Unique pure barium titanate foams with three-dimensional interconnecting pore channels and their high-k cyanate ester resin composites at very low barium titanate loading
High loading of ceramics has been the biggest shortcoming of fabricating high-k ceramic/polymer composites. Herein, unique pure barium titanate (BT) foams with three-dimensional interconnecting foam channels, coded as BTFs, were synthesized using a polymer foam replication method, and the BT content of foams is adjustable. In addition, various loadings of BTF were embodied into cyanate ester (CE) resin to develop a new kind of high-k composite. The spatial structure and content of BTF on the thermal and dielectric properties of BTF/CE composites were systematically researched, and compared with those of traditional composites based on commercial BT powders and ground BTF powders (BTFp), respectively. The results show that BTF/CE composites exhibit a much higher dielectric constant at very low concentrations of BTF than those of BT/CE and BTFp/CE composites. Typically, when the BTF content is as low as 33.5 vol%, the dielectric constant of the resultant BTF6(1200)/CE composite reaches 141.3 (100 Hz), about 8.4 and 14.1 times of those of traditional BT/CE and BTFp/CE composites, respectively; in fact, the BTF6(1200)/CE composite has the highest dielectric constant among non-semiconductive ceramic/polymer composites reported to date; meanwhile the dielectric loss of BTF6(1200)/CE is only about 0.276. The nature behind the excellent dielectric properties of BTF/CE composites was intensively discussed and proven to be attributed to the unique three-dimensional foam structure of BTF in CE resin. This study establishes a new method of preparing novel foam ceramics with three-dimensional interconnecting foam channels and a pure high-k ceramic skeleton as well as high-k ceramic/polymer composites with good processing characteristics at a very low loading of ceramics.