Shape-memory Polymer Nano-composites And Their Properties

As one kind of novel smart materials, shape memory polymers (SMPs) exhibit excellent shape memory effect, which can be attributed to the net-point and reversible switch units among their polymer network. SMPs can remember one or more temporary shapes, but also recover to their original shape when exposed to external stimuli such as heat, light, water and so on. SMPs attract a wide range of attention because of their possession with prominent stimuli-responsiveness and actuation. Among the new and high technology with national primary support in 2015, SMPs materials and their application technique hold the position in a high profile. In recent years, the researches in the combination of SMPs with nano-materials have become one of the popular hot topics among the world. Shape memory polymer nano-composites are able to tremendously strengthen or broaden the properties of SMPs, improving the application technique of SMPs. In this dissertation, functional shape memory polyurethane served as the main substrates, by combination with silver nanowires (AgNWs), carbon nanotubes (CNTs) and Au, a series of novel composites nanostructures were designed and fabricated. This dissertation concentrates on the exploration of the multi-stimuli responsive and sensing properties of the nano-composites systems, including properties of heat, electricity, water and light sensing. The main contents are shown as following:(1) AgNWs/SMPU nano-composites were fabricated with bi-layer structure by transfer method. The micro morphologies and structures of the nano-composites have been characterized by SEM It was found that AgNWs were incorporated into the surface layer of SMPU substrates. The analysis for their properties were conducted by equipment such as electronic universal testing machine, electrochemical workstation and so on. These nano-composites were flexible, stretchable and electrically conductive, particularly exhibiting reversible strain-dependent conductivity. As a result, the nano-composites recovered to their original shape when triggered by electricity and heat; while thermal stimulus triggered the pre-stretched nano-composites to recover to their original shape, their conductivity recovered in the meanwhile. The findings disclosed that the conductive shape memory composites were able to respond to external thermal stimulus by variation of the electrical signals in a desired manner, which may be served as an ideal conductive temperature-sensitive materials.(2) CNTs/SMPU nano-composites were fabricated with bi-layer structure via transfer method. The micro morphologies, structures and propertied of the nano-composites have been characterized by SEM, contact angle instrument and electrochemical workstation. CNTs not only endow the composites with electrical conductivity but also improve the hydrophilicity due to the polar groups on the surface of the modified CNTs. The shape memory effect of these nano-composites was investigated when triggered by electricity and water stimuli. The result showed that the nano-composites were possessed with dual-responsiveness. Based on these two stimuli-responsiveness, a swelling programing was designed to test the water-sensing effect of the materials. It was found that the shape memory thermo-mechanical programming enlarged magnitudes of the resistivity variation, which meaned the improving of water-sensitivity.(3) Au/SMPU nano-composites were fabricated via shape memory thermo-mechanical programming and vacuum magnetron sputtering. Atomic Force Microscopy (AFM) characterization of wrinkles was conducted under ambient conditions in a contact mode. The wavelength and amplitude of wrinkles were obtained by using the section analysis function in the Nanoscope software (SPIP 6). It was found that Au micro/nano wrinkles were formed on the surface layer of the nano-composites with secondary island-like nanostructure, and that different pre-stretched ratio left influence on the morphology of micro/nano wrinkles. surface-enhanced Raman scattering (SERS) data were collected on UV Laser Raman Spectroscopy in the mode of D1 with 10s exposure time under 17mV laser (633nm). It was proved that Au/SMPU nano-composites have their potential in SERS with the enhanced ratio of 7-8 for Poly(3-hexylthiophene-2,5-diyl)(P3HT) as tunable platforms.