(621h) 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.