3.11 nm

1. Nanostructural Control of Optical Properties in Polymers with Electroactive SubunitsPadma Gopalan, University of Wisconsin-Madison, DMR 0449688 1 2 3 4 5 Intensity (a.u.) 6 q (nm-1) Hydrogen bond (a) (b) Linear-diblock EO domain ~50 nm Normalized SHG: 1.0 Linear-dendron EO domain <5 nm Normalized SHG: 1.6 • Electro-optic (EO) materials are commonly designed as a guest-host composite. In this research we focus on maximizing the EO activity for a given chromophore by controlling the nanomorphology. Block copolymer (BCP) templates are used to systematically control the size and shape of chromophore domains and study its correlation to EO coefficient. • Our studies have shown that while well-ordered phase separated systems such as BCPs show: • at least a two fold increase in the electro-optic coefficient of a given chromophore over the guest-host systems. • a more effective approach is to explore polymer chains end functionalized with chromophores. • poling within confined BCP domains is considerably more complex than in conventional homopolymer systems. • Achieving poled order in confined domains depends on the polymer host architecture, domain size, nature of interaction between the chromophore and polymer host, and concentration of the chromophore within the domains. • The results of this study are applicable to a broader field of nanostructured photonic materials in which periodic modulation of spatial optical properties is defined via chemical processes. • Reference: Melvina Leolukman, Peerasak Paoprasert, Yao Wang, Varun Makhija, David McGee, Padma Gopalan. Macromolecules 2008; 41(13); 4651-4660. PS – b – P4VP 3.16 nm q = 0.198 nm-1 H-bond acceptor H-bond acceptor 3.11 nm Lamella d-spacing = 73 nm 100 nm 300 nm (c) (d) H-bond donor (e) E Field Figure 1. TEM images of block copolymer encapsulated with EO chromophores (shown in orange) with a weight fraction (a) of 0.38 in linear-diblock resulting in lamellar EO domain (d-spacing ~73 nm), (b) of 0.12 in a linear-dendron resulting in EO domains of < 5nm, effectively doubling the EO activity for a given chromophore. The corresponding X-ray data for the linear-block and linear-dendron are shown in (c) and (d) respectively, and (e) shows the proposed mechanism of poling chromophores within confined block copolymer domains. 150 oC 115 oC Cool to r. t. E Field E Field

2. Nanostructural Control of Optical Properties in Polymers with Electroactive SubunitsPadma Gopalan, University of Wisconsin-Madison, DMR 0449688 • Two graduate student MelvinaLeolukman and PeerasakPaoprasert participate in this grant. This project has provided an ideal platform for the students to gain expertise in SEM, TEM, X-ray diffraction (Argonne National Lab), and electro-optic measurement methods. • Two chemistry undergraduates Ian Mandal, and Lydia Grundahl, conducted their research in the Gopalan group on chromophore and polymer synthesis. • Hosted REU student KimyYueng for research on chromophore synthesis as part of the REU in Nanotechnology program. • Ian Mandal, was awarded the ACS Daniel L. Sherk Award for Excellence in Undergraduate Research following his poster presentation in May 2007 from the Wisconsin Section of the American Chemical Society (ACS). Figure 2: REU student Kimy Yueng (left) receiving the certificate of participation from Dr. Greenberg at the poster presentation for UW-Madison, REU program in summer 2007 and undergraduate student Ian Mandel received the Shrek award for best poster from the Wisconsin section of ACS.