ABSTRACT
Try and encapsulate microparticles inside the cores of microcapsules and you will often find that particles adhere to the liquid-liquid interface in a phenomenon known as Pickering stabilization. Particles will remain irreversibly trapped and embedded within the subsequently formed microcapsule membrane. In cases where the encapsulant particles must remain suspended inside the microcapsule core to retain their desired properties or behaviours, Pickering stabilization is detrimental. Here we demonstrate a general procedure using yield stress materials as the core material, where the yield stress of the gel is strong enough to suspend particles against sedimentation, but weak enough to allow spatial manipulation of encapsulant particles using an external field. This external field imparts enough force on particles to disrupt the supporting network and allow particle mobility after encapsulation.
ABSTRACT
When forming composite microcapsules through the emulsification of a dispersed phase laden with microparticles, one will find that the microparticles become irreversibly embedded in the resulting microcapsule membrane. This phenomenon, known as Pickering stabilization, is detrimental when the end function of the microcapsules relies on the mobility of encapsulated microparticles within the capsule core. In this work, a robust microencapsulation route using density matching of non-Brownian microparticles in a binary solvent is shown to easily and effectively encapsulate particles, with >90% of particles retaining mobility within the microcapsules, without the necessity for prior chemical/physical modifications to the microparticles. This is proposed as a generalized method to be used for all manner of particle chemistries, shapes, and sizes.
ABSTRACT
Pour sand into a container and only the grains near the top surface move. The collective motion associated with the translational and rotational energy of the grains in a thin flowing layer is quickly dissipated as friction through multibody interactions. Alternatively, consider what will happen to a bed of particles if one applies a torque to each individual particle. In this paper, we demonstrate an experimental system where torque is applied at the constituent level through a rotating magnetic field in a dense bed of microrollers. The net result is the grains roll uphill, forming a heap with a negative angle of repose. Two different regimes have been identified related to the degree of mobility or fluidisation of the particles in the bulk. Velocimetry of the near surface flowing layer reveals the collective motion of these responsive particles scales in a similar way to flowing bulk granular flows. A simple granular model that includes cohesion accurately predicts the apparent negative coefficient of friction. In contrast to the response of active or responsive particles that mimic thermodynamic principles, this system results in macroscopic collective behavior that has the kinematics of a purely dissipative granular system.
ABSTRACT
This work demonstrates the fabrication of surface-textured microcapsules formed from emulsion droplets, which are stabilized by an interlocking mesh of needle-like crystals. Crystals of the small-organic-compound decane-1,10-bis(cyclohexyl carbamate) are formed within the geometric confinement of the droplets, through precipitation from a binary-solvent-dispersed phase. This binary mixture consists of a volatile solvent and nonvolatile carrier oil. Crystallization is facilitated upon supersaturation due to evaporation of the volatile solvent. Microcapsule diameter can be easily tuned using microfluidics. This approach also proves to be scalable when using conventional mixers, yielding spikey microcapsules with diameters in the range of 10-50 µm. It is highlighted that the capsule shape can be molded and arrested by jamming using recrystallization in geometric confinement. Moreover, it is shown that these textured microcapsules show a promising enhanced deposition onto a range of fabric fibers.