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1.
Rotational diffusion of coumarin 6 (C6) laser dye has been examined in n-decane and methanol as a function of temperature. The rotational reorientation of this probe has been measured in these solvents.
It is observed that the decrease in viscosity of the solution is responsible for the decrease in the rotational relaxation
time of the probe molecule. The molecule C6 has long reorientation times in n-decane solvent as compared to methanol over all temperatures. It is found that the coumarin 6 rotates slower in n-decane than in methanol especially at higher values of viscosity over temperature. Two methods are chosen to determine the
ground state and excited state dipole moments. The change in dipole moments is estimated from Bakhshiev-Chamma-Viallet equations
and, the ground and excited state dipole moments from Kawski et al. equations, by using the variations of the Stokes shifts
with the dielectric constant and refractive index of the solvent. Our results are quite reliable which are solvatochromic
correlation obtained using solvent polarity functions. The reported results show that excited state dipole moment is greater
than ground state dipole moment, which indicates that the excited state is more polar than the ground state. 相似文献
2.
3.
Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol−1) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol−1) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted
by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also
the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of
complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG
mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane
and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly
with the non-polar solvent environment. 相似文献
4.
The ultrasonic absorption coefficients in binary mixtures
of 2-methyl-1-propanol with hexane were measured within the frequency range
from 10 to 80 MHz in the whole concentration range at 293.15 K. The results
of the measurements in connection with literature data were used to
calculate classical ultrasound absorption expressed as, αcl/f2,
and some related properties, i.e. difference between experimental and
classical absorption, Δ α/f2, and the ratio α/αcl for the pure
components. They were also used for finding out the values of volume
viscosity, ηV, which cannot be measured directly. The composition
dependences of ultrasonic absorption were discussed in terms of the gradual
breakage of alcohol oligomers and entropy effects connected with structural
changes of non-polar solvent resulting in displacement of the solvate
equilibrium. 相似文献
5.
Ananthaiah J Rajeswari M Sastry VS Dabrowski R Dhara S 《The European physical journal. E, Soft matter》2011,34(8):74
We report simultaneous measurements of shear viscosity (η) and dielectric constant (ε) of octyloxy cyanobiphenyl (8OCB) in the nematic (N) and smectic-A (SmA) phases as functions of temperature and electric
field. With increasing electric field η increases in the N phase whereas it decreases in the SmA phase and saturates beyond a particular field in both the phases.
The flow curves in the intermediate-field range show two Newtonian regimes in the N phase. The temperature-dependent behavior
of η and ε at zero or at small electric field suggests the occurrence of several structures that results from precessional motion of
the director along the neutral direction as reported in similar other system. We show that the precessional motions are gradually
suppressed with increasing electric field and the effective viscosity resembles with the Miesowicz viscosity η
1 at high enough electric field. In the intermediate field range the temperature-dependent η exhibits anomalous behavior across the N-SmA phase transition which is attributed to the large contribution of Leslie coefficient
α
1. 相似文献
6.
The molecular dynamics (MD) simulation, based on a realistic atom-atom interaction potential, was performed on 4-n-pentyl-4'-cyanobiphenyl (5CB) in the nematic phase. The rotational viscosity coefficients (RVCs) γ
i, (i = 1, 2) and the ratio of the RVCs λ = - γ
2/γ
1 were investigated. Furthermore, static and frequency-dependent dielectric constants and ε were calculated using parameters obtained from the MD simulation. Time correlation functions were computed and used to determine
the rotational diffusion coefficient, D
⊥. The RVCs and λ were evaluated using the existing statistical-mechanical approach (SMA), based on a rotational diffusion
model. The SMA rests on a model in which it is assumed that the reorientation of an individual molecule is a stochastic Brownian
motion in a certain potential of mean torque. According to the SMA, γ
i are dependent on the orientational order and rotational diffusion coefficients. The former was characterized using: i) orientational
distribution function (ODF), and ii) a set of order parameters, both derived from analyses of the MD trajectory. A reasonable
agreement between the calculated and experimental values of γ
i and λ was obtained.
Received 22 March 2000 and Received in final form 8 October 2000 相似文献
7.
The rotational dynamics of three structurally similar polar molecules viz., coumarin 440, coumarin 151 and coumarin 450 has
been studied in alcohols at room temperature using steady-state fluorescence depolarization method and time correlated single
photon counting technique. The observed reorientation times of all the three probes are found to be longer than those predicted
by Stokes–Einstein–Debye (SED) hydrodynamic theory with stick boundary condition and a deviation towards super-stick behavior
is noted. Dielectric friction theories of Nee–Zwanzig and van der Zwan–Hynes, which treat the solute as a point dipole, overestimate
the dielectric friction contribution exhibited by all the three coumarins in alcohols. Results are discussed in the light
of theoretical models and the possibility of hydrogen bonding between the amino group of the probe molecules and the hydroxyl
group of the alcohols. 相似文献
8.
Values of dielectric constant (ε′) and loss factor (ε″) have been experimentally determined for binary liquid mixtures of ethyl methyl ketone+ethylenediamine and methyl isobutyl
ketone+ethylenediamine at 9.44 GHz microwave frequencies at 30°C. The values ofε′ andε″ have been used to evaluate the molar polarization, apparent polarization and the excess permittivities. Excess refractive
index, viscosity and activation energy of viscous flow have also been estimated. These parameters have been used to explain
the formation of 1:1 complexes for both the systems. 相似文献
9.
Nasser Demir Steffen A. Bass 《The European Physical Journal C - Particles and Fields》2009,62(1):63-68
Ultrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) are thought to have created a Quark–Gluon
Plasma, characterized by a very small shear viscosity to entropy density ratio η/s, close to the lower bound predicted for that quantity by string theory. However, due to the dynamics of the collision, the
produced matter passes through a phase characterized by an expanding and rapidly cooling hadron gas with strongly increasing
η/s. Such a rise in η/s would not be compatible with the success of (viscous) hydrodynamics, which requires a very small value of η/s throughout the full evolution of the reaction in order to successfully describe the collective flow seen in the experiments.
Here we show that the inclusion of a pion-chemical potential, which is bound to arise due to the separation of chemical and
kinetic freeze-out during the collision evolution, will reduce the value of η/s, and argue that introduction of other chemical potentials could ensure the successful application of (viscous) hydrodynamics
to collisions at RHIC. 相似文献
10.
Dielectric measurements on three heterocyclic compounds namely pyrrolidine, piperidine and 2-acetylpyridine in paraffin oil
and paraffin oil + cyclohexane mixtures over the temperature range (294–318 K) at 9.8 GHz have been made. The data have been
analysed using the method of Higasiet al and their dependence on macroscopic viscosity has been examined. The effect of solvent viscosity on the dipolar rotational
process of the molecules in highly viscous media is also discussed. 相似文献
11.
Excess molar volumes (V
E) and deviation in isentropic compressibilities (Δβ
s) have been investigated from the density ρ and speed of sound u measurements of six binary liquid mixtures containing n-alkanes over the entire range of composition at 298.15 K. Excess
molar volume exhibits inversion in sign in one binary mixture, i.e., n-heptane + n-hexane. Remaining five binary mixtures,
n-heptane + toluene, cyclohexane + n-heptane, cyclohexane + n-hexane, toluene + n-hexane and n-decane + n-hexane show negative
excess molar volumes over the whole composition range. However, the large negative values of excess molar volume becomes domainant
in toluene + n-hexane mixture. Deviation in isentropic compressibility is negative over the whole range of composition in
the case of all the six binary mixtures. Existence of specific intermolecular interactions in the mixtures has been analyzed
in terms of excess molar volume and deviation in isentropic compressibility. 相似文献
12.
Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the conditiona = b
m(m is a constant) between metric potentials andη ∞θ whereη is the coefficient of shear viscosity andθ the scalar of expansion in the model. The coefficient of bulk viscosity (ς) is taken as constant. The physical and geometrical
aspects of the model are also discussed. 相似文献
13.
Molecular rotors are a group of environment-sensitive fluorescent probes whose quantum yield depends on the ability to form
twisted intramolecular charge-transfer (TICT) states. TICT formation is dominantly governed by the solvent’s microviscosity,
but polarity and the ability of the solvent to form hydrogen bonds play an additional role. The relationship between quantum
yield ϕ
F
and viscosity η is widely accepted as a power-law, fF = C ·hx\phi_F = C \cdot \eta ^x. In this study, we isolated the direct influence of the temperature on the TICT formation rate by examining several molecular
rotors in protic and aprotic solvents over a range of temperatures. Each solvent’s viscosity was determined as a function
of temperature and used in the above power-law to determine how the proportionality constant C varies with temperature. We found that the power-law relationship fully explains the variations of the measured steady-state
intensity by temperature-induced variations of the solvent viscosity, and C can be assumed to be temperature-independent. The exponent x, however, was found to be significantly higher in aprotic solvents than in protic solvents. We conclude that the ability
of the solvent to form hydrogen bonds has a major influence on the relationship between viscosity and quantum yield. To use
molecular rotors for the quantitative determination of viscosity or microviscosity, the exponent x needs to be determined for each dye-solvent combination. 相似文献
14.
The laser light scattering technique for non-invasivein situ simultaneous measurements on elastic constants and viscosity coefficients of nematic liquid crystals is introduced. By measuring
the autocorrelation function of the scattered light from nematic liquid crystals at different scattering angles, the splay
and twist elastic constantsK
11 andK
22 are obtained from the amplitudes of the autocorrelation function, and the viscosity coefficients ofη
Splay andη
Twist are determined using the viscoelastic ratiosK
11/η
Splay andK
22
η
Twist from the telaxation parameters of the two modes. 相似文献
15.
Veerabahu Ramakrishnan Andrei Sarua Martin Kuball Anis Fathima Abdullah 《Journal of Raman spectroscopy : JRS》2009,40(8):921-935
A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3‐phenoxybenzaldehye (3Phbz) and 4‐ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self‐association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. Γi(ηc), 3Phbz—solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well‐resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen‐bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
16.
The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C1) and 6-methoxy-4-azidomethyl coumarin (C2) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ
g
) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ
e
) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s
shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated
by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground
state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating
a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins. 相似文献
17.
《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
18.
The dielectric constant (ɛ′) and dielectric loss (ɛ″) for dilute solutions of sulfolane in carbon tetrachloride solution have been measured at 9.885 GHz at different temperatures
viz. 25°C, 30°C, 35°C and 40°C by using standard microwave techniques. Following the single frequency concentration variational
method, the dielectric relaxation time (τ) and dipole moment (μ) have been calculated. It is found that dielectric relaxation process can be treated as the rate process,
just like the viscous flow. Based on the above studies, monomer structure of sulfolane in carbon tetrachloride has been inferred.
Energy parameters (ΔH
g
, ΔF
g
, ΔS
g
) for dielectric relaxation process of sulfolane in carbon tetrachloride at 25°C, 30°C, 35°C and 40°C have been calculated
and compared with the corresponding energy parameters (ΔH
η
, ΔF
η
, ΔS
η
) for the viscous flow. 相似文献
19.
Densities ρ, viscosities η, and refractive indices nD, of the binary and ternary mixtures formed by cyclohexanone + N,N-dimethylacetamide + N,N-diethylethanolamine were measured at (298.15, 308.15, and 318.15) K for the liquid region and at ambient pressure for the whole composition ranges. The excess molar volumes VmE, viscosity deviations Δη, and refractive index deviations ΔnD, were calculated from experimental densities and refractive indices. The excess molar volumes are positive over the mole fraction range for binary mixtures of cyclohexanone(1) + N,N-dimethylacetamide (2) and N,N-dimethylactamide (2) + N,N-diethylethanolamine (3) and increase with increasing temperatures from (298.15 to 318.15) K. The excess molar volumes of cyclohexanone (1) + N,N-diethylethanolamine (3) are S-shaped dependence on composition with negative values in the N,N-diethylethanolamine rich-region and positive values at the opposite extreme and increase with increasing temperatures from (298.15 to 318.15) K. The excess molar volumes are positive over the whole mole fraction ranges for the ternary mixtures at all temperatures. Viscosity deviations are negative over the mole fraction range for all binary and ternary mixtures and decrease with increasing temperatures from (298.15 to 318.15) K. Refractive index deviations are negative over the mole fraction range for all binary and ternary mixtures and increase with increasing temperatures from (298.15 to 318.15) K. The experimental data of constitute were correlated as a function of the mole fraction by using the Redlich–Kister equation for binary and , Cibulka, Jasinski and Malanowski , Singe et al., Pintos et al., Calvo et al., Kohler, and Jacob–Fitzner for ternary mixture, respectively. McAllister's three body, Hind, and Nissan–Grunberg models were used for correlating the kinematic and dynamic viscosity of binary mixtures. The experimental data of the constitute binaries are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures. 相似文献
20.
The fluorescence of styrylthiazoloquinoxaline (STQ) in the solvent mixture methanol and dichloromethane (DCM) and 2-octanol have many common characteristics: biexponential fluorescence decay, wavelength-dependent amplitudes, a negative amplitude for the short-lifetime component at long emission wavelengths, and a time-dependent red shift of the emission spectrum. In octanol, the fluorescence lifetime decreases with increasing temperature, whereas the lifetime increases with temperature in the methanol/DCM mixture. The fluorescence characteristics in 2-octanol ( = 7.29 cP) are readily explained by the conventional model of excited-state relaxation kinetics by solvent reorientation. This model is not applicable for low-viscosity ( = 0.455 cP) solvent mixtures. A model of excited-state relaxation kinetics involving solvent exchange (versus solvent reorientation in pure solvents) in the excited state is proposed for the solvent mixture. The model assumes that the solvent compositions around the solute are different in the ground and excited states and the solvent composition is temperature dependent. 相似文献