Temperature ( ° C)

1. ndislocation (#/mm2) ndisclination (#/mm2) Temperature (°C) Research Accomplishment: Order to Disorder in Cylindrical Block Copolymer Monolayers - E.J. Kramer (UCSB) Order in single layers of cylindrical domain block copolymer films observed by ion beam etching and AFM Highly ordered cylinder arrays are obtained by lateral confinement (graphoepitaxy) and slowly cooling from above the bulk order-disorder temperature (ODT) to sufficiently low temperature AFM height image Densities of defects (dislocations and disclinations) depend on final annealing temperature (see plots); thermal equilibrium ensured by comparing layers heated from the ordered state (red points) to layers cooled from disordered state (blue points) (cylinder monolayer) Low temperature (“ 2D nematic”) phase shows algebraically decaying (quasi long range) orientational order (cylinder bilayer) Dislocation density in nematic phase follows nDislocation ~ exp (-EDislocation/kBT ) AFM phase image Above 195 ºC, layer shows only short range orientational order (“isotropic” phase) due to unbinding of disclination pairs (isotropic) Nematic – Isotropic transition for monolayer film occurs ~ 20 ºC below bulk ODT (see images; sample was annealed at 205 ºC, between TN-I and TODT(bulk) ) (nematic) Hammond, M. R.; Cochran, E.; Fredrickson, G. H.; Kramer, E. J. Macromolecules2005, 38, 6575-6585.

2. Broader Aspects of Research Accomplishment The work on the order-disorder of 2D block copolymer cylinder monolayers forms a major part of the PhD thesis of Matthew Hammond. Besides his considerable experimental skill, Matt has proved adept at collaborating with a wide range of theorists on this project, from David Nelson at Harvard, whose theory of the melting of 2D smectics with John Toner (Phys. Rev. B198123, 316) has provided a very useful framework for understanding these experiments, to Glenn Fredrickson and his post-docs, Eric Cochran and Scott Sides. Eric’s simulations provided estimates of Edislocation, while Scott and Matt teamed up to show that both experiment and simulations demonstrate that the domains which compose dislocation cores in vertically oriented cylinder arrays adjust their sizes (5-fold coordinated cylinders contract and 7-fold coordinated cylinders expand) in response to the stress field associated with the defect (Macromolecules200336, 8712). Katie Schaefer and Cheng-Yuk Lee analyzing a copolymer synthesized by Cheng using a living radical polymerization Katie Schaefer, who was herself an REU student at UCSB in the summer of 2002, is now an NSF Graduate Fellow bridging the groups of Craig Hawker, Glenn Fredrickson and Ed Kramer, at UCSB. Following simulation results of Ed Feng and Glenn on diblock copolymers whose joints are formed using multiple hydrogen bonding groups (MHBG), Katie is using quasiliving RAFT polymerization under the guidance of Craig Hawker to construct model polymers with complementary MHBG to test Feng’s simulating results. As a part of preparing The way for aharacterizing these materials, she is mentoring Cheng-Yuk Lee, an REU summer student who will be a senior in Chemical Engineering at U. Mass. in the fall. Cheng is using RAFT to synthesize symmetric diblock copolymers of the same type that Katie expects to make by hydrogen bonding. Matt Hammond is shown here annealing samples in high vacuum. He was an undergraduate in Chemistry at Harvey Mudd and has served as a mentor in the REU summer program, most recently for Dave Statti in 2003. He will defend his PhD thesis in September 2005.