(Keynote) Controlling Size and Dispersity in Nanoparticle Synthesis: Some Theoretical Results

Abstract

Polymeric nanoparticles are of increasing interest in nanotechnology and nanomedicine. One promising approach to preparing nanoparticles in a controlled manner is self-assembly from solution, e.g., in microfluidic devices. Molecular parameters such as the polymer length and architecture as well as process parameters such as mixing speed and shear rate can be used to control the size and shape of the particles. Here we use self-consistent field theory and field-based simulations to investigate some of the main physical mechanisms underlying this control. The talk will have two parts. In the first part, we examine the influence of molecular parameters on the resulting particles, with particular focus on the effect of molecular dispersity. Traditionally, theoretical studies us model systems of idealized monodisperse polymers. In reality, however, most synthetic polymers are inherently polydisperse, and this has a significant impact on the size and dispersity of the nanoparticles. In the second part, we examine mechanisms of size control by tuning process parameters. We examine the so-called co-solvency method, where a collapse of polymeric nanoparticles from solution is induced by mixing bad solvent into a polymer dispersion. Experimentally, it is found that the particle size can be tuned by varying the mixing speed. We show that this control essentially happens in the initial stage of polymer-solvent demixing and derive scaling laws which are in agreement with experiments. Then, we study the effect of high shear rates on self-assembly. Shear mainly affects the later stages of self-assembly. It can reduce potential barriers for particle fusion and thus assist the production of larger particles. Furthermore, it can induce irreversible shape changes and be exploited to make particles with unconventional shapes.