Novel PSBM Triblock Copolymer Nanoparticle Morphologies via Flash NanoPrecipitation

Abstract

The behavior of diblock copolymers under nanoparticle confinement is well documented in prior research, including for those nanoparticles fabricated using the continuous Flash NanoPrecipitation (FNP) technique developed by Johnson et al (2003)1. However, less is known about the non-equilibrium morphologies triblock copolymers assume under kinetic entrapment via FNP. In this thesis, we focus on a single triblock copolymer, poly(styrene-block-butadiene(1,4)-block-methyl methacrylate), and identify fabrication conditions at which stable colloidal suspensions can form via FNP. Various parameters adjusted to change the particles include polymer concentrations, addition of surfactants, and solvents. We utilize dynamic light scattering (DLS) techniques to identify particle size distributions, and transmission electron microscope (TEM) imaging to view particle morphologies. To better understand the unique influences of FNP kinetic trapping, as opposed to equilibrium precipitation, we also use near-equilibrium dialysis precipitation to compare the obtained morphologies. Our experiments indicate that colloidal suspensions are less prone to aggregation upon addition of nonionic surfactant Tween 80 to the suspension. Additionally, samples containing Tween 80 typically show one of two morphologies: a spherical PMMA domain-filled “honeycomb” structure, or a “disjointed parallel” structure with layers of PS and PMMA similar to the diblock copolymer lamellar morphology. Sequential precipitation of polymer blocks, as opposed to all three simultaneously, also reveals interesting intermediate micellar morphologies. These findings, which explain some of the mechanisms behind the formation of kinetically trapped structures, can be used to inform future triblock copolymer FNP fabrication for internally structured colloidal engineering applications.