Polymer hollow particles with controllable holes in their surfaces

Colloidal particles with hollow interiors play important roles in microencapsulation - a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores < 10 nm is often a slow process. To solve this problem, macroporous capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets. Here we report the preparation of another class of macroporous capsules - polymer shells with controllable holes in their surfaces. After loading of functional materials, the holes can be closed by means of thermal annealing or solvent treatment.