Excerpts from an interesting approach to creating hollow polymer microspheres from a pickering emulsion.
A solid-stabilized multiple w/o/w or o/w/o emulsion was prepared in a two-step process. Various nanocomposite polymer microspheres with multihollow armored closed pores were fabricated easily by suspension polymerization of the multiple Pickering stabilized emulsions.
Self-assembly of solid particles at the liquid?liquid interface to stabilize so-called Pickering emulsions has been well documented and offers a straightforward pathway for the production of organized nanostructures.? Pickering emulsion droplets have been used as templates to prepare highly controlled elastic membranes and other supracolloidal structures. In addition, some attempts have been made to improve the stability of multiple or double emulsions by introducing solid particles. Both particles and surfactants have been employed usually in combination to form multiple emulsions.
The first step involves the formation of a primary and simple w/o emulsion by homogenizing water (fw ? 0.2) into a dispersion of hydrophobic silica nanoparticles in styrene with 2,20-azobisisobutyronitrile (AIBN) via
ultrasonification. In the second step, the w/o emulsion just made is re-emulsified into an aqueous dispersion of hydrophilic Fe2O3 nanoparticles by shaking by hand. The volume fraction of w/o emulsion in the final multiple emulsion is 0.17. Subsequently, the produced w/o/w emulsion is polymerized for 8 h at 60C and dual nanocomposite polystyrene (PS) microspheres with aqueous multicores or dual nanocomposite multihollow PS microparticles are obtained as shown in Fig. 1.
Light microscopy images of the primary water-in-styrene (w/o) emulsion (a) and the relative multiple water-in-styrene-in-water (w/o/w) Pickering emulsion (b) are illustrated in? Fig. 2. It is obvious that many water drops exists inside styrene globules in Fig. 2b and the structure of multiple emulsion is formed.
Fluorescence image of microgels redispersed in water is presented in Fig. 3b. The hybrid microgels have a good dispersibility in water. The PAm microgels withmultiple compartment structure are clearly observed in the Fig. 3b. Moreover, rhodamine B-stained clay is used to produce multihollow hybrid PAm microgels for CLSM testing (see ESI for details?). It is surprising that the is clay located on both inner and outer interfaces of the gel beads, not only on the inner interface.
Dual nanocomposite multihollow hydrophobic or hydrophilic polymer microspheres could be facilely prepared via suspension polymerization based on multiple Pickering emulsion. Embedding inorganic nanoparticles will endow polymeric matrices with versatile functionality, such as optical, magnetic and electric properties.? Aqueous or oil multi-cores will enable the polymer microspheres to encapsulate an abundance of substances, such as drug, protein, enzyme and other biomolecules. This kind of hybrid multihollow polymer microspheres is expected to have wide potential applications in materials science and biotechnology.
The full article “Dual nanocomposite multihollow polymer microspheres prepared by suspension polymerization based on a multiple pickering emulsion“? was published in Polym. Chem., 2010, 1, 75-77 (DOI: 10.1039/b9py00255c).
A downloadable pdf? of polymer microspheres prepared by suspension polymerization? article is also available.