FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Science for Extreme Environment: Advanced Materials and Interfacial Processes for Energy
Results and Accomplishments
We report, for the first time, that naturally occurring light harvesting antennae can alter the phase
behavior of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-
PEO) block copolymer system from micellar to lamellar structures mimicking their role in maintaining
the supramolecular architecture of the photosynthetic membrane. Small-angle neutron scattering shows
that PEO 43 -PPO 16 -PEO 43 micelles undergo a phase transition from a micellar state to a lamellar structure
with a ~60 Å spatial repetition in the presence of plant light harvesting complex II (LHCII). In addition,
spectrophotometric analysis indicates that the protein self-assembles in the synthetic membrane structure.
The significance of this work is that it provides a novel approach for developing a new class of
membrane-based smart material with a well-controlled architecture that is dependent on the assembly of
interacting components, and it could also have important implications in self-repair and control of energy
transfer in photoconversion devices.
Combined Kumada catalyst-transfer polymerizations were used to synthesize novel amphiphilic
electroactive poly(3-hexylthiophene)-g-poly(ethylene oxide) (PT-g(EO) x ) 30 block copolymers. The
(PT-g-(EO) x ) 30 copolymers significantly increase the rate and yield of LHCII-mediated photodependent
hydrogen production. The platinum catalyst was formed in situ, allowing direct electronic communication
with LHCII. For instance, in the presence of (PT-g-(EO) 3 ) 30 , hydrogen production was sustained for
greater than 100 hours with a maximum rate of 12.1 mol H 2 /h/mg Chl, a 57.6-fold increase compared to
LHCII alone. Hydrogen production is more stable under red light compared to white light, suggesting that
LCHII is susceptible to photodegradation. Analysis of the fluorescence quenching data indicates that the
LHCII molecules are closely associated with the copolymers. LHCII is primarily known for its role in
excitation energy transfer. This work provides evidence that, in the absence of a photosynthetic reaction
center, it can also perform electron transfer, a role not known to occur in vivo. The ability of LHCII to act
as a mediator for photodependent H 2 production shows great promise for the development of a biohybrid
solar fuel system. A manuscript is currently being written describing these results.
Information Shared
Iwuchukwu , I., M. Vaughn, N. Myers, H. O’Neill, P. Frymier, and B. D. Bruce. 2010. “Self-assembled
photosynthetic nanoparticle for cell free hydrogen production.” Nat. Nanotechnol. 5, 73–79.
05090
Synthesis, Assembly, and Nanoscale Characterization of Confined,
Conjugated, and Charged Polymers for Advanced Energy Systems
Jimmy Mays, John Ankner, Philip Britt, Mark Dadmun, Kunlun Hong, and S. M. Kilbey II
Project Description
Conjugated polymers hold the key to future fundamental advances in science and technology. A major
barrier that hinders the application of conjugated polymers for energy conversions has been a lack of
understanding of how conjugation affects structure and properties, which springs directly from a lack of
well-defined materials. The objectives of this project are to develop the chemistry necessary for creating
tethered, interfacial layers of poly para-phenylene (PPP) and their derivatives on solid substrates and to
study how the self-organization and confinement of these polymers impact their nanoscale structure and
properties. The surface-tethered layers will be created by functionalized polycyclohexadiene (PCHD)
chains with complementary functionality on the substrate. Then they will be converted to PPP brushes by
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