High pressure fiber optic light scattering spectrometer

A high-pressure fiber-optic light-scattering spectrometer has been constructed for in situ observation of molecular dissolution/association as well as the polymerization process in supercritical fluids. Single (or multiple) fiber-optic probes, each comprised of a single optical fiber (or multiple optical fibers) and a graded index microlens, are used to transmit the incident laser beam and to receive the scattered light as well as the transmitted light from the high pressure cell. The direct immersion in the scattering medium of the fiber-optic probes makes the spectrometer more compact and more flexible with an easier alignment process. With the miniaturization and flexibility, our high-pressure light-scattering cell can be transported and adapted in combination with other physical techniques, such as synchrotron small angle x-ray scattering which requires a different set of windows (e.g., made of diamond) suitable for x-ray transmissions. This spectrometer has been successfully used for the in situ study of the molecular association behavior of a diblock copolymer of 1,1-dihydroperfluorooctylacrylate and vinyl acetate in supercritical carbon dioxide under pressures up to 552 bar.