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위정재,Hua Jin,정상기,김성철,최우진 한국고분자학회 2010 Macromolecular Research Vol.18 No.4
Organifiers with multiple cationic sites were synthesized to examine their effect on polyurethane (PU)/organoclay nanocomposites. The number of cationic sites was varied from 1 to 4 and the molecular weight of organifiers was also varied from 4,456 to 10,327. By increasing the number of cationic sites, higher physical ionic crosslinking was observed from the rheometer measurement. In this study, the chain length between two cationic sites was defined as the inner chain, and the chain length attached to the end group of the organifier was defined as the outer chain. The molecular weight of the inner and outer chain was varied to investigate the effect of the inner and outer chain length on the properties of organoclays and nanocomposites. A higher inner chain length led to a better dispersion of clay in the PU matrix, as observed in SEM and TEM images and higher mechanical properties of PU/organoclay nanocomposites, as shown in the tensile test. Lower mechanical properties were observed when the organifier had a shorter inner chain length, even though the organifier has a higher molecular weight and larger number of cationic sites. The tensile strength and glass transition temperature increased from 26 to 59 MPa and from -19.1 to -10.8 oC, respectively, with a 3 wt% loading of the 2K-H-2K organoclay because it has the highest organifier inner chain length among the organifiers prepared.
Replica molding of vertically aligned liquid crystalline polymer microstructures
위정재,( Hangbo Zhao ),( Davor Copic ),( Alvin Orbaek White ),( Sanha Kim ),( A. John Hart ) 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0
Molecularly anisotropic polymers can be manufactured into a wide variety of forms capable of actuation upon application of external stimuli. In particular, incorporation of the liquid crystal molecules in polymeric networks enables facile route to align mesogenic units within microstructures. Most studies of current thermomechanical actuation of liquid crystalline polymers have used millimeter-scale and larger shapes, and only a few studies reported thermally responsive liquid crystal polymer microstructures. Here we present the thermomechanical response of glassy azobenzene-functionalized liquid crystalline polymer networks in micropillar geometries. Large-arrays of uniform polymer microstructures are fabricated by replica molding of using a polydimethylsiloxane (PDMS) template, and the molecular orientation of the polymer is manipulated by applying a magnetic field during photocuring the molten monomer mixture in the mold. We discuss how the micropillar and liquid crystal geometry influence the stimuli response from the highly crosslinked polymer network.
Rational Molecular Design of Polymeric Materials Toward Efficient Triboelectric Energy Harvesting
위정재 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1
Halogenated carbon-based polymers are widely known as extremely negative triboelectric polymers. The negative triboelectric characteristics of these polymers originated from large electron affinity (EA=-270~-349 kJ/mol) of halogenic elements, allowing the polymers to accommodate extra electrons. In case of the PTFE, two carbon bonds are sacrificed to construct polymeric backbone, instead of chemically bonding with halogenic elements. Herein, we employed inverse-vulcanized sulfur-based polymers to have maximum of four chemical bonding with halogenic elements via hypervalency of sulfur. In addition to the two extra halogenic elements per sulfur in comparison with carbon, electron affinity of sulfur (EA=-200 kJ/mol) is significantly larger that that of carbon (EA=-122 kJ/mol). We report 3 folds increase in triboelectric energy outputs in both voltage and currents in comparison with commercial PTFE film with the novel yellow-chemistry based inorganic polymers.
The effects nanoscale interfaces on polyurethane nanocomposites for soft robot applications
위정재 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
Anomalous nanoscale phenomena have extensively been reported in polymer nanocomposites including breakdown of Stokes-Einstein relation, expansion of polymer dimension, non-Einstein-like viscosity reduction. In order to observe these nanoscale phenomena, homogeneous dispersion of nanofiller is essential to generate nanoscale interfaces. In this study, we demonstrate two drastically different dispersion quality of iron oxide nanoparticles in thermoplastic polyurethane (TPU) matrix via conventional solvent evaporation and rapid precipitation techniques despite the identical chemical compositions of polymer nanocomposites. Remarkably, nanoscale interfaces in TPU nanocomposites by rapid precipitation prevented typical evolution of soft and hard segments of TPU supported by single TGA peak. We will also discuss soft robotics applications with these polymer nanocomposites and importance of the dispersion quality of nanoparticles.