Temperature-sensitive materials (TSMs) attract a lot of attention in recent years. The physical properties of TSMs can be tuned by temperature. Among TSMs, room-temperature switchable materials (RTSMs), which responses automatically around room temperature, is more interesting for researchers. Because they have great potentials in smart switches, smart building, high sensitive sensors, automatic filters, energy storage and can be used in daily life.
In this paper, we prepared the room-temperature switchable materials by dispersing chemical functionalized CNTs into hexadecane. The DC conductivity, thermal conductivity and dielectric constant of RTSMs can be regulated simultaneously in a narrow temperature range around phase change point. By changing the volume fraction of octadecylamine-grafted MWCNTs in hexadecane, the switching ratio of DC conductivity, thermal conductivity and dielectric constant reaches 5 orders of magnitude, 3 times and 106.4 respectively. To our best knowledge, it is the highest switching ratio at room temperature in existing materials. The multifunctional switch is caused by the rearrangement of the fillers in hexadecane matrix during phase transition. During the freezing course, the fillers are squeezed into the grain boundaries of solid matrix to form percolating conducting networks. The conducting networks enhance the electrode injection, improve the interior electron migration and decrease the interface resistance at the same time. The interface between filler and solid matrix give rise to strong Maxwell-Wagner relaxation. These reasons make the DC conductivity, thermal conductivity and dielectric constant of frozen sample increase a lot. When the composite is remelting, the re-dispersion of fillers results in the DC conductivity, thermal conductivity and dielectric constant of sample decreasing again. The switch shows good stability during temperature cycles. The switching ratio can be easily regulated by the volume fraction of filler and temperature ramping rate. By using different long chain alkane as matrix, other multifunctional switchable composites with various trigger temperature can be easily achieved.