Jiajun Ma

Ultra-low dielectric closed porous materials via incorporating surface-functionalized hollow silica microspheres: preparation, interface property and low dielectric performance

One effective route to reduce the dielectric constant is to directly incorporate hollow silica (HoSiO2) microspheres into a polymeric matrix. However, the incompatibility between silica and hydrophobic polymers possibly results in interfacial defects and polarization, and thus a high dielectric loss. In this study, the HoSiO2 microspheres were coated by polystyrene using a surface-initiated ATRP method in order to enhance interfacial property. TGA results indicated that the weight percentage of polystyrene in resulting microspheres (HoSiO2@SI-PS) reached around 33 wt%. OM images showed that the thickness of the polystyrene layer reached around 2 μm. HoSiO2@SI-PS microspheres with a weight percentage of 25% were incorporated into polyethylene (PE) to prepare the composites. The dielectric measurement results indicated that the dielectric constant of the composites was reduced to 2.05, while maintaining low dielectric loss at the level of 10−4. In comparison, when HoSiO2@C-PS microspheres, which were prepared by conventional vinyl-initiated free radical polymerization, were incorporated into polyethylene, the dielectric loss was greatly elevated to 0.007. SEM images and water absorption experiments further revealed that the low dielectric loss of PE/HoSiO2@SI-PS was related to the dense interfacial structure, strong interfacial interaction and low water absorption ability.

Selectively detecting trace picric acid by reduced perylene bisimide with POSS substituents and their nanoaggregates

Reduced perylene bisimides (PBIs) with two substituents of polyhedral oligomeric silsesquioxane (POSS) are designed and synthesized for rapid and selective detection of picric acid in THF solution. Nanoaggregates of the reduced PBI show fluorescence that is also sensitive to the concentration change of picric acid.

Coherent random lasing from nano-scale aggregates of hybrid molecules by enhanced near zone scattering

Nano-scale aggregates of hybrid molecules, such as N,N′-di-[3-(isobutyl polyhedral oligomeric silsesquioxanes)propyl] perylene diimide (DPP) which is composed of perylene diimide (PDI) as gain group and polyhedral oligomeric silsesquioxanes (POSS) as scattering group at a mole ratio of 1:2, are formed in carbon disulfide (CS2) solution within a concentration range from 3 × 10−5 M to 10−3 M. The aggregation of DPP in the solution was characterized using ultraviolet visible (UV-vis) and fluorescence spectroscopy. Under pumping of a 532 nm pulse laser, coherent random laser (RL) is produced from the aggregates in CS2 solution with a threshold of 17.4 μJ and a Q value of 2440 at a DPP concentration of 10−4 M. Enhanced near zone scattering by aggregation is thought to boost coherent RL. This research not only extends the RL system to the extremely weak scattering regime but also provides a new direction for research on nano-scale materials for lasers using molecular design.

Quantitative analysis of “Δl = ls − lg” to coherent random lasing in solution systems with a series of solvents ordered by refractive index

This work systematically illustrated the effects of solvents on random lasing in active scatterer solution systems. The scatterer, N,N′-di[3-(isobutyl polyhedral oligomeric silsesquioxanes)propyl]perylene diimide (DPP), was chemically synthesized from gain group perylene diimide (PDI) and scattering group polyhedral oligomeric silsesquioxanes (POSS) at a mole ratio of 1:2 through chemical bonding. Random lasing action was detected in such solutions with a series of solvents ordered by refractive index (RI), from which it was found that solution systems with larger RI solvent facilitate boosting of random laser (RL) for a suitable “Δl = ls − lg” (ls > lg). There are two potential situations for solvents with smaller RI: in one, a small RI difference between scatterers and surroundings results in extremely large ls, and the extremely large Δl in these samples means that there is no observation of random lasing; in the other, there is increased lg as characterized by UV-Vis spectroscopy, although the ls remains almost unchanged for the large RI fluctuations between scatterers and surroundings, resulting in smaller Δl with no detection of random lasing as the laser pumping energy cannot compensate for the gain loss. Results from this work will aid in quantitatively judging the necessary condition of “Δl = ls − lg” to RL in solutions, and aid in designing suitable solution systems to boost RL.