Jinguk Kim

A novel cross-linked nano-coating for carbon dioxide capture

Ultra-thin (∼100 nm) films with uniform thicknesses can facilitate high CO2 permeation and are of potential technological significance for CO2 capture. Among many approaches for obtaining such materials, the recently developed continuous assembly of polymers (CAP) technology provides a robust process, allowing for the production of defect-free, cross-linked and surface-confined thin films with nanometer scale precision. Through utilization of this nanotechnology, we have constructed composite membranes containing cross-linked ultra-thin surface films. The membrane materials formed exhibited significantly high permeances as well as excellent gas separation selectivity.

Highly permeable membrane materials for CO2 capture

The release of large quantities of CO2 into the atmosphere has been linked to global warming and climate anomalies. Membrane processes offer a potentially viable energy-saving alternative for CO2 capture in comparison with conventional technologies such as amine absorption. However, gas separation membranes that are currently available have insufficiently high permeance (flux) for large scale applications such as the treatment of high volume flue gas with low concentration of CO2. Here we demonstrate a class of thin film composite (TFC) membranes, consisting of a high molecular weight amorphous poly(ethylene oxide)/poly(ether-block-amide) (HMA-PEO/Pebax® 2533) selective layer and a highly permeable polydimethylsiloxane (PDMS) intermediate layer which was pre-coated onto a polyacrylonitrile (PAN) microporous substrate. In contrast to the performance of conventional materials, the selective layer of TFC membranes shows super-permeable characteristics and outstanding CO2 separation performance. This unprecedented result arises from the introduction of HMA-PEOs into the Pebax® 2533 matrix, leading to high CO2 permeability and flux. These results provide an encouraging direction to further develop TFC membranes for efficient CO2 capture processes.

The effect of soft nanoparticles morphologies on thin film composite membrane performance

Well-defined branched and densely cross-linked soft nanoparticles (SNPs) were synthesized and incorporated into a poly(ether-b-amide) (Pebax®) matrix to form the selective layer of thin film composite (TFC) membranes. The fabricated TFC membranes exhibited distinct gas separation abilities. These results reveal the effect of SNP morphologies on the membrane performance. This study may provide insights and novel strategies to fabricate highly permeable membrane materials for carbon dioxide (CO2) capture.

Cyclodextrin-based supramolecular polymeric nanoparticles for next generation gas separation membranes

Cyclodextrin-based supramolecular assemblies derived from poly(dimethylsiloxane) (PDMS) functionalized polyrotaxanes (PRXs) were self-assembled into core–shell morphologies and used as soft nanoparticle (SNP) additives in the selective layer of thin film composite (TFC) membranes for the first time. Various weight percentages (wt%) of the PRX SNP additives were combined with Pebax® 2533 to form the selective layer, and the gas transport properties of the TFC membranes were studied in detail. Increasing the amount of PRX SNP additives led to a significant increase in CO2 permeance of the membranes, with only a slight decrease in the CO2/N2 selectivity, which was attributed to the dynamic nature (i.e., translational and rotational freedom) of the conjugated PDMS chains on the PRXs. In comparison, the performance of membranes prepared using a conventional analogue with fixed PDMS chains was inferior. The excellent gas transport properties observed for membranes are attributed to the novel self-assembly process of the dynamic PRX SNP additives; the sliding nature of the conjugated PDMS chains allow for increased exposure of the CO2-philic PEG backbone and increased size of the hydrophobic core leading to improved membrane selectivity and permeability. The effect of varying operating conditions (feed pressure and temperature) was also investigated and compared between the dynamic and fixed additive systems. Interesting trends were observed with the dynamic PRX system which diverges from conventional systems. This study opens up new avenues for CD-based supramolecular chemistry in the field of membrane technologies for gas separation.

Continuous assembly of polymers via solid phase reactions

The continuous assembly of polymers in the solid state via ring-opening metathesis polymerization (ssCAPROMP) is reported as an effective method for the fabrication of smooth, surface confined, cross-linked nanostructured films. Macrocross-linkers, polymers pre-functionalized with polymerizable pendent groups, were first deposited onto initiator-modified substrates via spin-coating, followed by film cross-linking via ssCAPROMP. The film thickness is tunable by adjusting the reaction time, and multilayered films can be achieved through reinitiation steps, generating complex and unique film architectures with nanometer precision. The technique developed herein allows for controlled and directional growth of cross-linked thin films from the substrate surface in the solid state.

Spatial-controlled nanoengineered films prepared via rapid catalyst induced cross-linking

A new top-down approach to generate stable nanoscale films via catalyst induced cross-linking (CIC) is demonstrated. Polymers with various compositions and bearing pendent norbornene groups (defined as macrocross-linkers) are initially spin-coated onto substrates to form nanometre-thick films; when the films are brought into contact with a catalyst solution, ring-opening metathesis polymerization (ROMP)-mediated cross-linking efficiently occurs to lock the film into place. CIC provides a new paradigm for the fabrication of stable nanoscale films and provides an alternative to traditional methods that use external stimuli (e.g., heat or light) to trigger film cross-linking. The process requires short cross-linking times (<3 min) to generate covalently bonded and stable nanoscale films. This facile nanoengineering approach allows for the creation of complex multi-layered and multi-compositional patterned films, enables excellent control over film properties such as thickness and swellability, and provides access to nanoscale free-standing polymer sheets. To highlight the versatility of the CIC approach, cross-linked, nanostructured and stratified multi-layered films with tunable film thickness were prepared from norbornene functionalised poly(oligo(ethylene glycol) methacrylate), poly(ethylene glycol) and poly(3-hexylthiophene) macrocross-linkers. CIC proceeds at low catalyst concentrations and allows the catalyst solution to be recycled multiple times, as demonstrated through repetition of 10 individual CIC cycles, making the process economical, scalable and applicable to advanced manufacturing techniques. Furthermore, the technique can be used to produce patterned films through selective exposure of specific regions of the polymer film to the catalyst solution. The CIC approach mediated by ROMP is highly efficient, rapid, robust and versatile, providing new opportunities in film assembly, and complementing existing nanoscale film fabrication methodologies.