Shape memory-enhanced water sensing of conductive polymer composites
Introduction
Polymeric composites containing various types of nanofillers have been widely explored towards implanting with the reinforced mechanics as well as novel functions [1], [2]. The carbon nanotubes (CNTs) are one set of the most prominent candidates to construct functional polymer composites. The CNT-containing polymer composites commonly possess superior electrical conductivity, which have been applied as the sensory materials, such as gas [3], pressure [4] and strain [5] sensing. The combination of the shape memory polymers (SMPs) and nanofillers lead to shape memory polymer composites. The previous studies of the conductive shape memory polymer composites emphasized on the mechanical reinforcement and electro-responsiveness. However, there has been little literature concerning the stimuli sensing of the polymer composites by far. The electrical conductivity of the composites varies along with the shape changes in a typical shape memory thermo-mechanical programming. By virtue of the shape-dependent conductivity, we once exploited a novel temperature sensing silver nanowire-shape memory composites [1]. Herein, a shape memory-enhanced water sensing was unprecedentedly reported for CNT-containing polymer composites. Compared to the direct immersion into water, the composites experiencing shape memory programming exhibited enlarged magnitudes of the variation in resistivity. The findings may greatly benefit the development of the conductive shape memory polymer composites in the fields of the sensory materials and flexible electronics.
Section snippets
Experimental
The CNT–SMPU composites were fabricated via transfer process according to our previous study [2], which was briefly described as below: multi-wall CNTs suspension in methanol was dip-coated onto a glass substrate before adding the SMPU solution in dimethylacetamide; the composite films were peeled off after solidification in vacuum. The composite films, cut into the size of 15 mm*3 mm*60 μm (length*width*thickness), were labeled as PUC-01, PUC-02 and PUC-03, representing for the CNTs contents of
The morphological, mechanical and structural investigations
The CNT–SMPU composites were in bi-layer structure, consisting of the conductive layer constructed by the CNTs and the SMPU matrix (are shown in Fig. 1a and b). It was clearly found that the fibril-like CNTs network whose one part was embedded into the matrix meanwhile the other part was left on the surface, making the composites single-side electrically conductive [2]. Acid treatment endowed the CNTs with an abundant of polar groups. The thickness of the CNTs layer could be well controlled by
Conclusions
CNT–SMPU composites in bi-layer structure were fabricated via transfer process. The CNTs constructed a percolating conductive network, mechanically reinforcing the composites. Moreover, the CNTs content promoted water absorption percentages and improved the thermal stability of the composites. The water sensing of the composites was comparatively studied, exhibiting a shape memory enhanced effect. The underlying mechanism may be the re-orientation and local movements of the CNTs driven by
Acknowledgments
The authors thank the National Natural Science Foundation of China (Nos. 51203191, 51273048, and 51203025), the Special Funded Project of Pearl River in Guangzhou City of Nova of Science and Technology (2014J2200090), and Science and Technology Planning Project of Guangdong Province, China (2013B021700001) for providing financial support.
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