Solvent Bath Research Articles

Femtosecond transient absorption with chirped pump and supercontinuum probe: Perturbative calculation of transient spectra with general lineshape functions, and simplifications

Femtosecond transient UV/vis absorption spectra of molecules in solution show vibronic structure initially while pump and probe pulses overlap, superimposed on bands which broaden and shift on several time scales. Third-order perturbation theory is used simulate and understand such spectra under experimental conditions, i.e., with chirped pump pulses and 40–80 fs pump/probe correlation time. The electronic system is coupled to a solvent bath whose fluctuations enter through a lineshape function g( t). This approach has two advantages. (i) In the general case when g( t) is modelled realistically it provides a distinction of coherent and sequential contributions to early transient spectra. The time-zero stimulated emission band can be extracted, giving access to the relaxation function for the emission frequency. (ii) For limiting forms of g( t) corresponding to the Bloch approximation and to inhomogeneous broadening the threefold time integrals underlying the theory reduce to a single integral. In such cases the lineshape formulation of transient absorption spectra can be used for data fitting.

Mode-specific energy absorption by solvent molecules during CO2 vibrational cooling

Non-equilibrium molecular dynamics (NEMD) simulations of energy transfer from vibrationally excited CO(2) to CCl(4) and CH(2)Cl(2) solvent molecules are performed to identify the efficiency of different energy pathways into the solvent bath. Studying in detail the work performed by the vibrationally excited solute on the different solvent degrees of freedom, it is shown that vibration-to-vibration (V-V) processes are strongly dominant and controlled by those accepting modes which are close in frequency to the CO(2) bend and symmetric stretch vibration.

Novel Approach for Fabricating Highly Ordered Colloidal Crystals using Fluorinated Solvent

AbstractA novel technique for fabricating highly ordered colloidal photonic crystals has been developed. In this method, a droplet of water containing polystyrene microspheres was added to the surface of a fluorinated solvent bath. Consequently, the two liquids remained separated and the colloidal particles self-assembled into close-packed structures at the interface between them. By transferring the droplet onto a glass slide, a highly ordered crystal was obtained. This technique offers a new, potentially easier, and more effective approach than currently used. We believe that it will open new ways for fabricating materials based on colloidal crystals as well as applying the colloidal photonic crystals to optical devices.

Multidimensional infrared spectroscopy of water. I. Vibrational dynamics in two-dimensional IR line shapes

In this and the following paper, we describe the ultrafast structural fluctuations and rearrangements of the hydrogen bonding network of water using two-dimensional (2D) infrared spectroscopy. 2D IR spectra covering all the relevant time scales of molecular dynamics of the hydrogen bonding network of water were studied for the OH stretching absorption of HOD in D2O. Time-dependent evolution of the 2D IR line shape serves as a spectroscopic observable that tracks how different hydrogen bonding environments interconvert while changes in spectral intensity result from vibrational relaxation and molecular reorientation of the OH dipole. For waiting times up to the vibrational lifetime of 700 fs, changes in the 2D line shape reflect the spectral evolution of OH oscillators induced by hydrogen bond dynamics. These dynamics, characterized through a set of 2D line shape analysis metrics, show a rapid 60 fs decay, an underdamped oscillation on a 130 fs time scale induced by hydrogen bond stretching, and a long time decay constant of 1.4 ps. 2D surfaces for waiting times larger than 700 fs are dominated by the effects of vibrational relaxation and the thermalization of this excess energy by the solvent bath. Our modeling based on fluctuations with Gaussian statistics is able to reproduce the changes in dispersed pump-probe and 2D IR spectra induced by these relaxation processes, but misses the asymmetry resulting from frequency-dependent spectral diffusion. The dynamical origin of this asymmetry is discussed in the companion paper.

Ribbon-to-Fiber Transformation in the Process of Spinning of Carbon-Nanotube Dispersion

We describe a phenomenon of ribbon-to-fiber transformation observed in the process of spinning of single wall carbon nanotubes dispersed in polymer solutions. In the process of spinning, a gel-like ribbon comprised of nanotube bundles bound by polymer is withdrawn from a solvent bath. We show that upon crossing the liquid-air interface, the ribbon may either retain its flat shape or fold into a compact hairlike fiber. The ribbon-to-fiber transformation is caused by the capillary action of the liquid meniscus embracing the ribbon. Only sufficiently stiff ribbons can withhold the capillary compression. The critical conditions of folding, as well as the number of folds in the contractive ribbon, depend on the ribbon width, its flexural rigidity, and the solvent surface tension. We show that the ribbon rigidity can be efficiently modulated by varying the solvent composition, allowing us to control the pore structure of carbon-nanotube fibers.

Role of heme propionates of myoglobin in vibrational energy relaxation

The role of heme propionates of myoglobin in vibrational energy relaxation was studied by time-resolved resonance Raman spectroscopy. Time-resolved anti-Stokes spectra were measured to monitor the vibrational energy relaxation of the heme. The decay rates of the band intensities were compared between wild-type myoglobin and etioheme-substituted myoglobin where the heme lacks hydrogen-bonding side chains. The decay rates of the anti-Stokes intensities of the latter were less than those of the former, providing strong support for a theoretical proposal that the propionates and their coupling to solvent bath play an important role in the dissipation of excess energy of the excited heme in solvated wild-type myoglobin.

Formalism for calculation of polymer-solvent-mediated potential

A simple theoretical approach is proposed for calculation of a solvent-mediated potential (SMP) between two colloid particles immersed in a polymer solvent bath in which the polymer is modeled as a chain with intramolecular degrees of freedom. The present recipe is only concerned with the estimation of the density profile of a polymer site around a single solute colloid particle instead of two solute colloid particles separated by a varying distance as done in existing calculational methods for polymer-SMP. Therefore the present recipe is far simpler for numerical implementation than the existing methods. The resultant predictions for the polymer-SMP and polymer solvent-mediated mean force (polymer-SMMF) are in very good agreement with available simulation data. With the present recipe, change tendencies of the contact value and second virial coefficiency of the SMP as a function of size ratio between the colloid particle and polymer site, the number of sites per chain, and the polymer concentration are investigated in detail. The metastable critical polymer concentration as a function of size ratio and the number of sites per chain is also reported for the first time. To yield the numerical solution of the present recipe at less than on a personal computer, a rapid and accurate algorithm for the numerical solution of the classical density functional theory is proposed to supply rapid and accurate estimation of the density profile of the polymer site as an input into the present formalism.

The effect of ‘hot’ electrons on the heterogeneous adiabatic charge transfer reactions

The spin-less version of the Anderson Hamiltonian is extended to describe the adiabatic electron transfer reactions at a metal electrode involving ‘hot’ electrons which can be reached by the subpicosecond laser pump. The latter presumes high temperatures of the electron gas in the metal substrate, significantly exceeding the temperature of solvent bath. Some analytical formulas are derived and employed to construct the adiabatic free energy surfaces along the solvent coordinate as a function of the electrode overpotential. The model calculations show a noticeable decrease of the reaction barrier resulted from the effect of ‘hot’ electrons. A difference in the kinetics of adiabatic and diabatic electron transfer induced by ‘hot’ electrons was found to be noticeable. The dependencies of the symmetry coefficient vs. the overpotential are discussed, as well as the contribution from vibrationally excited states.

ZnTe electrodeposition from organic solvents

The electrodeposition of zinc telluride was investigated from various organic solvent baths such as methanol, acetonitrile, propylene carbonate. The potential window increases with increasing boiling point of the solvents. In particular, ZnTe with high crystallinity could be obtained in propylene carbonate by the under-potential deposition (UPD) of Zn. The current efficiency for ZnTe deposition in propylene carbonate was enhanced considerably compared to that in acidic aqueous solutions. A single-phase ZnTe film close to the ideal stoichiometric composition of ZnTe could be obtained at 423 K and −0.8 V versus Ag/AgCl in propylene carbonate with a molar ratio of Zn(II)/Te(IV) = 10 and a low Te(IV) concentration; the film had a smooth and dense granular crystal morphology.

Computer simulation of polymer networks: Swelling by binary Lennard-Jones mixtures

The swelling of regular, tightly meshed model networks is investigated by a molecular-dynamics-Monte Carlo hybrid technique. The chemical equilibrium between two simulation boxes representing the gel phase and a solvent bath, respectively, is obtained by subjecting the Lennard-Jones particles of a binary mixture, serving as explicit solvent, to the particle transfer step of Gibbs ensemble-Monte Carlo. The swelling behavior, especially preferential absorption of a single component, whose dependence on temperature, pressure, and fluid composition is studied, also depends significantly on the size of the central simulation cell. These finite-size effects correlate well with those exhibited by the density of solvent-free (dry) networks. A theoretical expression, whose derivation is based on network elasticity (of dry networks) yields finite-size scaling behavior in good accord with simulation results for both dry networks and gels in contact with solvent baths. This expression can be used to extrapolate the swelling behavior of simulated finite systems to infinite system size.

Influence of Solvent-Solvent and Solute-Solvent Interaction Propertieson Solvent-Mediated Potential**The project supported by National NaturalScience Foundation of China under Grant No. 20206033

A recently proposed universal calculational recipe for solvent-mediatedpotential is applied to calculate excess potential of mean force between twolarge Lennard–Jones (LJ) or hard core attractive Yukawa particles immersedin small LJ solvent bath at supercritical state. Comparison between thepresent prediction with a hypernetted chain approximation adopted forsolute-solute correlation at infinitely dilute limit and existing simulationdata shows high accuracy for the region with large separation, andqualitative reliability for the solute particle contact region. Thecalculational simplicity of the present recipe allows for a detailedinvestigation on the effect of the solute-solvent and solvent-solventinteraction details on the excess potential of mean force. The resultantconclusion is that gathering of solvent particles near a solute particleleads to repulsive excess PMF, while depletion of solvent particles awayfrom the solute particle leads to attractive excess PMF, and minor change of thesolvent-solvent interaction range has large influence on the excess PMF.

Swelling Behavior of Partially Cross-Linked Polymers: A Ternary System

Cross-linked polymer networks, irrespective of the method of cross-linking, contain a fraction of unattached polymer (sol macromolecules). During swelling in a solvent of low molecular weight, the sol macromolecules participate in the swelling process as an athermal solvent. Also, sol macromolecules begin to diffuse out of the swollen polymer into the surrounding solvent bath until equilibrium is reached between the sol macromolecules within the polymer specimen and the molecules in the surrounding bath. Thus, a partially cross-linked polymer during swelling should be treated as a ternary system consisting of polymer network, a high molecular weight solvent, and a low molecular weight solvent. On the basis of the Flory-Rehner theory, a first model has been developed to predict the swelling behavior of such ternary system. Transient states are considered as quasi-steady state, and the final condition of equilibrium is evaluated. The effect of polymer molecules in the surrounding solvent bath on the swelling behavior was also studied. Swelling experiments of partially cross-linked high-density polyethylene in p-xylene were performed to evaluate the model predictions. The presence of sol macromolecules within the swollen gel increased the swelling while sol molecules in the surrounding bath decreased the swelling of the partially cross-linked polymer.

Quantitative Description of Potential of Mean Force BetweenMacroparticles in Fluid with Attactive Forces

A statistical mechanics method is proposed for calculation ofpotential of mean force (PMF). In the case of solvophobic or solvophilicmacroparticles immersed in solvent bath of soft sphere or Lennard-Jonesparticles, prediction accuracy for the PMF and MF from the simplestimplementation of the proposed method, where hypernetted chain approximationis adopted for correlation of the macroparticle-macroparticle at infinitelydilute limit, is comparable to that of a recent more sophisticated approachbased on mixture Ornstein–Zernike integral equation / bridge function fromfundamental measure functional. Adaptation of the present method for generalcomplex fluids is discussed, and method for improving the accuracy issuggested. Differences and relative merits of the present recipe comparedwith that based on potential distribution theory is discussed.

Isostructural solid–solid transitions in binary asymmetrical hard sphere system: Based on solvent-mediated potential

Size dependence is imparted onto a modified bridge functional, adopted for a recently proposed semi-analytical hard sphere reference system theory for calculation of solvent-mediated potential (SMP). The SMP for two large hard sphere particles immersed in a small hard sphere solvent bath predicted by the present improved version is in satisfactory agreement with the prediction from a theoretically based fitting formula. Isostructural solid–solid transitions in the binary asymmetrical hard sphere system are investigated based on a single-component macrofluid approximation combined with the improved version. It is found that the isostructural solid–solid transition appears when size asymmetry increases. The limiting asymmetry size ratio is near 1 / 8 . As the size asymmetry increases, critical density for both large and small hard sphere components for the fcc isostructural solid–solid transition increases and decreases, respectively.

Local Solvent Density Augmentation around a Solute in Supercritical Solvent Bath: 1. A Mechanism Explanation and a New Phenomenon

A recently proposed partitioned density functional (DF) approximation (Phys. Rev. E 2003, 68, 061201) and an adjustable parameter-free version of a Lagrangian theorem-based DF approximation (LTDFA: Phys. Lett. A 2003, 319, 279) are combined to propose a DF approximation for nonuniform Lennard-Jones (LJ) fluid. Predictions of the present DF approximation for local LJ solvent density inhomogeneity around a large LJ solute particle or hard core Yukawa particle are in good agreement with existing simulation data. An extensive investigation about the effect of solvent bath temperature, solvent-solute interaction range, solvent-solute interaction magnitude, and solute size on the local solvent density inhomogeneity is carried out with the present DF approximation. It is found that a plateau of solvent accumulation number as a function of solvent bath bulk density is due to a coupling between the solvent-solute interaction and solvent correlation whose mathematical expression is a convolution integral appearing in the density profile equation of the DF theory formalism. The coupling becomes stronger as the increasing of the whole solvent-solute interaction strength, solute size relative to solvent size, and the closeness to the critical density and temperature of the solvent bath. When the attractive solvent-solute interaction becomes large enough and the bulk state moves close enough to the critical temperature of the solvent bath, the maximum solvent accumulation number as a function of solvent bath bulk density appears near the solvent bath critical density; the appearance of this maximum is in contrast with a conclusion drawn by a previous investigation based on an inhomogeneous version of Ornstein-Zernike integral equation carried out only for a smaller parameter space than that in the present paper. Advantage of the DFT approach over the integral equation is discussed.

Mechanism of Ligand Exchange Studied Using Transition Path Sampling

The mechanism of intermolecular ligand exchange has been studied using transition path sampling (TPS) based molecular dynamics (MD) simulations. Specifically, the exchange of solvent molecules bound to unsaturated Cr(CO)5 in methanol solution has been investigated. The results of the TPS simulations have shown that there are multiple steps in the reaction mechanism. The first involves partial dissociation of the coordinated solvent from the Cr metal center followed by association with a new methanol molecule between the normally void first and second solvent layers. After diffusive motion of the exchanging ligands, the last step involves the originally bound methanol molecule moving into the bath continuum followed by solvation of the Cr metal fragment by the exchanging ligand. It has been found that the reaction center (defined as the organometallic fragment and two exchanging ligands only) and the solvent bath have favorable interactions. This is likely due to the adiabatic nature of the ligand exchange transition. The ability to understand the microscopic molecular dynamics of a chemical process based on a free energy analysis is also discussed.

Semi-analytical hard sphere reference system theory for solvent-mediated potential (III): test and application to system with general interaction potentials

A semi-analytical hard sphere reference system theory for calculation of solvent-mediated potential (SMP) is formulated for asymmetrical binary hard sphere mixture based on a recently proposed universal framework by the first two Letters of the series. Accuracy of the present semi-analytical theory for SMP and solid–liquid transition is affirmed. A theoretical way is devised to apply the reference system theory to SMP for case of general potentials, here a Lennard–Jones solvent bath, and the agreement between theory and available simulation data is satisfactory.

Universal calculational recipe for solvent-mediated potential: based on a combination of integral equation theory and density functional theory

A universal formalism, which enables calculation of solvent-mediated potential (SMP) between two equal or non-equal solute particles with any shape immersed in solvent reservior consisting of atomic particle and/or polymer chain or their mixture, is proposed by importing a density functional theory externally into OZ equation systems. Only if size asymmetry of the solvent bath components is moderate, the present formalism can calculate the SMP in any complex fluids at the present development stage of statistical mechanics, and therefore avoids all of limitations of previous approaches for SMP. Preliminary calculation indicates the reliability of the present formalism.

Development of innovative shredder residue separation and recycling system

Shredder residue is an unavoidable by-product of the treatment of end of life vehicles and household appliances. NKK has developed a new post-treatment process in which the residue is introduced in a bath of solvent made of hot tar and gives an overflow of plastics and metallic sediments. The recovered plastics can be injected into the blast furnace and the metallic parts recycled in the steel shop. This new process allows a high recycling rate of treated materials.

Vibrational Energy Transfer in Highly Excited Bridged Azulene-Aryl Compounds: Direct Observation of Energy Flow through Aliphatic Chains and into the Solvent

Intra- and intermolecular vibrational energy flow in vibrationally highly excited bridged azulene-(CH2)n-aryl (n = 0,1,3; aryl = benzene or anthracene) compounds is observed using time-resolved pump−probe laser spectroscopy. Light absorption in the azulene S1-band, followed by fast internal conversion, leads to vibrational excitation at the azulene side of the molecules. Subsequent energy flow through the aliphatic chain to the aryl group at the other side of the molecules and vibrational energy transfer into a surrounding liquid solvent bath are measured either by probing the red edge of the azulene S3-absorption band at 300 nm and/or the anthracene S1-absorption band at 400 nm. The data are analyzed by representing the intramolecular energy flux as a diffusion process and using hot absorption spectra of the two chromophores of the compounds for measuring their energy contents. A fit to all of the experimental signals leads to an energy conductivity of a single C−C bond of κCC = (10 ± 1) cm-1 K-1 ps-1 (with energies measured in cm-1). Depending on the substituent and the length of the chain, this models yield intramolecular energy transfer times of 1.2−4 ps. Energy transfer to the solvent 1,1,2-trichloro-trifluoro-ethane, on the other hand, is characterized by an exponential loss profile with a cooling time constant of (21 ± 2) ps, independent of the substituent and the same as for bare azulene.