric Heaters.

We describe a process to transform commercial textiles and threads into electric heaters that can be cut/sewn or woven to fashion lightweight fabric heaters for local climate control and personal thermal management. Off-the-shelf fabrics are coated with a 1.5 µm thick film of a conducting polymer, poly(3,4-ethylenedioxythiophene), using an improved reactive vapor deposition method. Changes in the hand feel, weight, and breathability of the textiles after the coating process are imperceptible. The resulting fabric electrodes possess competitively low sheet resistances-44 Ω/□ measured for coated bast fiber textiles and 61 Ω/□ measured for coated cotton textiles-and act as low-power-consuming Joule heating elements. The electrothermal response of the textile electrodes remain unaffected after cutting and sewing due to the robustness of the conductive coating. Coated, conductive cotton yarns can also be plain-woven into a monolithic fabric heater. A demonstrative circuit design for a soft, lightweight, and breathable thermal glove is provided.

Rapid concentration of deoxyribonucleic acid via Joule heating induced temperature gradient focusing in poly-dimethylsiloxane microfluidic channel.

This paper reports rapid microfluidic electrokinetic concentration of deoxyribonucleic acid (DNA) with the Joule heating induced temperature gradient focusing (TGF) by using our proposed combined AC and DC electric field technique. A peak of 480-fold concentration enhancement of DNA sample is achieved within 40s in a simple poly-dimethylsiloxane (PDMS) microfluidic channel of a sudden expansion in cross-section. Compared to a sole DC field, the introduction of an AC field can reduce DC field induced back-pressure and produce sufficient Joule heating effects, resulting in higher concentration enhancement. Within such microfluidic channel structure, negative charged DNA analytes can be concentrated at a location where the DNA electrophoretic motion is balanced with the bulk flow driven by DC electroosmosis under an appropriate temperature gradient field. A numerical model accounting for a combined AC and DC field and back-pressure driven flow effects is developed to describe the complex Joule heating induced TGF processes. The experimental observation of DNA concentration phenomena can be explained by the numerical model.