The intelligent use of processes such as self-assembly, combined with the ability to manipulate the chemical structure of polymers, can lead to a wide array of materials. Such functional materials could be a solution to many of the challenges that the modern world faces, including improved biomedical devices and strategies for renewable energy. Here, we present two types of polymer-based soft materials that combine these two elements: polyelectrolyte self-assembly and nanocomposite materials. In the first case (work in M. Tirrell's lab), complex coacervation (i.e. a liquid-liquid phase separation phenomenon) has been utilized as a platform for soft material design. Using polypeptides as a model system we have studied many aspects of complex coacervation. We explored the thermodynamics of coacervate formation, identified how external parameters affect complexation, and studied the rheological and interfacial properties. More complex molecular design has been utilized wherein polyelectrolyte domains are connected to neutral polymer blocks. These neutral domains stabilize microphase separation of the coacervate phase. For example, mixing of a polypeptide block-copolymer with an oppositely charged polypeptide homopolymer resulted in the formation of nanometer-sized micelles or hydrogels with coacervate core domains. The second case (work in N. Hadjichristidis' and J. Mays' labs) includes the development of a carbon nanotube (CNT) polymer functionalization strategy that helps circumvent CNTs' inherent insolubility, and considerably widens the scope of nanocomposite materials that can be produced. The strategy involved covalent attachment of substituted benzocyclobutenes to CNTs using a Diels-Alder [4 + 2] cycloaddition reaction. With a judicious choice of substitution, initiators for most popular polymerization techniques were attached onto the CNT surface. Complete control over grafting percentage of initiator and surface-initiated polymerizations allowed synthesis of nanocomposite materials with desired compositions, which is essential for any application. The resulting nanocomposite materials exhibited improved mechanical and thermal properties when compared to pure polymers.

Polymer-based soft materials: Coacervate assemblies, carbon nanotube nanocomposites

246th National Meeting (2013)

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