Mechanistic Study on Microstructural Tuning of Metal Nanoparticle/Polymer Composite Thin Layers: Hydrogenation and Decomposition of Polyimide Matrices Catalyzed by Embedded Nickel Nanoparticles

Magnetic composite nanostructures composed of a dielectric matrix containing magnetic nanoparticles offer opportunities for the fabrication of next-generation magnetic devices, in addition to providing a fundamental understanding of nano-magnetism. However, a synthetic strategy for the fine-tuning of such composite nanostructures is required. Herein, we report an analytical study on the structural tuning of composite thin layers of a polyimide matrix containing nickel nanoparticles. Control of the composite layer microstructure was achieved by decomposition of the polyimide matrix using the nickel nanopartides as a catalyst, which resulted in weight loss and thus shrinkage of the composite layer volume. Several analytical experiments were conducted for films annealed at a constant temperature for different time intervals and hydrogen partial pressures to identify the chemical structures of decomposition products and to elucidate the reaction mechanism of the metal-catalyzed decomposition process. The decomposition rate was highly dependent on the hydrogen partial pressure; the hydrogenation of amide bonds generated by cleavage of imide rings, which leads to breaking of the polyimide matrix backbone, was the rate-determining step of the decomposition process. The mechanism of the decomposition process is of importance for control of the interparticle distance between nickel nanoparticles with fixed size through volume change of composites, which provides an effective methodology for fine-tuning of the magnetic interactions in these composite nanostructures.