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The effect of laser wavelength on the photorefractive characteristics of PMDA-DR19 based photorefractive polymeric materials
(1997-09-01)
Chang, CJ
;
Wang, HC
;
Liao, GY
;
Whang, WT
;
Liu, JM
The photoconductivity and photorefractive characteristics of PMDA-DR19-based photoconducting nonlinear optical polymeric films with different compositions were studied using red and green lasers. Contributions of dopants and the host to the photoconductive and photorefractive properties are systematically discussed. The virgin nonlinear optical material PMDA-DR19 was neither photoconductive nor photorefractive in nature. However, it became photoconductive and photorefractive once the charge transport material was incorporated into the PMDA-DR19/PVB polymer film. Films containing more nonlinear optical chromophore exhibited higher diffraction efficiency. Response speed was further elevated when an additional charge generation material was doped in. Diffraction grating was observed under zero electric field and was confirmed due to a photorefractive effect by the two-beam coupling effect. In addition to composition modification, the laser light source was also an important factor in changing the PR response speed. The photorefractive response speed was tremendously improved when films were written and read by two different laser beams, either red/green lasers or green/red lasers. (C) 1997 Elsevier Science Ltd.
A study of the relationship between the electroluminescence characteristics and compositions of PPV-PVA-based polymers
(1996-08-01)
Chang, WP
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of poly(p-phenylene vinylene) (PPV)-poly(vinyl alcohol) (PVA)-based polymers were prepared from the PPV precursor and PVA aqueous solution mixtures. The luminescence characteristics of the PPV-PVA-based polymers were dependent on their composition and the following treating conditions. The emitted light of the PPV-PVA-based light-emitting diodes (LEDs) shifted from yellow-green (550 nm) to blue (485 nm) as the PVA component increased. The infra-red (i.r.) absorption spectra showed that some part of the PPV precursor could react with PVA to form C-O-C linkages and interrupted the conjugation of PPV polymer chains. This resulted in decrease of the conjugated chain length, as evidenced in ultraviolet-visible u.v.-vis. absorption spectra. The relative photoluminescence (PL) intensity increases with decreasing the conjugated chain length. The relative electroluminescence (EL) decreases with the increase of the PVA component in the polymers. However, both PL and EL intensity normalized with PPV molar ratio of PPV-PVA-based polymers were higher than that of pure PPV. The relative low threshold voltage at 4-6 V was found in these PPV-PVA-based polymer LEDs with Al (negative) and indium-tin oxide ITO (positive) as the two electrodes. Copyright (C) 1996 Elsevier Science Ltd.
Effect of the sensitizer on the properties of fully functionalized photorefractive epoxy polymers and their performance in the hologram image storage
(1999-06-01)
Chang, CJ
;
Whang, WT
;
Hsu, KY
;
Hsieh, ML
;
材料科學與工程學系
The 3-amino-9-ethyl carbazole (AEC)/Dispersed Orange 3 (DO3)/diglycidyl 1,2 cyclohexanedicarboxylate (DCD) main chain copolymers are synthesized and studied on their photorefractive (PR), photoconductive, and holographic characteristics. They are good hologram recording media because not only the stored hologram exhibits excellent fringe contrast with the resolution at about 20 mu m, but also the image can be stored, erased, and overwritten. The UV/Vis spectra shows that AEC segments may form charge transfer complexes with either DO3 segments or TNF sensitizers. By incorporating the sensitizer or increasing the charge transfer component concentration, the grating growth rate can be speeded up. Applying an electric field on the polymer film containing no sensitizer helps to elevate the grating growth speed, but it shows little influence on the grating growth speed of the films with sensitizers. More nonlinear optical (NLO) segments in the copolymer result in higher diffraction efficiency. The dark decay of the film depends on the dark conductivity. Incorporating sensitizers or more charge transport segments leads to more dark decay because of increasing dark conductivity. The dark decay of the PR properties at elevated temperature can also be evaluated by the thermal stimulated discharge current (TSDC) spectroscopy technique. (C) 1999 John Wiley & Sons, Inc.
Effects of morphology and surface characteristics of poly(imide siloxane)s and deep UV/O-3 surface treatment on the interfacial adhesion of poly(imide siloxane)/alloy-42 leadframe joints
(1999-07-01)
Jwo, SL
;
Whang, WT
;
Hsieh, TE
;
Pan, FM
;
Liaw, WC
The effect of surface characteristics and morphology of poly(imide siloxane) (PIS) on the true interfacial adhesion between PIS films and alloy-42 substrates was studied. The effect of the viscosity of PIS films and the surface treatment of deep UV/O-3 (d-UV/O-3) on alloy-42 plates on the peel strength of PIS films/alloy-42 joints has also investigated. 3,3',4,4'-benzophenone tetracarboxylic dianhydride/2,2'-bis[4-(3-aminophenoxy)phenyl]sulfone (BTDA/m-BAPS) based PIS films with alpha,omega-bis(3-aminopropyl)polydimethyl siloxane (APPS) molecular weight M-n = 996 g/mole (PIS9Siy) show two phases in all compositions and the linear dependence of the critical surface tension on the surface concentration of the silicon, [Si-surf], on the PIS films. The PIS films with the APPS M-n = 507 g/mole (PIS5Siy) or M-n = 715 g/mole (PIS7Siy) exhibit a morphology change from a homogeneous phase to an inhomogeneous phase starting at the mole ratio (y) of APPS/PIS = 2.7% and 1.1%, respectively. The curves of critical surface tension dependence on the [Si-surf] discontinue or deflect at these two compositions, respectively. The treatment of d-UV/O-3 on alloy-42 plates improves the wetting on the alloy surface and promotes the peel strength between the PIS films and alloy-42 plates by a magnitude of greater than or equal to 20%. These results show that the flowability of the same PIS films bonding at different temperatures significantly affects the bonding strength of the joints, but the flowability of different PIS films bonding at the same temperature, e.g. 400 degrees C, is not the key factor governing the bonding strength of the joints. The true interfacial adhesion of the PIS5Si0.6/alloy-42 joint is 80% higher than that of the unmodified BTDA/m-BAPS based polyimide film/alloy-42 joint. However, zero true interfacial adhesion is obtained between the PIS9Siy films and alloy-42 plates. The wetting kinetics experiment shows that the higher the siloxane content in the PIS, the higher the activation energy for the adhesive bonding process. Moreover, the phase sepration significantly increases the activation energy. The scanning electron micrographs of the peeled-off PIS film surfaces from the PIS/alloy-42 joints reveal the rougher surface morphology from the sample with the higher interfacial adhesion.
Synthesis and relationships between the nonlinear optical and holographic properties of dual functional azocarbazole chromophores based on photorefractive polymers
(1999-08-24)
Chang, CJ
;
Whang, WT
;
Hsu, CC
;
Ding, ZY
;
Hsu, KY
Two kinds of dual functional carbazole-based chromophores are synthesized to enhance the photorefractive (PR) performance of the polymers by attaching the electron-donating and electron-accepting groups with a diazo bridge on the 3- and 6-positions of the N-ethylcarbazole. The electron-donating group is N,N-diethanol aminophenyl. The electron-accepting group is either p-nitrophenyl or 5-nitrothiazole. The peak maximum of the UV/vis absorption spectra of the 5-nitrothiazole-containing chromophore PANTAC at 535 nm is longer than that of the p-nitrophenyl-containing PANPAC at 477 nm. Both chromophores exhibit a large first hyperpolarizability in the hyper-Rayleigh scattering experiment due to the extended chain length. The first hyperpolarizability of PANTAC is 1100 x 10(-30) esu, almost the double of that of PANPAC (590 x 10(-30) esu). The diffraction efficiencies of both polymers are the function of the film thickness and the laser beam wavelength with a maximum eta(max) at a thickness d(max) between 15 and 23 mu m Surprisingly, the PANPAC-based PR polymer reveals a higher maximum diffraction efficiency (eta(max)) and better fringe of the stored holograms than the PANTAC-based PR polymer does. Both the PR polymers written/read by the green/red laser have greater eta(max) values than those written/read by the green/green laser. These phenomena are related to the balance between absorption and transmission of the laser beam through the PR polymer.
Effects of the solubility parameter of polyimides and the segment length of siloxane block on the morphology and properties of poly(imide siloxane)
(1999-12-13)
Jwo, SL
;
Whang, WT
;
Liaw, WC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The dependence of morphology of the poly(imide siloxane)s (PISs) on the solubility parameter of unmodified polyimides and the molecular weight and content of alpha,omega-bis(3-aminopropyl) polydimethylsiloxane (APPS) has been studied. The effect of the morphology on the mechanical properties is also under investigation. The domain formation in the PISs with the APPS molecular weight M-n = 507 g/mol is not found until the mol ratio of APPS/PIS greater than or equal to 0.5% in the pyromellitic dianhydride/p-phenylene diamine (PMDA/p-PDA)-based PISs, and at a mol ratio greater than or equal to 2.7% in the 3,3',4,4'-benzophenone tetracarboxylic dianhydride/2,2'-bis[4-(3-aminophenoxy)phenyl] sulfone (BTDA/m-BAPS)-based PISs. As the APPS M-n = 715 g/mol, the critical APPS concentrations of the domain formation in both types of PISs are equal to 0.1 and 1.1%, respectively. The critical concentration is equal to 0.6% in the BTDA/m-BAPS-based PIS film with the APPS M-n = 996 g/mol. The isolated siloxane-rich phase in the BTDA/m-BAPS-based PISs becomes a continuous phase as the ,ol ratio of APPS/PIS greater than or equal to 7.7, 10.0, and 16.6% as the APPS M-n = 996, 715, and 507 g/mol, respectively. Dynamic Mechanical Analysis (DMA) shows two T(g)s in the PIS films having phase separation: one at -118 similar to -115 degrees C, being the siloxane-rich phase, the other at 181-244 degrees C, being the aromatic imide-rich phase. The SEM micrographs show a significant deformation on the fractured surfaces of the BTDA/m-BAPS-based PIS films with a continuous siloxane-rich phase. This phenomenon of plastic deformation is also observed in the tensile tests at -118 degrees C and at room temperature. The highest elongation in the PIS films is found at the critical siloxane content of the continuous siloxane-rich phase formation. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2832-2847, 1999.
Phenanthrenequinone-doped poly(methyl methacrylate) photopolymer bulk for volume holographic data storage
(2000-04-01)
Lin, SH
;
Hsu, KY
;
Chen, WZ
;
Whang, WT
;
材料科學與工程學系
We present the design and fabrication of a phenanthrenequinone-doped poly(methyl methacrylate) photopolymer material. Large blocks of samples were made, and the material showed negligible shrinkage after optical exposures. We recorded and reconstructed 250 holograms at a single spot, using a 1-cm(3) block. (C) 2000 Optical Society of America OCIS codes: 210.2860, 210.4810, 160.5470.
Significant improvement on the electroluminescence characteristics of MEH-PPV by blending with PMMA
(2000-09-01)
Chao, CS
;
Whang, WT
;
Chuang, KR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A significant improvement on the electroluminescence threshold voltage from 5.5 volts down to 2.9 volts of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in the Ca/polymer/ITO diode is observed by incorporating a non-conjugated PMMA into MEH-PPV. The threshold voltage of the material decreases with the poly(methyl methacrylate) (PMMA) content. Near-field scanning absorption and photoluminescence micrographs show that the PMMA domains dispersed in the continuous MEH-PPV phase appear to be similar to sesame seeds embedded in the MEH-PPV pancakes. The resistivity of PMMA is two orders lower than that of MEH-PPV. The excellent electrical conduction of PMMA in Ca/PMMA/ITO glass devices is not due to a pin-hole defect mechanism but may result from the electron hopping from Ca through the carbonyl groups in the PMMA. The significant improvement in the threshold Voltage may be due to the combination of the electron hopping in the thin PMMA sesame seeds and the thinner thickness effect of MEH-PPV in the light emitting layer.
Low dielectric polyimide/poly(silsesquioxane)-like nanocomposite material
(2001-04-01)
Tsai, MH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A new type of low dielectric polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid nanocomposite material is successfully prepared from the polyimide (ODA-ODPA) precursor containing phenyltrialkoxysilane IPTS) at two chain ends and monoaryltrialkoxysilane with a self-catalyzed sol-gel process. We employ p-aminophenyltrimethoxysilane (APTS) to provide bonding between the PTS and ODPA-ODA phase, It is shown by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) that the PSSQ-like domain sizes with uniform size are fairly well separated in the hybrid films. The silica domain sizes of 5000-PIS and 5000-PIS-50-PTS films are in the range of 30-100 nm, of 5000-PIS-100-PTS and 10000-PIS-100-PTS in the range of 80-200 and 300-600 nm, respectively. The dielectric constant can be 2.79 for 5000-PIS-140-PTS with fairly good mechanical properties. The PI/PSSQ-like hybrid films have higher onset decomposition temperature and char yield in thermogravimetric analysis (TGA) and higher T-g in differential scanning calorimetry (DSC) than the pure PI. Moreover, the PI/PSSQ-like hybrid films have excellent transparency even under high PTS content. In the series of X-PIS hybrid films, the coefficient of thermal expansion (CTE) below T-g increases with the PI block chain length, but in the series of X-PIS-y-PTS films, it slightly increases with the PTS content. However, above T-g the CTE of X-PIS and X-PIS-24-PTS is much lower than that of the pure PI. The dielectric constant and water absorption of X-PIS-V-PTS films decrease with the PTS content because of the higher free volume and hydrophobicity. (C) 2001 Elsevier Science Ltd. All rights reserved.
High temperature lifetime of polyimide/poly(silsesquioxane)-like hybrid films
(2001-06-01)
Tsai, MH
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Decomposition kinetics in thermogravimetric analysis (TGA) and dynamic mechanical relaxation in dynamic mechanical analysis (DMA) are used to study the high temperature lifetime of the new type of polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid films, which are designed to form three-dimensional structures with linear polyimide blocks and a crosslinked PSSQ-like structure. Both TGA and DMA analysis reveal that the PI/PSSQ-like hybrid films have a longer lifetime (are more reliable) with regard to their thermal and mechanical characteristics than that of pure PI. Even just 2 wt% of p-aminophenyltrimethoxysilane (APTS) in a PI/PSSQ-like hybrid film can significantly improve the service lifetime by as much as at least four times in a TGA decomposition kinetic study. The dynamical relaxation data are well fitted to the calculated WLF (Williams-Landel-Ferry) master curves. In a series of X-PIS (PI modified with APTS) hybrid films, decreasing the PI block chain length increases the decomposition activation energy, lifetime (in both TGA and DMA) and relaxation modulus. In a series of X-PIS-y-PTS [PI modified with APTS and phenyltrimethoxysilane (PTS)] films, the decomposition activation energy and lifetime (in TGA) increase with the PTS content. Interestingly, the dynamic mechanical relaxation modulus of 10000-PIS-100-PTS film is lower than that of the corresponding 10000-PIS film at frequency > 10(2) rad/sec, but higher at frequency < 10(2) rad/sec. The 10000-PIS-100-PTS has a lower relaxation time than the 10000-PIS at the modulus 5x10(8) Pa, but the relaxation time of the former becomes higher at 5x10(7) Pa.

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