Elsevier

Materials Letters

Volume 161, 15 December 2015, Pages 189-192
Materials Letters

Shape memory-enhanced water sensing of conductive polymer composites

https://doi.org/10.1016/j.matlet.2015.08.105Get rights and content

Highlights

  • CNT–SMPU composites exhibited water sensing property via changes in resistivity.

  • Shape memory thermo-mechanical experience enlarged magnitudes of Rs variation.

  • Re-orientation and local movements of the CNTs may be the mechanism.

Abstract

Electrically conductive polymer composites have been widely utilized as the sensory materials being capable of response to various types of stimuli. A shape memory-enhanced water sensing was unprecedentedly reported for polymer composites comprising of carbon nanotubes (CNTs) and shape memory polyurethane (SMPU). The morphological, thermal, mechanical and micro-structural properties of the CNT–SMPU composites were investigated. Two swelling processes were specifically designed to measure the water sensing of the composites. It was found that the shape memory thermo-mechanical programming enlarged magnitudes of the resistivity variation, which may be attributed to the combination of the swelling effect and the re-orientation/local movements of the CNTs along with stress/strain energy release. The findings may greatly benefit the applications of the smart polymers in the fields of sensory materials and flexible electronics.

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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