Browsing by Author "Chang, FC"

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A new strategy for the one-step synthesis of block copolymers through simultaneous free radical and ring opening polymerizations using a dual-functional initiator
(2005-02-14)
Huang, CF
;
Kuo, SW
;
Lee, HF
;
Chang, FC
;
應用化學系
Block copolymers are fascinating and complex materials that have been used in a range of diverse scientific and technological capacities. We demonstrate that a single one-step approach based on dual simultaneous polymerizations is a viable technique for the synthesis of a wide range of block copolymers by combining two dissimilar polymerization systems and using a dual-functional initiator. The main advantage of this methodology is that a simple, one-step, and simultaneous polymerization occurs in the bulk, which makes this process very attractive from both industrial and academic points of view. We plan to study the reaction kinetics and evaluate how well the ring opening catalyst [in this case, Sn(oct)(2)] works under reverse ATRP conditions. (C) 2004 Elsevier Ltd. All rights reserved.
A novel preparation of polyimide/clay hybrid films with low coefficient of thermal expansion
(2001-01-10)
Gu, AJ
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A novel polyimide (PI)/clay hybrid nanocomposite, designated as PI (PAAS)/CM, has been developed from the poly(amic acid) salt of triethylamine and organomontmorillonite (CM) using a mixture solution of tetrahydrofuran (THF) and methanol (MeOH). For comparison, two other PI/clay hybrids derived from poly(amic acid) and CM in THF/MeOH solution and N,N'-dimethylacetamide (DMAc) solution, denoted as PI/CM (T/M) and PI/CM (DMAc), respectively, were also prepared. Dispersion of CM in polymer matrix, tensile properties, and thermal expansion properties of the three hybrids were investigated. Results show that PI (PAAS)/CM has the best dispersion of CM in polymer matrix, highest elongation, and lowest coefficient of thermal expansion values in all hybrids presented in this report. In addition, PI/CM (T/M) has better dispersion of CM and lower coefficient of thermal expansion value than PI/CM (DMAc). (C) 2000 John Wiley & Sons, Inc.
A relevance feedback image retrieval scheme using multi-instance and pseudo image concepts
(2005)
Chang, FC
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Content-based image search has long been considered a difficult task. Making correct conjectures on the user intention (perception) based on the query images is a critical step in the content-based search. One key concept in this paper is how we find the user preferred image characteristics from the multiple positive samples provided by the user. The second key concept is that when the user does not provide a sufficient number of samples, how we generate a set of consistent "pseudo images". The notion of image feature stability is thus introduced. The third key concept is how we use negative images as pruning criterion. In realizing the preceding concepts, an image search scheme is developed using the weighted low-level image features. At the end, quantitative simulation results are used to show the effectiveness of these concepts.
Advanced electrical imaging of dislocations in Mg-In-codoped GaN films
(2006-01-01)
Chen, SH
;
Hou, SP
;
Hsieh, JH
;
Chang, FC
;
Chen, WK
Conducting atomic force microscopy and scanning surface-potential microscopy have been applied to image the surfaces of Mg-In-codoped GaN films grown by low-pressure metal-organic chemical-vapor deposition. Biscyclopentadienylmagnesium (CP2Mg) and trimethylindium (TMIn) have been used as the codoping sources in the experiment. The dislocation density at the film surface reduces to the lowest level (similar to 1.0 X 10(9) cm(-2)) when the TMIn/CP2Mg flow rate ratio is about 1. The dislocation density tends to rise when the flow ratio increases, and carriers of the film accumulate near the rim of the dislocation at an accelerated speed. The work function of dislocation is also found lower than that of nondislocation areas. Such electrical unevenness may seriously influence the light emission of the component, which should not be ignored during fabrication and deserves careful attention. (c) 2006 American Vacuum Society.
An image retrieval scheme using multi-instance and pseudo image concepts
(2004)
Chang, FC
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Content-based image search has long been considered a difficult task. Making correct conjectures on the user intention (perception) based on the query images is a critical step in the content-based search. One key concept in this paper is how we find the user preferred image characteristics from the multiple samples provided by the user. The second key concept is that when the user does not provide a sufficient number of samples, how we generate a set of consistent "pseudo images". The notion of image feature stability is thus introduced. In realizing the preceding concepts, an image search scheme is developed using the weighted low-level image features. At the end, quantitative simulation results are used to show the effectiveness of these concepts.
An implementation of a simple DAVIC server using orbix
(1996)
Chang, FC
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An MPEG-4 IPMPX design and implementation on MPEG-21 test bed
(2005)
Fan, CW
;
Chang, FC
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
With the growing demand for distributing digital media contents, the issues of protecting the rights of digital contents are becoming more and more important. In this paper, we introduce the MPEG-4 IPMPX (Intellectual Property Management and Protection Extension) specifications and design its implementation architecture on the MPEG-21 Multimedia Test Bed. This flexible system is capable of integrating lPMPX tools such as encryption/decryption and digital watermarking into it. The main contributions are (1) we design and integrate a software architecture of the IPMPX system and its APIs into the standard-compliant MPEG-21 Test Bed; (2) the implementation of the IPMPX architecture is close to the original IPMPX concepts and thus provides a good validation of the IPMPX capabilities; (3) we develop an application example on the IEPMPX-enabled MPEG-21 Test Bed to show its powerful functionalities. The IPMP subsystem together with the application example has been completed and described in this paper.
An unusual, completely miscible, ternary hydrogen-bonded polymer blend of phenoxy, phenolic, and PCL
(2005-05-31)
Kuo, SW
;
Chan, SC
;
Wu, HD
;
Chang, FC
;
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.
Behavior and surface energies of polybenzoxazines formed by polymerization with argon, oxygen, and hydrogen plasmas
(2004-11-15)
Chen, JK
;
Lin, IK
;
Ko, FH
;
Huang, CF
;
Chen, KS
Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma-polymerization technique with, as the energy source, plasmas of argon oxygen or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high-energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties aid morphologies in their surfaces. High-energy argon atoms provide a thermodynamic factor to initiate the ring-opening polymerization of BZZ and result in the polymer surface having a grid-like structure. The ring-opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and Results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma-polymerization time. By estimating changes in thickness, we found that tie PBZZ film synthesized by the oxygen plasma-polymerization process undergoes the slowest rate of etching in CF(4) plasma. (C) 2004 Wiley Periodicals, Inc.
Blends of poly(propylene) and polyacetal compatibilized by ethylene vinyl alcohol copolymers
(2003-08-08)
Huang, JM
;
Cheng, HJ
;
Wu, JS
;
Chang, FC
;
應用化學系
Polymer blends of poly(propylene) (PP) and polyacetal (polyoxymethylene, POM) with ethylene vinyl alcohol (EVOH) copolymers were investigated by differential scanning calorimetry (DSC), rheological, tensile, and impact measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The PP-POM-EVOH blends were extruded with a co-rotating twin-screw extruder. The ethylene group in the EVOH is partially miscible with PP, whereas the hydroxyl group in the EVOH can form hydrogen bonding with POM. The EVOH tends to reside along the interface, acting as a surfactant to reduce the interfacial tension and to increase the interfacial adhesion between the blends. Results from SEM and mechanical tests indicate that a small quantity of the EVOH copolymer or a smaller vinyl alcohol content in the EVOH copolymer results in a better compatibilized blend in terms of finer phase domains and better mechanical properties. (C) 2003 Wiley Periodicals, Inc.
Chain conformation and crystallization behavior of the syndiotactic polystyrene nanocomposites studied using Fourier transform infrared analysis
(2001-04-24)
Wu, HD
;
Tseng, CR
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Analyses of the effects of montmorillonite (clay) on the chain conformation and crystallization of syndiotactic polystyrene (s-PS) thin films are investigated using FTIR spectroscopy, X-ray diffraction, and TEM. The clay is dispersed into the s-PS matrix using a solution blending with scale in 1-2 nm or in a few tenths to 100 nm, depending on whether a surfactant is added or not. Upon adding clay, the chain conformation of s-PS tends to convert to TTTT from rTTGG after drying because the highly dispersed clay overcomes the energy barrier of chain conformation transformation. This phenomenon leads to a change in a conventional mechanism of molecular packing for s-PS in the drying stage. During melt-crystallization, clay plays a vital role in facilitating the formation of the thermodynamically favored all-trans p form crystal, particularly on the s-PS thin film. When the s-PS is melt-crystallized at a cooling rate of 1 degreesC/min from 320 degreesC, the highest absolute crystallinity of beta form up to 0.56 occurs in the clay dispersibility of few tenths to 100 nm in the s-PS matrix; then dispersibility is of 1-2 nm (0.49), and the final one is of pure s-PS (0.42). Evidently, clay significantly affects the chain conformation and crystallization of s-PS.
Characteristics of p-type GaN films doped with isoelectronic indium atoms
(2002-12-01)
Chang, FC
;
Shen, KC
;
Chung, HM
;
Lee, MC
;
Chen, WH
The method of isoelectronic doping, is employed to prepare p-type GaN films using metalorganic chemical vapor deposition. With the addition of In atoms, the film surface becomes much smoother, and the corresponding hole concentration and resistivity are also improved, to 8.7 x 10(17) cm(-3) and similar to 1 Omega-cm, respectively. More interestingly, it is found that an ohmic I-V characteristic can be obtained in such types of films without any dehydrogenation treatment.
Characterization and properties of new silicone-containing epoxy resin
(2000-07-01)
Wang, WJ
;
Perng, LH
;
Hsiue, GH
;
Chang, FC
;
應用化學系
A new epoxy monorner, triglycidyloxy phenyl silane (TGPS) has been synthesized. By curing of TGPS, Epon 828 and DER 732, with 4,4-diaminodiphonyl methane (DDM), the curing rate and conversion efficiency of these epoxy resins are in the order of TGPS > Epon 828 > DER 732. In the mixed epoxy system of TGPS/Epon 828/DDM, homogenous products are obtained from all proportions. In addition, the glass transition temperature of the blend decreases with increasing amount of TGPS from 140 to 100 degrees C. By using TGA in a Nz environment, the onset decomposition temperature of silicone-containing epoxy resin system of TGPS is 80 degrees C lower than that of Epon 828, and the decomposition of TGPS is a two-stage process with maxima weight loss rates at 330 and 430 degrees C, respectively. The first stage involves the breaking of the silicons-containing group in TGPS and the second-stage is carbonization. In the second stage of carbonization, the temperature for maximum weight loss rate is 15 degrees C higher than that of the Epon 828 in the first stage. This result indicates that the silicone-containing group is in favor of the carbonization mechanism and the solid char yield at 800 degrees C for TGPS is 40 wt%. Based on EDX analysis on the surface elements, the presence of Si and C is indicative of the above observation. In addition, the result by using TGA in an air environment shows that the silicon-containing carbon residue is superior in preventing oxidative burning. The high limiting oxygen index (LOI) of TGPS at 35 is considered as an excellent flame retardant in the epoxy system. (C) 2000 Elsevier Science Ltd. All rights reserved.
Characterization of crystallization in syndiotactic polystyrene thin film samples
(2000-11-28)
Wu, HD
;
Wu, ID
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Characterization of poly(vinyl pyrrolidone-co-isobutylstyryl polyhedral oligomeric silsesquioxane) nanocomposites
(2004-02-15)
Xu, HY
;
Kuo, SW
;
Huang, CF
;
Chang, FC
;
應用化學系
Poly(vinyl pyrrolidone-co-isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP-POSS) were synthesized by one-step polymerization and characterized 13 using FTIR, high-resolution H-1-NMR, solid-state C-13-NMR, Si-29-NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The T-g of the PVP-FOSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self-association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low FOSS content, the role as diluent dominates, resulting in a decrease in T-g. At a relatively high POSS content, the last two factors dominate and result in T-g increase of the PVP-POSS hybrid. (C) 2003 Wiley Periodicals, Inc.
Characterizations for blends of phosphorus-containing copolyester with poly(ethylene terephthalate)
(1998-09-01)
Chang, SJ
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
High molecular weight phosphorus-containing copolyesters, poly(ethylene terephthalate)-co-poly(ethylene DDP) (PET-co-PEDDP)s, were prepared and characterized with the objective of producing a non-halogen flame retardant system for practical applications. The phosphorus-containing copolyester with 30 wt% phosphorus (P30 copolyester) was blended with PET to evaluate their characteristics and flame retardancy. Higher phosphorus content results in lower crystallinity and higher char formation after thermal degradation. The rheological behavior remains similar to that of PET. The P30/PET blend possesses higher crystallization rate than the corresponding phosphorus-containing copolyester containing equal phosphorus content. Thermal and rheological behaviors of P30/PET blends are similar to PET or the phosphorus-containing copolyesters. The P30/PET blends are miscible or compatible base on single T(g)s detected by DSC or DMA. The SEM/EDX phosphorus mapping image of the P30/PET blend shows uniform distribution of the phosphorus moieties within the P30/PET matrix, another indication of a compatible or miscible blend between the phosphorus-containing copolyester P30 and PET. Flame retardancy of the P30/PET blend is identical to that of the phosphorus-containing copolyester with identical phosphorus content. Blending of high phosphorus content copolyester with virgin PET provides a feasible method to obtain a flame resistant PET with LOI greater than 28.
Combined encryption and watermarking approaches for scalable multimedia coding
(2004)
Chang, FC
;
Huang, HC
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Intellectual Property (IP) protection is a critical element in a multimedia transmission system. Conventional IP protection schemes can be categorized into two major branches: encryption and watermarking. In this paper, a structure to perform layered access protection by combining encryption and robust watermarking is proposed and implemented. By taking advantage of the nature of cryptographic schemes and digital watermarking, the copyright of multimedia contents can be well protected. We adopt the scalable transmission method over the broadcasting environment. The embedded watermark can be thus extracted with high confidence. Then, the next-layer secrets can be perfectly decrypted and reconstructed. Finally, the media contents are recovered.
Comparative study of Schottky diode characteristics in Ni, Ta and Ni/Ta metal contact schemes on n-GaN
(2001-07-01)
Chen, GL
;
Chang, FC
;
Chuang, WC
;
Chung, HM
;
Shen, KC
We have reported current-voltage characteristics of Ta/- and Ni/Ta/n-GaN Schottky diodes under various thermal treatments. Experimental data indicate that the electrical characteristics of Ni/Ta diodes are controlled by the interfacial properties of the Ta and GaN heterointerface for the as-deposited samples and strongly affected by the presence of an oxide layer (Ta2O5) in those high-temperature-annealed diodes. In regard to Ta/Ni diodes, probably because of thermal stability and wide-bandgap properties of tantalum oxide, dramatic improvement in Schottky diode performance was resulted after annealing at high temperatures. The corresponding barrier height and ideality factor values can reach 1.17 cV and 1.09, respectively, even at an annealing temperature of 800 degreesC.
Comparison of hydrogen bonding interaction between PMMA/PMAA blends and PMMA-co-PMAA copolymers
(2003-05-01)
Huang, CF
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A series of miscible PMMA/PMAA blends and PMMA-co-PMAA copolymers with different compositions were prepared in this study. T(g)s of PMMA-co-PMAA copolymers are significantly higher than average values or from the Fox equation. The proton spin-lattice relaxation time in the rotating frame (T-1p(H)) determined by high resolution solid state C-13 nuclear magnetic resonance indicates single composition-dependent from all blends and copolymers, implying a good miscibility with chain dynamics on a scale of 1-2 nm. However, T(1p)(H)s of copolymers are still smaller than those of blends, implying that degrees of homogeneity of copolymers are higher than those of blends. On the basis of Kovacs' free volume theory, the free volume of the copolymer obtained is decreased which is another indication of greater homogeneity of the copolymer than that of the corresponding blend. According to Fourier transform infrared spectroscopy analyses, the above results can be rationalized that the hydrogen bonding interaction of the copolymer is stronger than the blend. (C) 2003 Elsevier Science Ltd. All rights reserved.
Compatibilization and elastomer toughening of polyamide-6 (PA6)/poly(phenylene ether) (PPE) blends
(1999-10-03)
Chiou, KC
;
Wu, SC
;
Wu, HD
;
Chang, FC
;
應用化學系
In the elastomer-modified (polyamide-6/poly(phenylene ether) (PA6/PPE) = 50/50 blends, poly(styrene-co-maleic anhydride) (SMA) was demonstrated to be an efficient reactive compatibilizer. The G1651 elastomer was shown to be an effective impact modifier to result in superior toughness and heat-deflection temperature (HDT) than is the 1901X elastomer for the SMA-compatibilized blends because G1651 particles exclusively reside within the dispersed PPE phase but 1901X particles tend to distribute in the PA6 matrix and/or along the interface. The apparent average diameter of the dispersed PPE phase is insignificantly dependent on the elastomer content in the G1651-modified blend, whereas it increases with increase of the elastomer content in the 1901X-modified blend. Moreover, there exists a critical elastomer content, 15 phr, for the ductile-brittle transition of the G1651-modified SMA-modified PA6/PPE blends. (C) 1999 John Wiley & Sons, Inc.