Unravelling free volume in branched-cation ionic liquids based on silicon

The branching of ionic liquid cation sidechains utilizing silicon as the backbone was explored and it was found that this structural feature leads to fluids with remarkably low density and viscosity. The relatively low liquid densities suggest a large free volume in these liquids. Argon solubility was measured using a precise saturation method to probe the relative free volumes. Argon molar solubilities were slightly higher in ionic liquids with alkylsilane and siloxane groups within the cation, compared to carbon-based branched groups. The anion size, however, showed by far the dominant effect on argon solubility. Thermodynamic solvation parameters were derived from the solubility data and the argon solvation environment was modelled utilizing the polarizable CL&Pol force field. Semiquantitative analysis was in agreement with trends established from the experimental data. The results of this investigation demonstrate design principles for targeted ionic liquids when optimisation for the free volume is required, and demonstrate the utility of argon as a simple, noninteracting probe. As more ionic liquids find their way into industrial processes of scale, these findings are important for their utilisation in the capture of any gaseous solute, gas separation, or in processes involving the transformation of gases or small molecules.

The branching of ionic liquid cation sidechains utilizing silicon as the backbone was explored and it was found that this structural feature leads to fluids with remarkably low density and viscosity.     

Studies on the free volume and the volume expansion behavior of amorphous polymers

In order to estimate the free volume contribution on the volume change, we investigated the relationship between the volume expansion behavior by Pressure–Volume–Temperature measurement apparatus and the free volume behavior by Positron Annihilation Lifetime Spectroscopy for some amorphous polymers. From these results, the free volume fraction of the amorphous polymers was calculated by assuming that the core volume increases at a constant rate with temperature. It was found that the amount of free volume was not constant even in the glassy state and it played a very important role in the volume expansion.     

Comparison of eluents in supercritical fluid chromatography as based on density and free volume

A comparative study of chromatographic properties of different supercritical eluents has been performed by considering the retention at equal density or at equal free volume for different mobile phases. At equal density, the temperature dependence of the capacity ratios of aromatic hydrocarbons is the same for different alkane mobile phases, whereas significant deviations are observed when carbon dioxide is employed as the mobile phase. At equal free volume, a comparison of the capacity ratios measured in carbon dioxide and in alkane eluents showed a pronounced similarity for the different mobile phases when the free volume was low, i.e., at high densities. With increasing free volume, the chemical differences of the alkanes on the one hand and carbon dioxide on the other become more apparent in their elution behavior. Furthermore, it is demonstrated that the free volume can also be used as a reference basis for the data of solvatochromic shift experiments.     

PALS study on the defect structure of yttria-stabilized zirconia

Powders of stabilized ZrO₂–8 mol% Y₂O₃ (YSZ) have been obtained by mechanical milling in zirconia vials. The samples were characterized by X-ray diffraction (XRD). Positron annihilation lifetime (PALS) measurements were performed to investigate the lattice defects originated by the incorporation of yttria and those mechanically induced. The XRD results indicate the formation of tetragonal YSZ solid solution. PALS results indicate that positron trapping occurs at different kinds of defects such as vacancy-like defects, grain boundary and associated defects.     

Effect of chain-end free volume on the diffusion of oligomers

We have used the pulsed-gradient spin-echo technique to measure self-diffusion in low-molecular-weight polymers in the melt and dissolved in identical polymers of high molecular weight. Specimens used were cis-polyisoprenes and polydimethylsiloxane. We find that, except for substantial free-volume corrections, self-diffusion in unentangled polyisoprene melts scales inversely with molecular weight. The results include sensitive determinations of chain-end free volume.     

Influence of the plasticization on free volume in polyvinyl chloride

Positron lifetime measurements in pure polyvinyl chloride (PVC) and in the plasticized PVC have been performed. Tricresyl phosphate was used as a plasticizer. Samples of the PVC were prepared with eight different plasticizer concentrations (from 0 to 35% of the plasticizer in the PVC). All of the measurements were performed in air at room temperature. A conventional fast–slow coincidence lifetime spectrometer was used for the measurements. Mean free volumes radii and fractional free volumes were calculated from the lifetime data. It has been found that the mean free volume radius is in the investigated region of the plasticizer concentrations, a linear function of the concentration of the tricresyl phosphate in the PVC. It seems that a polynomial fit can be used to describe the fractional free volume vs. the plasticizer concentration in the PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1839–1845, 1998     

Study of free volume parameters of polystyrenes of different molecular architecture by positron annihilation lifetime measurement

Differences of size, content and size distribution of free volumes in linear branched and three-armed polystyrenes, synthesized by radical and anionic processes, were observed by positron annihilation lifetime measurements. The temperature dependence of an average free volume radius was quite similar among polystyrenes of different architectures and molecular weight distributions. The free volume radius increased with temperature, from 0.27 nm (T:60 K) to 0.29 nm (T:260 K) and 0.30 nm (T _g:363 K), then to 0.35 nm (423 K), showing turning at and transition temperature. The free volume content decreased from 60 K to 220 K to 300 K showing peculiar minimum at 220 K to 300 K depending on the molecular shape, increased above 320 K, upto 340 to 360 K. The free volume contents decreased with an increase of molecular weight and by an addition of oligomer or plasticiser, suggesting differences in relaxation time or molecular motion between the edge and middle portions of molecular chain and filling effect of smaller molecules in free volumes, respectively. The apparent free volume fraction showed clear variations atT andT _g. Size distribution of free volumes suggested more complicated behavior of free volume upon the molecular relaxations and filling effect.     

基于密度泛函理论的CO2氧化含氮焦炭的机理研究

本研究基于密度泛函理论,选取简化的含吡咯氮（N-5）或吡啶氮（N-6）焦炭模型,在分子水平上对CO₂氧化含氮焦炭的异相反应机理进行研究。结构优化采用B3LYP-D3/6-31G（d）方法,单点能计算采用B3LYP-D3/def2-TZVP方法。计算结果表明,CO₂氧化含氮焦炭过程分为CO₂吸附、CO脱附和NO脱附三个阶段。CO₂异相氧化含吡咯氮焦炭的反应中,CO₂分子倾向于以C-O-down模式（N-O结合、C-C结合）吸附形成含氮和氧的五元杂环结构。然后五元环中原CO₂分子的C-O键断裂形成表面羰基和表面氮氧结构,分别解吸附出CO和NO。该反应吸热401.2 kJ/mol,决速步能垒为197.6 kJ/mol。CO₂异相氧化含吡啶氮焦炭的反应中,CO₂分子以C-O-down和C-C结合、C-O结合模式吸附后倾向于先形成含氮和氧的六元杂环,再发生CO和NO分子的脱附。该反应吸收598.6 kJ/mol的热量,决速...     

Temperature dependence of the free volume in polytetrafluoroethylene studied by positron annihilation spectroscopy

The temperature dependence of the free volume holes in pure polytetrafluoroethylene (PTFE) and doped with 25% glass have been studied in the temperature range (30–250 °C) using positron annihilation lifetime spectroscopy. The data clearly revealed the glass transition temperatures for pure and doped PTFE are 130 and 110 °C, respectively. As the temperature increases, the free volume distribution becomes positioned at larger free volume hole size. A good correlation between the electrical conductivity and the o-Ps parameters was achieved.     

The influence of the plasticization on free volume in polyvinyl chloride

Positron lifetime measurements in polyvinyl chloride (PVC), plasticized with the aid of dibutyl phthalate and tricresyl phosphate have been made. The plasticizers, the first range plasticizers, are an organic and an inorganic ester, respectively. The influence of the different concentration of the plasticizer in the PVC on positron lifetimes in the polymer have been investigated. A conventional fast-slow coincidence lifetime spectrometer with plastic scintillators has been used for the lifetime measurements. All the measurements have been performed in air, at room temperature. Mean free volumes radii have been calculated from the lifetime data.     

Study of the size and numerical concentration of the free volume of carbon filled HDPE composites by the positron annihilation method

In this paper, the size and numerical concentration of free volume of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with changing the temperature of HDPE/CB composite containing 25 phr CB. It was found that the important parameters of PALS show their fluctuation around the percolation threshold. The conductivity of HDPE/CB is controlled by CB contribution, and that can be reflected in o-Ps lifetime. The temperature dependence of positron lifetimes reveals that the existence of glass transition temperatures and the size of free volume holes increases when temperature increases above glass transition. The results observed from the second set of samples suggest that positive temperature coefficient is in some way related with free volume expansion. The experiment facts implied that the conductivity of HDPE/CB was related with not only the size of free volume holes but also the number of free volume holes. The Doppler-broadening of HDPE/CB was also investigated.     

Incorporating the excluded solvent volume and surface charges for computing solvation free energy

Gauss's law or Poisson's equation is conventionally used to calculate solvation free energy. However, the near‐solute dielectric polarization from Gauss's law or Poisson's equation differs from that obtained from molecular dynamics (MD) simulations. To mimic the near‐solute dielectric polarization from MD simulations, the first‐shell water was treated as two layers of surface charges, the densities of which are proportional to the electric field at the solvent molecule that is modeled as a hard sphere. The intermediate water was treated as a bulk solvent. An equation describing the solvation free energy of ions using this solvent scheme was derived using the TIP3P water model. © 2013 Wiley Periodicals, Inc.     

On the nature of the free volume in amorphous polymers

In a previous publication¹ it was shown that the free volume in amorphous polymers cannot consist of empty sites according to the quasilattice model. In this paper it is demonstrated why theories which are based on the assumptions of this model are nevertheless partly successful. It is even possible to calculate all three jumplike alterations in the second derivatives of Gibbs free energy at the glass transition in accordance with the experimental results. As far as we know, this is the first time that, in addition to the steplike changes in the thermal expansion coefficient Δα and the specific heat Δc_p, the analogous change in the compressibility Δ_χ can also be described correctly by a theory. The parameters for accommodation however reveal, that the quasilattice model does not apply. Consequently better-founded equations are derived, which despite their simplicity, give excellent agreement with the experimental data. One conclusion is that if the free volume consists of cavities in the material, their mean size has to be at least ten times smaller than that of a segment of the chainlike polymer molecules.     

HPLC-ECD检测羟自由基方法的研究

采用高效液相色谱结合库仑阵列多电极检测器体系(HPLC-ECD)建立了一套操作简便、高效、快速测定羟自由基的方法,并探究了检测的灵敏性,浓度和响应因子之间的线性关系,系统的稳定性等.2,3-二羟基苯甲酸(2,3-DHBA)、 2,5-二羟基苯甲酸(2,5-DHBA)以及水杨酸(SA)的相关系数分别为0.9999、 0.9996、 0.9968.2,3-DHBA和2,5-DHBA的检出限都低于0.1 ng/mL,SA的检出限均低于10 ng/mL,各种物质的方法回收率为100.5%～102.9%.     

Molecular weight-dependence of free volume in polystyrene studied by positron annihilation measurements

Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o-Ps) lifetime (τ₃) and intensity (I₃) were measured from 5°C to T_g + 30°C for each sample. From these data, the free volume hole size, 〈v_f(τ₃)〉, and fractional free volume h_ps=CI₃〈v_f(τ₃)〉 were calculated. The temperature dependences of τ₃, 〈v_f(τ₃)〉 and h_ps show a discrete change in slope at an effective glass transition temperature, T_g,ps, which is measurably below the conventional bulk T_g. This suggests that τ₃ is sensitive to large holes which retain their liquid-like mobility in the glassy state. Good agreement was found for T > h_g,ps between h_ps and the theoretical free volume fraction h_th deduced from experimental P-V-T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below T_g,ps, deviations between h_ps and h_th are observed, h_ps falling increasingly below h_th as temperature decreases. Whereas h_ps and h_th depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with h_ps in the glassy state. © 1994 John Wiley & Sons, Inc.     

Estimation of relative binding free energy based on a free energy variational principle for the FKBP-ligand system

Predicting an accurate binding free energy between a target protein and a ligand can be one of the most important steps in a drug discovery process. Often, many molecules must be screened to find probable high potency ones. Thus, a computational technique with low cost is highly desirable for the estimation of binding free energies of many molecules. Several techniques have thus far been developed for estimating binding free energies. Some techniques provide accurate predictions of binding free energies but high large computational cost. Other methods give good predictions but require tuning of some parameters to predict them with high accuracy. In this study, we propose a method to predict relative binding free energies with accuracy comparable to the results of prior methods but with lower computational cost and with no parameter needing to be carefully tuned. Our technique is based on the free energy variational principle. FK506 binding protein (FKBP) with 18 ligands is taken as a test system. Our results are compared to those from other widely used techniques. Our method provides a correlation coefficient (r ² ) of 0.80 between experimental and calculated relative binding free energies and yields an average absolute error of 0.70 kcal/mol compared to experimental values. These results are comparable to or better than results from other techniques. We also discuss the possibility to improve our method further.     

Study on the mechanism of Schiemann reaction by mass spectrometry

Schiemann reaction of 12 aryl diazonium fluoborates was studied by mass spectrometry. The products and by-products of the reactions were identified and the possible pathways were explored. It is shown that Schiemann reaction proceeds by free-radical mechanism.     

Experimental free volume aspects of the polymer rheology as obtained by positron annihilation lifetime spectroscopy

The ortho‐positronium (o‐Ps) annihilation parameters, i.e. the mean o‐Ps lifetime, τ₃, and the o‐Ps relative intensity, I₃, in cis‐1,4‐polybutadiene (cis‐1,4‐PBD) and polyisobutylene (PIB) over a wide temperature range including the glass‐liquid transition have been measured by means of positron annihilation lifetime Spectroscopy (PALS). From them the free volume microstructural characteristics, i.e. the mean free volume hole size, V_h, and the free volume hole fraction, f_h, have been determined via a semiempirical quantum‐mechanical model of o‐Ps in a spherical hole or a phenomenological model of volumetric and free volume hole properties, respectively. Consequently, the literature rheological data for both the above‐mentioned polymers have been related to the free volume hole fractions via the WLF‐Doolittle type equation. It has been found that i) in the case of PIB this equation holds over 130K above the glass transition temperature T_g and ii) in the case of cis‐PBD the WLF‐Doolitle equation is valid in the temperature range over 60K above 1.3T_g, but below 1.3T_g down to T_g the modified WLF‐Doolittle‐Macedo‐Litovitz equation with the additional activation‐energy term describes the shift factor data better.     

Studies on formation mechanism of polypyrrole microtubule synthesized by template‐free method

The influence of the polymerization time and rate as well as the solution's ionic strength on the morphology, conductivity, and molecular structure of the polypyrrole (PPy) microtubule [synthesized by the template‐free method in the presence of β‐naphthalene sulfonic acid (β‐NSA) as the dopant] were investigated. It was found that the formation of the PPy‐NSA microtubule was a slow and self‐assembled growth process. Moreover, the β‐NSA dopant played a “templatelike” role in the formation of tubular PPy‐NSA, which might be relative to its surfactant characters. This assumption was further confirmed by the phenomenon that the morphology of PPy‐NSA could be modified by increasing the ionic strength by adding inorganic salt. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 997–1004, 2001