Facile and highly efficient microencapsulation of a phase change material using tubular microfluidics

This paper presents a microfluidic approach towards the fabrication of highly monodisperse polyurea microcapsules, 35-500μm in size, containing n-octadecane (phase change material, PCM). The synthesis consisted of the following two steps: (i) emulsification of n-octadecane, isophorone diisocyanate (IPDI) and dibutyltin dilaurate (DBTDL) in an aqueous mixture of tetraethylenepentamine (TEPA), poly (vinyl alcohol) and sodium dodecyl sulfate (SDS)and (ii) in situ polycondensation between TEPA and IPDI along and outside the tube length. The resulting PCM@polyurea microcapsules underwent a rapid and repeated liquid/solid phase transformation at different temperatures. The average sizes and morphology of the microcapsules were controlled by tuning the flow rate of either the continuous or discontinuous phase. The morphology, polycondensation and phase change behavior of the microcapsules were investigated by optical microscopy equipped with a thermostat plate, scanning electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. The effect of the hydrophobic Fe₃O₄ nanoparticles (NPs) on the crystallization behavior was also examined in cases of microcapsules with or without NPs.