Infrared optical constants of highly diluted sulfuric acid solution droplets at cirrus temperatures

Complex refractive indices for supercooled sulfuric acid solution droplets in the mid-infrared spectral regime (wavenumber range 6000-800 cm(-1)) have been retrieved for acid concentrations ranging from 33 to 10 wt % H2SO4 at temperatures between 235 and 230 K, from 36 to 15 wt % H2SO4 at temperatures between 225 and 219 K, and from 37 to 20 wt % H2SO4 at temperatures between 211 and 205 K. The optical constants were derived with a Mie inversion technique from measured H2SO4/H2O aerosol extinction spectra that were recorded during controlled expansion cooling experiments in the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. The new data sets cover a range of atmospherically relevant temperatures and compositions in the binary sulfuric acid/water system for which infrared refractive indices have not been published so far, namely, the regime when supercooled H2SO4/H2O solution droplets at T < 235 K are subjected to an environment that is supersaturated with respect to the ice phase. With increasing ice supersaturation, the H2SO4/H2O aerosol particles will continuously dilute by the uptake of water vapor from the gas phase until freezing of the solution droplets eventually occurs when the acid concentration has dropped below a critical, temperature-dependent threshold value. With the aid of the new measurements, the homogeneous freezing process of supercooled H2SO4/H2O solution droplets at cirrus temperatures can be quantitatively analyzed by means of Fourier transform infrared spectroscopy, thereby overcoming a major drawback from previous studies: the need to use complex refractive indices that were measured at temperatures well above 235 K to deduce the composition of the low-concentrated H2SO4/H2O aerosol particles. As in the case of the complex refractive indices for sulfuric acid solutions with acid concentrations greater than 37 wt % H2SO4, the new low-temperature optical constants for highly diluted droplets also reveal significant temperature-induced spectral variations in comparison with the refractive indices for higher temperatures, which are associated with a change in the equilibrium between sulfate and bisulfate ions.     

A diffusive anomaly of water in aqueous sodium chloride solutions at low temperatures

Molecular dynamics simulations are presented for the self-diffusion coefficient of water in aqueous sodium chloride solutions. At temperatures above the freezing point of pure water, the self-diffusion coefficient is a monotonically decreasing function of salt concentration. Below the freezing point of pure water, however, the self-diffusion coefficient is a non-monotonic function of salt concentration, showing a maximum at approximately one molal salt. This suggests that sodium chloride, which is considered a structure-making salt at room temperature, becomes a structure-breaking salt at low temperatures. A qualitative understanding of this effect can be obtained by considering the effect of ions on the residence time of water molecules near other water molecules. A consideration of the freezing point depression of aqueous sodium chloride solutions suggests that the self-diffusion coefficient of water in supercooled sodium chloride solutions is always higher than that in pure (supercooled) water at the same temperature.     

Infrared and Raman spectra of crystalline para-bromoaniline at low temperatures

The polarization characteristics of the i.r. absorption bands of oriented p-bromoaniline crystal films have been studied at low temperatures. Raman spectra of this compound in solution and in the polycrystalline state have been recorded as an aid to the vibrational assignment of the crystal bands. The vibrational spectra are interpreted to deduce the crystal factor group (D_2h) and the molecular site symmetry (C_s). The observed factor group splittings and dichroic ratios suggest the crystal unit cell of p-bromoaniline to be isostructural with that of p-chloroaniline.     

Enthalpy of crystallization of lithium chloride from aqueous solution at 25°C

The enthalpies of crystallization of LiCl and LiCl·H₂O from aqueous solutions at 25°C are reported as measured by a calorimetric method and derived from the previously published concentration dependence of the enthalpy of solution data. The results are compared with those obtained from the concentration dependence of activity coefficients and from the temperature dependence of solubilities.     

Investigating the adhesion of water droplets at low temperatures

Adhesion of droplets to solid surfaces at low temperatures is crucial for antifogging and antifreezing, etc. So far, most reports on adhesion measurements have been carried out in air-liquid-solid systems, but it remains difficult to precisely investigate the adhesion at low temperatures due to the uncontrollable condensation. On the basis of the liquid-liquid-solid system, a new method to measure the adhesion of water droplets at low temperatures was developed and employed. Moreover, the reported method could be viable in other liquid-liquid-solid systems with wider temperature window; thus, it will find applications in broad fields such as crude oil recovery, ore-dressing, and transfer printing.     

Further study of individual ion activities in pure aqueous sodium chloride solution

The e.m.f. values between a chloride electrode and a reference electrode were measured in aqueous NaCl solutions between 10(-5) and 6 m, saturated KC1 and 1M KNO(3) bridges being used. The effect of the various liquid junctions is calculated and discussed. The consistency of the results is inspected, assuming either the MacInnes or the Guggenheim convention. The choice of different reference points for the standardization of the e.m.f.'s and for the activity coefficients is discussed. A comparison is made between the results obtained with an Ag/AgCl electrode of the second kind and a solid membrane chloride electrode.     

Thermodynamic and NMR study of aggregation of dodecyltrimethylammonium chloride in aqueous sodium salicylate solution

The complex aggregation processes of dodecyltrimethylammonium chloride (DTAC) have been studied in dilute solutions of sodium salicylate (NaSal) by isothermal titration calorimetry and electrical conductivity at temperatures between 278.15 K and 318.15 K. A structural transformation that was dependent on the concentrations of DTAC and NaSal was observed. The micellization process in dilute solutions of DTAC has been subjected to a detailed thermodynamic analysis and shown to occur at considerably lower critical micelle concentrations than reported for DTAC in water and NaCl solutions. Gibbs free energy, Δ _mic G ^o, and entropy, Δ _mic S ^o, were deduced by taking into account the degree of micelle ionization, β, estimated from conductivity measurements. From the temperature dependence of the enthalpy of micellization, Δ _mic H ^o, the heat capacities of micellization, D_mic c_p^o {\Delta_{{{\rm mic} }}}c_p^o were determined and discussed in terms of the removal of large areas of non-polar surface from contact with water upon micellization. The process is exothermic at all temperatures, indicating, in addition to the hydrophobic effect, the presence of strong interactions between surfactant and salicylate ions. These were confirmed by ¹H NMR spectroscopy and diffusion NMR experiments. Salicylate ions not only interact with the headgroups but also insert further into the micelle core. At c _NaSal/c _DTAC > 2.5, the structural rearrangements occur even at relatively low concentrations of NaSal.     

Sodium chloride interaction with solvated and crystalline cellulose: sodium ion affects the cellotetraose molecule and the cellulose fibril in aqueous solution

Inorganic salts are a natural component of biomass which have a significant effect on the product yields from a variety of biomass conversion processes. Understanding their effect on biomass at the microscopic level can help discover their mechanistic role. We present a study of the effect of aqueous sodium chloride on the largest component of biomass, cellulose, focused on the thermodynamic and structural effect of a sodium ion on the cellotetraose molecule and the cellulose fibril. Replica exchange molecular dynamics simulations of a cellotetraose molecule reveal a number of preferred cellulose-Na contacts and bridging positions. Large scale MD simulations on a model cellulose fibril find that Na⁺ perturbs the hydroxymethyl rotational state population and consequently disrupts the ‘native’ hydrogen bonding network.     

Optical absorption spectra of an aqueous frozen solution of neodymium chloride at various temperatures and pressures

A dilute aqueous solution of neodymium chloride NdCl₃ has been taken through two thermodynamic cycles along transformations with varying pressure (between 1 bar and 3.3 kbar) and temperature (between 300 K and 77 K). The characteristic optical line absorption spectrum which shows a Stark splitting of the Nd³⁺ electronic levels due to a quasi-crystalline surrounding of the ions appears only in that part of the cycles where pure ice I_h phase would be present. In any other part of the cycles where pure ice phases II, III, IX and I_C would be present such a phenomenon does not exist. It is shown that ice I_h may constitute a frame for neodymium aquo-ions.     

Aerosol chamber study of optical constants and N2O5 uptake on supercooled H2SO4/H2O/HNO3 solution droplets at polar stratospheric cloud temperatures

The mechanism of the formation of supercooled ternary H(2)SO(4)/H(2)O/HNO(3) solution (STS) droplets in the polar winter stratosphere, i.e., the uptake of nitric acid and water onto background sulfate aerosols at T < 195 K, was successfully mimicked during a simulation experiment at the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. Supercooled sulfuric acid droplets, acting as background aerosol, were added to the cooled AIDA vessel at T = 193.6 K, followed by the addition of ozone and nitrogen dioxide. N(2)O(5), the product of the gas phase reaction between O(3) and NO(2), was then hydrolyzed in the liquid phase with an uptake coefficient gamma(N(2)O(5)). From this experiment, a series of FTIR extinction spectra of STS droplets was obtained, covering a broad range of different STS compositions. This infrared spectra sequence was used for a quantitative test of the accuracy of published infrared optical constants for STS aerosols, needed, for example, as input in remote sensing applications. The present findings indicate that the implementation of a mixing rule approach, i.e., calculating the refractive indices of ternary H(2)SO(4)/H(2)O/HNO(3) solution droplets based on accurate reference data sets for the two binary H(2)SO(4)/H(2)O and HNO(3)/H(2)O systems, is justified. Additional model calculations revealed that the uptake coefficient gamma(N(2)O(5)) on STS aerosols strongly decreases with increasing nitrate concentration in the particles, demonstrating that this so-called nitrate effect, already well-established from uptake experiments conducted at room temperature, is also dominant at stratospheric temperatures.     

Infrared spectroscopic study on the crystallization of water in poly(vinyl methyl ether) aqueous solution during heating

The Fourier transform infrared (FTIR) results are consistent with the differential scanning calorimetric results and verify the anomalous crystallization of water in 50% poly(vinyl methyl ether) aqueous solution during heating. Below about ?34 °C, the water/polymer complex was not damaged, and the water still associated with the polymer. When heating to about ?34 °C, the associated water started to free from the unpolar (methyl group) and polar‐site (ether‐oxygen group) interaction fields of polymer gradually. Then crystallization of water was induced in this system at temperatures ranging from ?34 to ?24 °C. The FTIR data also indicate that the structure of water started to change first upon forming strong H bonds among water molecules, and then the dehydration of the polymer began to proceed subsequently when the anomalous crystallization of water occurred. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2772–2779, 2002     

Investigation of the structure of concentrated aqueous solution of LiCl at low temperatures by the method of integral equations

Peculiarities of the formation of the structure of aqueous LiCl solution (at a salt: water molar ratio of 1:5.3) in the temperature range 298-138 K were studied by the method of integral equations. Analysis of the results obtained suggests that transition of the system into the supercooled and glassy state is accompanied by an increase in the tetrahedral ordering of solvent molecules and a decrease in the number of interactions between the water molecules in unbound solvent. Lowering the temperature leads to an increase in the degree of structurization of water molecules surrounding the cation. Preferable formation of hydrogen bonds with the anion under extreme conditions was established. The glassy state of the solution is characterized by the absence of direct anion-cation correlations and increased (compared to standard conditions) probability of the formation of ion-water chains. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1881–1886, October, 1999.     

γ-Radiolysis of benzophenone aqueous solution at elevated temperatures up to supercritical condition

A product analysis study of γ-irradiated benzophenone aqueous solutions from room temperature to 400 °C has been carried out by the combination of a flow irradiation system and a liquid chromatographic method. At room temperature, the main decomposition products are phenol and hydroxybenzophenone isomers. In high temperature and supercritical water solutions, 9-fluorenone appears as an important product and the G-value of benzophenone consumption depends significantly on the water density under supercritical conditions.     

Complex formation of vinylidene chloride with hydrogen chloride in the solid phase at low temperatures

Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 170–174, March–April, 1992.     

Thermodynamic study of aqueous sodium and potassium chloride and chromate systems at the temperature 298.15 K

The solubilities of ( m₁NaCl  + m₂Na₂ CrO ₄)(aq) and ( m₁KCl  + m₂ K ₂CrO ₄)(aq) where m denotes molality have been investigated at the temperature T =  298.15 K by the physico-chemical analysis method. Only the crystallization of the simple salts NaCl, Na ₂CrO ₄·4H ₂O, KCl, and K ₂CrO ₄have been established. The ternary solutions have been simulated thermodynamically at T =  298.15 K using the Pitzer model. The necessary thermodynamic parameters (binary and ternary ion-interaction parameters, thermodynamic solubility products) have been calculated and the theoretical solubility isotherms plotted. A very good agreement is found between calculated and experimental solubility isotherms. The standard molar Gibbs energies of formationΔ_rG_m^o of solid phases crystallizing in the systems under consideration have been estimated from theory.     

Determination of electrolytic conductivity of a 0.01D aqueous potassium chloride solution at various temperatures by an absolute method

A critical study of the conductance calibration standard, 0.01D aqueous potassium chloride solution, at 0°C, 18°C, and 25°C has been made using a highly precise thermostat and temperature program, a conductance measuring assembly of comparable precision, and a new type of absolute conductance cell. In spite of the high precision with which cell constants can be determined at any one temperature, the values at differents temperatures are only compatible with a linear temperature dependence within much larger limits.     

An estimation of the surface ionization constant of oleic acid in aqueous sodium chloride solution

The zeta potential () measurements and the site binding theory were utilized for calculations of the parameters of the electrical double layer (edl), ionization, and complexation constants for oleic acid-aqueous sodium chloride solution interface. Assuming that is equal to the diffuse layer potential ( _d ) of the edl, the charge of the diffuse part of the edl was calculated from the Gouy-Chapman equation. The intrinsic ionizaiton constant was then determined by an extrapolation method to be . Subsequently, the surface potential ( ₀) was calculated, and it was found that ₀ changes by 50 mV per pH unit (50 mV/pH) or 42.5 mV/pH for 10^–3 and 10^–2 M NaCl, respectively. For further calculations, the integral capacity of the outer zone of the compact part of the edl was assumed to be for both ionic strengths. It was established that the intrinsic complexation constant for the binding of Na⁺ ions with the surface of oleic acid ispK _Na ^int = 2.9±0.5 if the integral capacity of the inner zone of the compact edl (K ₁) is 80 for 10^–3 M NaCl, but 280 for 10^–2 M NaCl. The use of the sameK ₁ value for both ionic strengths gives a differentpK _Na ^int for different NaCl concentrations, and also provides unrealistic surface charge ( _o ) values greaterfor 10^–3 M NaCl than for 10^–2 M NaCl, at the same pH of the solution.