The spreading, imbibition and solidification of a hot two-dimensional droplet on a cooler porous substrate is studied. Lubrication theory and asymptotic reduction are used to derive a coupled system of evolution equations for the droplet thickness and vertical extents of the solid/melt boundary and the saturation front within the porous medium. This medium is assumed to be a membrane composed of an array of pores having fixed width. A precursor layer model and a disjoining pressure are used to relieve the singularity at the contact line. When the solidification and imbibition time scales are similar to those associated with spreading, the dynamics follow two stages: spreading and imbibition accompanied by solidification within the pores leading to their blockage, followed by contact line arrest and basal solidification of the droplet; the possibility of crust formation at the gas–melt interface is excluded from the present study. The dependence of the dynamics on the relevant system parameters is elucidated. Furthermore, our modelling predictions compare favourably with experimental data also obtained as part of the present work.

The fabrication of alginate hydrogel microparticles with embedded liposomes and magnetic nanoparticles for radiofrequency controlled release of encapsulated chemical cargo was considered. An extractive gelation process was implemented in a microfluidic device, which enabled the production of uniform composite microparticles of dimensions comparable to those of blood cells (between 5 and 10 μm). The critical parameters that control the extractive gelation process were systematically explored and feasible values that provide microgel particles of a defined size and morphology were identified. First, the initial water-in-oil droplet is formed in a flow-focusing junction whose size is controlled by the flow-rate of the oil phase. Then, the train of droplets is sandwiched between two streams of oil containing calcium ions. In that way, a flux of water molecules from the droplets towards the continuous phase as well as a transport of calcium ions towards the disperse phase are initiated. The final microparticle properties were thus found to be sensitive to three elementary sub-processes: (i) the initial droplet size; (ii) the extraction of water into the oil phase, which was controlled by the volume of the oil phase and its initial moisture content; and (iii) the kinetics of ionic cross-linking of the alginate matrix, which was controlled by the varying calcium concentration. The size and morphology of the final composite microgels were fully characterized

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