Synthesis and characterization of poly(N-isopropylacrylamide-co-N,N′-methylenebisacrylamide-co-acrylamide) core - Silica shell nanoparticles by far using reactive surfactant polyoxyethylene alkylphenyl ether ammonium sulfate

We report a novel approach based on using polyoxyethylene alkylphenyl ether ammonium sulfate (HS10) as an anion reactive surfactant, which greatly reduced the size of poly(N-isopropylacrylamide-co-acrylamide-co-N,N'-methylenebisacrylamide) [P(NIPAM/AM/MBA)] microgel core - silica shell particles. First, the microgel cores were synthesized by copolymerization of N-isopropylacrylamide (NIPAM), N,N'-methylenebisacrylamide (MBA) with a variation of acrylamide (AM) and HS10 concentration in water. It followed by silica encapsulation of the microgel cores via the addition of 3-glycidyloxypropyltrimethoxysilane (GLYMO) and tetraethyl orthosilicate (TEOS) at alkaline environment (pH 12). It is interesting to note that the size of both PNIPAM-based microgel cores and PNIPAM-based microgel core - silica shell particles were well-controlled by using a small level of HS10. Furthermore, SEM images of the hybrid core - shell particles show the well-defined spherical morphology with monodisperse particle size distribution. As expected, HS10-containing samples are covered by the porous silica shell layer, instead of continuous silica shell obtained from HS10-free samples observed in TEM images. This novel incorporation not only well controls the core size and shell morphology, leading to increase their specific surface area but also does not greatly affect the thermo-sensitivity of final products. The resultant thermo-responsive microgel core - silica shell particles with controlled particle morphology and physicochemical properties are useful for biomedical application fields.