Controlled release of microcargo from water-in-liquid crystal emulsions via interfacial shear induced by synthetic microstirrers

Abstract

Past studies demonstrated that the microcargo carrying aqueous droplets trapped in LCs through elastic stresses can be triggered to release by applying shear to LC-bulk interfaces. Herein, we report our investigations on the release mechanisms of such microcargo entrapped in aqueous droplets of W-in-LC emulsions via interfacial shear caused by the synthetic micro-stirrer microparticle assemblies of iron oxide particles rotated with a magnetic field. We show that a three fold control over the release rate of the tracer molecules is possible that have initial release rates of 14.3 ± 2.5 μg cm⁻² h⁻¹, 26.5 ± 3.4 μg cm⁻² h⁻¹, and 46.9 ± 4.6 μg cm⁻² h⁻¹ when the rotation of magnetic flux was 250, 500 and 1000 rpm, respectively. We measure the release rates to reduce to 5.4 ± 1.2 μg cm⁻² h⁻¹, 6.3 ± 0.7 μg cm⁻² h⁻¹, and 20.0 ± 3.2 μg cm⁻² h⁻¹ after 60 min of shearing at 250, 500 and 1000 rpm, respectively. We present evidence for the release mechanism resulting in such temporal release profiles that correlate with the magnitude of the shear applied to the interface, interfacial coverage of the microstirrers, and the creaming effect of the aqueous droplets doped with tracers. We also report that the influence of the interfacial density of the microparticles that showed an intermediate areal density is required to achieve a maximized release rate. Additionally, we found evidence of the influence of the droplet charge that critically determines the release. This study highlights the importance of the colloidal and interfacial phenomena in the release profiles of the dispersed droplets present in a LC medium.