###### Abstract  
Magnesium nanoparticles of various mean diameters (53-239 nm) were synthesised in this study via pulsed laser ablation in liquid (PLAL) from millimetre sized magnesium powders within isopropyl alcohol. It was observed via a 3 \(\times\) 3 full factorial design of experiments that the processing parameters can control the nanoparticle distribution to produce three size-distribution types (bimodal, skewed and normal). Ablation times of 2, 5, and 25 min where investigated. An ablation time of 2 min produced a bimodal distribution with the other types seen at higher periods of processing. Mg nanoparticle Ultraviolet-Visible spectroscopy (UV-Vis) absorbance at 204 nm increased linearly with increasing ablation time, indicating an increase in nanoparticle count. The colloidal density (mg/mL) generally increased with increasing nanoparticle mean diameter as noted via increasing UV-Vis absorbance. High laser scan speeds (within the studied range of 3000-3500 mm/s) tend to increase the nanoparticle count/yield. For the first time, the effect of scan speed on colloidal density, UV-Vis absorbance and nanoparticle diameter from metallic powder ablation was investigated and is reported herein. The nanoparticles formed dendritic structures after being drop cast on aluminium foil as observed via field emission scanning electron microscope analysis. Dynamic light scattering was used to measure the size of the nanoparticles. Magnesium nanoparticle inks show promise for use in the fabrication conductive tracks or thermal insulation in electronics. magnesium nanoparticles; laser scan speed; pulsed laser ablation in liquid; advanced manufacturing; powder metallurgy; surface science; nanoparticle size distributions; picosecond laser +
Footnote †: journal: Applied Sciences  
the processing parameters such as laser fluence (J/cm\({}^{2}\)), repetition rate (kHz), scan speed (mm/s), pulse width (ps), wavelength (nm) and ablation time (min). Other processing parameters that influence the PLAL process include the laser scan pattern (e.g., spiral or linear pattern) and hatch spacing (\(\upmu\)m); however, little attention has been paid to these in the literature. One of the most important factors during PLAL is the choice of liquid medium. The liquid medium influences the nanoparticle size, yield (mg/mL), ablation efficiency (mg/s), nanoparticle size distribution type (e.g., normal vs. skewed distribution), morphology, chemical composition and surface morphology, all of which directly influence the electrical/mechanical properties of these nanoparticles which directly express their usefulness in wearable industries. DI water is the most used liquid medium during PLAL owing to its simplistic nature [5; 6; 7; 8]. The as-fabricated colloid can be printed as a conductive ink on flexible material to fabricate flexible sensors [9] without the need of additional chemicals. Other liquid media have been used in PLAL including ethanol [10; 11; 12; 13], isopropanol alcohol [14; 15], 2- propanol [13] and methanol [16; 17]. These organic liquids are also non-toxic and have an advantage of having a lower boiling point than water, enabling a quicker evaporation of the liquid medium during 3D printing (e.g., inkjet printing or aerosol jetting) or drop casting. Various types of nanoparticles have been fabricated via PLAL including silver [18], copper [19] and magnesium [20; 21; 22]. Magnesium nanoparticles (Mg NPs) are of special interest in this report owing to their versatile uses. In 2020, [PERSON] et al. [23] reviewed the use of Mg/MgO/MgOH NPs in various fields including biomedical, micro-batteries, environmental (removal of heavy metals in water and air filtration), electronics and high-temperature uses. Mg NPs have gained so much attention in the literature owing to their diverse and excellent properties including high melting point (2852 \({}^{\circ}\)C for MgO), low density, biocompatibility, high specific strength, stiffness, electrical conductivity, absorption of vibrations, plasmonic effects and anti-bacterial effects [23; 24; 25].