Accomplishments in the second year:•Developed a phase field theory of photopolymerization induced crystallization in a blend of crystalline polymer and photo-curable monomer.•Applied this phase field theory to directional crystal growth in reactive polymer mixtures driven by photo-intensity gradient. •Fabricated various photonic crystals using wave interference holographic lithography.•Discovered an induced smectic phase in a nematic mixture containing a non-mesogenic functional hyperbranched polyester.

Objectives:•Fabricate photonic crystals based on wave interference holographic photolithography •Elucidate mechanisms of photopolymerization induced crystallization or liquid crystal ordering

Photopolymerization Induced Phase Transition and Evolution of Morphology Landscape in Holographic Polymer Dispersed Liquid Crystals and Photonic Crystals

Thein Kyu, University of Akron, DMR 0514942

Fig. 1. (a) Chemical structure of as-synthesized hyperbranched polyester, and (b) a 80/20 mixture of E7/hyperbranched polyester showing (left) an induced focal conic smectic phase from non-mesogenic HBPEAc-COOH and E7 nematic system at ambient and (right) nematic disclination at 65oC above the TNI of E7. (In collaboration with T. Nishikubo’s group of Kanagawa University, Japan).

Unusual Discovery: During the holographic photo-patterning of various conductive crystals and liquid crystals, we stumbled on a very interesting phenomenon of induced smectic phase from a hyperbranched polyester/nematic LC mixture both of which have no known smectic phase in their neat forms. The present work is the first to find an induced smectic phase in an amorphous hyperbranched system where there is no mesogenic group in the hyperbranched molecule. It is an outcome of our international collaboration with Professor T. Nishikubo of Kanagawa University.

Collaborations: Our recent international collaboration has resulted in a new discovery on induced smectic phase in mixtures of nematic liquid crystal and non-mesogenic hyperbranched (HB) polyester (In collaboration with T. Nishikubo’s group of Kanagawa University, Japan). This induced smectic phase has striking similarity to that found in a binary nematic system by the PI’s group about a decade ago and is also similar to the work in progress in collaboration with Dean Shila Garg’s group at Wooster College. Exchange of student and faculty visits is expected in coming years.

Broader Impact

Students Involved: Mr. P. Dayal graduated in May 2007, with a Ph. D. dissertation on “Modeling of electro-jet spinning of crystal-liquid crystal blends ”. He is now working as a post-doctoral research fellow under Professor A. Balazs at University of Pittsburgh. Mr. R. A. Matkar graduated in August 2007 with a thesis entitled “Phase diagram and dynamics of solid-liquid phase transitions of binary crystalline polymer blends,” is now working as a postdoctoral fellow under Prof. M. Chowdury at Lehigh University. Mr. P. Rathi (Ph. D. Candidate, theory and simulation polymerization induced phase transitions) and Ms. S. Park, (Ph. D. Candidate, experimental phase diagrams and photopolymerization induced phase transitions) are expected to graduate within 6 to 9 months. Mr. N. Kim, who discovers an induced smectic-A phase in E7/HBPEAc-COOH mixtures, is a Ph. D. candidate working on photo-patterning of advanced materials. Mr. T. Hwang, a Ph. D. candidate is hired recently under the present grant to develop holographic glucose sensors for noninvasive detection in collaboration with Professor Jun Hu, Department of Chemistry at University of Akron.

Education Outreach: A REU student, Garret O'Malley, a sophomore student from Physics Department, Bucknell University, PA, is receiving research training in the PI’s group. He has established a phase diagram of azobenzene/triacrylate system and subsequently performed wave interference holographic photolithography to fabricate photonic crystals. In addition, he is learning the computer codes for determining the coexistence lines of liquid-liquid and solid-liquid phase transitions. The PI gave a lecture on “Rhythms in Solidification of Soft matter: An Interdisciplinary Research” to a group of NSF-REU Summer students.

Photopolymerization Induced Phase Transition and Evolution of Morphology Landscape in Holographic Polymer Dispersed Liquid

Crystals and Photonic CrystalsThein Kyu, University of Akron, DMR 0514942