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Two kinds of thiophene monomers (thiophene and thiophene carboxylic acid) are used to synthesize a series of polythiophene matrix materials with different ratios. Polythiophene carboxylic acid can form strong hydrogen bonds between molecules, and the conjugated thiophene ring can be used to obtain higher thermal conductivity. The core–shell structure of polythiophene-coated polyethylene glycol and nano zinc oxide was synthesized by in situ polymerization to form a shaped phase change composite. The electron micrograph shows this phenomenon very well. Comparing the thermal conductivity and heat storage performance of two different polythiophene matrix composites, it can be explained that the chemical interaction between molecules is conducive to the formation of heat conduction pathways. Thermal decomposition temperature of polythiophene carboxylic acid and its polyethylene glycol composite structure is about 10 °C higher than that of polythiophene, which, on the other hand, also indicates the tight molecular arrangement. It is derived from the differentiation of its molecular structure, and this compact structure plays a positive role in the improvement of its thermal conductivity. However, excessive intermolecular force hinders the regular arrangement of polyethylene glycol. Under the condition that the amount of thermal conductive filler is 25%, the thermal conductivity is increased from 0.895 to 1.05 W · m –1 k –1 and the phase transition is decreased from 149 J/g to less than 135 J/g. Finally, the stability of the shaped phase change composite was good, the solid form was maintained near the phase transition temperature, and no leakage was observed.

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In the last couple of decades, attaching sensors permanently onto in-service engineering structures has been a key strategy for conducting in situ structural integrity assessments. [1-4] In this respect, a wide range of sensors, which include but are not limited to optical fibers, [5,6] piezoelectric transducers, [7-9] electromagnetic acoustic transducers, [10,11] and polyvinylidene fluoride film sensors, [12,13] have been used in practice. However, the existing technologies suffer from various limitations, which include narrow frequency bandwidth, redundant volume and mass, high cost, and stringent requirements on coupling. In pursuit for improved sensing systems, sensors that are lightweight, flexible, cost effective, convenient to fabricate, and sensitive over a broad frequency range have attracted much R&D effort. Carbon nanoparticle-based composite materials, which emerged from recent research, have demonstrated the potential for satisfying the demands of modern sensing systems. The nanostructures of these materials are piezoresistive, such that the overall electrical resistance of a material varies with mechanical deformations. This is mainly attributed to 1) the inherent piezoresistivity of the nanofillers in the material, and changes in 2) the macroscopic resistances and 3) the quantum tunneling resistances between adjacent nanofillers when the distances between the nanofillers change with mechanical deformations. The latter phenomenon is known as the quantum tunneling effect. Wearable strain sensors that are fabricated from carbon nanocomposite materials [14-16] exhibit abundant merits, which include negligible weight, high physical flexibility, remarkable manufacturability, and outstanding sensitivity to microscopic deformations. These attractive features also render carbon nanocomposite materials promising candidates for sensors that are used to monitor conditions of engineering structures. [16-19] It has been shown on many occasions that carbon nanocomposite sensors can be highly sensitive to ultrasonic waves, capable of responding to dynamic strains down to the microscale with frequencies up to hundreds of kilohertz. [20] Also, it is believed that for sensing strains in the ultrasonic regime, the quantum tunneling effect plays the dominant role in determining the piezoresistive responses of the sensors. [21] Nanocomposite ultrasonic sensors are mainly fabricated from three different types of carbon nanofillers, namely, carbon black

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