Polymerization of Electric Field-Centered Double Emulsion Droplets to Create Polyacrylate Shells

Abstract

Porous and hollow particles are widely used in pharmaceuticals, as solid phases for chromatography, as catalyst supports, in bioanalytical assays and medical diagnostics, and in many other applications. By controlling size, shape, and chemistry, it is possible to tune the physical and chemical properties of the particles. In some applications of millimeter-scale hollow shells, such as in high energy density physics, controlling the shell thickness uniformity (concentricity) and roundness (sphericity) becomes particularly important. In this work, we demonstrate the feasibility of using electric field-driven droplet centering to form highly spherical and concentric polymerizable double emulsion (DE) droplets that can be subsequently photopolymerized into polymer shells. Specifically, when placed under the influence of an ∼6 × 10(4) V(rms)/m field at 20 MHz, DE droplets, consisting of silicone oil as the inner droplet and tripropylene glycol diacrylate with a photoinitiator in N,N-dimethylacetamide as the outer droplet, suspended in ambient silicone oil, were found to undergo electric field-driven centering into droplets with ≥98% sphericity and ∼98% concentricity. The centered DE droplets were photopolymerized in the presence of the electric field. The high degrees of sphericity and concentricity were maintained in the polymerized particles. The poly(propylene glycol diacrylate) capsules are just within the sphericity requirements needed for inertial confinement fusion experiments. They were slightly outside the concentricity requirement. These results suggest that electric field-driven centering and polymerization of double emulsions could be very useful for synthesizing hollow polymer particles for applications in high energy density physics experiments and other applications of concentric polymer shells.

Electrohydrodynamics of a compound drop

“…They require less than about 1% concentricity for fusion-initiating inertia confinement to work. Experimental results show [20] that application of an electric field can lead to highly concentric shells.…”

Bifurcation Dynamics of a Particle-Encapsulating Droplet in Shear Flow

“…We envision that our results might potentially inspire new approaches of 'hydrodynamic centering' composite systems like emulsions to obtain a uniform shell in addition to electric centering methods [28,29], or vice versa, using hydrodynamic effect to generate emulsions with pre-designed nonuniform shell thickness [30] for programmed release of substances. We hope our study will motivate experiments in these directions.…”

Production of Highly Monodisperse Millimeter‐Sized Double‐Emulsion Droplets in a Coaxial Capillary Device

“…Double‐emulsion droplets have a significant potential for producing various microcapsules or other attractive candidates for a wide range of applications . Especially, the droplets ranging from 100 µm to a few millimeters are widely used in various areas, such as bioactive species delivery, controlled release, microreactors, heterogeneous catalysis, ion exchange, granular flow, and inertial confinement fusion (ICF) experiments . However, the millimeter‐scale double‐emulsion droplets were more vulnerable due to the complex rheology and the density stratification than micro‐scale ones.…”

“…Up to now, few researches were done to obtain millimeter‐sized double‐emulsion droplets via the microfluidic approach , , , , since challenges associated with millimetric emulsion generation in coaxial flows are variations in drop size and the metastability of the produced emulsion. In inertial fusion energy (IFE) experiments, Striet et al used a triple‐orifice droplet generator to form millimeter‐sized foam shells , , , , which was restricted by a higher request of assembly precision. A double T‐shaped channel and double coaxial capillary device were also used to produce large‐sized polymeric shells.…”