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1.
《Journal of Molecular Liquids》2006,123(2-3):92-104
Dielectric relaxation and dipole moment of binary mixtures of homologous series of mono alkyl ethers of ethylene glycol and of diethylene glycol, i.e., mono methyl, mono ethyl and mono butyl ethers of ethylene glycol (ROCH2CH2OH) and mono methyl, mono ethyl and mono butyl ethers of diethylene glycol (ROCH2CH2OCH2CH2OH) with ethyl alcohol (C2H5OH) of different concentrations were studied in dilute solutions of benzene, dioxane and carbon tetrachloride at 35 °C. Permittivity (ε′) and loss (ε″) at 10.1 GHz, static dielectric constant εo at 1 MHz and high frequency limiting dielectric constant ε∞ = nD2 at optical frequency of these molecules and their binary mixtures at different concentration were measured in dilute solutions of non-polar solvents. The average relaxation time τo, relaxation times corresponding to overall molecular reorientation τ1 and group rotations τ2 were determined using Higasi's single frequency measurement equations for dilute solutions. The evaluated values of relaxation times and free energy of activation ΔF were used to explore the solvent effect on molecular dynamics of these polar binary systems in non-polar solvents. The excess inverse relaxation time and excess free energy of activation were determined to confirm the existence of hydrogen-bonded heterogeneous cooperative domains of the ethers and alcohol molecules at different concentration their binary mixtures in non-polar solvents. The dipole moment of the binary mixtures was evaluated using Higasi's and Guggenheim's equation for dilute solutions. The evaluated values of dipole moments and computed dipole moment values using a simple mixing equation of the polar molecules binary mixture were used to explore the effect of non-polar solvent environment on heterogeneous molecular interactions between ethers and alcohol molecules. The effect of number of carbon atoms in the molecular structure of these homologous series molecules was also considered for the interpretation of various evaluated dielectric parameters. 相似文献
2.
Influence of polar solvents environment and polymer concentrations on the electrical properties (complex dielectric constant, ac electrical conductivity, complex electric modulus and complex impedance) of the solutions of poly(vinyl pyrrolidone) (PVP) in polar solvents, namely water, ethyl alcohol, ethylene glycol, diethylene glycol, poly(ethylene glycol), glycerol, dimethyl sulfoxide and dimethyl formamide, have been investigated in the frequency range 20 Hz–1 MHz at 25°C. Comparative analysis of the dielectric dispersion curves confirms that the solvent molecular size and number of its hydroxyl groups, and the solutions viscosity, are the major factors which governs the PVP chain segmental motion. The ionic conduction and electrode polarization phenomena has a dominant influence on the large increase of complex dielectric constant values of the solutions of PVP‐polar solvent in the lower frequency region. The values of relaxation times corresponding to these phenomena are also reported. 相似文献
3.
F. F. Hatta M. Z. A. Yahya A. M. M. Ali R. H. Y. Subban M. K. Harun A. A. Mohamad 《Ionics》2005,11(5-6):418-422
A series of conducting thin-film solid electrolytes based on poly (vinyl alcohol)/ poly (vinyl pyrrolidone) (PVA/PVP) polymer
blend was prepared by the solution casting technique. PVA and PVP were mixed in various weight percent ratios and dissolved
in 20 ml of distilled water. The samples were analyzed by using impedance spectroscopy in the frequency range between 100
Hz and 1 MHz. The PVA/PVP system with a composition of 80% PVA and 20 wt.% PVP exhibits the highest conductivity of (2.2±1.4)
× 10−7 Scm−1. The highest conducting PVA/PVP blend was then further studied by adding different amounts of potassium hydroxide (KOH) ionic
dopant. Water has been used as solvent to prepare PVA/PVP-KOH based alkaline solid polymer blend electrolyte films. The conductivity
was enhanced to (1.5 ± 1.1) × 10−4 Scm−1 when 40 wt.% KOH was added.
Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 –
8, 2005. 相似文献
4.
We investigated the dynamics of methyl groups in organic polycrystalline 1,2-O-(1-ethylpropylidene)-α-d-glucofuranose by the proton spin–lattice relaxation method. The temperature and nuclear magnetic resonance Larmor frequency
dependence of relaxation time is presented and interpreted in terms of simple possible dynamical model for the reorientation
of methyl groups: the random hopping for methyl groups, which are in a, b, and c sites in the crystal. The energy E
a
of 13.5 kJ mol−1 for the a-type methyl groups is typical for methyl groups in ethyl groups. In contrast, the b- and c-methyl groups characterized by the lower E
a
values of 9.5 and 6.5 kJ mol−1 are located in the crystal structure where the intermolecular interactions significantly influence the potential, leading
to a decrease in the total energy. 相似文献
5.
The temperature dependences of the rates of the degenerate electron transfer of various viologens (1,1′-di(hydrocarbyl)-4,4′-bipyridinium
salts) are measured in seven different solvents by means of electron spin resonance (ESR) line broadening. Rates vary between
1.7·108 and 1.1·109 M−1s−1 at room temperature and clearly show a solvent dynamical effect, which is inferred from the dependence of the rate constants
on the longitudinal relaxation time of the solvent. Activation energies ranging from 5.3 to 24.4 kJ mol−1 are found. For the first time, hyperfine coupling constants are reported for the radical cations of the hydroxyethyl viologen
and the amino viologen based on both continuous-wave ESR and electron-nuclear double resonance spectroscopy. Furthermore,
the temperature and the solvent dependence of the hyperfine coupling constants of the methyl viologen radical cation are reported. 相似文献
6.
The composition of surface-functionalized gold nanoparticles (diameter of the metallic core: 17–20 nm) was determined by elemental
analysis (C, H, N, S, Au, Na) after preparation of a larger batch. Gold nanoparticles were prepared and functionalized with
citrate according to the classical Turkevich method. The citrate-functionalized nanoparticles contained about 3.1 wt% of organic
material (135 ng cm−2 or 3.1 molecules nm−2). A partial exchange of citrate was accomplished by tris(sodium-m-sulfonato-phenyl)phosphine (TPPTS) which led to 2.1 wt% of citrate (90 ng cm−2 or 2.1 molecules nm−2) and 1.4 wt% TPPTS (61 ng cm−2 or 0.6 molecules nm−2). The citrate coating was quantitatively exchanged by poly(N-vinyl pyrrolidone) (PVP) after immersion in solutions with concentrations of 33, 66 and 128 mg L-1, respectively, leading to contents of 4 to 6 wt% of PVP (171–271 ng cm−2 or 9–15 PVP monomer units nm−2). 相似文献
7.
Zhu Pingping Liu Yuanli Yang Haiyang Chen Xiaoming 《Journal of Macromolecular Science: Physics》2013,52(6):1125-1134
An addition of a small amount of non‐solvent tetrahydrofuran (THF) to good solvent water gave rise to a strong solvent power for poly(N‐vinylpyrrolidone) (PVP). It was found that PVP coils in mixtures of water and THF first swelled as the fraction of THF was increased, and then the coils contracted after a critical composition of the solvent mixture based on the measurement of dilute solution viscosities. It was reached that the power of the mixed solvents was not the simple average of the power of individual components. The influence of the non‐ideal mixing of water and THF on the power of these mixtures for PVP and the dimensions of PVP coils was taken into account. Especially the formation of pseudo‐clathrate hydrate structure with the composition φ THF ≈ 0.44 was found to be an important factor to change the solvation and dimensions of PVP coils. Some other solvent mixtures for PVP and poly(methyl methacrylate) (PMMA) were also found to be non‐ideal mixtures. The viscosities of these solvent mixtures could show positive or negative deviation from the values obtained from the addition rule. It was shown again that the influence of the non‐ideality of these solvent mixtures on the dimensions of polymer coils was great. The action of mixed solvents changed the dimension of polymer coils, not only because of excluded volume effects but also because of the different molecular interactions present in these mixed solvents. 相似文献
8.
S. L. Bondarev V. N. Knyukshto A. A. Turban A. A. Ishchenko A. V. Kulinich 《Journal of Applied Spectroscopy》2006,73(1):25-34
We have studied the luminescent spectral properties and calculated the quadratic polarizability of dimethine, tetramethine,
and hexamethine merocyanines based on 1,3-dihydro-1,3,3-trimethyl-(2H)-indol-2-ylidene and malonodinitrile in solutions and
polymer films at room temperature and 77 K. We have shown that increasing the polarity of the solvent and lengthening the
polymethine chain in the studied merocyanines lead to an increase in fluorescence quantum yields and narrowing of the fluorescence
bands. This is explained by the decrease in bond length alternation and weakening of vibronic interactions in the singlet-excited
fluorescent state. The mirror symmetry in the structured absorption and fluorescence spectra of merocyanine dyes in ethanol
at 77 K, observed here for the first time, is due to enhancement of electrostatic interactions of the merocyanine and solvent
molecules. Increased stiffness of the medium considerably decreases the probability of nonradiative processes, and the major
channel for deactivation of the electronic excitation energy at 77 K is fluorescence. The higher values of the quadratic polarizability
(6.0·10−28 esu in ethanol and 3.3·10−28 esu in chloroform) for hexamethine merocyanine, estimated by the solvatochromic method, lets us consider this compound as
a promising material for designing nonlinear optical converters for harmonics of laser radiation.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 26–35, January–February, 2006. 相似文献
9.
We present in this paper a comparative study on the dynamics of benzene, cyclohexane, and methanol molecules, confined in
the pores of MCM-41 molecular sieve and HZSM-5 zeolite. The quasi-elastic neutron scattering (QENS) measurements revealed
that the physical state of these adsorbed molecules depended not only on the structural characteristics of the host matrix
but also on the chemical properties, such as dipole moment, of the guest molecules. Thus, while no motion was observed in
the time-scale of 10−10−10−12 s in the case of methanol, the larger size benzene and cyclohexane molecules are found to perform six-fold and three-fold
jump rotation, respectively, when adsorbed inside the cages of HZSM-5 at room temperature. At the same time, all the three
molecules are found to undergo a translational motion inside the pores of MCM-41 molecular sieves, the value of diffusion
constant being the lowest in case of methanol because of its higher polarity. Translationl motion of the guest molecules inside
the pores of MCM-41 can be satisfactorily described by Chudley-Eliott fixed jump length diffusion and accordingly the residence
time, jump length and diffusion constant are estimated. 相似文献
10.
11.
V. I. Vettegren V. B. Kulik A. V. Savitskii O. I. Fetisov V. V. Usov 《Technical Physics》2010,55(5):743-746
The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into
the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole
bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005
and 1015 cm−1 appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously,
water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN
molecule. Accordingly, a band at 2250 cm−1 arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water
molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide
limits and the band at 2250 cm−1 is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases
(the band at 2250 cm−1 narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally
strong” hydrogen bonds. 相似文献
12.
The rotational dynamics of four structurally similar polar molecules viz., coumarin 440, coumarin 450, coumarin 466 and coumarin
151 has been studied in binary mixtures comprising of dimethyl sulphoxide and water at room temperature using the steady state
fluorescence depolarization method and time correlated single photon counting technique. The binary mixtures are characterized
by the fact that at a particular composition the viscosity (η) of the solution reaches a maximum value that is higher than the viscosities of either of the two co-solvents. The dielectric
properties of the solution change across the composition range and the qualitative features of the solvent relaxation dynamics
in complex systems are known to differ from those in simple solutions. A hook type profile of rotational reorientation time
(τ
r
) vs viscosity (η) is obtained for all the solutes in dipolar aprotic mixture of dimethyl sulphoxide-water, with the rotational reorientation
times being longer in organic solvent-rich zone, compared to the corresponding isoviscous point in water-rich zone due to
strong hydrogen bonding. Fluorescence lifetimes as well as rotational reorientation times are sensitive to the composition
of the binary solvent system under study than to the viscosity suggesting the importance of local structure. The results are
discussed in the light of hydrodynamic and dielectric friction models.
Dedicated to Professor M.I. Savadatti on his 77th Birthday. 相似文献
13.
R. V. Ambartzumian L. M. Dorozhkin G. N. Makarov A. A. Puretzky B. A. Chayanov 《Applied Physics A: Materials Science & Processing》1980,22(4):409-413
The applicability of a pyroelectric detector (PED) to multiphoton absorption measurements (MPA) under ir laser excitation
of molecules was examined. The possibility of MPA measurement of SF6 molecules in the pressure range of 10−3÷10−1 Torr with a time resolution of ∼ 7 μs has been shown. It has been demonstrated that the degree of vibrational relaxation
of highly vibrationally excited molecules at PED surface does not depend on excitation level under the studied conditions. 相似文献
14.
In the present paper, the ionic conductivity and the dielectric relaxation properties on the poly(vinyl alcohol)-CF3COONH4 polymer system have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and
temperatures. The electrolyte samples were prepared by solution casting technique. The temperature dependence of the sample’s
conductivity was modeled by Arrhenius and Vogel-Tammann-Fulcher (VTF) equations. The highest conductivity of the electrolyte
of 3.41×10 − 3 (Ωcm) − 1 was obtained at 423 K. For these polymer system two relaxation processes are revealed in the frequency range and temperature
interval of the measurements. One is the glass transition relaxation (α-relaxation) of the amorphous region at about 353 K and the other is the relaxation associated with the crystalline region
at about 423 K. Dielectric relaxation has been studied using the complex electric modulus formalism. It has been observed
that the conductivity relaxation in this polymer system is highly non-exponential. From the electric modulus formalism, it
is concluded that the electrical relaxation mechanism is independent of temperature for the two relaxation processes, but
is dependent on composition. 相似文献
15.
D. Prevosto S. Napolitano P. Pingue S. Capaccioli M. Lucchesi 《The European physical journal. Special topics》2007,141(1):193-198
We studied dynamic properties of ultrathin films of
poly(ethylene terephthalate) spincoated on different substrates, by means of
dielectric spectroscopy and surface patterning experiments. We did not
observe any variations of structural dielectric relaxation dynamics for
films spincoated on aluminium substrate having thicknesses down to 40 nm. On
the same substrate, 13 nm thick films are instead characterized by a
reduction of the chains mobility. Surprisingly the chains dynamics as probed
by a surface nanopatterning experiment evidenced a strong dependence on the
substrate interaction even for 50 nm thick films, where dielectric
relaxation dynamics is unaffected. It can be deduced that different length
scales characterise dielectric relaxation dynamics and the processes related
to the surface patterning, even if both are related to the chain mobility.
Further experiments are wished to better understand this intriguing
scenario. 相似文献
16.
We use nanohole relaxation to study the surface relaxation of films of glassy isotactic poly (methyl methacrylate) (i-PMMA) films. These measurements allow us to obtain the time dependent relaxation function at a number of different sample temperatures for the first 2-3 nm of the free surface in a system often used as a model system for the effect of the substrate on thin film dynamics. The surface is observed to relax at temperatures up to 42 K below the bulk Tg value, even on systems where the thin film Tg is known to be greater than the bulk value. We are able to determine the range over which the substrate directly affects the free surface relaxation, and determine a surprisingly large (Mw independent) limiting thickness of approximately 180 nm where the free surface relaxation is not affected by the substrate. For thick films (h>200 nm) we find an unexpected linear Mw dependence of the near surface relaxation time. 相似文献
17.
The Jones–Dole B coefficients of the electrolyte Lithium bromide (LiBr), reference salts tetra butyl ammonium tetra phenyl borate (BU4NBPh4), tetra butyl ammonium bromide (BU4NBr), and potassium chloride (KCl) in dimethylsulfoxide (DMSO), water, and DMSO–water mixtures were obtained at different
temperatures range from 25 to 45 °C For this, the relative viscosities were measured for Lithium bromide (LiBr) and reference
salts in DMSO, water, and DMSO–water mixtures at above-mentioned temperatures. The B coefficients of these electrolytes were behaved as structure makers in DMSO, while in H2O and DMSO–H2O mixtures, the B-coefficient values were less positive showing the weak structure-making effect. Ionic viscosity B coefficients allow us to assess the behavior of ions in the solvent mixtures. In this study it was observed that all the
values of ionic B coefficient of (Li+) were positive and small showing the weak structure-making effects. It was also observed that Br− ions maintain negative B coefficient values in all DMSO–H2O mixtures, except in 60% DMSO mole fraction. From this it can be concluded that Br− ion behaved as a structure breaker in water and in all DMSO–H2O mixtures except in 60% DMSO mole fraction mixtures. The low B
± values of alkali metal ions and Br− ions in water are due to the breakdown of the tetrahedral structural of water and the formation of strongly structured solvated
ion. It is also observed that the values of the energy of activation of the flow for LiBr are greater in DMSO–water mixtures
and in pure water than in DMSO. This may be due the presence of a network of hydrogen bonds which cause the hindrance in the
flow of the solution of LiBr in DMSO–water mixtures and in pure water than in DMSO. 相似文献
18.
V. G. Kriger A. V. Kalenskii A. A. Zvekov 《Russian Journal of Physical Chemistry B, Focus on Physics》2012,6(1):15-18
The mechanisms of deactivation of electronically excited products of decomposition of silver azide (nitrogen molecules) are
examined. A model of dipole interaction with the electron subsystem of the crystal is used to estimate the rate constants
of deactivation with formation of electron-hole pairs (∼109 s−1) and energy transfer to a band hole (∼10−12 cm3 s−1). The values obtained confirm the basic postulate underlying the models of solid-phase chain reactions: the preferential
formation of electronic excitations of the crystal lattice during the deactivation of excited decomposition products. 相似文献
19.
The specific heat of undercooled liquid Ni80Fe10Cu10 alloy was experimentally measured by electromagnetic levitation drop calorimeter, and also numerically simulated by the molecular
dynamics method. The achieved maximum undercooling is up to 252 K (0.15 T
L) in the experiments, and the measured result is 41.67 J mol−1 K−1. The simulation provides calculated data within 0∼702 K undercooling range, which is much broader than the experimental regime.
The simulated value is 37.02 J mol−1 K−1. Although there exists a difference of 4.65 J mol−1 K−1 between them, the result is quite acceptable for simulation. Furthermore, the liquid structure of undercooled Ni80Fe10Cu10 alloy is studied in terms of the total and partial pair distribution functions, which display that the ordered degree of
atoms enhances from a normal liquid to metastable state. 相似文献
20.
Yoshio Kobayashi Hidekazu Kakinuma Daisuke Nagao Yasuo Ando Terunobu Miyazaki Mikio Konno 《Journal of nanoparticle research》2009,11(7):1787-1794
This article describes a method for silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone)
(PVP) as a stabilizer. The Co–Pt nanoparticles were prepared in an aqueous solution at 25–80 °C from CoCl2 (3.0 × 10−4 M), H2PtCl6 (3.0 × 10−4 M), PVP (0–10 g/L), and NaBH4 (4.8 × 10−3–2.4 × 10−2 M). The silica coating was performed for the Co–Pt nanoparticle colloid containing the PVP ([Co] = [Pt] = 3.0 × 10−5 M) at 25 °C in (1/4) (v/v) water/ethanol solution with tetraethoxyorthosilicate (TEOS) (7.2 × 10−5–7.2 × 10−3 M) and ammonia (0.1–1.0 M). Silica particles, which had an average size of 43 nm and contained multiple cores of Co–Pt nanoparticles
with a size of ca. 8 nm, were produced at 1.4 × 10−3 M TEOS and 0.5 M ammonia after the preparation of Co–Pt nanoparticles at 80 °C, 5 g/L PVP, and 2.4 × 10−2 M NaBH4. Their core particles were fcc Co–Pt alloy crystallites. Their saturation magnetization was 2.0-emu/g sample, and their coercive
field was 12 Oe. 相似文献