Abstract
Nanoprecipitation is a self-assembly process for forming nanoparticles by replacement of a good solvent in which multiple materials are dissolved with a poor solvent. It has demonstrated its advantages of easy setup, good size controllability for single component nanoparticles formation, the potential for mass production and the ability of being customized to form different kinds of composite nanoparticles. This research focuses on exploring the capabilities of the nanoprecipitation method for forming complex nanoparticles and attempting to gain a better understanding of the formation. Two distinct multi-component nanoparticle systems were selected as model systems: “immiscible blends of polystyrene (PS) and poly (methyl methacrylate) (PMMA)” and “perylene- tetracyanoquinodimethane (TCNQ) molecular co-crystals”. The nanoprecipitation processes were carried out with a typical stirred vessel set up for fast mixing and the systems were brought into a high supersaturation condition for the concentrations and solvent ratios used. This work demonstrates the formation of PSPMMA immiscible blend nanoparticles with a core-shell structure, while aggregation and network formation of PMMA was observed. A model taking into account the glass transition temperature (Tg) confinement effect is proposed in explaining the differences between PSPMMA blend samples and control group samples. This work reveals the importance of the nature of the polymers in the blend, especially the glass transition, on the behavior of the final products. Research on perylene-TCNQ co-crystal nanoprecipitation was a continuation of earlier work done by Nishida. The formation of 3:1 stoichiometry nano co-crystals (P3T1) by nanoprecipitation was demonstrated for an initial perylene/TCNQ ratio of 3:1, as its crystal structure was confirmed by powder X-ray diffraction (PXRD) spectrum. The finding was further supported by absorption spectra, dynamic light scattering (DLS) data and scanning electron microscopy (SEM) images. For an initial perylene:TCNQ ratio of 1:1, the resulting sample contained not just the 1:1 stoichiometry nano-crystals (P1T1), but also the P3T1 crystals as well as nanocrystals of pure TCNQ and possibly perylene. This work shows that the initial stoichiometry of materials is not the only factor dictating the final product of co-crystal nanoprecipitation, although the detailed mechanism is not yet well understood based on current experimental data.
