Hye Jin Jo

Thermally rearranged polymer membranes for desalination

Herein, we demonstrate thermally rearranged polybenzoxazole-co-imide (TR-PBOI) electrospun nanocomposite membranes for membrane distillation and membrane crystallization applications. We seek to demonstrate that a synergistic combination of TR polymers, porous nanofibrous membranes, and particle coating improves the long-term stability while maintaining high porosity and water flux. The fabricated membranes exhibit an excellent water flux (80 kg m−2 h−1) and NaCl rejection (>99.99%) with steady performance over more than 186 hours. In addition, for the first time, controlling the heterogeneous nucleation phenomena in membrane crystallization was clearly demonstrated using TR membrane morphology.

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography.

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.

Gas separation membranes made through thermal rearrangement of ortho methoxypolyimides

ortho-Methoxypolyimides were prepared from 3,3ʹ-dimethoxybenzidine (DMAB) and hexafluoroisopropylidene diphthalic anhydride (6FDA). High molecular weights of the resulting polymers were achieved, and the physical properties of the materials were investigated. The polyimides exhibited excellent thermal properties and film-forming capabilities. Polyimides were treated at high temperatures to promote thermal rearrangement (TR) processes. The final composition of the TR polymers seems not to correspond to TR-polybenzoxazoles, as was the case when analogous ortho-hydroxypolyimides were exposed to similar thermal treatments. A detailed study was carried out to elucidate the actual mechanism of the thermal rearrangement, comparing ortho-hydroxypolyimides, ortho-acetylpolyimides and ortho-methoxypolyimides. Results led to the conclusion that the chemical nature of the final TR polymers attained from ortho-methoxypolyimides is complex since imide, lactam and benzoxazole groups all seem to be present after thermal treatment. Gas permeation properties exhibited by thermally treated ortho-methoxypolyimides compared well with those of other TR-PBOs, showing CO2 permeability of 540 Barrers.