Temperature dependence of axial thermal expansion coefficient of multi-walled carbon nanotubes (A procedure based on measurements of coefficient of thermal expansion for aligned carbon nanotube/epoxy composites)

Abstract

In this study, to evaluate the temperature dependence of the coefficient of thermal expansion (CTE) of multi-walled carbon nanotubes (MWCNTs) in the axial direction, the CTEs of aligned MWCNT reinforced epoxy composites are measured, and the axial CTEs of the MWCNTs are computed using the rule of mixtures. The mean diameters of the MWCNTs used in this study are 25 nm and 41 nm. The composite samples whose length is along the direction in parallel to MWCNT alignment are heated using a hot plate, and the length change is measured by a laser displacement meter. We demonstrate that the thermal contraction is observed in the composites, i.e. the CTEs of the composites are negative. The axial CTEs of both MWCNTs are calculated to be negative in the temperature range from -5‒85°C, and they tend to increase with the increasing temperature. The MWCNTs with the mean diameter of 41 nm possess larger negative CTE in the above temperature range compared with the MWCNTs with the mean diameter of 25 nm. The CTEs of the MWCNTs with the mean diameter of 25 nm and 41 nm are -1.1 ‒ 0.1×10-5 K-1 and -1.9 ‒ -0.8×10-5 K-1, respectively. These values are in reasonable agreement with those of the CNTs reported previously. The negative CTEs may be explained by out-of-plane atomic vibrations predicted by theoretical and numerical studies.

Keywords

• carbon nanotubes
• polymer materials
• composites
• coefficient of thermal expansion
• rule of mixtures