Preparation of Aqueous Core/Polymer Shell Microcapsules by Internal Phase Separation

Abstract

Aqueous core/polymer shell microcapsules with mononuclear and polynuclear core morphologies have been formed by internal phase separation from water-in-oil emulsions. The water-in-oil emulsions were prepared with the shell polymer dissolved in the aqueous phase by adding a low boiling point cosolvent. Subsequent removal of this cosolvent (by evaporation) leads to phase separation of the polymer and, if the spreading conditions are correct, formation of a polymer shell encapsulating the aqueous core. Poly(tetrahydrofuran) (PTHF) shell/aqueous core microcapsules, with a single (mononuclear) core, have been prepared, but the low Tg (−84 °C) of PTHF makes characterization of the particles more difficult. Poly(methyl methacrylate) and poly(isobutyl methacrylate) have higher Tg values (105 and 55 °C, respectively) and can be dissolved in water at sufficiently high acetone concentrations, but evaporation of the acetone from the emulsion droplets in these cases mostly resulted in polynuclear capsules, that is, having cores with many very small water droplets contained within the polymer matrix. Microcapsules with fewer, larger aqueous droplets in the core could be produced by reducing the rate of evaporation of the acetone. A possible mechanism for the formation of these polynuclear cores is suggested. These microcapsules were prepared dispersed in an oil-continuous phase. They could, however, be successfully transferred to a water-continuous phase, using a simple centrifugation technique. In this way, microcapsules with aqueous cores, dispersed in an aqueous medium, could be made. It would appear that a real challenge with the water-core systems, compared to the previous oil-core systems, is to obtain the correct order of magnitude of the three interfacial tensions, between the polymer, the aqueous phase, and the continuous oil phase; these control the spreading conditions necessary to produce shells rather than "acorns".

Preparation of porous carbon particle with shell/core structure

“…Mathiowitz et al prepared double-walled microspheres by this one-pot method for controlled drug release [14,15]. Vincent et al prepared a series of polymer microcapsules with liquid cores also by this method [16][17][18]. In our work, PFR has been used as the shell material, and PMMA as the porogen.…”

Synthesis and Characterization of PLGA Shell Microcapsules Containing Aqueous Cores Prepared by Internal Phase Separation

“…Aqueous core-PLGA shell microcapsules were prepared by internal phase separation method adapted from the Vincent group (9,(11)(12)(13) with modifications. This method involves preparation of two phases: internal acetone-water phase and external oil phase.…”

“…SEM was also used to examine the internal structure of microspheres and microcapsules. To do so, dried particles were frozen with liquid nitrogen and then fractured by a glass rod before thawing (9,12,16). Fractured particles were prepared for SEM imaging and evaluated as mentioned above.…”

“…Therefore, very limited studies have addressed this point in the literature (6,7). These studies came mainly in an attempt to overcome drawbacks related to the conventional w 1 /o/w 2 double emulsion method (6)(7)(8)(9)(10). They involved in situ formation of w 1 /o/w 2 double emulsion from a single o/w emulsion via spontaneous self-emulsification by using either an appropriate emulsifier such as sodium dioctyl sulfosuccinate (Aerosol OT or AOT) (6) or a copolymer as poly(D,L-lactide)-b-poly(2-dimethylaminoethyl methacylate)(PLA-b-PDMAEMA) (7).…”

“…This approach was then utilized to prepare aqueous core microcapsules using three polymers: poly(tetrahydorfuran), poly(methyl methacrylate), and poly(isobutyl methacrylate) (9). This method involves onestep formation of acetone-water in oil emulsion.…”