Preparation And Properties Of Carbon Nanofibers /PDMS Composite

The large strain sensor with the high precision and good repeatability and stability is the main electronic components used in real-time detection of large strain. The resistance types sensor made of polymer composite materials is one of the main research focus. In this dissertation, the carbon nanofibers(CNF) was add into the polydimethylsiloxane(PDMS) matrix as conductive filler. Then, CNFs/PDMS composite was fabricated by blending method and CNF paper/PDMS composite was fabricated by hot pressing method. The function group on the surface of CNF under different surface treatment was qualitatively characterized by Infrared spectra and the microtopography of CNF and CNFs/PDMS composite were observed by Scanning Electron Microscope(SEM). By measuring the mechanical properties and electrical properties of composite prepared with blending method, under the conditions of different surface treatment and CNF content, the change law of mechanics, electricity and mechanical-electrical coupling performance were discussed with the change of temperature, loading speed and strain cycle. The conductive mechanism and its response rule of polymer composite was analysised in different circumstance. The main conclusions are as follow:1. Acid treated and SDS treat result of SEM indicated that these methods can improve the dispersion of CNFs in solution, decrease the entanglement of the fibers. The results of Infrared spectra show the hydroxyl and carboxyl functional group were found on the surface of CNF treated by acid.2. The electrical conductivity of CNF paper and CNFs/PDMS composite is poor when the CNF treated with acid. The tensile strength of CNF paper /PDMS composite prepared by hot pressing is about 0.83 Mpa and its elongation is just 23%. SEM shows that there are lots of pores in the fracture section of composite. On the contrary, the CNF with SDS treatment demonstrated good mechanical properties and electrical conductivity, can meet the performance requirements of the large strain sensor.3. For the PDMS matrix composite of different CNF content prepared by blending,its tensile strength reach the maximum value at 3wt% CNF. When the content was lower than 3wt%, the elastic modulus improved obviously as the increase of CNF. when the CNF contents exceed 3wt%,the improvement were not obvious. Compared with the composite without surface treatment, the composite with SDS treatment showed the better dispersion in matrix and the obvious improvement in tensile strength, elastic modulus and dynamic stability. The tensile strength of CNFs/PDMS composite with 3wt% CNF content decreased as the rise of temperature while the elastic modulus changes little. The dynamic mechanical properties is stable from 0℃ to 40℃.4. The CNFs/PDMS composite prepared by blending followed the Ohm’s law. And the resistivity decreased sharply with the increasing of CNF content.5. In the process of cyclic strain, the resistance of CNFs/PDMS composite changed periodically and regularly with the strain variation and showed good electrical response characteristics. The composite showed good repeatability from the first tensile deformation. The dynamical elctromechanical properties were temperature independent. The strain response curve indicated that the composite with 5wt% CNF has better stability than the 3wt% one. The measurement results of different load speed showed no significant changes of it’s elctromechanical properties.