Spontaneous, One-Pot Assembly of pH-Responsive Hydrogen-Bonded Polymer Capsules

We demonstrate a facile, one-pot spontaneous assembly of hydrogen-bonded polymer containers of controllable size in aqueous solution. Electron microscopy shows that capsule formation is nucleated by a pH-induced phase separation of an amphiphilic poly(carboxylic acid), followed by binding and in-growth of polymer complexes within the phase separated droplets. The simple selection of different molecular weights of a stabilizing polymer affords a wide array of capsule sizes, including those in a submicron range, which are difficult to prepare using the alternative layer-by-layer technique. The capsules can spontaneously coat silica particles, and be reversibly removed by varying pH. Furthermore, the capsule walls can be photo-cross-linked to preserve their integrity over the entire pH scale, resulting in pH-triggered "breathing" containers or responsive coatings on silica particles useful for encapsulation and controlled release.