Scalable Nanocomposites Synthesis Via Electrospray-Mediated Electroemulsification and Flash Nanoprecipitation

The objective of this work is to develop a robust nanocomposite synthesis platform, which incorporates electrospray techniques to overcome the challenges associated with current, small-scale nanocomposite synthesis methods. Conventional methods (i.e. sonication, film rehydration, dialysis) for producing nanocomposites are limited to mostly batch scales, confined to a low product volume and a long processing time, diminishing commercial application of these technologies. Recently, coaxial electrospray-enabled AEROsolization and subsequent self-assembly through Interfacial inStability (Aero-IS) and Flash NanoPrecipitation (FNP) were introduced to address these challenges. These approach are both used to fabricate nanoparticles comprised of amphiphilic block copolymers (i.e. PS-PEO) and hydrophobic encapsulants (i.e. nanoparticles, drug molecules). Aero-IS utilizes the coaxial electrospray technique, which generates oil in water emulsion droplets in aerosol form. The collected emulsion droplets undergo interfacial instability¹, which promotes the self-assembly of amphiphiles to encapsulate the hydrophobic cargoes. Flash NanoPrecipitation² utilizes either a confined jet mixer or a multi-inlet vortex mixer to promote nucleation and growth of amphiphiles by achieving rapid mixing of a water-miscible organic phase and an aqueous phase. Despite the significantly increased throughput achieved by both methods, challenges still remain. The Aero-IS process requires the addition of surfactants that are present at concentrations of more than 90X those of the product, presenting a purification challenge. Similarly, in FNP, solvent must be removed from the final product. In addition, in FNP high flow rates are required to ensure good mixing, which may limit the ability to process intermediate (pilot scale) quantities of material (i.e. ml min-1 scale in FNP). Hence, the goal of this research was to develop an improved nanocomposite synthesis platform, Liquid-Liquid Electrospray (LLE), that can operate over a range of flow rates with reduced purification requirements.

Unlike traditional electrospray techniques, in the LLE configuration, the electrospray needle is placed directly inside an aqueous medium, along with a grounding electrode. The needle is insulated with tightly fitted PTFE tubing, which prevents short-circuiting upon the application of a high voltage to the needle. The organic phase with amphiphlic block copolymers and the hydrophobic encapsulants is processed through the needle, and, depending on the miscibility of the organic phase in the aqueous phase, the applied high voltage enables either electroemulsification, or micromixing of the organic phase. For water-immiscible organic solvents (i.e. chloroform), instantaneous emulsification is followed by interfacial instability self-assembly of micelles. For water-miscible organic solvents (i.e. tetrahydrofuran), the high degree of mixing achieved using LLE promotes nucleation and growth of the hydrophobic components introduced into the aqueous medium. Nanocomposites synthesized via LLE-mediated electroemulsification and flash nanoprecipitation include micelles encapsulating quantum dots (QDs), and/or superparamagnetic iron oxide nanoparticles (SPIONs). Overall, this new nanocomposite synthesis platform provides the advantages of scale-up and high controllability without the requirement for surfactants, improving methods to develop nanocomposites at scale.

1.         Zhu, J., & Hayward, R. C. (2008). Spontaneous generation of amphiphilic block copolymer micelles with multiple morphologies through interfacial instabilities. Journal of the American Chemical Society, 130(23), 7496-7502.

2.         Akbulut, M., Ginart, P., Gindy, M. E., Theriault, C., Chin, K. H., Soboyejo, W., & Prud'homme, R. K. (2009). Generic method of preparing multifunctional fluorescent nanoparticles using flash nanoprecipitation. Advanced Functional Materials, 19(5), 718-725.