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.
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