Investigating Processes of Nanocrystal Formation and Transformation via Liquid Cell TEM

Recent ex situ observations of crystallization in both natural and synthetic systems indicate that the classical models of nucleation and growth are inaccurate. However, in situ observations that can provide direct evidence for alternative models have been lacking due to the limited temporal and spatial resolution of experimental techniques that can observe dynamic processes in a bulk solution. Here we report results from liquid cell transmission electron microscopy studies of nucleation and growth of Au, CaCO3, and iron oxide nanoparticles. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying nanoparticle crystallization as well as dynamic information that provide constraints on important energetic parameters not available through ex situ methods

Hierarchical Calcite Crystals with Occlusions of a Simple Polyelectrolyte Mimic Complex Biomineral Structures

Biominerals are complex inorganic-organic structures that often show excellent mechanical properties. Here a bio-inspired study of a remarkably simple synthetic system is presented in which only one charged polymer additive (poly(sodium 4-styrenesulfonate)) is able to induce hierarchical structuring of calcite similar to biominerals. The interaction of the negatively charged polymer with the nucleation and growth of the mineral, in particular via selective adsorption to internal and external (001) facets of the calcite lattice, implies structural features from the micrometer down to the nanometer level. The crystals exhibit a distinct rounded morphology and a controlled orientation. Moreover, the polymer molecules are occluded within the crystals with different concentrations in well-defined regions. This leads to the induction of a mesoscale structure based on 100 nm sized mineral building blocks with granular substructure and rough surface, as well as small modifications of the crystallographic structure. Such a combination of hierarchically organized structural features has previously only been reported for biogenic calcite, which is typically grown in a complex process involving multiple organic additives. It is also shown that the organic occlusions in the calcite-PSS hybrid crystals strongly affect the mechanical performance, as known for some biominerals