Size reduction and water dispersibility improvement of hexagonal boron nitride particles by femtosecond laser irradiation in water

Abstract

Controlling the size and surface state of inorganic particles, which strongly influence their dispersibility in solvents, is important for diverse applications. Intense femtosecond laser pulses can induce plasma formation in material–dispersed solvents and interact with both materials and solvents. In this study, femtosecond laser pulses are employed to modify hexagonal boron nitride (hBN) particles dispersed in water, with the aim of evaluating the effects of the femtosecond laser process on the size reduction and surface modification of hBN particles. Shadowgraph imaging reveals the formation of the reactive environment in hBN–dispersed water, resulting from the ionization of water molecules which leads to the generation of OH radicals. Evaluation of the hBN particle sizes suggests an overall reduction from 160 to 110 nm after 60 min of irradiation and the generation of nanodots between 5 and 10 nm in size. In addition, it is confirmed that the number of particles with higher zeta potentials increases after the samples are laser-irradiated, suggesting a change in the surface state. Consequently, the duration of hBN particle dispersion in water is significantly increased, with an improvement of at least one order of magnitude, for the laser-irradiated samples. This study presents a demonstration of the formation of a reaction field that affects hBN particles in size and dispersibility in water.

In-line monitoring and modelling of particle size reduction of hexagonal boron nitride (hBN) suspension in femtosecond laser processing

“…A femtosecond laser with a central wavelength of 800 nm, pulse width of 50 fs, and repetition rate of 10 Hz was focused onto hBN dispersed in water inside a quartz cuvette using an aspheric lens with a focal length of 12.5 mm. For details, please see the aforementioned paper [11,12]. Experiment S-T has already revealed, as reported in [12], that size reduction occurs by femtosecond-laser irradiation, and in this study, we conducted an additional measurement by TS on the same sample for the particle-size distribution.…”

“…For the 2 cm 3 experimental system (experiments S-T, S-E and S-C)shown in figure 1(a), we used the femtosecondlaser experimental system reported in an earlier paper [12]. A femtosecond laser with a central wavelength of 800 nm, pulse width of 50 fs, and repetition rate of 10 Hz was focused onto hBN dispersed in water inside a quartz cuvette using an aspheric lens with a focal length of 12.5 mm.…”

“…For example, their ionization of water molecules initiates the formation of hydrated electrons, which play a significant role in chemical reactions within aqueous environments [6][7][8]. Various studies on the generation of hydrated electrons by femtosecond lasers have been conducted [8][9][10], and the amount and spatial distribution of the generated hydrated electrons have been investigated using in-situ shadowgraph-imaging measurements via the pump-probe method [11,12].…”

“…These combined effects on materials and solvents offer new possibilities for modifying material properties and creating innovative applications, even for stable materials such as hBN. Past research has explored the application of femtosecondlaser processes to hBN for shaping, refining, and improving dispersion stability [5,12,13]. In these studies, the size reduction of hBN particles, including the synthesis of nanoparticles facilitated by functional groups derived from solvents, has been reported.…”

“…Because particle-size control is important in the manufacture of composite materials, we explored the treatment of hBN particles using a femtosecond laser, which produces plasma in aqueous media. It has been reported that at particle sizes of approximately a few hundred nm, the dispersion stability is more than 40 times improved by the change in surface state along with the size reduction induced by the femtosecond-laser process [12]. To evaluate the chemical properties of treated hBN particles and produce composite materials using hBN particles as fillers, a flow-type recirculating reactor system that increases the throughput of treated hBN particles will be necessary.…”