Activation Energy Distributions Predicted by Dispersive Kinetic Models for Nucleation and Denucleation: Anomalous Diffusion Resulting from Quantization

Rationale for the crystallization of titania polymorphs in solution

We use in situ X-ray absorption and diffraction studies to directly monitor the crystallization of different titania polymorphs in one and the same solution. We find that, despite the commonly accepted polymorphic-crossover from anatase to rutile triggered by the critical size of nanoparticles, in the solution their respective nucleation and growth are independent processes. Moreover, we find that 5.9 nm rutile nanoparticles are formed prior to the formation of 8.4 nm anatase nanoparticles. Our results suggest that the origins of this crystallization mechanism lie in the formation of an intermediate non-crystalline phase and in time-dependent changes in the chemical environment.

Quantitative investigations of thermal and photoinduced J- and H-aggregation of hydrophobic spirooxazines in binary solvent through UV/vis spectroscopy

Photo- and chemo-stimulable architectures.

Roles of nucleation, denucleation, coarsening, and aggregation kinetics in nanoparticle preparations and neurological disease

Kinetic models for nucleation, denucleation, Ostwald ripening (OR), and nanoparticle (NP) aggregation are presented and discussed from a physicochemical standpoint, in terms of their role in current NP preparations. Each of the four solid-state mechanisms discussed predict a distinct time dependence for the evolution of the mean particle radius over time. Additionally, they each predict visually different particle size distributions (PSDs) under limiting steady-state (time-independent) conditions. While nucleation and denucleation represent phase transformation mechanisms, OR and NP aggregation do not. Thus, when modeling solid-state kinetics relevant to NP processing, either the time evolution of the mean particle radius or the fractional conversion data should be fit using appropriate models (discussed herein), without confusing/combining the two classes of models. Experimental data taken from the recent literature are used to demonstrate the usefulness of the models in real-world applications. Specifically, the following examples are discussed: the preparation of bismuth NPs, the synthesis of copper indium sulfide nanocrystals, and the aggregation of neurological proteins. Because the last process is found to obey reaction-limited colloid aggregation (RLCA) kinetics, potential connections between protein aggregation rates, the onset of neurological disease, and population lifespan dynamics are suggested by drawing a parallel between RLCA kinetics and Gompertz kinetics. The physical chemistry underpinning NP aggregation is investigated, and a detailed definition of the rate constant of aggregation, k(a), is put forth that provides insight into the origin of the activation energy barrier of aggregation. For the two nanocrystal preparations investigated, the initial kinetics are found to be well-described by the author's dispersive kinetic model for nucleation-and-growth, while the late-stage NP size evolution is dominated by OR. At intermediate times, it is thought that the two mechanisms both contribute to the NP growth, resulting in PSD focusing as discussed in a previous work [Skrdla, P. J. J. Phys. Chem. C2012, 116, 214-225]. On the basis of these two mechanisms, a synthetic procedure for obtaining monodisperse NP PSDs, of small and/or systematically targeted mean sizes, is proposed.