I. Confinement: A Novel Procedure to create Ultra-Thin Materials using Supercritical Fluids
Mitchell Fourman, Ward Melville High School, East Setauket; John Jerome and Miriam Rafailovich,Department of Materials Science and Engineering, Stony Brook University

We have measured the phase separation of PS-PMMA in confinement and exposed to supercritical CO2. Then, following the film preparation, no phase separation occurred in the films. Phase separation of the blend is initiated by heating the film above the glass transition temperature of both polymers. We also observe complete phase separation after the polymer blend has been exposed to supercritical CO2 at 36°C for three hours. This investigation focused on the effects of supercritical fluids on PS-PMMA, dPS-PMMA, and PS-PB polymer blends confined between silicon and a silicon oxide (SiO2) layer.

Supercritical fluid (SCF) technology has recently been studied in applications such as polymer processing, polymer synthesis, reactor clean-up, and preparation of pharmaceutical products. SCFs, specifically supercritical carbon dioxide (SC CO2), has also been shown to compatibilize normally incompatible polymer blends.

Samples were analyzed using scanning electron microscopy (SEM), as well as atomic force microscopy (AFM). Witnessed on the samples was a phase separation in which one polymer formed a dot like pattern among a "sea" of the other polymer. Upon the application of cychlohexane acid, an acid that dissolves Polystyrene, the polymer that the dots were made out of was determined. When different concentrations of PS and PMMA (1:3 and 3:1) were used, we observed some lamellar transformation upon the removal of the SiO2 capping layer, especially in the 1:3 ratio of PS-PMMA. In this ratio, the size of the dots varied significantly, as well as their order being less uniform.

Applications can be found in laser technology, where ultra thin materials are needed to serve as a buffer between devices. These materials also can be used as a sheath for wires, thus allowing them to be bunched more densely, and more effectively. Future work will involve Polyethylene, which has a very high density, and thus will be very reactive in confinement, as well as in a supercritical environment.


II. The Effects of Supercritical Carbon Dioxide on PS-PMMA, PMMA-EVA, and PMMA-PB Polymer Blends
Mitchell Fourman, Ward Melville High School, East Setauket; Edmund Palermo, Cornell University; Ronald Occhiogrosso, HAFTIR; Miriam Rafailovich, Dept. Material Sciences and Engineering, Stony Brook University
Ductility and tensile strength are the two most important qualities of the ideal plastic. However, these two qualities are difficult to achieve in the same material, as most flexible polymers are very weak, and many strong polymers are very brittle. Therefore, a way to combine these qualities must be found. A polymer blend is one way to solve this problem. Because many polymer blends are incompatible, the blends that form are often brittle and weak . Supercritical fluids are the answer to this situation. Supercritical fluid exposure can cause a "foaming effect" in the material, which releases many of the "pressure points" formed because of incompatibilities.

The polymers analyzed in this investigation include Polystyrene (PS), Poly(methyl-methacrylate) (PMMA), Ethylene Co-Vinyl Acetate (EVA, also known as Elvax), and Polybutadiene (PB). These polymers were combined to produce PS-PMMA, PMMA-EVA, and PMMA-PB. Different proportions of the subject polymers were analyzed as well. The blends were created by a C.W. Brabender heat intercalation device. Samples were formed using mold templates, and the resulting materials were exposed to supercritical carbon dioxide (SC CO2).

Methods of analysis include Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) for surface and cross section scanning respectively. Dynamic Mechanical Analysis (DMA) testing was used to determine modulus vs. temperature as well as an approximate glass transition temperature (Tg). SEM and TEM data showed dramatic changes in material composition and topography after exposure to SC CO2. A sample such as PMMA-EVA showed a very chaotic surface before CO2 exposure, which was drastically evened out as a result of the exposure. DMA demonstrated a change in the slope of the modulus curve, and a merging of the two Tgs after exposure. Different proportions of the material witnessed different magnitude of reaction, indicating some polymers are more susceptible to SC CO2 than others. Future work involves the addition of PS-PB blends, as well as X-Ray analysis.

 

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