POLY 631 |
| PEO-PPO-PEO triblock copolymers are well known to form thermoreversible gels in water and their phase diagrams have been well reported. The basically cubic structure of some of these gels has also been established by SANS studies. This investigation was done as part of a project examining such thermoreversible gels as fouling release coating constituents, and as part of a study to increase the solid modulus of such materials. This study actually exemplifies the first example of microemulsion polymerization of an inorganic polymer, silica. The basic ternary microemulsion comprises water, TEOS (tetraethylorthosilicate), and surfactant, the well known Pluronic F127. We report the partial ternary phase diagram in the L1 region, and then present LV-TEM results emanating from the acid catalyzed hydrolysis of TEOS sequestered in the micellar cores. Our hypothesis in this study was to investigate whether silica chains might emanate outwardly from each micelle and result in the formation of a silica-based gel, co-continuous with the micellar continuous gel structures and the co-continuous water pseudophase. The results show a preponderance of silica nanoparticles in the 20 nm diameter range, and a few quite large particles, some approaching 2-3 microns in diameter. Careful examination of some of these larger structures, however, reveals that they are composed of collapsed strings or necklaces of silica nanoparticle chains, giving some credence to the original hypothesis. The greater contrast available via low-voltage TEM makes certain features visible that would be missed in more standard TEM analyses. These results suggest STEM as a powerful tool for examining soft systems, wherein the penetration voltage can be varied over a considerable range. |
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Imaging Techniques for the Characterization of Polymers and Polymer-Derived Materials
8:00 AM-12:35 PM, Thursday, August 23, 2007 Westin Boston Waterfront -- Otis, Oral
Division of Polymer Chemistry |