In Situ Sol–Gel Synthesis of Unique Silica Structures Using Airborne Assembly: Implications for In-Air Reactive Manufacturing

Abstract

Optical trapping enables the real-time manipulation and observation of morphological evolution of individual particles during reaction chemistry. Here, optical trapping was used in combination with Raman spectroscopy to conduct airborne assembly and kinetic experiments. Micro-droplets of alkoxysilane were levitated in air prior to undergoing either acid- or base-catalyzed sol–gel reaction chemistry to form silica particles. The evolution of the reaction was monitored in real-time; Raman and Mie spectroscopies confirmed the in situ formation of silica particles from alkoxysilane droplets as the product of successive hydrolysis and condensation reactions, with faster reaction kinetics in acid catalysis. Hydrolysis and condensation were accompanied by a reduction in droplet volume and silica formation. Two airborne particles undergoing solidification could be assembled into unique 3D structures such as dumb-bell shapes by manipulating a controlled collision. Our results provide a pipeline combining spectroscopy with optical microscopy and nanoscale FIB–SEM imaging to enable chemical and structural insights, with the opportunity to apply this methodology to probe structure formation during reactive inkjet printing.

Analysis and optimisation of mixing in binary droplet collisions

“…In ReJI, as well as several adaptive manufacturing techniques, the quality of the product and throughput depends on the speed of injection and size of the droplets (Stringer & Derby 2009). This imposes a limit on the Weber number for droplet stacking (Son et al 2008) and mid-air collisions (Barker et al 2022). Furthermore, the complexity in the modelling of additive manufacturing processes increases from the idealised droplet collision.…”

“…2008) and mid-air collisions (Barker et al. 2022). Furthermore, the complexity in the modelling of additive manufacturing processes increases from the idealised droplet collision.…”

Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors

“…The size and morphologies of SNPs were controlled by varying the ratio of TEOS to NH 4 OH (NH 4 OH:TEOS = 4:1, 2:1, and 1.5:1). The particle size was affected by the amount of NH 4 OH that controls the rate of hydrolysis and condensation in the silica sol–gel reaction. − Figure shows uniform spherical SNPs and their increasing diameter from (a) to (c) with the decreasing NH 4 OH amount. Using different sizes of SNPs as silicate sources (seeds), we synthesized the size-controlled Ca 2–0.05 SiO 4 : 0.05 Eu 3+ .…”