Understanding the\nFormation Dynamics and Physical\nProperties of Nanocapsules Using Charge Detection Mass Spectrometry

Characterizing the size, structure, and composition of\nnanoparticles\nis vital in predicting and understanding their macroscopic properties.\nIn this work, charge detection mass spectrometry (CDMS) was used to\nanalyze nanocapsules (∼10–200 MDa) consisting of a liquid\noleic acid core surrounded by a dense silica outer shell. CDMS is\nan emerging method for nanoparticle analysis that can rapidly measure\nthe mass and charge of thousands of individual nanoparticles. We find\nthat increasing the feed volume of the tetraethylorthosilicate (TEOS)\nprecursor added to form the silica shell of the nanocapsules yielded\nboth higher and broader nanocapsule mass distributions with differentiable\ndensities. A two-dimensional mass versus charge analysis also revealed\nthe formation of two distinct populations of nanocapsules. These two\nnanocapsule morphologies were also present in transmission electron\nmicroscopy (TEM) images and exhibited low-density spherical cores\nand crescent-shaped cores where the remainder of the core volume was\n“filled in” by more dense silica. Nanocapsule shell\ngrowth kinetics over a ∼48-h synthesis period were also monitored\nby sampling the reaction mixture at various times, quenching the sampled\naliquots, and then characterizing these time-resolved samples by CDMS.\nThe CDMS data reveal three distinct growth phases in nanocapsule formation;\nrapid initial nucleation, an “inverted” distribution\nof silica growth, and a final slow growth phase where the rate of\nmass increase and final nanocapsule masses are dictated by the initial\nTEOS feed volumes. CDMS-enabled understanding of the diverse nanocapsule\nsizes, morphologies, and growth dynamics will allow us to better predict\nnanocapsule properties while reducing the experimental burden in optimizing\nnanocapsules for real-world applications.