Elaboration of a double emulsion within a microfluidic device: application to the encapsulation of a hydrophilic active substance by polyurea

While the demand for encapsulated substances is growing, the current production of microcapsules is based on energy-consuming and polluting techniques. The PROMETHEE team of M2P2 is working on the coupling of a new chemistry, polyurea, replacing melamine formaldehyde identified as an endocrine disruptor, and a new technology based on microfluidics. This allows a new kind of production that is more respectful of the environment and health. The encapsulation of a hydrophobic substance by polyurea is commonly done and the process is well developed [1 - 3]. However, the transposition of this protocol for the encapsulation of a hydrophilic core by polyurea has limitations [4 - 6]. A common problem is polyurea formation in the continuous phase due to the migration of amine from the inner aqueous phase to the outer oil one. Therefore, it at least makes the continuous phase gets turbid and hard to observe [4], and worst of all, it may make it extremely hard to separate the capsules from reactive media [5]. Also due to the amine migration, the obtained polyurea shell is generally thinner than that generated via an O/W emulsion [4] under the same synthetic conditions. Besides, to eliminate the toxic amine monomers in the droplet phase, the isocyanate monomers are generally in excess in the continuous phase [4] and this causes unnecessary loss of isocyanates which are generally expensive.

The aim of this thesis is to design, develop and optimize an innovative process for the encapsulation of a hydrophilic substance such as vitamin C, a subject of particular interest in the field of cosmetics. The encapsulation of this water-soluble antioxidant makes it possible to protect this active substance from a possible damage and to release it at the time of use by mechanical rupture. The encapsulation process is based on two consecutive steps, i) the elaboration of a simple emulsion and ii) the interfacial polymerization reaction. The aim here is to study the change of step i by the elaboration of a double W/O/W emulsion (water-in-oil-in-water) using a microfluidic device which will be commercial or home-made microchips. This type of device allows precise control of capsule properties such as size, wall thickness and morphology. 

We foresee different phases of study such as:

  • Elaboration of the W/O emulsion: choice of the hydrophobic microchip, hydrodynamic study, map of the flow regimes and their transition, influence of the presence of the active substance (vitamin C);
  • Elaboration of the W/O/W emulsion: choice of the hydrophilic microchip, study of the operating conditions and coupling with the hydrophilic microchip;
  • Interfacial polymerization reaction: fabrication of the capsules and analysis of their properties (size, shell thickness, confinement, encapsulation efficiency…)

Contact : Pierette.Guichardon@centrale-marseille.fr

[1] Du J., Preparation of polyuria microcapsules calibrated in size and shell thickness by a microfluidic process for the absorption of ultraviolet, thesis, Aix Marseille Université, (2021)
[2] Du J., Ibaseta N., Guichardon P., Generation of an O/W emulsion in a flow-focusing microchip: importance of wetting conditions and of dynamic interfacial tension, Chemical Engineering Research and Design, 159, (2020), 615-627
[3] Du J., Ibaseta N., Guichardon P., Characterization of polyurea microcapsules synthesized with a less toxic isocyanate and eco-friendly esters via microfluidics: shape, shell thickness, morphology and encapsulation efficiency, Chemical Engineering Research and Design, 182, (2022), 256-272
[4] Polenz, I., Datta, S. S., & Weitz, D. A. (2014). Controlling the Morphology of Polyurea Microcapsules Using Microfluidics. Langmuir, 30(44), 13405-13410. doi: 10.1021/la503234z 
[5] Zhao, L., Yang, X., Ma, L., & Li, Q. (2020). Preparation of imidazole embedded polyurea microcapsule for latent curing agent. Journal of Applied Polymer Science, 137(43), 49340. doi: 10.1002/app.49340 
[6] Polenz, I., Brosseau, Q., & Baret, J.-C. (2015). Monitoring reactive microencapsulation dynamics using microfluidics. Soft Matter, 11(15), 2916-2923. doi: 10.1039/C5SM00218D