PIC micelles as versatile structuring agents
Résumé
Polyion Complex (PIC) or Complex Coacervate Core (C3M) Micelles [1] have been used as structuring agents to template ordered mesostuctured porous silica materials [2]. PIC micelles assemble by electrostatic complexation of oppositely charged polyelectrolytes, one of them being a double hydrophilic block copolymer (DHBC). Compared to classical structuring agents obtained from amphiphilic molecules, PIC micelles offer several advantages: first, they can be recovered and reused in several mesoporous material synthesis cycles [2]. Secondly, they allow single step preparation of drug loaded porous materials [3]. Finally, tuning the characteristics of the porous material does no longer require the synthesis of new structuring agents: they can be adjusted by playing with the physico-chemical conditions, using a unique polyelectrolyte system. The present work aims at correlating the characteristics of the porous materials and the physico-chemical properties of the PIC micelles.Mesostructured materials have been prepared by condensation of TEOS in the presence of PIC micelles of polyethylene oxide-b-poly(acrylic acid) (POE-b-PAA) copolymer complexed with neomycin (NM) or oligochitosan (OC). TEM, sorption measurements and X-ray diffraction have shown that varying structures and pore sizes can be achieved by simply varying concentration and pH. On the other hand, using osmometry, specific ion potentiometry, elemental analysis and small angle X-ray scattering, the associative phase separation of poly(acrylic acid) in the presence of neomycin has been studied as a model system for the core of the PIC micelles.The hybrid materials obtained right after drying (without calcination) are porous. This is related to the high degree of swelling of the core of the PIC micelles that contains at least 50% of water in weight. The water content in the micelles varies with concentration because it is determined by osmotic equilibrium between the core and the suspending solution. This translates into variation of porous volume and allows fine tuning of the pore size in the hybrid material. These features are preserved after calcination. Finally, the pH of material synthesis has been shown to determine the drug loading: neomycin concentration in the hybrid porous material increases as pH increases.In conclusion, PIC micelles offer numerous advantages and opportunities in the domain of functional ordered mesostructured materials due to the sensitivity of their characteristics to physico-chemical parameters, allowing the reversibility of their assembling in water, the possible delivery of functional molecules and the possibility to control the swelling of PIC micelles core.References: [1] Voets, I. K.; de Keizer, A.; Stuart, M. A. C. Adv. Colloid Interface Sci., 2009, 147-48, 300-318.[2] Baccile, N.; Reboul, J.; Blanc, B.; Coq, B.; Lacroix-Desmazes, P.; In, M.; Gerardin, C. Angew. Chem. Int. Ed., 2008. 47(44), 8433-8437.[3] Molina, E.; Warnant, J.; Mathonnat, M.; Bathfield, M.; In, M.; Laurencin, D.; Jérôme, C.; Lacroix Desmazes, P.; Marcotte, N.; Gérardin, C. Langmuir, 2015. 31, 12839-12844.