The influence of increasing fused thiophene rings for the corresponding conjugated polymers [polythiophene (PT), poly(thieno[3,2-b]thiophene) (PTT) and poly(dithieno[3,2-b:2’,3’-d]thiophene) (PDTT)] on their photophysical and electrochemical properties, morphology and electrochromic performance are investigated in detail in this study. PDTT is the easiest of the three polymers to prepare and has the lowest onset oxidation potential of 1.17 V because of its increased donor ability, lower than those of PTT (1.41 V) and PT (1.82 V). PDTT also exhibits the best electrochemical and thermal stability because of its extended conjugated skeleton. The PT, PTT and PDTT polymers present poor, good and moderate electrochromic properties, respectively, with increasing fused thiophene rings. PTT displays the highest ΔT of 35% in 700 nm, the fastest response time of 1.0 s and the maximum colouration efficiency (CE) of 94 cm² C^-1, which is attributed to its enhanced morphology, since the PTT film is conducive to the promotion of ions to dope and dedope. Flexible electrochromic devices are fabricated and PTT exhibits the highest ΔT (60% in 480 nm and 16% in 660 nm), as well as excellent stability with less than a 5% ΔT reduction after successive cycling of 1000 s. All these findings indicate that the precise regulation of the fused thiophene is crucial in achieving high performance in electrochromism, which provides insight for the design of electrochromic conjugated polymers and flexible electrochromic devices.

Frequency selective surfaces (FSSs) with reconfigurable resonant frequency show significant potential for engineering applications. In this study, we propose a flexible FSS with a buckling dipole prepared by releasing the substrate pre-strain to buckle the locally adhered two-dimensional precursors, which can withstand large mechanical tensile deformation and change their resonant frequency during deformation. When the FSS is subjected to uniaxial tensile deformation, the capacitive effect between the adjacent buckled metal unit cells is significantly reduced due to the increase in the gap between the unit cells and period. This significant change in the equivalent circuit parameters due to the geometry change is highly beneficial for actively tuning the resonant frequency of the FSS. Electromagnetic (EM) experiments and simulations and equivalent circuit calculations are used to explore the EM tuning mechanism of the FSS and consistent conclusions are obtained. The results show that the FSS exhibits band-stop EM wave transmission characteristics with a resonant frequency of 6.1 GHz in the unstretched state and 21% uniaxial stretching strain can introduce a ~1.1 GHz increase in the resonant frequency. The corresponding parameter analysis shows that when the gap of the buckling dipoles in the width direction is reduced, the change in the resonant frequency caused by uniaxial stretching can be significantly increased, even to 2.5 GHz, which may help the FSS adapt to complex practical applications by tailoring the geometry of the buckling dipole.

Significant progress has been achieved for flexible polymer thermoelectric (TE) composites in the last decade due to their potential application in wearable devices and sensors. In sharp contrast to the exceptional increase in TE studies at room temperature, the mechanical performance of polymer TE composites has received relatively less attention despite the significance of the application of TE composites in high-temperature environments. The TE and mechanical performances of flexible poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotube (PEDOT:PSS/SWCNT) composite films with an ionic liquid (IL) (referred to as “PEDOT:PSS/SWCNT-IL”) at high temperatures are studied in the present work. The fabricated composite films show increasing TE performance with increasing temperature and SWCNT content. The maximum value of the power factor reaches 301.35 μW m^-1 K^-2 at 470 K for the PEDOT:PSS/SWCNT-IL composite. Furthermore, the addition of the IL improves the elongation at break of the composites compared to the IL-free composites. This work promotes the advancement of flexible polymer TE composites and widens their potential applications at different temperature ranges.

Magnetism and magnetic monopoles are among the most classical issues in physics. Conventional magnets are generally composed of rigid materials and may face challenges in extreme situations. Here, as an alternative to rigid magnets, we propose, for the first time, the generation of fluidic endogenous magnetism and construct a magnetic monopole through tuning with a liquid metal machine. Based on theoretical interpretation and conceptual experimental observations, we illustrate that when liquid metals, such as gallium alloy, in a solution rotate under electrical actuation, they form an endogenous magnetic field inside. This explains the phenomenon where two such discrete metal droplets can easily fuse together, indicating their reciprocal attraction via the N and S poles. Furthermore, we reveal that a self-fueled liquid metal motor also runs as an endogenous fluidic magnet owing to the electromagnetic homology. When aluminum is added to liquid gallium in solution, it forms a spin motor and dynamically variable charge distribution that produces endogenous magnetism inside. This explains the common phenomena where reflective collision and attractive fusion between running liquid metal motors occur, which are partially caused by the dynamic adjustment of their N and S polarities, respectively. On this basis, more experimental approaches capable of generating dynamic electrical fields also work for the same target. Finally, we propose that such a fluidic endogenous magnet could lead to a magnetic monopole and four technical routes to realize this are suggested. The first involves matching the interior flow of liquid metal machines. The second is the superposition between an external electric effect and the magnetic field. The third route involves composite construction between magnetic particles and a liquid metal spin motor. Finally, chemical methods, such as via galvanic cell reactions, are proposed. Overall, the present theory and identified experimental evidence illustrate the role of a liquid metal machine as a fluidic endogenous magnet and highlight promising methods for the realization of magnetic monopoles. A group of unconventional magnetoelectric devices and applications could therefore be possible in the near future.

Portable flexible electronics based on petroleum-based polymers have stepped onto the stage of modern technology. Increasing environmental problems facilitate emerging technologies based on cellulose because of its abundant sources and the nature of CO₂ consumption and biodegradability. Bacterial cellulose (BC) stands out among all cellulose materials because of its unique features, including the abundant hydrogen bonds, small diameter, three-dimensional nano-networked structures, high purity and crystallinity, and the degree of polymerization. The adequate properties impart BC and its nano-nano composites with superior balance among ductility, strength, and porosity, which are crucial for wearables. The principles of this balance, the fabrication of the nano-nano composites, and the wearable electronic applications based on BC are discussed in detail in this review.