Characterization of Polystyrene/Polyisoprene Janus Particles Fabricated by the Dialysis NanoPrecipitation Method

Abstract

Anisotropically structured, compartmentalized colloids have sparked great interest in recent research due to their ability to exhibit multiple functionalities. One such superstructure that self-assembles is polymer Janus particles with biphasic geometry. Many methods have been developed to fabricate Janus particles yet its complete characterization and scalability have remained a challenge. The formation of Janus particles using the Dialysis NanoPrecipitation method remains unexplored and can provide valuable information about these challenges. In this study, the effects of overall polymer concentration, relative homopolymer ratio, and polymer molecular weight were studied on polystyrene/polyisoprene Janus particles fabricated by the Dialysis NanoPrecipitation method. Additionally, timed experiments were conducted with increasing duration of dialysis in order to understand the assembly mechanism of Janus particles. It was found that Janus particle molecular weight and size can be independently tuned by varying the overall concentration of the polymer feed. Furthermore, the surface domain composition of Janus particles made by Dialysis NanoPrecipitation can be tuned by altering the ratio of homopolymers that constitute the two domains. Particles made using high molecular weight polymers (> 1,000 kg/mol) exhibited multi-faced structures, departing from the Janus morphology. Lastly, the results of the work suggest that particle growth is characterized by two regimes, one marked by rapid nucleation and phase separation followed by a second regime of fusion and growth.