Wax@SiO2 thermo-stimulable core shell particles  Encapsulation is widely used in very diverse applications, from drug delivery to carbon-free self-copying paper. Various techniques allow for a compound to be protected from its surroundings, and vice-versa, until delivery is needed. Encapsulation is also used to ensure a steady and slow delivery of a chemical, usually a drug.Previous research led to an original synthetic pathway to prepare thermo-responsive capsules made of a wax core surrounded by a silica shell, allowing the delivery of the encapsulated compound in response to a temperature elevation[1].The process is based on the elaboration of a wax in water emulsion above the wax melting temperature, using particles to stabilize the liquid wax droplets (Pickering emulsions). The use of silica nanoparticles allows a high droplets monodispersity thanks to the limited coalescence phenomenon and a direct control of the droplets' size by varying the nanoparticles/wax ratio.The emulsion is then cooled down at room temperature, below the wax melting point, and the obtained wax crystals suspension is mineralized by the hydrolysis and condensation of a silica precursor at the wax-water interface.Under heating, the inner wax expands and the shell breaks leading to the liquid oil release, as seen on fig.1. By an appropriate choice of the wax, the temperature of release can easily be tuned. Such capsules that allow triggered deliverance provoked by an external stimulus belong to the class of smart materials. Figure 1 : Steps of wax liberation from a wax@SiO2core shell particle under heating. Toward capsules complexification  Even though the temperature-controlled release of the wax core otherwise encapsulated by the silica shell may lead to several applications on its own, its hydrophobic nature forbids the use of hydrophilic adjuvants.To address that issue we propose two new synthetic pathways using the same concept, namely the use of wax expanding when melting and thus breaking the silica shell, applied to more complex emulsions.We explored two different and complementary approaches : using a wax in water in oil double emulsion (fig. 2), and a water in wax in water double emulsion. The mineralization process was very similar to the one used previously on the simple capsules. Figure 2 : wax@water@SiO2 double capsule We show that we obtain thermo-stimulable double capsules using both synthetic pathways, opening the way to the encapsulation of any type of adjuvant and its release at the desired temperature[2, 3]. The simple syntheses and the use of emulsions allow an easy scaling up of the processes.Moreover, the demonstration that this concept works with double emulsions opens the path to the use of other multiple emulsions or of the millifluidic tool to increase the complexity of the thermo-stimulable capsules in order to use them in applications such as multi-therapy delivery.[1] M. Destribats, V. Schmitt and R. Backov. Langmuir 2010, 26, 1734[2] M. Nollet, M. Depardieu, M. Destribats, R. Backov and V. Schmitt. Particle 2013, 30, 62[3] M. Depardieu, M. Nollet, M. Destribats, V. Schmitt and R. Backov. Particle 2013, 30, 185

Thermostimulable multi-core-shell capsules

248th National Meeting (2014)

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