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1.
Jin-Woo Oh In Kyu Moon Nakjoong Kim 《Journal of photochemistry and photobiology. A, Chemistry》2009,201(2-3):222-227
We investigated the photosensitizers effect on the photorefractive (PR) properties in five poly[methyl-3-(9-carbazolyl)propylsiloxane] (PSX-Cz)-based PR composites which were doped with various photosensitizers having each different electron affinity, such as 2,4,5,7-tetranitro-9H-fluorine-9yilden malonitrile (TeNFM), 2,4,7-trinitro-9-fluorenone (TNF), 9-dicyanomethylene-2,4,7-trinitro-fluorenone (TNFM), tetracyanoethylene (TCNE), and 7,7,8,8-tetracyanoquinnodimethane (TCNQ). At 632.8 nm, photo-charge generation efficiencies, photoconductivities, space charge field, four wave mixing diffraction efficiencies, and PR grating buildup times were measured as a function of external electric field. The photo-charge generation, which is dependent on the light absorption, was achieved through the charge transfer (CT) complexes between the PSX-Cz and each of the photosensitizers. The photon energy of the CT transition decreased with increasing electron affinity of the photosensitizer. In composites doped with TeNFM, TNF, and TNFM, the space charge field (Esc) increased as the photo-charge generation efficiency increased; the grating buildup in these composites is rate-limited by the photo-charge generation speed. In sample doped with TCNE, and TCNQ, the hole mobility was reduced due to the larger amount of photosensitizer anion traps produced by photoreduction of the photosensitizer. Then, the grating buildup speed became hole mobility limited, and smaller buildup rates were observed. The magnitude of space charge field was sustained as the charge and trap density increased. In all composites, the refractive index modulation is increased with the magnitude of space charge field. 相似文献
2.
Structural changes during thermally induced crystallization and alkaline hydrolysis of Poly(l-lactic acid) (PLLA) films were investigated using differential scanning calorimetry (DSC), FTIR spectroscopy, weight loss, HPLC and optical microscopy. It was shown that crystallinity (χc), glass transition temperature (Tg) and melting temperature (Tm) were found to be strongly annealing temperature (Ta) dependent. The FTIR study of PLLA films suggested that the bands at 921 and 956 cm−1 could be used to monitor the structural changes of PLLA. An independent infrared spectroscopic method was developed for the first time to determine crystallinity of PLLA before degradation and it showed good qualitative correlation with DSC crystallinity. The higher crystallinity values determined by FTIR were attributed to the intermediate phase included in the IR crystallinity. Both the weight loss data and the percentage of lactic acid obtained by HPLC showed that the alkaline hydrolysis of PLLA films increased with increasing crystallinity. The DSC observation showed an increase in Tg and no significant change in Tm and heat of fusion, while IR showed an increase in IR crystallinity with increasing hydrolysis time. The increase in IR crystallinity and Tg with hydrolysis time suggested that degradation progressed from the edges of the crystalline lamellas without decreasing lamellar thickness, but increased the intermediate phase and the short-range order. 相似文献
3.
K. Sreedhar M. McElfresh D. Perry D. Kim P. Metcalf J. M. Honig 《Journal of solid state chemistry》1994,110(2)
Measurements of the temperature dependence of the electrical resistivity ρ(T), magnetic susceptibility χ(T), and Seebeck coefficient S(T) have been carried out on the n = 2, 3, and ∞ members of the homologous lanthanum nickel oxide systems Lan+1NinO3n+1 that were annealed in air. With increasing n, a progressive decrease in the electrical resistivity and a gradual change from insulating to metallic behavior are observed. La3Ni2O7 is nonmetallic, showing a gradual increase in ρ when T decreases (dp/dT < 0) from 300 to 4.2 K, whereas La4Ni3O10 and LaNiO3 exhibit metallic resistivity (dp/dT > 0). A minimum in ρ(T) near 140 K is observed for La4Ni3O10, while LaNiO3 exhibits a T2 dependence for ρ(T) below 50 K. The magnetic susceptibility of LaNiO3 is Pauli-like, but the χ(T) data for La3Ni2O7 and La4Ni3O10 below 350 K show a decrease with decreasing temperature. The Seebeck coefficient of all these compounds is negative at high temperatures; La3Ni2O7 and La4Ni3O10 exhibit a sign change in S at low temperatures. These results suggest a crossover from a fluctuating-valence to a Fermi-liquid-like behavior with increasing n. 相似文献
4.
Tsuyoshi Kiyotsukuri Naoto Tsutsumi Koichi Ayama Minoru Nagata 《Journal of polymer science. Part A, Polymer chemistry》1988,26(3):807-817
Copolyamides containing siloxane moieties in main chain were prepared by a melt polycondensation with 1,3-bis(3-aminopropyl)tetramethyldisiloxane (E), hexamethylenediamine (N6), and adipic acid (6). Glass transition temperature (Tg), cold crystallization temperature (Tcc), and melting temperature (Tm) were measured by differential thermal analysis (DTA). The depression of Tm for copolyamide was fitted by the Flory curve. Melting peak remarkably broadens with increasing E6 component in copolyamide. The change of Tg was fitted by the Gibbs and Dimarzio's equation in which the number of flexible bond is considered. The difference between Tg and Tcc increased with increasing E6 component. These DTA studies suggest that the crystallization of N66 component in copolyamide is hindered by the bulky siloxane moiety, while the micro-Brownian motion of amorphous segment is promoted by the flexible siloxane bond. Tensile strength and Young's modulus decreased with increasing E6 component. The solubility in various solvents increased with increasing E6 component. Permeability of oxygen and nitrogen increased with an increase of temperature and E6 component. The separation coefficient of oxygen to nitrogen rapidly increased near 50 mol% of E6 concentration and then leveled out above 70 mol%. The contact angle with water and methylene iodide increased with an introduction of the siloxane moiety into polymer chain. 相似文献
5.
A number of samples of sodium and silver phosphate glasses doped with
various compositions of some transition metals viz. iron, manganese and zinc
chlorides alongwith undoped samples of sodium and silver phosphate glasses
were synthesized and characterized by X-ray diffraction, IR spectral, electrical
conductivity and differential scanning calorimetry (DSC). The glass transition
temperature (T
g)
and crystallization temperature (T
c)
values obtained from DSC curves were found to increase with increasing concentration
of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses
and the following sequence is observed:
T
g(–FeCl3)>T
g(–MnCl2)>T
g(–ZnCl2)
T
c(–FeCl3)>T
c(–MnCl2)>T
c(–ZnCl2)
The increase in T
g
and T
c values indicate
enhanced chemical durability of the doped glasses. The electrical conductivity
values and the results of FTIR spectral studies have been correlated with
the structural changes in the glass matrix by the addition of different transition
metal cations as dopants. 相似文献
6.
K. A. Aly A. Dahshan Yasser B. Saddeek 《Journal of Thermal Analysis and Calorimetry》2010,100(2):543-549
The present paper reports on the effect of MoO3 on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
(x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions
for the studied glasses were reported and discussed. The values of the glass transition temperature (T
g) and the peak temperature of crystallization (T
p) are found to be dependent on heating rate and MoO3 content. From the compositional dependence and the heating rate dependence of T
g and T
p, the values of the activation energy for glass transition (E
g) and the activation energy for crystallization (E
c) were evaluated and discussed. Thermal stability for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
glasses has been evaluated using various thermal stability criteria such as ΔT, H
r
, H
g and S. Moreover, in the present work, the K
r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with
increasing MoO3 content up to x = 0.5 mol%, and decreases beyond this limit. 相似文献
7.
Dissociation rates of molecular hydrogen in electrical discharges have been calculated at different electron (Te) and gas (Tg) temperatures (10000 Te 23000 K, 500 Tg 4000 K), at different pressures p (5 p 50 torr) and electron number densities ne (0 ne 1012 cm−3).The results have been obtained by solving a system of master equations, including V---T (vibration-translation), V---V (vibration---vibration) and e---V (electron---vibration) microscopic processes.The results obtained at ne ≠ O show a “laser-type mechanism” in the dissociation of molecular hydrogen in electrical discharges. In particular one notices a strong increase of dissociation rates with decreasing gas temperature and pressure.The results show that this mechanism is as important as the mechanism of direct dissociation by electron impact. 相似文献
8.
L. Michael Hayden Won‐Kook Kim Andrew P. Chafin Geoffrey A. Lindsay 《Journal of Polymer Science.Polymer Physics》2001,39(9):895-900
Second harmonic generation (SHG) was used to measure the temperature dependence of the reorientation activation volume (ΔV*) of a syndioregic main‐chain hydrazone (SMCH) nonlinear optical polymer. The decay of the SHG signal from poled films of SMCH was recorded at hydrostatic pressures up to 2924 atm and at temperatures between 25 °C below the glass‐transition temperature (Tg) to 20 °C above it. ΔV* for pressures less than 500–1000 atm and T > Tg decreased as the temperature was increased. For pressures greater than 1000 atm, ΔV* was essentially constant for all temperatures. In addition, the size of ΔV* indicated that the chromophore in this main chain was internally flexible. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 895–900, 2001 相似文献
9.
The purpose of this study was to conduct a thermal analysis of the hydrolysis and degradation behavior of biodegradable polymers
and bio-composites at 50°C and 90% relative humidity (RH). With increasing hydrolysis time, the thermal stability and degradation
temperature of polybutylene succinate (PBS) slightly decreased. The glass transition temperature (T
g) and melting temperature (T
m) of PBS and the anti-hydrolysis agent treated PBS did not vary significantly with increasing hydrolysis time, whereas those
of the trimethylolpropane triacrylate (TMPTA)-treated PBS slightly increased. With increasing hydrolysis time, the storage
modulus (E’) values of the bio-composites decreased, whereas those of the TMPTA treated bio-composites slightly increased. Also, the
tan values of the anti-hydrolysis agent and TMPTA treated PBS-BF bio-composites were slightly lower than those of the non-treated
bio-composites, due to the reduction in their degree of hydrolysis. The tanδmax peak temperature (T
g) of the anti-hydrolysis agent treated bio-composites was not significantly changed, whereas that of the TMPTA treated bio-composites
was increased. 相似文献
10.
Using the pulse saturation method the spin-lattice relaxation rate T1−1 for Cu(II) in Zn(II)-bis(diethyl-diselenocarbamate) was measured in the temperature range 1.5 < T < 33 K. From the T-dependence of T1−1 the Debye temperature of the host crystal was obtained. The angular dependence of T1−1 as well as the influence of the hyperfine interaction on T1−1 are discussed. 相似文献
11.
Glasses with compositions 60B2O3–40PbO, 60B2O3–40Bi2O3, and 60B2O3–30Bi2O3–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated
under non-isothermal conditions. From dependence of the glass transition temperature (T
g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the
crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures,
such as the glass transition temperature, T
g, the onset temperature of crystallization, T
in
, the temperature corresponding to the maximum crystallization rate, T
p, beside the kinetic parameters, K(T
g) and K(T
p). The results revealed that the 60B2O3–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the
glass crystallizes after the thermal process have been identified by X-ray diffraction. 相似文献
12.
M. Ban M. Kyoto A. Uedono T. Kawano S. Tanigawa 《Journal of Radioanalytical and Nuclear Chemistry》1996,210(2):479-484
The glass transition and relaxation processes in polystyrene resins with the number average molecular weight ranging from 7.0·102 to 9.8·104 were studied with the positron annihilation technique. The pick-off annihilation lifetime of ortho-positronium (3) and its intensity (I
3) were measured in the temperature range from 20 to 430 K. The glass transition temperature (T
g) was determined as an onset temperature coefficient of 3.T
g shows the molecular weight dependence in these samples. BelowT
g, local motions were detected by measurements ofI
3. The local motions could be observed above 100 K in this experiment.I
3 show the minimum at around 250 K and it does not show molecular weight dependence. 相似文献
13.
Kaiwen Liang Hossein Toghiani Guizhi Li Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》2005,43(17):3887-3898
Cyanate ester (PT‐15, Lonza Corp) composites containing the inorganic–organic hybrid polyhedral oligomeric silsesquioxane (POSS) octaaminophenyl(T8)POSS [ 1 ; (C6H4NH2)8(SiO1.5)8] were synthesized. These PT‐15/POSS‐ 1 composites (99/1, 97/3, and 95/5 w/w) were characterized by X‐ray diffraction (XRD), transmission election microscopy (TEM), dynamic mechanical thermal analysis, solvent extraction, and Fourier transform infrared. The glass‐transition temperatures (Tg's) of the composite with 1 wt % 1 increased sharply versus the neat PT‐15, but 3 and 5 wt % 1 in these cyanate ester composites depressed Tg. All the PT‐15/POSS composites exhibited higher storage modulus (E′) values (temperature > Tg) than the parent resin, but these values decreased from 1 to 5 wt % POSS. The loss factor peak intensities decreased and their widths broadened upon the incorporation of POSS. XRD, TEM, and IR data were all consistent with the molecular dispersion of 1 due to the chemical bonding of the octaamino POSS‐ 1 macromer into the continuous cyanate ester network phase. The amino groups of 1 reacted with cyanate ester functions at lower temperatures than those at which cyanate ester curing by cyclotrimerization occurred. In contrast to 1 , 3‐cyanopropylheptacyclopentyl(T8)POSS [ 2 ; (C5H9)7(SiO1.5)8CH2CH2CH2CN] had low solubility in PT‐15 and did not react with the resin below or at the cure temperature. Thus, phase‐separated aggregates of 2 were found in samples containing 1–10 wt % 2 . Nevertheless, the Tg and E′ values (temperature > 285 °C) of these composites increased regularly with an increase in 2 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3887–3898, 2005 相似文献
14.
The apparent melt shear viscosity of polypropylene (PP) composites filled with aluminium hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) was measured by means of a melt flow rate instrument under experimental conditions of temperature ranging from 170 to 195 °C and load varying from 2.16 to 12.5 kg, to identify the effects of particle size and content. The results showed that the melt shear flow of the composites obeyed the power law under the experimental conditions, the dependence of the melt apparent shear viscosity (ηa) on temperature was consistent with the Arrhenius equation, and the sensitivity of the ηa for the composite melts to temperature increased with addition of flame retardant. The ηa of the composites decreased with increasing apparent shear rate. The ηa increased with an increase of the content of flame retardant, but this rate of increase decreased with a rise of temperature or load. When the particle size of flame retardant was smaller than 5 μm, the ηa of the composites increased with increase of particle size of flame retardant, and then reduced with a further increase of particle size of flame retardant. 相似文献
15.
Shuizhu Wu Fang Zeng Fengxian Li Yinlan Zhu Heping Zhao 《Journal of Polymer Science.Polymer Physics》1999,37(23):3302-3306
In this study, photorefractive polymer composites were developed in which polycarbonate was doped with a dual-function dopant and a photocharge generation sensitizer. The dual-function dopant has the function of providing both charge transport and optical nonlinearity. The composites' photoconductivity and electrooptic coefficient were investigated experimentally. The effects of the glass-transition temperature (Tg), dual-function dopant content, and electric field on the composites' photorefractive properties were studied as well. The results show that the composites' photorefractive properties are enhanced with decreasing Tg, increasing dual-function dopant content, and increasing electric field. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3302–3306, 1999 相似文献
16.
H.-S. Kim H.-S. Yang H.-J. Kim B.-J. Lee T.-S. Hwang 《Journal of Thermal Analysis and Calorimetry》2005,81(2):299-306
In this study, the thermal properties of agro-flour-filled polybutylene succinate (PBS) bio-composites were investigated. PBS is one of the biodegradable polymers made from the condensation reaction of glycols and dicarboxylic acid and is naturally degraded by natural soil burial system. The thermal properties of the bio-composites were analyzed according to the agro-flour content and mesh size. On increasing agro-flour content, the thermal stability, degradation temperature and derivative thermogravimetric curve (DTGmax) temperature of the bio-composites decreased while the ash content increased. The thermal degradation of the bio-composites was not affected by agro-flour mesh size. The glass transition (Tg) and melting (Tm) temperatures of the bio-composites were not significantly changed. The storage modulus (E’) of the bio-composites was higher than that of neat PBS, because the incorporation of agro-flour increased the stiffness of the bio-composites. At higher temperatures, E’ of the bio-composites decreased due to the increasing viscosity and chain mobility of neat PBS. The thermal properties of bio-composites have an important effect on the manufacturing system and application methods. 相似文献
17.
Summary The sorption property of water vapor by poly(vinyl acetate) (PVAc) of relatively low glass transition temperature (T
g) was studied at temperatures nearT
g.Tcg of humidity-controlled samples of various moisture contents was measured and its variation with the moisture content was determined.T
g of the dry sample was estimated by dilatometry and DSC methods, and to confirm the value, the temperature dependence of mutual diffusion coefficient of the system of water vapor + PVAc was determined. A difference between the sorption mechanisms of water vapor by PVAc at 20 and 30 °C was observed: two sorption mechanisms are involved at 30 °C, while three mechanisms at 20 °C are involved which include the above two and another intermediate one. In earlier stage of sorption, at both 20 and 30 °C, water molecules sorbed by PVAc showed a tendency towards aggregation, while a mixing effect was found at higher stage of the sorption.
With 7 figures 相似文献
Zusammenfassung In der Arbeit werden Wasserdampfsorptionseigenschaften von Polyvinylacetat mit relativ niedriger Glastemperatur (T g) in der Nähe vonT g untersucht. Es wurden Plastizitätseinflüsse und Veränderungen vonT g mit dem Wassergehalt studiert. Es wurde gefunden, daß bei 30 °C ein 2-Stufen-Sorptionsmechanismus, bei 20 °C ein 3-Stufen-Mechanismus existiert.
With 7 figures 相似文献
18.
M. M. A. Imran D. Bhandari N. S. Saxena 《Journal of Thermal Analysis and Calorimetry》2001,65(1):257-274
Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T
g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T
g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T
g, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T
c–T
g and the enthalpy released during the crystallization process. Below T
g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
19.
The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature (Tg) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures (Tc) of less than or equal to 195 °C. The equilibrium melting temperature () for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be 248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the Tc range of 190–205 °C. At a given Tc, the 97PTT/3PEN blend exhibited a half-time of crystallization (t0.5) value that was lower, while it exhibited reciprocal half-time (), Avrami rate constant (KA), and spherulitic growth rate (G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t0.5 value increased, while the , KA, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at 194 °C (467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies (σ and σe) and the work of chain folding (q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm−2, and 2.4–3.6 kcal mol−1, respectively. Lastly, the effect of both the Tc and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing Tc and PEN content. 相似文献
20.
Reactive melt blends of an ethylene‐propylene‐diene terpolymer (EPDM) based thermoplastic elastomer (TPE), maleic anhydride grafted polypropylene (MAH‐g‐PP), and nylon 6 were prepared in a single screw extruder and evaluated in terms of morphological, rheological, thermal, dynamic mechanical, and mechanical properties of the blends. It was found that MAH‐g‐PP‐co‐nylon 6 copolymers were in situ formed and acted as effective compatibilizers for polypropylene (PP) and nylon 6. Phase separation of PP and EPDM in TPE increased with the addition and increasing amount of MAH‐g‐PP and nylon 6, leading to decreased glass transition temperature (Tg) of TPE and increased crystalline melting temperature (Tm) of PP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献