(413e) Photodirected Assembly and Self-Rupture of Polyelectrolyte-Based Soft Materials

Polyelectrolyte complexes (PECs) form spontaneously through the association of oppositely charged polymers and attract widespread interest as materials for an array of existing and emerging applications. Their shapes, however, are typically limited to rather simplistic (spherical, cylindrical or planar) structural motifs. Here, to extend PEC formation to a broader range of custom-designed structures, we present a simple photolithographic approach to preparing PECs with customized shapes. In this approach, a polyelectrolyte is mixed with an oppositely charged monomer and a photoinitiator. Upon photoirradiation, the monomer undergoes site-specific polymerization and, by locally generating an associating polyanion/polycation mixture, forms solid PECs with shapes that match the photoirradiation pattern. Like other PECs, the resulting custom-shaped complexes are stimulus-responsive and can be either swollen or dissolved on demand by varying the pH and ionic strength of their environments. Further, by generating gradients in irradiation intensity within the regions of photoirradiation, PECs with differential swelling and, thus, stimulus-responsive actuation properties can be prepared.

Besides demonstrating the preparation and properties of PECs formed through photodirected assembly, we will describe how polyelectrolyte gels with self-rupturing properties (i.e., the ability to break into fragments after a predetermined delay) can be prepared by synthesizing them to have highly non-uniform crosslink densities. This self-rupture is caused by highly-differential swelling, which generates stresses strong enough to overcome covalent bonds. The time required for these polyelectrolyte gels to rupture can be tubed by varying their: (1) crosslink content/uniformity; (2) size and internal morphology; and (3) ambient pH and ionic strength. In addition to their ability to self-destruct, these self-rupturing gels also can be prepared to contain liquid-filled payload compartments, which enable them to potentially serve as timed/delayed release devices.