Acoustic relaxation and ionic conductivity of oxyethylene aliphatic polyionenes

Polyionenes composed of oxyethylene and aliphatic hydrocarbon units were studied by differential scanning calorimetry, wide-and small-angle X-ray scattering, and dielectric spectroscopy. These polymers are characterized by the variation of T _g with the concentration of ionic centers. Polyionenes with short ethylene oxide segments are amorphous; however, as the average number of monomer units in the oxyethylene segments increases to 20, a crystalline structure typical of poly(ethylene oxide) is formed. Oxyethylene-aliphatic polyionenes are microphase-separated systems. Polyionenes from this series are characterized by a high ionic conductivity, which increases with an increase in the concentration of ionic sites—the conductivity at room temperature is 10^?5–10^?4 Ω^?1 cm^?1. By means of acoustic spectroscopy, it was found that the isotherms of the ultrasound absorption (frequency domain) and ultrasound speed had two dispersion regions. The mechanism of the dispersions was associated with the softening of the quasi-lattice produced by cationic sites and with the motion of chain segments connecting these sites, The speed of sound in polyionene is abnormally high (1800–2100 m/s) for polymers, a result which is due to a high level of intermolecular interactions.     

High pressure study of molecular dynamics of protic ionic liquid lidocaine hydrochloride

In this paper, we investigate the effect of pressure on the molecular dynamics of protic ionic liquid lidocaine hydrochloride, a commonly used pharmaceutical, by means of dielectric spectroscopy and pressure-temperature-volume methods. We observed that near T(g) the pressure dependence of conductivity relaxation times reveals a peculiar behavior, which can be treated as a manifestation of decoupling between ion migration and structural relaxation times. Moreover, we discuss the validity of thermodynamic scaling in lidocaine HCl. We also employed the temperature-volume Avramov model to determine the value of pressure coefficient of glass transition temperature, dT(g)/dP|(P = 0.1). Finally, we investigate the role of thermal and density fluctuations in controlling of molecular dynamics of the examined compound.     

First-principles study of liquid gallium at ambient and high pressure

The static and dynamic properties of liquid Ga close to the melting line have been studied by first-principles molecular dynamics simulations at ambient and elevated pressure up to 5.8 GPa. Below 2.5 GPa, the nearest neighbor Ga-Ga separation shows little change, while the second and third coordination shells are compressed to shorter distances. This behavior is attributed to the gradual occupation of the interstitial sites. Detail analysis of the local geometry and dynamical behavior refutes the proposed existence of Ga(2) dimers in the liquid state. In fact, both the structure and electronic properties of the liquid are found to closely resemble that of the underlying Ga-II and Ga-III crystalline phases.     

Spectrophotometric determination of nicoumalone, acebutolol hydrochloride and procainamide hydrochloride

A sensitive spectrophotometric method is described for the determination of nicoumalone (NIC), acebutolol hydrochloride (ACBH) or procainamide hydrochloride (PAH) either in pure form or in pharmaceutical formulations. The method is based on the oxidative coupling reaction through the involvement of an aromatic primary amino group (released through reduction in NIC or hydrolysis in ACBH or existing free in PAH) in the drug with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of ferric chloride [Fe(III)]. The resulting chromophores are measured at 620 nm for NIC and ACBH and 580 nm for PAH. The concentration measurements are reproducible within a relative standard deviation of 1%.     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.      

Dilatometric study on the melting of polypropylene at elevated pressure

Summary Using high pressure dilatometers, the specific volume of isotactic polypropylene has been measured as a function of temperature and pressure up to 3.5 kbar. Up to 1 kbar this has been done not only for a commercial whole polymer, but also for sharp fractions. The slope of the curve of the melting temperature as a function of pressure has been determined accurately for low pressure (38 K/kbar) and has been found to remain constant almost up to 1 kbar. Because of uncertainties of the published data on crystal density, the accuracy of the volume change at the melting point is low, hence the enthalpy of fusion has been evaluated invoking theClausius-Clapeyron equation with an accuracy of only 15 %. The transition data volume, enthalpy and entropy are also given as function of pressure. The pronounced dependence of the melting point on the molecular weight has been explained by imperfect tacticity.

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Zusammenfassung Mit Hochdruckdilatometern wurde das spezifische Volumen von isotaktischem Polypropylen in Abhängigkeit von der Temperatur and bei Drucken bis 3,5 kbar gemessen. Bis 1 kbar wurde dies nicht nur an einem technischen Polymer durchgeführt, sondern auch für scharfe Fraktionen. Die Anfangssteigerung der Schmelzpunktskurve caber dem Druck konnte recht genau zu 38 K/kbar bestimmt werden. Sie bleibt bis beinahe 1 kbar konstant. Wegen der experimentellen Unsicherheit der veröffentlichten Kristalldichten kann der Volumensprung Kristall-Schmelze nur ungenau ausgewertet werden. Daher ist auch unsere nachClausius-Clapeyron bestimmte Schmelzentropie und entbalpie von nur auf etwa 15% genau. Die Größen Schmelztemperatur, -volumen, -entropie und-enthalpy werden bis 3,5 kbar als Funktion des Drucks angegeben. Die beobachtete starke Molekulargewichtsabhängigkeit des Schmelzpunkts wird durch unvollständige Taktizität begründet.

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With 7 figures and 3 tables     

Study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogel dried at ambient pressure

The experimental results on the study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogels dried at ambient pressure, are reported. Silica sol was prepared by keeping the MeOH/TEOS molar ratio, Acidic water (Oxalic acid) and basic water (NH₄OH) concentrations constant at 16.5, 0.001 and 1 M, respectively throughout the experiments and the HMDZ/TEOS molar ratio (h) was varied from 0.34 to 2.1. Finally, the surface modified wet gels were dried at an ambient pressure. The thermal conductivity of the aerogel samples was measured. Further, the humidity study was carried out in 80% humid surrounding at 30 °C temperature over 80 days. The best quality aerogels in terms of low bulk density, thermal conductivity and durability (no moisture absorption) with an only 2% of weight gain were obtained for TEOS: MeOH: Acidic H₂O: Basic H₂O: HMDZ molar ratio at 1:16.5:0.81:0.50:0.681, respectively. The thermal stability and hydrophobicity of the aerogel have been confirmed with Thermo gravimetric and Differential Thermal (TG–DT) analyses and Fourier Transform Infrared Spectroscopy (FTIR), respectively. Microstructural studies were carried out by Scanning Electron microscopy (SEM).     

Molecular dynamics at ambient and elevated pressure of the amorphous pharmaceutical: nonivamide (pelargonic acid vanillylamide)

Broadband dielectric spectroscopy was employed to investigate the relaxation dynamics of supercooled and glassy nonivamide-the synthetic form of capsaicin being the most spicy-hot substance known to man. The material is of great importance in the pharmaceutical industry because it has wide usage in the medical field for relief of pain, and more recently it has been shown to be effective in fighting cancers. Dielectric measurements carried out at various isobaric and isothermal conditions (pressure up to 400 MPa) revealed very narrow α-loss peak and unresolved secondary relaxations appearing in the form of an excess wing on the high frequency flank. Moreover, our studies have shown the shape of dielectric loss spectrum at any fixed loss peak frequency is invariant to different combinations of temperature and pressure, i.e., validity of the time-temperature-pressure superpositioning. We also found the fragility index is nearly constant on varying pressure. This property is likely due to the unusual structure of nonivamide, which has a part characteristic of van der Waals glass-former and another part characteristic of hydrogen-bonded glass-former.     

压力下流化床流动特性的实验研究

利用摄像技术在φ60mm×800mm压力为0.1MPa～1.5MPa的冷模加压流化床实验装置上, 对两种不同粒径颗粒的最小流化速度和床层膨胀高度进行了研究。研究结果表明,大粒径聚苯乙烯颗粒的Umf与p-0.3成比例,小粒径石英砂的Umf与p-0.21成比例,并根据实验值拟合出压力下最小流化速度公式为: Umf=μdp ρg｛［(34.15)2+0.05916×dp3 ρg( ρs- ρg)gμ2］12-34.15｝ 床层膨胀高度随气速的增大而不断增高,在相同U Umf下床层膨胀高度随压力的增大而增高,在大于0.7MPa时,压力对膨胀高度的影响减弱。对于聚苯乙烯颗粒,相同的H/Hmf下,U Umf随压力的增大而逐渐减小,当H/Hmf＝1.4～1.6时,U Umf与p-0.52～p-0.58成比例。     

Densification of silica glass at ambient pressure

We show that densification of silica glass at ambient pressure as observed in irradiation experiments can be attributed to defect generation and subsequent structure relaxation. In our molecular dynamics simulations, defects are created by randomly removing atoms, by displacing atoms from their nominal positions in an otherwise intact glass, and by assigning certain atom excess kinetic energy (simulated ion implantation). The former forms vacancies; displacing atoms and ion implantation produce both vacancies and "interstitials." Appreciable densification is induced by these defects after equilibration of the defective glasses. The structural and vibrational properties of the densified glasses are characterized, displaying resembling features regardless of the means of densification. These results indicate that relaxation of high free-energy defects into metastable amorphous structures enriched in atomic coordination serves as a common mechanism for densification of silica glass at ambient pressure.     

Dynamics of alkyl ammonium intercalants within organically modified montmorillonite: Dielectric relaxation and ionic conductivity

The low-frequency (0.01 Hz-10 MHz) dynamic characteristics of alkyl quaternary ammonium exchanged montmorillonite (SC20A) were investigated to determine the correlation between temperature-dependent changes in the interlayer structure and collective mobility of the surfactant. From 25 to 165 degrees C, SC20A exhibits two interlayer transitions, one ascribed to the melting of the intercalated alkyl chains of the surfactant (20-40 degrees C) and another associated with an abrupt decrease in the interlayer's coefficient of thermal expansion (100 degrees C). For this temperature range, the excess surfactant and residual electrolytes present in commercially manufactured SC20A enhance the direct current conductivity and increase low-frequency space-charge polarization, which is believed to occur across percolation paths established by the surfaces of the SC20A crystallites. In contrast, a higher-frequency relaxation, which was less sensitive to process history and impurity content, is ascribed to relaxation within the interlayer at the surfactant-aluminosilicate interface electrostatic couple. The temperature dependence of these dielectric relaxations indicated a drastic increase in mobility as the interlayer organic phase transitions from static and glasslike into molten and mobile. Overall, SC20A displayed features of alternating current universality, including time-temperature superposition, common in other types of disordered ion-conducting media. The presence of long-range transport and its sensitivity to low amounts of impurities imply that from a dynamic perspective the local environment of the surfactants are substantially diverse and a minority fraction, such as at the edge of the crystallite (gallery and aluminosilicate layer), may dominate the lower-frequency dielectric response.     

Reversed-phase retention thermodynamics of pure-water mobile phases at ambient and elevated temperature

The use of pure water at superheated temperatures, between 100 and 200 degrees C, as a mobile phase for reversed-phase separations is explored. The thermodynamics of the retention process at low temperature (15-55 degrees C) are compared to the thermodynamics at elevated temperature (125-175 degrees C). Significant differences in the enthalpy of the retention process are observed between the two temperature ranges. This is possibly due to changes in the hydrogen-bond network of the pure-water mobile phase, which would change the solvation, and therefore retention, of non-polar solutes. The change in thermodynamic values between the two temperature regions invalidates extrapolation of retention as a function of temperature between the two temperature regions for the prediction of room-temperature pure-water retention factors. The thermodynamic changes observed as the temperature is increased are similar to those seen when mobile phase composition is changed (by adding organic modifier) at constant temperature.     

Synthesis and ionic conductivity of polymer ionic liquids

Four vinyl monomers containing a covalently bonded cation ethylimidazolium and various anions—Br^?, (CF₃SO₂)₂N^?, (CN)₂N^?, and CF₃SO ₃ ^? —have been synthesized. High-molecular-mass polymers (M _w up to 1.84 × 10⁶) having the structure of ionic liquids have been prepared via the free-radical polymerization of 1-vinyl-3-ethylimidazolium in bulk and molecular and ionic solvents. The thermal stability and heat resistance of the resulting polymer salts have been estimated. It has been demonstrated that the thermal characteristics of these salts significantly depend on the nature of anions. The glass-transition temperatures of the polymers range from 19 to 235°C. The ionic conductivity of the polymer salts and their compositions with individual ionic liquids has been studied in the frequency range 50–10⁶ Hz. The highest conductivity (1.5 × 10^?5 S/cm) is exhibited by the polymer containing the (CN)₂N^? anion.     

A molecular dynamics study and molecular level explanation of pressure dependence of ionic conductivity of potassium chloride in water

Experimental ionic conductivity of different alkali ions in water shows markedly different dependences on pressure. Existing theories such as that of Hubbard-Onsager are unable to explain these dependences on pressure of the ionic conductivity for all ions. We report molecular dynamics investigation of potassium chloride solution at low dilution in water at several pressures between 1 bar and 2 kbar. Two different potential models have been employed. One of the models successfully reproduces the experimentally observed trend in ionic conductivity of K(+) ions in water over the 0.001-2 kbar range. We also propose a theoretical explanation, albeit at a qualitative level, to account for the dependence of ionic conductivity on pressure in terms of the previously studied Levitation Effect. It also provides a microscopic picture in terms of the pore network in liquid water.     

Evaporation of ionic liquids at atmospheric pressure: study by ion mobility spectrometry

A conventional ion mobility spectrometry (IMS) was used to study atmospheric pressure evaporation of seven pure imidazolium and pyrrolidinium ionic liquids (ILs) with [Tf₂N], [PF₆], [BF₄] and [fap] anions. The positive drift time spectra of the as-received samples measured at 220 °C exhibited close similarity; the peak at reduced mobility K₀ = 1.99 cm² V⁻¹ s⁻¹ was a dominant spectral pattern of imidazolium-based ILs. With an assumption that ILs vapor consists mainly of neutral ion pairs, which generate the parent cations in the reactant section of the detector, and using the reference data on the electrical mobility of ILs cations and clusters, this peak was attributed to the parent cation [emim]. Despite visible change in color of the majority of ILs after the heating at 220 °C for 5 h, essential distinctions between spectra of the as-received and heated samples were not observed. In negative mode, pronounced peaks were registered only for ILs with [fap] anion.     

Enhanced stability and sensitivity of ionic liquid-carbon paste electrodes at elevated temperatures

We describe the operation of ionic liquid-carbon paste electrodes at elevated temperatures and the effect of heating on the electrode performance and response. Using cyclic and square wave voltammetry and amperometry, it is shown that signals can be enhanced and stabilized by increasing the temperature of the operating solution. At low temperature, the electrode was susceptible to electrode fouling and showed poor stability, sensitivity, and linearity. An order of magnitude improvement of response for ascorbic acid was possible by operating the electrode at 60 degrees C compared to 0 degrees C. This study represents the first report showing that the analytical response of ionic liquid-carbon paste electrodes can be improved by operating them at elevated temperatures for a number of applications.     

Vibrational relaxation of liquid dichloromethane at high pressure

The Raman spectra of two symmetric bands ν₁ and ν₃ of CH₂Cl₂ have been measured as a function of pressure to 300 MPa (3 kbar) and over the temperature range 303–363 K. For all bands the isotropic width increases with inreasing pressure and temperature. The experimental vibrational relaxation times are compared with the predictions of different combination of mass factors using the Fischer—Laubereau vibrational dephasing model.     

The liquid-glass and liquid-liquid transitions of TPP at elevated pressure

We studied the polyamorphism of the liquid triphenyl phosphite by means of broadband dielectric spectroscopy at ambient and elevated (p=500 MPa) pressures. The effect of pressure on fragility, liquid-liquid phase transition, and its kinetics is discussed in relation to the two-order-parameter model proposed by Tanaka. The experimental evidence in support of this model is presented.