Artavazd Kirakosyan

Controlled morphology of MWCNTs driven by polymer-grafted nanoparticles for enhanced microwave absorption

The development of a lightweight electromagnetic (EM) wave absorber with a wider bandwidth and reflection loss at a low loading is of great interest for applications ranging from conventional electronic devices to specific devices or instruments of the military and aerospace. Although nano-filler (i.e. carbon nanotubes, magnetic nanoparticles, etc.) based polymer nanocomposites (PNCs) have shown great promise in this area of research, typically poor control of their surface modification and dispersion has prevented further development of these materials for application in EM wave absorbers. Here, we introduce and demonstrate a simple and robust platform based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, providing a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement. At equal loadings of nano-fillers (1 wt% of MWCNTs), much deeper reflection loss (RL = −26.9 dB at 5.4 GHz) and a wider bandwidth (4.9 GHz for RL < −10 dB) are observed compared to the conventional PNCs. We show that polymer-grafted nanoparticles serve as a matrix for unfunctionalized CNTs and show a much enhanced dispersion of CNTs, providing a novel opportunity for the multi-functional PNCs by combining functions arising from the controlled dispersion of heterogeneous materials (i.e. inorganic nanoparticles and CNTs) in a new type of CNT/NP/polymer nanostructure.

Electron-Irradiated Polymer Brushes for Hollow Carbon Nanosphere Arrays

A thermally stable 2D array of spheres and their morphology control become important for the fabrication of novel nanostructures. Here, a simple method is presented for fabrication of large-area and well-ordered arrays of carbonized polystyrene (PS) hollow spheres with a controlled (close-packed or non-close-packed hexagonal) morphology, prepared by combining the self-assembly of PS-grafted silica nanoparticles, etching, electron irradiation, and subsequent thermal annealing. Fine control in the 2D or 3D nanostructure of carbon materials can open up new opportunities for high-performance nanoscale applications that require an efficient fabrication method for preparation of the porous carbon array.

Self-assembled polymer-grafted nanoparticles for photonic coating applications

Control of a regular arrangement of nanoparticles and their mechanical stability in a form of arrays and films becomes important in various particle-based technologies such as photonic bandgap materials. Here, we present that polymer-grafted nanoparticles (i.e. polystyrene-grafted silica nanospheres), synthesized by surface-initiated atom radical polymerization (SI-ATRP), can achieve ordered yet mechanically robust films by tuning the polymer brush architecture such as molecular weight and grafting density. Evolution of the particle arrangement in the polymer-grafted nanoparticle films is observed and associated with their wavelength at the maximum reflectance as well as their mechanical characteristics. This could open up new opportunities for fabrication of durable and highly ordered colloidal crystal structures such as photonic coating applications.

Uniform PMMA-CH3NH3PbBr3 Nanoparticle Composite Film for Optoelectronic Application

Organometal halide perovskite materials, due to the tunability of their electronic and optical properties by control of composition and structure, have taken a position of significant importance in optoelectronic applications such as photovoltaic and lighting devices. Despite numerous studies on the structure - property relationship, however, practical application of these materials in electronic and optical devices is still limited by their processability during fabrication. Achieving nano-sized perovskite particles embedded in a polymer matrix with high loading density and outstanding photoluminescence performance is challenging. Here, we demonstrate that the careful control of nanoparticle formation and growth in the presence of poly(methyl methacrylate) results in perovskite nanoparticle - polymer nanocomposites with very good dispersion and photoluminescence. Furthermore, this approach is found to prevent further growth of perovskite nanoparticles, and thus results in a more uniform film, which enables fabrication using the perovskite nanoparticles.