RESUMEN
Raman spectra were recorded experimentally and calculated theoretically for bithiophene, terthiophene, and quaterthiophene samples as a function of excitation polarization. Distinct spectral signatures were assigned and correlated to the molecular/unit cell orientation as determined by X-ray diffraction. The ability to predict molecular/unit cell orientation within organic crystals using polarized Raman spectroscopy was evaluated by predicting the unit cell orientation in a simulated terthiophene crystal given a random set of simulated polarized Raman spectra. Polarized Raman spectroscopy offers a promising tool to quickly and economically determine the unit cell orientation in known organic crystals and crystalline thin films. Implications of our methodologies for studying individual molecule conformations are discussed.
RESUMEN
Binary polymer nanoparticles were synthesized by the reprecipitation of poly(4-vinylpyridine) in the presence of poly(diallyldimethylammonium chloride) and further used to make polymer-coated Ag nanoparticles. Polymer shells around Ag nanoparticles were formed by two methods: the reduction of Ag(2)O in the presence of the polymer nanoparticles and by mixing the polymer nanoparticles with already-made Ag nanoparticles. The resulting nanoparticles were coated with layers of the two polymers with the hydrophilic polymer on the outside providing their stability in water. The exposure of the polymer-coated Ag nanoparticles to unmodified Ag nanoparticles resulted in spontaneous self-assembly due to the electrostatic attraction. The polymer-coated nanoparticles and the nanoparticle assemblies were characterized by UV-vis, surface-enhanced Raman scattering spectroscopy, and transmission electron microscopy.
