We describe here am ethod to synthesize ultrasmall nanocapsules with ad iameter of 6nm, exhibiting aw elldefined core-shell morphology.Remarkably,the nanocapules are synthesized in aminiemulsion process without the need of large amounts of surfactant as commonly used in the microemulsion process.U ltrasmall nanocapsules with an oil core and as ilica shell are formed by the concurrent processes of as ol-gel reaction and Ostwald ripening. Using solvents with different water solubilities and alkoxysilanes with different reactivities,wedemonstrate that sizes of obtained nanocapsules depend on the ripening rate and alkoxysilane conversion rate. The method can be also used for encapsulating natural oils such as peppermint oil and limonene.This work shows that the Ostwald ripening phenomenon can be employed beneficially for the preparation of very small colloids.
We describe a facile strategy to synthesize hybrid nanocapsules with an oil core for hindering interactions between payloads and silica shell. Polycaprolactone/silica nanocapsules are synthesized by an interfacial sol−gel process occurring simultaneously with internal phase separation of the polymer produced by a miniemulsion-solvent evaporation technique. The localization of the polycaprolactone in the nanocapsules is depending on the ratio between polymer and silica. Formation of hybrid nanocapsules is found to significantly hinder interactions of drugs such as ibuprofen and carbamazepine with the silica surface.
We
describe here a method to decrease particle size of nanoparticles
synthesized by miniemulsion polymerization. Small nanoparticles or
nanocapsules were obtained by generating an osmotic pressure to induce
the diffusion of monomer molecules from the dispersed phase of a miniemulsion
before polymerization to an upper oil layer. The size reduction is
dependent on the difference in concentration of monomer in the dispersed
phase and in the upper oil layer and on the solubility of the monomer
in water. By labeling the emulsion droplets with a copolymer of stearyl
methacrylate and a polymerizable dye, we demonstrated that the migration
of the monomer to the upper hexadecane layer relied on molecular diffusion
rather than diffusion of monomer droplets to the oil layer. Moreover,
surface tension measurements confirmed that the emulsions were still
in the miniemulsion regime and not in the microemulsion regime. The
particle size can be tuned by controlling the duration during which
the miniemulsion stayed in contact with the hexadecane layer, the
interfacial area between the miniemulsion and the hexadecane layer
and by the concentration of surfactant. Our method was applied to
reduce the size of polystyrene and poly(methyl methacrylate) nanoparticles,
nanocapsules of a copolymer of styrene and methyl methacrylic acid,
and silica nanocapsules. This work demonstrated that a successful
reduction of nanoparticle size in the miniemulsion process can be
achieved without using excess amounts of surfactant. The method relies
on building osmotic pressure in oil droplets dispersed in water which
acts as semipermeable membrane.
We describe here a method to synthesize ultrasmall nanocapsules with a diameter of 6 nm, exhibiting a well‐defined core–shell morphology. Remarkably, the nanocapules are synthesized in a miniemulsion process without the need of large amounts of surfactant as commonly used in the microemulsion process. Ultrasmall nanocapsules with an oil core and a silica shell are formed by the concurrent processes of a sol–gel reaction and Ostwald ripening. Using solvents with different water solubilities and alkoxysilanes with different reactivities, we demonstrate that sizes of obtained nanocapsules depend on the ripening rate and alkoxysilane conversion rate. The method can be also used for encapsulating natural oils such as peppermint oil and limonene. This work shows that the Ostwald ripening phenomenon can be employed beneficially for the preparation of very small colloids.
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