RESEARCH

Rzayev Research Group

 

Molecular Templating


Organic tubular structures of nanometer dimensions are versatile platforms for a wide array of applications, such as selective ion transport, chemical catalysis, biosensors and nanocomposites. We have developed a new method for the fabrication of organic nanotubes by molecular templating of core-shell bottlebrush copolymers (DOI: 10.1021/ja901936g). This strategy allows one to control the structural characteristics (length and pore size) and functional composition (exterior and interior) of the prepared nanotubes in an unprecedented fashion.

Atomic force microscopy image of individual bottlebrush macromolecules deposited on a mica surface.

Periodic Nanostructures by Solid State Assembly


Block copolymer self-assembly is a powerful tool for creating materials with periodic nanostructures, which are useful for a variety of applications. Linear block copolymers can provide nanostructures with domain spacings of up to 50 nm. Attaining larger periodicities is much more challenging due to the difficulties associated with the synthesis and slow self-assembly kinetics of very long linear polymers. Recently, we have shown that bottlebrush block copolymers, unlike their linear analogs, are able to organize into highly ordered nanostructures with domain spacings over 200 nm. DOI: 10.1021/ma802304y

Photonic crystal obtained from a bottlebrush block copolymer with a lamella domain spacing of 165 nm.

Bottlebrush copolymers are transformed into nanotubes by intramolecular cross-linking of the exterior layer, and selective etching of the polyester core. The dimensions of tubular structures prepared by this method closely resemble those of the precursor bottlebrush copolymers. By using multicomponent bottlebrush copolymers we have prepared nanotubes with controlled functionalities on the interior and exterior nanotube surfaces, polypyrrole nanotubes, degradable nanotubes based on disulfide linkages, photo-cross-linked nanotubes, and anisotropically functionalized nanotubes that aggregate into 1D superstructures. E.g. DOI: 10.1021/ja204296v

In this research, we study how molecular bottlebrushes come together to form a nanostructured material. We manipulate various structural characteristics, such as side chain length and asymmetry, backbone length and asymmetry, side chain distribution along the backbone, and chemical identity of the backbone and end groups to control the macromolecular packing in the solid state. E.g. DOI: 10.1021/nl103747m All of these structural manipulations require extensive synthetic efforts and development of new protocols for the preparation of complex multicomponent bottlebrush copolymers. We collaborate with scientists from Argonne National Lab and Brookhaven National Lab to elucidate the structure of the generated nanomaterials.

Discrete Nanostructures by Solution Assembly


Amphiphilic block copolymers, composed of covalently connected hydrophilic and hydrophobic polymer chains, have found widespread use in a variety of applications as surfactants, emulsifiers, rheological modifiers, structure directing agents and drug delivery vehicles due to their ability to self-assemble at interfaces and form micellar aggregates in solution. We are interested in understanding how bottlebrush copolymers with hydrophilic and hydrophobic components organize in aqueous solutions to produce highly stable and uniform aggregates, one dimensional assemblies and multicompartment nanostructures. In this research, we use bottlebrush copolymers as a platform for building blocks with directional interactions to achieve biomimetic assembly.

We have shown that side chain asymmetry can be used to control the interfacial curvature and aggregate morphology during amphiphilic bottlebrush copolymer assembly in solution. Aqueous assembly of bottlebrush copolymers with hydrophilic, biodegradable polylactic acid (PLA) side chains and hydrophilic, bioinert polyethylene oxide (PEO) side chains produces uniform aggregates with extremely low critical micelle concentrations, desirable for biological applications. DOI: 10.1021/ja503283r Amphiphilic bottlebrush copolymers with coumarin-functionalized PLA side chains exhibit excellent paclitaxel uptake capacities, and upon photo-irradiation can be covalently cross-linked into biodegradable PLA nanoparticles. DOI: 10.1021/acs.macromol.6b02182

We gratefully acknowledge financial support from the following agencies:

Bottlebrush copolymers are densely grafted macromolecules with a comb-like architecture. When the backbone is much longer than the branches, these molecules adopt cylindrical shape in solutions.

Block copolymers are composed of two or more chemically distinct segments (blocks). Due to the incompatibility of the segments, block copolymers phase separate to form nanostructured morphologies.

Cryogenic transmission electron microscopy image of highly uniform spherical micelles obtained from the aggregation of amphiphilic bottlebrush block copolymers in water.

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Nanoporous Materials/Membranes


Nanoporous polymer materials are often characterized by the presence of spherical, cylindrical or network pore structures, high pore densities and uniform pore sizes. They can be classified based on the pore diameter (dpore) as microporous (dpore < 2 nm), mesoporous (2 nm > dpore < 50 nm) and macroporous (dpore > 50 nm). Primary characteristics distinguishing nanoporous polymeric materials from their inorganic counterparts are facile tunability of their properties by manipulating the organic chemical framework and their processability. High surface area associated with these materials renders them useful for an array of applications, such as ultrafiltration, water purification, selective crystallization, nanomaterial templating, catalyst support and hydrogen gas storage. We are interested in developing new approaches that allow for the scalable fabrication of nanoporous polymers with controlled pore dimensions and geometries and enhanced mechanical and transport properties.

In this research, we are utilizing a number of different approaches based on end-reactive bottlebrush copolymers, side chain asymmetric bottlebrush copolymers, and ultrahigh molecular weight linear block copolymers for the preparation of mesoporous polymer frameworks, nanoporous monoliths, and ultrathin water filtration membranes. E.g. DOI: 10.1021/acsnano.7b03214

Size based separations, such as ultrafiltration and nanofiltration, rely on nanoscopic channels/pores that allow small molecules, such as water, to pass through, but prevent passage of larger components (e.g. viruses or bacteria). The effectiveness of ultrafiltration membranes depends on a number of parameters, including pore size uniformity, pore density, membrane thickness, and resistance to fouling.

Morphological control in solution self-assembly of linear block copolymers is achieved by varying the lengths of the constituent blocks.

Cone shaped macromolecules prepared from side chain asymmetric bottlebrush copolymers organize into cylindrical nanostructures. Bottlebrush architecture provides unique avenues for macromolecular shape control that affects interfacial curvature during self-assembly.

Scanning electron microscopy image of a mesoporous polymer framework prepared by interconnecting bottlebrush copolymers through reactive ends.