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1.
The relaxations of rubbing-induced birefringence (RIB) in several glass-forming polymers, including polycarbonate and polystyrene
(PS) derivatives with various modifications to the phenyl ring side group, are studied. Significant relaxations of RIB are
observed at temperatures well below the glass transition temperature T
g . The relaxation times span a wide range from ∼ 10 s to probably geological time scale. Physical aging effects are absent
in the RIB relaxations. The model proposed for the interpretation of RIB in PS describes well the RIB relaxations in all the
polymers investigated here. The energy barriers are of the order of a few hundred kJ/mol and decrease with decreasing temperature,
in opposition to the trend of Vogel-Fulcher form for polymer segmental relaxations above T
g . The relaxation behaviors of different polymers are qualitatively similar but somewhat different in quantitative details,
such as in the values of the saturated birefringence, the shape of the initial barrier density distribution functions, the
rates of barrier decrease with decreasing temperature, and the dependence of relaxation times on temperature and parameter
, etc. The RIB relaxations are different from any of the other relaxations below T
g that have been reported in the literature, such as dielectric relaxations or optical probe relaxations. A microscopic model
for the relaxations of RIB is much desired. 相似文献
2.
K.-I. Akabori K. Tanaka A. Takahara T. Kajiyama T. Nagamura 《The European physical journal. Special topics》2007,141(1):173-180
Mechanical relaxation behavior in ultrathin polystyrene
(PS) films supported on silicon oxide (SiOx) and gold (Au) substrates
has been studied by dynamic viscoelastic measurement. Based on the method,
effects of free surface and substrate interface on the segmental dynamics
were discussed. In the case of thin PS films with a thickness of
approximately 200 nm, αa-relaxation process corresponding to
the segmental motion did not show any deviation from the bulk behavior. In
contrast, for the films thinner than about 50 nm, the relaxation time
distribution for the αa-process became broader, probably due to
a mobility gradient in the surface and interfacial regions. When we
sandwiched an ultrathin PS film between SiOx layers, another relaxation
process, in addition to the original αa-process, appeared at a
higher temperature side that we assigned to the interfacial αa-relaxation
process. However, this was never seen for an ultrathin PS
film between Au layers, implying that restriction from the substrate
interface might be weak in this case. 相似文献
3.
Kiyokazu Fuke Koji Kaya Takashi Kajiwara Saburo Nagakura 《Journal of Molecular Spectroscopy》1976,63(1):98-107
The electronic absorption spectra of perylene crystals in the α- and β-forms were measured by the normal incidence reflection method in the spectral region from 20 000 to 60 000 cm?1. From the absorption spectrum polarized perpendicular to [10] axis of the α-form crystal, the bands around 24 000 cm?1 were determined to be polarized along the long molecular axis. Two strong bands with different polarizations were observed around 50 000 cm?1 for each of the α- and β-perylene crystals and were assigned to the transitions to the 1B2u and 1B3u states. The observed polarized absorption spectra as a whole were consistent with the theoretical results by Hummel and Ruedenberg and the reflection method was found to be suitable to the polarized absorption measurement of strong bands of crystals. The observed factor-group splittings were compared with the theoretical values, the oriented gas model being found to be applicable to the β-form crystal. 相似文献
4.
Samples of polystyrene (PS) have been irradiated with 64Cu (50 and 120 MeV) and 12C (70 MeV) ion beams (fluence=1011 to 1013 ions cm?2) in order to study the induced modifications using UV‐VIS and FTIR spectroscopy. UV spectra of irradiated samples reveal that the optical band gap decreases from 4.36 to 1.46 eV in PS. The decrease in optical band gap is more pronounced with the Cu‐ion beam due to high electronic energy loss as compared to the C ion beam. The effect of low energy (50 MeV) Cu ions on the optical properties of PS is larger than that due to high energy (120 MeV) Cu ions. The correlation between the optical band gap and the number of six member carbon rings inside the largest carbon clusters embedded in the network of polystyrene is discussed. FTIR spectra reveal the formation of hydroxyl, alkene, and alkyne groups in the Cu‐ion irradiated PS. Changes in the intensity of the absorption bands on irradiation with C‐ion relative to pristine samples have also been observed and are discussed. 相似文献
5.
M.Y. Louge R.K. Hanson E.C. Rea R.A. Booman 《Journal of Quantitative Spectroscopy & Radiative Transfer》1984,32(4):353-362
A spectral survey of NCO absorption near the P2 + pQ12 head of the [A2Σ + (0000)←X2Πi(0010)] band was obtained at 1450°K, 0.6 atm using a remotely located cw ring dye laser source and a shock tube. Mixtures of hydrogen cyanide, oxygen and nitrous oxide diluted in argon were shock heated to provide a reproducible steady-state concentration of NCO, and narrow-line absorption was measured in repeated experiments with the laser set at different wavelengths. The peak absorption was found at 440.479 nm (vac). The experimental spectrum was compared with a theoretical model to yield an average Voigt parameter a ? 0.1. Additional experiments, in mixtures of cyanogen, oxygen and nitrous oxide diluted in argon, provided a known plateau level of NCO, which was used to infer an absolute absorption coefficient β(1450°K, 0.60 atm) = 110(-50, +130) cm-1 atm-1 at 440.479 nm. This value of β corresponds to an oscillator strength of 0.0026 for the (0000←0010) band.Similar experiments were conducted to monitor the absorption around the R1 head of the [B2Πi(1010)←X2Πi(0010)] band of NCO, using a frequency doubled cw ring dye laser. The observed spectrum displayed strong broadening, indicating predissociation of the upper state. At the peak absorption wavelength (304.681 nm, vac), we inferred β(1470°K, 0.63 atm) = 40(-19, +48) cm-1 atm-1 and a ? 9. This value of β corresponds to an oscillator strength of 0.0031 for the (1010←0010) band. 相似文献
6.
《Nuclear Physics A》1995,588(1):c333-c337
The r-process abundances are evaluated with the use of three different β-decay models, i.e., the second version of the Gross Theory, the semi-Gross Theory and a QRPA approach. The necessary Qβ-values, as well as the neutron separation energies, are obtained from the TUYY, ETFSI and FRDM mass predictions. A comparison is made among the β-decay half-lives predicted by these β-decay models for the nuclei on a typical r-process path, as well as among the resulting r-process abundances. 相似文献
7.
Abstract The infrared spectrum of acetonitrile vapour has been obtained in the range below 100 cm?1. There is an absorption band located at 78 cm?1 which is assigned to overlapping intermolecular vibrations of dimer molecules in equilibrium with the monomer species. The equilibrium constant calculated from the pressure dependence of the band intensity amounts to 42 ± 26 1·mol?1. 相似文献
8.
E. Birckner U.-W. Grummt H. Rost A. Hartmann S. Pfeiffer H. Tillmann H.-H. Hörhold 《Journal of fluorescence》1998,8(1):73-80
The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV)
derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λa = 380–450 nm, ε = 20,000–60,000 M−1 cm1 and fluorescence maxima, quantum yields, and decay times of λr = 440–530 nm, Φf = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the
bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum
yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence
and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly
the same absorption spectra, fluorescence spectra, and radiative rate constantsk
f= Φf/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φf and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting
the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep
energy transfer processes between different oriented segments. 相似文献
9.
Lina Jia Yanping Wang Bing Wang Mingjia He Qianru Zhang 《Journal of Macromolecular Science: Physics》2013,52(2):378-383
Hansen solubility parameters and Lewis acid–base parameters are two groups of parameters that are used to characterize solvents, polymers, and the interactions between polymer matrix and additives. Although their definitions are very different, they can well explain the interactions in polymer composites. Therefore, some relations should exist between them. In this paper, the Lewis acid–base parameters of three polymers (PET, PS, and PVA) were measured by IGC technique. Including five other polymers (PE, PMMA, PC, PVC, and PVDF), the relationship between total Lewis acid–base intensity (K a+K b) and total polar intensity (δ2 p+δ2 h) of the eight kinds of polymers are discussed, where δp and δh are the polar components of the Hansen parameters. It is found that these polymers are all Lewis base polymers according to the values of K b/K a. Generally, a polymer with a larger (K a+K b) value possesses a higher (δ2 p+δ2 h) value. 相似文献
10.
The IR and Raman spectra of plasticized poly(methyl methacrylate) (PMMA) are measured and analyzed in the frequency range 10–120 cm?1, in which the absorption and scattering due to the individual (85–90 cm?1) and correlated librational vibrations (15–20 cm?1, boson peak) preceding the appearance of relaxation dynamics manifest themselves. It is demonstrated that the presence of the boson peak as an indication of the solid-state behavior of the polymer material in the low-frequency spectra is associated with the correlation of librational vibrations not only inside macromolecules (in segments corresponding in length to the Kuhn segment) but also in segments of neighboring chains. 相似文献
11.
F. Kong X.L. Wu G.S. Huang R.K. Yuan C.Z. Yang P.K. Chu G.G. Siu 《Applied Physics A: Materials Science & Processing》2006,84(1-2):203-206
We report the temperature-dependent photoluminescence (PL) behavior of two poly (p-phenylene-vinylene) derivatives with different backbones, a homopolymer poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and a copolymer poly-{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene]-alt-[2,5-diphenylene-1,3,4-oxadiazole-vinylene]} (MEH-OPPV). The PL peak positions of the MEH-PPV in both solid solution and film are blue shifted with increasing measurement temperature because the thermally induced torsion and libration modes reduce the conjugation lengths of the polymer, but the shift rate is smaller in the MEH-PPV film than that in the solid solution. The PL peak position of the MEH-OPPV film is independent of measurement temperature because there is a large dihedral angle between the adjacent monomer units. The large dihedral angle increases the conformational disorder to eliminate the effect of the disorder induced by the thermally induced torsion and libration modes on the conjugation lengths of the MEH-OPPV. PACS 73.61.Ph; 78.55.Kz 相似文献
12.
《Infrared physics》1984,24(2-3):209-213
Measurements of the FIR absorption spectra of polysaccharides and their constituent monoand disaccharides have been made between 30 and 650 cm−1, using FTS. Some of the structure of the saccharides is found to show up in the polymers. 相似文献
13.
Raman spectra of the new polytype δ-GaSe are given in the low-frequency region (ω < 60 cm-1) and their relation to lattice vibrations of the simpler polytypes γ, ? is discussed. A simple lattice dynamical model is used to describe the phonon modes in all 3 modifications. First observation of Davydov splitting in ?-GaSe is reported. Particular weakness of one component of this doublet is shown to be a consequence of the specific “molecular” nature of layer crystal. 相似文献
14.
In this paper, a novel structure for quantum ring inter-subband photodetectors (QRIP) is proposed to reduce its dark current. Some additional layers including asymmetric multi-barrier resonant tunneling (AMBRT) in absorption region layers are exploited to provide near unity tunneling probability for generated photocurrents and completely reject thermally generated electrons. AMBRT structure consists of three asymmetric AlGaAs barriers and two InGaAs wells which are designed for operation wavelength of generated photocurrents by absorption of 20 μm. Simulation results show that AMBRT can considerably reduce the dark current compared to previously proposed resonant tunneling structure about three orders of magnitude. As a consequent, higher specific detectivity for AMBRT-QRIP is obtained in the order of ∼1011 cm Hz1/2/W at 100 K. 相似文献
15.
V. V. Bruevich T. Sh. Makhmutov S. G. Elizarov E. M. Nechvolodova D. Yu. Paraschuk 《Journal of Experimental and Theoretical Physics》2007,105(3):469-478
The intermolecular charge-transfer complex (CTC) between the conjugated polymer MEH-PPV and the low-molecular organic acceptor trinitrofluorenone (TNF) has been studied by Raman and optical absorption spectroscopy. On mixing MEH-PPV with TNF, an absorption band due to the CTC appeared in the optical gap of the polymer, whereas, in the Raman spectra, characteristic bands of the polymer are shifted and their widths and intensities change. The low-frequency shift of the strongest band at 1580 cm?1 in the Raman spectrum of the polymer, assigned to the symmetric stretching vibration of the phenyl group, is shown to be due to electron density transfer from the π-conjugated system of the polymer to the acceptor and is as large as 5 cm?1, which corresponds to a charge transfer on the order of 0.1e ?1. Even at a low acceptor concentration (one TNF molecule per 10 monomer units of the polymer), most Raman-active conjugated chains are involved in the CTC. It is suggested that conjugated segments of the polymer can form a CTC of variable composition MEH-PPV: TNF = 1: X, where 0.1 ≤ X ≤ 0.5 (for each monomer unit of the polymer), and one TNF molecule can thereby interact with two conjugated segments of MEH-PPV. The conjugated polymer chains involved in the CTC can become more planar, and their interaction with the local environment can noticeably change; however, their conjugation length, most likely, remains unaltered. 相似文献
16.
The optically induced fission of singlet excitons in both α- and β-perylene crystals is investigated at room temperature. In the monomeric β-perylene the fission thresold coincides with the energy of two triplet excitons whereas it is blueshifted by ~3500 cm-1 in the excimer forming α-crystal. This indicates that the excimer is formed prior to the fission of the initially excited monomer state and it implies that the rate of excimer formation is exceeding 1012 s-1. Theoretical estimates led to kexc ≈ 1012-1013 s-1. Analysis of the experimental data shows also that two adjacent perylene molecules in the α-crystal, each of them in the T1 electronic state, are bound with the binding energy B2T1 ≈ 350 cm-1. 相似文献
17.
D. Meier 《Journal of Quantitative Spectroscopy & Radiative Transfer》1978,20(2):129-133
Line shapes of the hyperfine NO2 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δF=δJ=δN=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10-5 cm-1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10-4 cm-1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ?10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line. 相似文献
18.
M. Dehghany 《Journal of Molecular Spectroscopy》2008,247(2):123-127
The rotationally resolved spectra of 15N15N16O dimer for the polar and nonpolar isomers are studied in the region of the N-N stretching fundamental of the monomer (∼2150 cm−1) using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. These spectra are very similar to the corresponding spectra of the normal species, (14N14N16O)2. Structural parameters and vibrational shifts obtained here are compared with those of the normal species and ab initio values. These results confirm that the nonpolar isomer has a centrosymmetric slipped-antiparallel structure while the polar isomer consists of two slipped and (approximately) parallel monomer units. 相似文献
19.
P. M. Ratheesh Kumar C. Sudha Kartha K. P. Vijayakumar F. Singh D. K. Avasthi 《辐射效应与固体损伤》2013,168(7):635-644
ZnO thin films, irradiated by 80 MeV Ni+ ions, were analysed with the help of different characterization techniques like X-ray diffraction, optical absorption, transmission, photoluminescence (PL), electrical resistivity, photosensitivity (PS) and thermally stimulated current (TSC) measurements. Crystallinity and absorption edge were hardly affected by irradiation. PL spectrum of pristine sample showed a broad peak at 517 nm, whereas irradiated film had two emissions at 517 and 590 nm. Intensity ratio between these two emissions (I517/I590) decreased with the fluence, and finally at a fluence of 3×1013 ions/cm2, the emission at 517 nm completely disappeared. Electrical resistivity of the sample irradiated with a fluence of 1×1013 ions/cm2 drastically increased. However, on increasing the fluence to 3×1013 ions/cm2, resistivity decreased, probably due the onset of hopping conduction through defects. PS also decreased due to irradiation. TSC measurements on pristine sample could reveal only one defect level at 0.6 eV, due to interstitia1 zinc (ZnI). But, irradiation at a fluence of 1×1012 ions/cm2, resulted in three different defect levels as per TSC studies. Interestingly, the sample irradiated at a fluence of 3×1013 ions/cm2 had only one defect level corresponding to a deep donor. The possible origin of these defect levels is also discussed in the paper. 相似文献