Poly(ethylene glycol)@Silica hybrid microparticles prepared via a non-aqueous sol-gel process: A method for merging both classes of hybrid materials

The facile one-pot synthesis of poly(ethylene glycol)@silica hybrid microparticles (PEG@silica HMPs) by an oil-in-oil (o/o) emulsification and non-aqueous sol-gel method is reported. The HMPs preparation process begins with the emulsification of PEG and formic acid in heptane containing a polymeric surfactant and tetraethyl orthosilicate (TEOS). Then, a non-aqueous sol-gel process takes place at the interface of the droplets in which the formic acid reacts with TEOS to create the silica shell. In addition, part of the PEG reacts with silica intermediates to form hybrid microparticles (class II hybrids). The durability and stability of the HMPs were investigated by testing the effect of different parameters such as the surfactant type and its concentration, the TEOS and PEG weight ratio, the time for the microparticles to form, the weight ratio between the two oil phases, and the type of PEG. The results show the clear impact of the chemical composition on the stability and the structural properties of PEG@silica HMPs. Moreover, it has been found that besides the covalently bonded PEG, which participates in the hybrid network, forming Si-O-C bindings, a portion of free PEG exists within the porous matrix, which acts as a solvent in the voids of PEG@silica HMPs (class I hybrids).