Eric W. Cochran
Assistant Professor
1035 Sweeney Hall
Iowa State University
Ames, IA 50011-2230
Phone (515)294-0625
Fax (515)294-2689
ecochran@iastate.edu
Education
PhD, ChE, University of Minnesota - Twin Cities, Minneapolis, MN, 2004
BS, ChE, Iowa State University, Ames, IA, 1998
Awards
CAREER Award, NSF Division of Materials Research, 2009
Camille and Henry Dreyfus New Faculty Awardee, 2006
Frank J. Padden Jr. Award for Excellence in Polymer Physics, American Physical Society, 2004
Doctoral Dissertation Fellowship, University of Minnesota, 2003 – 2004
Graduate Research Fellowship, National Science Foundation, 2000 – 2003
Graduate School Fellowship, University of Minnesota, 1999 – 2000
Research Overview
We are interested in the equilibrium and dynamic properties of polymeric systems that undergo self-assembly at pertinent length scales ranging from nanometers to microns. A number of systems belong to this generic class of materials; thanks to an unprecedented series of advances in polymer chemistry over the past decade, the associated parameter space continues to grow beyond what we are currently able to comprehend. A particular focus of our research will be the identification of the guiding principles in systems that feature multiple self-assembly processes.
Research Areas
Thermodynamics of Side-Chain Liquid Crystalline Block Copolymers
Most block copolymer (BCP) research over the past few decades has focused on the behavior of systems that feature Gaussian chain conformations. In these materials, unfavorable interactions between dissimilar sequences of monomers, or blocks, drives the formation of ordered periodic phases with a characteristic length scale on the order of a few multiples of the radius of gyration. The incorporation of a semi-crystalline block into a BCP system introduces another self-assembly process, crystallization, with a much smaller length scale; the study of the competition amongst BCP/semi-crystalline assembly mechanisms has been addressed in significant detail. Other secondary assembly processes may be introduced into BCPs via the attachment of pendant mesogens to the main chain with a flexible alkyl spacer of adjustable length. This motif allows one to vary the flexibility of one or more blocks, gradually diverging from the limit of ideal Gaussian chain statistics. In addition, the presence of the mesogenic moieties introduces the potential of smectic and nematic ordering processes that will compete with the block self-assembly. In this area we are interested in the discovery of new self-assembled structures and elucidating the pertinent factors that lead to their formation. We will also study how these inherently anisotropic materials couple to externally applied mechanical (e.g. shear), electric, or magnetic fields.
Structure and dynamics of block copolymer nanocomposites
Toyota in the 1970s discovered that the incorporation of a small amount (< 5%) of simple clays into homopolymer melts led to dramatic improvements in a host of physical properties – toughness, elastic moduli, barrier properties, etc… Clays, such as montmorillonite (MMT), consist of stacks of roughly circular sheets of anionically charged silicate material with characteristic dimensions of ~100 nm x 2 nm. The key to potential property enhancement with nanoparticulate fillers such as MMT is the large surface-to-mass ratio and the use of surface modification to promote strong interfacial adhesion. An obstacle that currently hinders the widespread commercial success of polymer/clay systems is the difficulty of fully separating the clay sheets from one another to promote maximal dispersion. Diffusion of polymer chains between clay sheets is retarded by the small interlayer spacing. In contrast, small organic molecules, including monomers and polymerization initiators, enjoy a much higher mobility and, accordingly, greater interlayer penetration. Here we propose to exploit this feature through the functionalization of MMT clay surfaces with ATRP polymerization initiators; the subsequent sequential introduction of monomer will lead to the synthesis of BCP brushes tethered to the nanoparticle surface. Steric repulsion from growing brushes may enhance the dispersion of silicate layers, leading to nanocomposite materials with enhanced properties. This bottom-up approach is extendable to other nanoparticles; an extended goal is to understand how nanoparticle geometry influences BCP/nanocomposite structure and dynamics.
Theory and Simulation
Complementing our experimental efforts will be a theoretical/computational program that will use Field Theoretic models to simulate the equilibrium/near-equilibrium phenomena of complex polymeric fluids. This work will build upon the now-mature self-consistent field theory (SCFT) of block copolymers to include not only the experimental areas outlined above but other relatively unexplored areas (e.g. triblock copolymers). Students will adapt and implement existing theories for computational study, as well as learn to manipulate the bare statistical thermodynamics at the pencil-and-paper level to develop new models. This program will establish an internal mechanism for theoretical-experimental synergism, and will also continue to foster collaborations with other pure theorists from the field.
Publications
Eric W. Cochran, Carlos J. Garcia-Cervera, and Glenn H. Fredrickson, "Stability of the Gyroid Phase in Diblock Copolymers at Strong Segregation," Macromolecules, 39, 2449-2451 (2006).
Matthew R. Hammond, Eric W. Cochran, Glenn H. Fredrickson and E. J. Kramer, "Temperature Dependence of Order, Disorder, and Defects in Laterally Confined Diblock Copolymer Cylinder Monolayers," Macromolecules, 38, 6575-6585 (2005).
Thomas H. Epps, III, Eric W. Cochran, Travis S. Bailey, Ryan S. Waletzko, Cordell M. Hardy and Frank S. Bates, "Ordered Network Phases in Linear Poly(isoprene-b-styrene-b-ethylene oxide) Triblock Copolymers," Macromolecules, 37, 8325-8341 (2004).
Thomas H. Epps, III, Eric W. Cochran, Cordell M. Hardy, Travis S. Bailey, Ryan S. Waletzko and Frank S. Bates, "Network Phases in ABC Triblock Copolymers," Macromolecules, 37, 7085-7088 (2004).
Eric W. Cochran and Frank S. Bates, "Shear-Induced Network-to-Network Transition in a Block Copolymer Melt," Physical Review Letters, 93, 087802/1-087802/4 (2004).
Lifeng Wu, Eric W. Cochran, Timothy P. Lodge and Frank S. Bates, "Consequences of Block Number on the Order-Disorder Transition and Viscoelastic Properties of Linear (AB)n Multiblock Copolymers," Macromolecules, 37, 3360-3368 (2004).
Eric W. Cochran, David C. Morse, and Frank S. Bates, "Design of ABC Triblock Copolymers near the ODT with the Random Phase Approximation," Macromolecules, 36, 782-92 (2003).
Eric W. Cochran and Frank S. Bates, "Thermodynamic Behavior of Poly(cyclohexylethylene) in Polyolefin Diblock Copolymers," Macromolecules, 35, 7368-74 (2002).
