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Artificial Chlorosomes for Controlled Exciton Transport

Group members working on this project: Charlotte Stewart-Sloan
Collaborators: Tim Swager - Department of Chemistry, MIT
      Caroline Ross - Department of Materials Science and Engineering, MIT
      Alfredo Alexander-Katz - Department of Materials Science and Engineering, MIT
      Marc Baldo - Department of Electrical Engineering and Computer Science, MIT

Chlorosomes, one of the most efficient light harvesting structures in nature, are the organelles responsible for light capture in green sulfur bacteria which live in deep ocean extremely low light conditions.  They are composed of aggregates of bacteriochlorophyll molecules enveloped in a lipid layer, and so can be conceived of as the self-assembly of dye molecules inside an amphiphilic shell.  Inspired by this system, we are developing new materials which use block copolymers as structure directing agents for excitonic nanostructures.  Hierarchical structural characterization and photophysical measurements allow us to understand which morphologies are necessary for forming devices which can efficiently capturing and transporting solar energy through soft materials.

Incorporation of chlorophyll into block copolymer self-assembled thin films.

Use of diblock copolymer and chlorophyll to pattern artificial chlorosome structures.

Co-Assembly in Di-block Copolymer-Nanoparticle mixtures

Group members working on this project: Vinay Raman
Collaborators: T. Alan Hatton - Department of Chemical Engineering, MIT

Ordering in self-assembly of block copolymers is an active area of research given the need for precise orientational and translational order of block copolymer domains for applications such as nanolithography, optoelectronics, functional thin films and nanoporous membranes etc. A variety of techniques have been developed to align block copolymers both in bulk and in thin films. We are developing a new technique to align the diblock copolymers using superparamagnetic nanoparticles and external magnetic fields. Nanoparticles can be used to mediate interfacial interactions, or interact favorably with the solvent vapor during solvent annealing, leading to control of domain orientation. By chaining the superparamagnetic nanoparticles using in-plane magnetic fields the block copolymer domains can be oriented in the direction of the magnetic field if there is sufficient interaction between the nanoparticles and the domains. Hybrid Particle-Field (HPF) simulations reveal an interesting interplay of nanoparticle density, nanoparticle size, nanoparticle magnetization, and particle-polymer interactions on the co-assembly of the nanoparticles and diblock copolymer. We study this co-assembly process both experimentally and theoretically with aim of bettering the ordering of BCP domains.

Simulations of magnetic nanoparticle alignment within block coplymer films.

Demonstration of the BCP alignment using chaining of superparamagnetic nanoparticles in external magnetic fields