PEO

1. Confined Crystallization in Nanolayered Films Anne Hiltner, University of Texas at Austin, DMR 0423914 The design and fabrication of ultra-thin polymer layers with very high gas barrier is of increasing importance due to the rapid development in fields such as electronics, health care, food and medicine (Figure 1). Packaging with enhanced gas barrier could dramatically reduce the amount of food waste, thereby reducing world hunger, greenhouse gas generation, and the load on global water and energy supplies We discovered a unique morphology that emerges as polyethylene oxide (PEO) or polycaprolactone (PCL) layers are made progressively thinner. This was achieved by using an innovative layer-multiplying process to obtain assemblies with thousands of PEO or PCL nanolayers confined between layers of another polymer, in this case polystyrene. Direct observation by atomic force microscopy revealed that when the thickness confinement occurs on the 20 nm size scale, the PEO layers crystallize as single, high aspect ratio lamellae that resemble large, impermeable “single crystals” oriented in the plane of the layer (Figure 2). Analysis of the increased gas diffusion pathway between crystals estimates lamellae aspect ratio as high as 250-300, corresponding to a lateral dimension greater than 2 μm. The large aspect ratio these oriented lamellae has resulted in a two order of magnitude enhancement in oxygen barrier of PCL or PEO nanolayers. This work represents the first time that a “single crystal” structure has been obtained by a continuous melt process. Figure 1 High Barrier Polymer Film Applications 100nm PEO layer PEO “Single Crystal” A B PS PEO PS Figure 2 AFM images of PEO Nanolayers PEO (120) PEO/PCLSingle Crystals Figure 3. Effect of layer thickness confinement on oxygen permeability of PEO and PCL Layer.

2. All-Polymer Distributed Feedback LasersAnne Hiltner, University of Texas at Austin, DMR 0423914 The centerpiece of the distributed feedback (DFB) laser are layered active polymeric photonic crystals. The active component being laser dyes rhodamine 6G (R6G) and 1,4-bis-(a-cyano-4-methoxystyryl)-2,5-dimethoxy-benzene (C1RG) doped into one of the polymer layers. To fabricate DFB lasers, we use multilayer coextrusion, capable of producing hundreds of layers continuously using a melt process. Our design incorporates 128 layers of alternating poly(styrene-co-acrylonitrile) (SAN25, n = 1.56) and a fluoroelastomer terpolymer THV (n = 1.37) with laser dye doped into SAN25. The large difference in refractive index (Dn) between the two polymers produces a vivid array of reflective colors which can be selectively tuned by the thickness of the polymer layers. Necessary to the design of efficient DFB lasers is the need for a barrier layer which is capable of preventing dye diffusion in the melt during processing. Micrographs show THV serves as an excellent barrier layer to R6G (fig.1 Bottom left) by confining the dye molecules in one layer. Strong laser action emitted normal to the film surface is observed in our 128 layer DFB lasers. We report a threshold of 238 mJ/cm2 and a lasing efficiency of 2.6%. Roll-to-roll processing by multilayer coextrusion of active photonic and electronic devices such as wavelength-agile polymer lasers could open new approaches to display, sensing, optical communication, and data storage technologies. Figure 1: (Top left) Illustration of C1RG DFB laser being continuously melt processed. (Top right) Schematic of the architecture of a DFB laser. (Bottom left) Micrograph showing SAN25 + R6G layers (colored) and THV layers (white). (Bottom right) Strong laser action of R6G in a 128 layered SAN25/THV film.

3. Enhanced Dielectric Properties of Nanolayered FilmsAnne Hiltner, University of Texas at Austin, DMR 0423914 Capacitors are used in nearly all electronics and electrical power systems (Figure 1). They perform important functions such as noise smoothing, frequency filtering, and pulsed power production. Since state-of-the-art capacitors are generally bulky, there is a need to increase the energy density. On a material level, the maximum energy density of a capacitor is proportional to the material’s dielectric constant and the square of the breakdown strength. Using microlayer coextrusion technology we have produced multilayered films with enhanced dielectric properties by combining a high breakdown strength material (polycarbonate) with a high dielectric constant material (polyvinylidene fluoride based polymer) (see Figure 2). The improved breakdown strength of our layered films was attributed to treeing, a damage mechanism, that was not observed in the control monolayer films (Figure 2). These high performance films were used to build several prototype capacitors. Capacitor Figure 1: Devices that depend on the electrical functions that capacitors provide. 256 Layers 1 mm 0 50 µm 0 10 mm Figure 2: Left: Microlayered film of PC/PVDF-HFP was used to build a capacitor. Right: Treeing damage at the dielectric breakdown site of a microlayered film.

4. Future Science StarsAnne Hiltner, University of Texas at Austin,DMR 0423914 The Future Science Stars (FSS) is a new pre-college initiative in the Center for Layered Polymeric Systems (CLiPS), an NSF-funded Science and Technology Center at Case Western Reserve University. The initiative targets students in elementary to high school grades who are traditionally underrepresented in science and technology professions. The key goals of the new initiative are to excite students about STEM fields through hands-on, inquiry-based science learning experiences and create opportunities for the students to directly engage with university scientists, college undergraduate and graduate students pursuing science degrees. This summer, 90 middle/high school students visited the Case campus for a half day of science experimentation and personal encounters with scientists and college students. In other activities, a graduate student made polymer “slime” out of glue, water and borax soap (Figures 1,2) and an undergraduate led a paper bridge building activity with 19 rising 4th grade girls who were participating in a summer enrichment academy at a local school. All of the youth organizations who participated in the FSS events have a long-term relationship with their students and therefore the youth will have opportunities to participate in future FSS activities. Quote from parent of a student participant, “Antonio was the most excited about education that I have seen in the last year. He made the connection between who he is and who he would like to become! This experience for him was REAL. That is Divine.” Figure 1: Students crosslinking a polyvinyl alcohol based polymer glue by adding borax (sodium tetraborate) solution which acts as a physical crosslink binding the polymer chains together making the chains harder to move around and the solution thicker. Figure 2: PVOH crosslink reaction with sodium tetraborate Figure 3. Graduate student demonstrating how potassium benzoate and aspartame in diet soda combined with the surface roughness of Mentos allow carbon dioxide bubbles to rapidly escape the bottle, forming a geyser.

5. Unmodified PDOPA PODPA-g-PEG A Biofouling-Resistant Membrane Surface ModificationAnne Hiltner, University of Texas at Austin,DMR 0423914 Water treatment membranes suffer dramatic decreases in flux as biological impurities cause biofilm formation on the membrane surface. Dopamine has been found to polymerize to “polydopamine” (PDOPA) and to deposit in solution on seven types of water purification membranes, forming a thin but robust coating. Additionally, poly(ethylene glycol) (PEG) has been easily grafted to the PDOPA surface (forming PDOPA-g-PEG). The early stages of biofilm formation involve the adhesion of proteins and bacteria to the substrate surface; the PDOPA and PDOPA-g-PEG coatings have demonstrated success in reducing this adhesion. With less adhesion, deleterious biofilms should be slower to develop, thereby maintaining flux and increasing membrane lifetime. Fluorescent photographs of a membrane surface after contact with tagged proteins. Bright fluorescence indicates high protein adhesion to the membrane surface. Insets were taken at longer exposure times to visualize difference between PDOPA and PDOPA-g-PEG surfaces. Luminescence of seven different polymer membrane surfaces (in unmodified and modified forms) after contact with a bioluminescent bacteria, Pseudomonas aeruginosa. High luminescence indicates high bacterial adhesion to the surface.

6. Pre-College Mentoring through Membrane ScienceAnne Hiltner, University of Texas at Austin,DMR 0423914 The Center for Layered Polymeric Systems (CLiPS) provides many research and mentorship opportunities for high school, undergraduate, and graduate students. Undergraduates are advised by graduate students throughout the year. A group of local high school students work in the laboratory over the summer. To prepare for this work, graduate students teach fundamentals of membrane and polymer science. Students are chosen from minority groups and actively contribute to research activities. Graduate students also conduct “Science Sundays” at the Austin Children’s museum where local families may engage in hands-on science activities. Science Sundays take place when the museum is free of charge, allowing participation of economically-disadvantaged families. Graduate student instruction of high school students in preparation for laboratory work. Hands-on science activities with local families at the Austin Children’s Museum. Graduate student mentorship of undergraduate and high school students in the laboratory.