Darrin Pochan, University of Delaware, Newark, DE
Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. By considering peptidic or charged synthetic polymer molecules in the bottom-up materials self-assembly design process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. Synthetic block copolymers with charged corona blocks can be assembled in dilute solution containing multivalent organic counterions to produce micelle structures such as toroids. These ring-like micelles are similar to the toroidal bundling of charged semiflexible biopolymers like DNA in the presence of multivalent counterions. Micelle structure can be tuned between toroids, cylinders, and disks simply by using different concentrations or molecular volumes of organic counterion. Not only can novel micelle geometries be constructed by taking advantage of charged corona-multivalent counterion complexations, but also completely new assembly strategies have been observed that can create complex, one-dimensional nanostructures through manipulation of charged, amphiphilic block copolymer kinetics in solution. One result of this new assembly strategy is forced spherical micelle aggregation along a preferred direction leading to formation of cylindrical nanostructures with alternating stripes of block copolymer chemistry perpendicular to the primary cylinder axis. The resulting cylinders were used to template gold nanoparticle assembly in a periodic fashion. The second example is the construction of cylindrical micelles with multicompartment cores of phase separated block chemistries.