Chain Dynamics and Layering within Polyelectrolyte Multilayer Films Svetlana A. Sukhishvili, Stevens Institute of Technology, DMR Understanding and controlling the internal structure of layer-by- layer (LbL) polymer films is critically important for applications of such films in optics or for sequential drug delivery from surfaces. We aim to explore major factors that affect interdiffusion of polymer chains within polyelectrolyte multilayer films (PEMs). Using controlled radical polymerization techniques, we have synthesized well-defined PDMA and PDEA homopolymers, 1 as well as converted them to cationic QPDMA and QPDEA copolymers with various charge densities. 2 Attaching fluorescent labels to these polymers or to PMAA 3 allows tracking molecular mobility at surfaces using fluorescence recovery after photobleaching (FRAP). With the same films, internal layering was studied using neutron reflectometry (NR) (Spallation Neutron Source, Oak Ridge National Laboratory). We found that diffusion of polymer chains within PDMA(or PDEA)/polyacid LbL films is highly anisotropic, with chains diffusing fold faster in the direction parallel rather than perpendicular to the substrate (Fig. 1). This novel observation reveals the mechanism by which LbL can exhibit sustained internal layering during their use as functional coatings. 5 We also established a correlation between the rate of polymer interdiffusion and the type of ionic pairing in the film. Steric hindrance was shown to be more important than chain hydrophobicity in determining the internal structure and mobility of polyelectrolyte chains. Fig. 2 shows that multilayers with larger interionic distance within ionic pairs (i.e. PDEA/polyacid) demonstrated higher rates of polymer interdiffusion. Fig. 2. Effect of steric bulk to ionic pairing on salt-induced interdiffusion of polymers within PEM films: QPDMA/PSS (left) and QPDEA/PSS (right) systems. [Macromolecules 2011 DOI: /ma200986d] Fig. 1. Studies of anisotropy of chain motions: measuring diffusion coefficients of polymer chains in directions parallel and perpendicular to the surface (D II and D  ) using FRAP and NR, respectively.

Results of the project are now being incorporated into one course 1 and presented in three conference presentations 2, as well as at the Research and Entrepreneurship Day at Stevens in April 2011, which gathers a broad audience of NY/NJ entrepreneurs, National Lab representatives, and high school teachers. Graduate students involved in the project are significantly enriching their knowledge through systematic interactions with researchers at NIST and ORNL. Specifically, two graduate students. LI Xu and Alex Zhuk (Fig.1, in white), have travelled twice to ORNL to perform neutron reflectivity experiments (Fig. 2). Experience obtained at ORNL is disseminated to undergraduate and high school students. In summer of 2011, one undergraduate student, Rachel Turner (Fig. 1, in blue), and two high-school students (Fig.1, in grey) have been working on the NSF project. We are now shaping the Polymers in Our Lives module for implementation in high school classrooms. To that end, graduate students meet with Debra Brockway (Fig. 3), a science educator from Stevens’ Center for Innovation in Engineering and Science Education (CIESE) to discuss implementation of the module. CIESE is a nationally recognized center whose goal is to improve K-12 science and mathematics education through internet-based curriculum materials and bringing cutting-edge research into K-12 classrooms. Chain Dynamics and Layering within Polyelectrolyte Multilayer Films Svetlana A. Sukhishvili, Stevens Institute of Technology, DMR Fig. 1. Graduate, undergraduate and high-school students during summer of 2011: graduate students Li Xu (in white, left) Alex Zhuk (in white, right), an undergraduate student Rachel Turner (in blue), two high- school students - Omara Ali (in grey, left, Liberty Science Center Partners in Science program) and Carmen Velez (in grey, right, ACS SEED program), participate in the project Fig. 3. A science educator Debra Brockway collaborating with graduate students Li Xu (Fig.1, left) and Alex Zhuk (Fig. 1, right, in white) to promote the development and implementation of Polymers in Our Lives module into the high school setting. Fig. 2. Spallation Neutron Source (Oak Ridge National Laboratory) used by Ph.D. students Li Xu and Alex Zhuk to perform neutron reflectivity experiments.