Understanding Assembly In Nano Spray Dried Block Copolymer Nanoparticles

Block copolymers (BCP) are known to self-assemble into highly ordered and periodic nanoscale structures. When BCP self-assembly is confined in macro and nano spheres, a variety of morphologies including onion, core and shell, bud and pupa-like can be achieved, making them attractive materials for optical, catalytic and biological applications. The BCP nanoparticles (NP) morphologies can be controlled by tailoring BCP chemical composition, solvents, confining sphere size, surface tension, and process parameters. Up until now, BCP confinement into NP was mainly achieved through emulsion processes. Nano Spray drying (NSD) of polymers offers a new route for BCP NP fabrication through confinement of the BCP within sprayed nano-droplets.

In this research, we study the assembly of BCP micro and nano particles through NSD. In NSD, an atomizer separates a BCP solution into droplets, which are then sprayed into a large tube. Inert gas is heated to the evaporation point of the solvent and flown through the tube, drying the falling particles that are then collected at the bottom. Poly(styrene-block-methyl methacrylate) (PS-b-PMMA), poly(styrene-block-2-vinyl-pyridine) (PS-b-P2VP) and poly(styrene-block-4-vinyl-pyridine) (PS-b-P4VP) were spray dried from toluene and chloroform. Scanning and transmission electron microscopy (SEM and TEM, respectively) were used to study the relationship between the BCP NP morphologies and the BCP chemistry, solvent composition, and NSD process parameters. Following the NSD, PS-b-P4VP NP were suspended in a polyvinyl alcohol (PVA) aqueous solution, and solvent annealed with chloroform in order to tune the internal NP morphology. Finally, hybrid organic-inorganic particles were created through Sequential Infiltration Synthesis (SIS), a method based on atomic layer deposition chemistry that enables growth of metal oxides within polymers. Using SIS, alumina and zinc-oxide were selectively grown in the BCP polar domains, transforming the BCP NP into hybrid organic-inorganic NP.