Browsing by Author "Yun, SI"
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- ItemBiodegradable polyhydroxyalkanoates/SWNT nanocomposite spheres and films prepared by spray-drying method(American Chemical Society, 2008-04-06) Yun, SI; Gadd, GE; Russell, RA; Holden, PJThe nanocomposite microspheres and films of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO) with single wall carbon nanotubes (SWNTs), were prepared by spray-drying method. The TEM immages showed that SWNTS well dispersed in PHB abd PHO indicating that rapid evaporation by spray drying effectively prevents aggregation of SWNTs. The Optical microscopy showed that the crystalline size substantially decreased for PHB/SWNTs nanocomposites with a 1% weight fraction of SWNTs relative to PHB (PHB/(1%)SWNTs), indicating the effective nucleation of PHB crystallization by SWNTs. Mechanical properties of the nanocomposite films were measured by nanoindentation. Both polymer nanocomposite films showed an increase in hardness (H) and Young's modulus (E), with SWNTs concentration.
- ItemDetermination of solution properties of poly(3-hydroxybutyrate) and deuterated poly(3-hydroxybutyrate) by SANS.(American Chemical Society, 2008-04-06) Yun, SI; Russell, RA; Holden, PJPolyhydroxyalkanoates (PHAs) are natural, linear, thermoplastic polyesters synthesized by micro-organisms as intracellular carbon reserves and ion sinks in response to limited nutrient availability and imposed stress conditions. We bio-synthesized PHB and deuterated PHB (d-PHB) and performed SANS on the dilute solutions of these molecules. In this paper, we report the conformational properties of PHB and d-PHB in d-chloroform and chloroform, respectively.
- ItemEffect of carbon nanotube functionalization on the structure and properties of poly(3-hydroxybutyrate)/MWCNTs biocomposites(Springer Link, 2014-07) Huh, M; Jung, MH; Park, YS; Kim, BJ; Kang, M; Holden, PJ; Yun, SIMulti walled carbon nanotubes (MWCNTs) covalently functionalized with an alkyl chain exhibited a better dispersion in poly(3-hydroxybutyrate) (PHB) solutions and cast films as compared with acid-treated MWCNTs (MWCNT-COOH) due to the much improved solubility in chloroform. The alkylated MWCNTs more effectively strengthened PHB composites than non-alkylated MWCNTs due to their uniform dispersion as well as stronger interaction of alkylated MWCNTs with the PHB matrix. Both acid-treated and alkylated MWCNTs added to PHB matrix facilitated crystallization kinetics. However the crystallization kinetics were found to be slower for the alkylated MWCNTs/PHB composites than acid-treated MWCNTs composites. The results may be ascribed to the inhibitory effect on PHB crystallization caused by the steric hindrance of the long alkyl chains attached to MWCNTs. © The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht 2014.
- ItemFabrication of honeycomb-structured porous films from poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) via the breath figures method(Wiley, 2011-12-27) Huh, M; Jung, MH; Park, YS; Kang, TB; Nah, C; Russell, RA; Holden, PJ; Yun, SIFormation of porous films from poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) using the breath figures (BF) method was investigated by evaporating solutions in chloroform in humid air and examining film structure using optical and scanning electron microscopy (SEM). BF films were successfully fabricated from PHB (Mw = 486,000 g/mol) and displayed hexagonal arrays of pores, which varied in diameter (D = 7–2 μm) with solution concentrations (0.5–2.00%). SEM of fractured films also showed subsurface closed nano-pores (D = 500–700 nm). BF films cast from PHBV (5% HV) formed arrays with smaller pores and apparent surface defects. Differential scanning calorimetry showed that porous PHB and PHBV films produced using the BF method were more crystalline than nonporous solvent cast films of PHB and PHBV. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
- ItemInteractions of cationic dendrigraft polymers with oligonucleotides and morphology of the resulting complexes.(American Chemical Society, 2008-04-06) Yun, SI; Hammerton, KM; Gauthier, MThe high density of negatively charged phosphate groups on ONs allows the formation of stable complexes with synthetic cationic polyelectrolytes (PEs). Even though DNA complexes with quaternized poly-vinylpyridine linear chains were previously reported to increase the efficiency of cell transformation, no report has been made for DNA complexes with dendrigraft PEs. For the current investigation, cationic dendrigraft polymers with pH-independent fully charged quaternized amine groups were synthesized. The structure of dendrigraft PEs and their complexes with ONs in solution was investigated by small-angle neutron scattering (SANS).
- ItemMechanical properties of biodegradable polyhydroxyalkanoates/single wall carbon nanotube nanocomposite films(Springer Nature, 2008-04-15) Yun, SI; Gadd, GE; Latella, BA; Lo, V; Russell, RA; Holden, PJThe nanocomposite films of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO) with single wall carbon nanotubes (SWCNTs), were prepared. The Optical microscopy showed that the crystalline size substantially decreased for PHB/SWCNTs nanocomposites with a 1 % weight fraction of SWCNTs relative to PHB (PHB/(1%)SWCNTs), indicating the effective nucleation of PHB crystallization by SWCNTs. Mechanical properties of the nanocomposite films were measured by nanoindentation. Both polymer nanocomposite films showed an increase in hardness (H) and Young’s modulus (E), with SWCNTs concentration. The PHB/SWCNTs nanocomposite films are found to be more brittle than neat PHB films. © 2008 Springer-Verlag
- ItemMorphology of composite particles of single wall carbon nanotubes/biodegradable polyhydroxyalkanoates prepared by spray drying(Springer, 2010-01) Yun, SI; Lo, V; Noorman, J; Davis, J; Russell, RA; Holden, PJ; Gadd, GESpray drying was investigated as a strategy for producing single wall carbon nanotube (SWCNT)/polymer composites. The spray-drying method produced SWCNT/poly(3-hydroxybutyrate) and SWCNT/poly(3-hydroxyoctanoate) composite particles in which the SWCNTs have been trapped in a well-dispersed state throughout the polymer matrix. Increasing SWCNT content in the composite led to a change in particle morphology from spherical and smooth to rosette shape with angular distortions. The technique shows potential for bulk carbon composite fabrication. © 2010, Springer.
- ItemSpray-dried microspheres as a route to clay/polymer nanocomposites(Wiley-Blackwell, 2008-05-05) Yun, SI; Attard, DJ; Lo, V; Davis, J; Li, HJ; Latella, BA; Tsvetkov, F; Noorman, H; Moricca, SA; Knott, RB; Hanley, HJM; Morcom, M; Simon, GP; Gadd, GEA new strategy for the preparation of well-dispersed clays in a polymer matrix by a spray-drying method is presented. Scanning electron microscopy and transmission electron microscopy measurements show that the spray-drying process produces clay/polymer microspheres in which the clay is trapped in a well-dispersed state throughout the polymer matrix. The microspheres have been successfully extruded into clay/poly(methyl methacrylate) nanocomposite bulk structures without any perturbation of the well-dispersed clay nanostructure in the original microspheres. Transmission electron microscopy and small-angle X-ray scattering show that the clay particles in the extruded materials range from single platelets to simple tactoids composed of a few stacked clay platelets, indicating an excellent degree of dispersion. The results show that sprayed microspheres are very good precursors for further processing such as extrusion or melt blending with other polymers for bulk nanocomposite fabrication. © 2008, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com