Browsing by Author "Chan, SC"

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A numerical analysis of horizontal flame spread over a thin fuel in normal and elevated gravity regime
(1995)
Chen, CH
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Chan, SC
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交大名義發表
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機械工程學系
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National Chiao Tung University
A numerical model is developed to simulate flame spread over a thin solid fuel horizontally in a gravitational field. In this paper, the burning behaviors in normal and elevated gravity are analyzed. In normal gravity, the flame structures are investigated in detail in order to find the essential features of such spreading flame. The flame can be separated into an upper flame and a lower flame by the fuel plate. There are three high temperature regions: two of them are at the upper and lower flame fronts, respectively, and the other one is at the combustion plume, just behind the burnout point. The induced flow moves upward and forms a thermal plume above the fuel plate. An entrainment of air moves toward the flame, opposed to the upper spreading flame. Below the fuel plate, the induced flow moves concurrently with the lower spreading flame. From the reaction rate distribution, the characteristics of triple-reaction-zone is identified. The heat flux on the bottom side is more intensive and extends further upstream than that on top side, confirming that the controlling mechanism is determined by the spreading flame underneath the fuel plate. A qualitative comparison with experiments is given. A parametric study by elevating gravity is followed. A blowoff limit occurs at about g = 5.5. During the process, the horizontal flame spread rate is found to be slower than the downward one behind g = 2.5, where the lower flame is broken due to the up-rising induced flow. The variation in flame structures as a function of gravity is discussed.
An unusual, completely miscible, ternary hydrogen-bonded polymer blend of phenoxy, phenolic, and PCL
(2005-05-31)
Kuo, SW
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Chan, SC
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Wu, HD
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Chang, FC
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應用化學系
We have investigated the miscibility and hydrogen-bonding behavior of ternary blends of phenoxy, phenolic, and poly(e-caprolactone) (PCL) by using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy. On the basis of DSC analyses, we observed a rare totally miscible ternary hydrogen-bonded polymer blend in the amorphous phase: all compositions of this ternary blend display a single glass transition temperature. In addition, these single glass transition temperatures can be predicted well by extending the Kwei equation from the binary polymer blend to this ternary polymer blend. The infrared spectra indicate that the intermolecular hydrogen bonding of each pair of binary components still exists in the ternary polymer blend. We used the ternary totally miscible blend to determine the interassociation equilibrium constant between the hydroxyl groups of phenolic and the hydroxyl groups of phenoxy indirectly from the fraction of hydrogen-bonded carbonyl groups of PCL. Quantitative analyses suggest that interassociation between the hydroxyl groups of phenolic and the hydroxyl groups of phenoxy is more favorable than the hydroxyl-carbonyl interassociations of either phenolic/PCL or phenoxy/PCL and the hydroxyl-hydroxyl self-association of the pure phenolic and phenoxy homopolymers at room temperature.
Crystallization kinetics and morphology of binary phenolic/poly(epsilon-caprolactone) blends
(2004-01-01)
Kuo, SW
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Chan, SC
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Chang, FC
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應用化學系
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Department of Applied Chemistry
For the first time, quantitative analyses of the crystallization kinetics, surface free energy of chain folding, and morphology in phenolic/poly(epsilon-caprolactone) (PCL) binary blends have been studied. The spherulite growth rate and the overall crystallization rate depend on the crystallization temperature and PCL content in the blend. In addition, the crystallization and melting temperatures of the PCL phase decrease with an increase in the phenolic content. An Avrami analysis shows that the addition of phenolic to PCL results in a decrease in the overall crystallization rate of the PCL phase. The presence of an amorphous phenolic phase results in a reduction in the rate of the spherulite growth of PCL. The surface free energy of folding increases with increasing phenolic content, and the crystal thickness of a phenolic/PCL blend, according to small-angle X-ray scattering (SAXS), is greater than that of pure PCL because of the increase in the surface free energy of chain folding and the decrease in the degree of supercooling. The observed domain size of the crystalline/amorphous phase (5.9 nm) from SAXS is also consistent with that from solid-state NMR (3-20 nm). All these results indicate that the crystallization ability of PCL decreases with increasing phenolic content in the blends. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 117-128,2004.
Effect of hydrogen bonding strength on the microstructure and crystallization behavior of crystalline polymer blends
(2003-08-26)
Kuo, SW
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Chan, SC
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Chang, FC
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應用化學系
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Department of Applied Chemistry
Combinations of differential scanning calorimetry, Fourier transform infrared spectroscopy, optical microscopy, and small-angle X-ray scattering were used to investigate the influence of hydrogen bonding strength on the crystallization kinetics and morphologies in poly(epsilon-caprolactone) (PCL) blends with three different well-known hydrogen bond donating polymers, i.e., phenolic, poly(vinylphenol) (PVPh), and phenoxy. The strength of the intercomponent interactions in the blend system depends on the hydrogen bond donor group and occurs, based on the Painter-Coleman association model, in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL. Significantly reduced overall crystallization kinetics and crystal growth rate in PCL crystalline phase were also in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL, which is consistent with the relative strengths of their intermolecular hydrogen bonding. Our experimental findings show that the hydrogen bonding strength has a greater effect on the rate of crystallization than does the influence of the blend's glass transition temperature, which is related to its chain mobility. In addition, values of the surface free energy of chain folding and crystalline thickness in PCL blends depend strongly on the relative ratio of the interassociation equilibrium constant and the self-association equilibrium constant (K-A/K-B). In phenolic/PCL and PVPh/PCL blends, the values of the surface free energies of chain folding in the PCL crystalline phase are increased with an increase in the content of the hydrogen bond donating polymer since the K-A is greater than the K-B in these two blend systems. In contrast, in the phenoxy/PCL blend system, the smaller K-A relative to the K-B induces a smaller value for the surface free energy of chain folding than that of pure PCL. Various miscible crystalline/amorphous binary polymer blends exhibiting either strong hydrogen bonding or weak interactions are also reviewed.
Miscibility enhancement on the immiscible binary blend of poly(vinyl acetate) and poly(vinyl pyrrolidone) with bisphenol A
(2002-06-01)
Kuo, SW
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Chan, SC
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Chang, FC
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應用化學系
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Department of Applied Chemistry
The miscibility behavior and hydrogen bonding of ternary blends of bisphenol A (BPA)/poly(vinyl acetate) (PVAc)/poly(vinyl pyrrolidone) (PVP) were investigated by using differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). The BPA is miscible with both PVAc and PVP based on the observed single T-g over the entire composition range. FTIR was used to study the hydrogen-bonding interaction between the hydroxyl group of BPA and the carbonyl group of PVAc and PVP at various compositions. Furthermore, the addition of BPA is able to enhance the miscibility of the immiscible PVAc/PVP binary blend and eventually transforms into miscible blend with single T-g, when a sufficiently quantity of the BPA is present due to the significant Deltachi and the DeltaK effect. (C) 2002 Elsevier Science Ltd. All rights reserved.
Miscibility, specific interactions, and spherulite growth rates of binary poly(acetoxystyrene)/poly(ethylene oxide) blends
(2004-06-01)
Kuo, SW
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Huang, WJ
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Huang, CF
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Chan, SC
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Chang, FC
The binary poly(acetoxystyrene)/poly(ethylene oxide) (PAS/PEO) blend system is fully miscible, as evidenced by a single glass transition temperature over a full range of compositions when analyzed by differential scanning calorimetry analysis, as a result of weak C-(HO)-O-... hydrogen-bonding interactions between the carbonyl groups of PAS and the methylene groups of PEO. One- and two-dimensional correlation spectroscopies provide positive evidence for this specific interaction between the two polymers. In addition, a negative polymer-polymer interaction parameter "chi(12)" was calculated using the Flory-Huggins equation based on the melting depression of PEO. The presence of an amorphous PAS phase results in a reduction in the spherulite growth rate of PEO. Both the values of nucleation constant and the surface free energy of chain folding of PEO decrease with increasing PAS content, which indicates that the crystallization ability of PEO increases correspondingly.
Synthesis of the organic/inorganic hybrid star polymers and their inclusion complexes with cyclodextrins
(2005-04-19)
Chan, SC
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Kuo, SW
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Chang, FC
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應用化學系
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Department of Applied Chemistry
In this study, we synthesized a series of the organic/inorganic hybrid star PCLs. These star PCLs can form inclusion complexes (ICs) with alpha- and gamma-CD, but not with beta-CD. These CD ICs were characterized by XRD, solid-state C-13 CP/MAS NMR spectroscopy, H-1 NMR spectroscopy, FT-IR spectroscopy, DSC, and TGA. Our results suggest that the PCL chains of these star polymers lose their original crystalline properties and were included inside the channels provided by the CDs to form a columnar crystalline structures. The stoichiometries (PCL:CD) that we determined by H-1 NMR spectroscopy for all of the ICs with alpha- or gamma-CD are higher than those of the corresponding CD/linear PCL ICs because of the steric hindrance around the bulky POSS core, which causes some of the c-caprolactone units near the core to be free from complexation with the CDs. From these analyses, we proposed some possible structures for the CD/star PCL ICs.