Synthesis Of Ethylene Oxide Based Block Copolymers And Their Application In Adsorption Flocculation Processes

Author : Guodong Deng
Publisher :
ISBN 13 :
Total Pages : 149 pages
Book Rating : 4.:/5 (133 download)

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Download or read book Self-assembly of Poly(ethylene Oxide)-block-poly(ethyl Acrylate)-block-polystyrene with Phenolic Resins written by Guodong Deng and published by . This book was released on 2014 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mesoporous carbon materials (2-50 nm) have received considerable attention for their remarkable physicochemical properties, which bring about widespread applications, such as absorption, separation, catalysis, drug delivery, and energy conversion and storage. One general route to fabricate mesoporous carbons is through soft-templating, namely cooperative self-assembly of an amphiphilic block copolymer (BCP) with a carbon precursor (e.g. phenolic resin). The precursor is selective to hydrophilic domains to tune the microphase separation of BCP. Typical soft templating involves the use of A-B or A-B-A block copolymers as the template, which in most cases, only spheres, cylinders, and lamellae morphologies were obtained. Switching to an A-B-C type triblock copolymer provides greater flexibility in the design of the morphology, potentially opening up larger processing windows for bicontinuous morphologies. In this study, we designed and synthesized a new non-frustrated triblock copolymer poly(ethylene oxide)-block-poly(ethyl acrylate)-block-polystyrene (PEO-b-PEA-b-PS) using reversible addition-fragmentation chain transfer (RAFT) polymerization. We discuss efforts to prepare bicontinuous porous carbon thin films through cooperative self-assembly of this novel triblock copolymer with phenolic resins (resol) with different processing methods. Initially, we spun-cast a series of polymer/resol thin films with variant resol concentrations. These polymer/resol films were processed by three thermal processing steps: thermal annealing to induce ordering of BCP and resol's crosslinking (120 °C), calcination to remove BCP template to yield mesopores (400 °C), and carbonization to produce mesoporous carbon films (800 °C). After template removal AFM results suggest that a network of homogeneous fibrous nanostructures (~20 nm diameter cylinders) with high porosity (~60%) were produced over a range of resol concentration (25 ~ 33 wt%). Other kinetically trapped structures, such as parallel cylinders and mixed parallel lamella/cylinders are also found at higher resol concentration (40 ~ 60 wt%). These kinetically trapped mesostructures are attributed to the high glass transition temperature of PS segments leading to slower self-assembly ordering rate of BCP than resol's crosslinking rate. Next, solvent vapor annealing (SVA) with methyl ethyl ketone (MEK) was performed on as prepared polymer/resol films prior to the thermal processing steps. The MEK solvent vapor plasticized the polymer (i.e. enhancing the mobility of segments) allowing it to self-assemble into a series of highly ordered structures such as parallel cylinders, perpendicular cylinders, and double gyroids, as evidenced by AFM and GISAXS results. Further thermopolymerization of these films produced long range ordered mesostructures through an order-order transition during thermal crosslinking, including a small window of bicontinuous gyroid morphology. It was found that the formation of gyroid phase from order-order transition (cylinder to gyroid) is a strong function of the aging of the resol, as well as the processing conditions, including SVA time and resol composition. Subsequent calcination and carbonization of this bicontinuous gyroidal film yielded an ordered bicontinuous gyroidal mesoporous carbon with high porosity (50 %) and narrow pore size distribution (12 ± 2 nm).