Incorporation Of Solvent Molecules Research Articles

Structural Organization of Water-Containing Nafion: The Integral Equation Theory

Using the mutually consistent variant of the integral equation polymer reference interaction site model (RISM) theory and the chemically realistic rotational isomeric state (RIS) model, we perform a molecular level modeling of the specific structural organization of perfluorosulfonic acid ionomer (Nafion) with certain amount of physisorbed water. Our results establish molecular scale information necessary for understanding the equilibrium structure and thermodynamics of water-containing Nafion as well as water distribution and ionic (molecular) transport phenomena in hydrated Nafion membranes. As a first step in this direction, semi-empirical, quantum mechanical calculations on the molecular structures and energies of the polymeric backbone and pendant chains of Nafion with and without additional water molecules are carried out. These data are used in the single-polymer RIS Monte Carlo simulation, in which the short-range intramolecular interactions are taken into account via appropriate matrices of statistical weights. The local structure and morphology of the entire bicomponent water-containing system is calculated consistently on the basis of the RISm theory at different contents of absorbed water. We find that the addition of even a relatively small amount of water leads to the strong intensification of aggregation processes observed for polar sulfonic acid (SO 3 H) groups. Water molecules and polar SO 3 H groups form mixed aggregates with a three-layer structure. Incorporation of water molecules inside the aggregates results in an increase of their stability and leads to the increase of the number of associating groups in a stable aggregate. With increasing the number of incorporated solvent molecules, the average size of mixed aggregates increases. The results obtained in the present study support the concept of an irregularly shaped cluster surfaces. Such geometries are favorable to the formation of long channels of connected water-containing aggregates providing the unique permeability characteristics of Nafion membranes. In addition, we investigate the clustering and continuum percolation in the water phase, using the formalism of pairconnectedness correlation functions. The mean cluster size found theoretically is in reasonable agreement with the corresponding experimental estimates existing in the literature.

Investigation of over-compressed spread l-dipalmitoyl phosphatidylcholine films and the influence of solvent vapour in the gas phase on Π/ A isotherms measured by using the captive bubble technique

Π/ A isotherms of spread l-DPPC ( l-dipalmitoyl phosphatidylcholine) layers were determined up to the over-compressed state by using the captive bubble method. The influence of solvent vapour in the gas phase on the interfacial behaviour of monolayers was studied as traces of the spreading solution usually stay in the bubble. This was done for two cases; the pendant drop technique with spread 1-monoglyceride monolayer, where the partial pressure of solvents remains constant, and the captive bubble with spread l-DPPC layers, where the partial pressure increases during monolayer compression. Two cases of spreading solvents are distinguished: solvents, which do adsorb at the interface (chloroform), and those, which do not (heptane). Using a model, which takes into account only a small number of accessible parameters, the influence of none adsorbing solvents can be sufficiently described by an increasing cohesion pressure when the partial pressure remains constant. The influence of polar solvents may be quantified by a factor, which considers the apparent increase of the minimum molecular area demand. Spread DPPC monolayers determined by the captive bubble technique show a plateau in the range of about 50 mN m −1, which depends on the amount of spreading solvent in the atmosphere of the bubble. By monolayer compression, the solvent molecules are squeezed out of the monolayer. Over-compression of the DPPC monolayer occur when all solvent molecules are removed and the surface tension further decreases down to almost zero. In contrast to monolayer collapse the surface pressure do not decrease abruptly for DPPC-layer expansion. This was explained by a monolayer-folding. Both, the process of squeezing out solvent molecules and the over-compression are accompanied by an apparent loss of DPPC molecules, indicated by a shift of the Π/ A isotherms to higher surface coverage. Monolayer cycling leads to a stepwise decrease of solvent molecules in the bubble atmosphere. The solvent molecules are assumed to be irreversibly incorporated into collapsed and lamellar structures, which may be formed by monolayer folds. Over-compressed collapsed or folded structures may be packed together and removed from the interface by forming visible particles. Lamellar structures are discussed as preliminary forms of liposomes, which may also incorporate solvent molecules, remove them during monolayer expansion from the interface, and causing an apparent loss of lipid molecules.

The role of anions, solvent molecules and solvated electrons in layer formation processes on anode materials for rechargeable lithium batteries

Abstract The reactivity of anions, solvent molecules and solvated electrons against anode materials are coupled in a given electrolyte solution. The ratio between anion and solvent decomposition depends on the potential and the electrolyte composition. The life time of trapped solvated electrons within the growing SEI layer depends on the donor–acceptor properties of the incorporated solvent molecules and is in the range among 3–10 s. The places of the trapped electrons are the origin of `metallic' lithium clusters within the forming layer. Their growth will lead to the well-known lithium dendrites on lithium–metal or the progressive irreversible capacity loss on lithium–carbons and therefore causes a lot of problems. Suggestions will be made how to solve these problems in order to achieve a homogeneous SEI with a reduced dendrite growth or decreased irreversible capacity loss.

Novel organic metals based on nonplanar Bis(1,3-Dithiole) donors

Novel nonplanar bis(1,3-dithiole) donors with small on-site Coulomb repulsion afforded unusual cation radical salts as single crystals whose properties were strikingly affected by the incorporated solvent molecules.

Structures of the multireceptor vaulted cyclidene complexes

The preparations and structures of three vaulted cyclidene complexes are compared with the two previously reported. All show similar structures with large rigid cavities partly closed off by the piperidine risers, illustrating in particular the attractive effect of van der Waals forces resulting in the incorporation of solvent molecules or [PF 6] − ions nesting on the edges of the cavities. However, the detailed geometries vary, according to the nature of the ligand substituents, the metal, the counter-ion and the lattice solvent molecules. These give rise to differing orientations of the capping aromatic rings and the piperidine risers.

Structures and complexing properties of crown ethers incorporating 1,8-dioxyxanthones

The X-ray crystal structures of three crown ethers containing the 1,8-dioxyxanthone residue are reported. 1,8-[(3,6,9-Trioxaundecane-1,11-diyl)dioxy]xanthone, 1(n= 3), and 1,8-[(3,6,9,12,15-pentaoxaheptadecane-1,17-diyl)dioxy]xanthone, 1 (n= 5), have been crystallized from acetonitrile and their crystals shown to incorporate acetonitrile. Crystals of the former also contain water which forms a tight hydrogen-bonded bridge between the xanthone carbonyl oxygen and the most remote oxygen of the 18-membered macrocycles. Crystals of 1,8-[(3,6,9,12-tetraoxatetradecane-1,14-diyl)dioxy]xanthone, 1 (n= 4), from toluene do not incorporate solvent molecules.

Unusual cation radical salts of non-planar bis(1,3-dithiole) donors incorporating solvent molecules

Novel non-planner bis(1,3-dithiole) donors showing one-stage two-electron oxidation afford unusual cation radical salts as single crystals, whose properties are strikingly affected by the incorporated solvent molecules.

Solvent intercalation in cobalt dimethylglyoximato complexes: A miniature host-guest system

When crystallized from appropriate solvents, the complex aqua-bis(dimethylglyoximato)nitrocobalt (III) may incorporate solvent molecules, thus forming a variety of mixed crystals. In the resulting host-guest crystals, the space groupP2l/m and the packing motif of the pure host compound are retained. Lattice constantsa andb remain essentially unaltered upon intercalation, whereasc and the monoclinic angleΒ depend largely on the clathrated guest. Space filling and intermolecular contacts are discussed.

The Effect of Solvation in Conducting Polymers

Abstract The incorporation of solvent molecules into solid-state organic conductors affects both electrical and mechanical properties of the conducting complexes. Evidence for this has been appearing from the numerous laboratories currently involved in conducting polymer research. On compiling these examples, common rationale for the observed effects can be formulated based largely on the behavior of smaller molecules as found in the organic literature. Nonetheless, the examples must be considered on a case-to-case basis. In assigning the source of solvent effects, the determination of whether solvation is occurring on the charged polymer backbone or on the (oppositely charged) dopant counterion is critical. Among the proposed causes of solvent effects are solvent-separated ion pairing, charge depinning, and plasticization.

Paramagnetic complexes of benzidine

1. Incorporation of solvent molecules in the crystalline complex of benzidine (B) with tetracyanoquinomethane (TCQ): B-TCQ, affects the value of the charge transfer energies as a function of the change in the B-TCQ interplanar distances. The decrease in the charge transfer energies is due to the formation of a H bond in the excited state of the complex. 2. The paramagnetism of B-TCQ complexes is primarily determined by the TCQ−· anion radicals which arise during the electron transfer reaction.

Nitration of Hexamethylbenzene and Hexamethylbenzene-d18 in Acetic Acid. Deuterium Isotope Effect on the Product Distribution. Mechanism of Side-chain Substitution of Arenes

Abstract The reaction in acetic acid of hexamethylbenzene and hexamethylbenzene-d18 with nitric acid in the dark has been investigated under various conditions using a high-pressure liquid chromatographic method. Pentamethylbenzyl nitrate, pentamethylphenylnitromethane, pentamethylbenzyl acetate, and pentamethylbenzyl alcohol were formed immediately after the mixing of reactants; their relative amounts remained almost unchanged up to nearly 50% conversion. The addition of sodium nitrite gave little influence on the composition of the product mixture, while urea was found to depress somewhat the formation of nitromethane. In the presence of lithium nitrate, the reaction was modestly accelerated and the nitrate formation seems to be slightly favored over the nitromethane formation. Hexamethylbenzene-d18 reacted with nitric acid at the same rate as the non-labeled hydrocarbon did, but the benzyl nitrate/phenylnitromethane ratio in the product mixture was considerably higher in the former. Based on the quantitative data obtained, the mechanism for the side-chain substitution has been discussed in terms of the SN1′ pathway: nitronium ion makes an ipso attack on the substrate to form the arenium ion, which releases a proton from the activated methyl group para to the site of attack to give the 3-methylene-6-nitro-1, 4-cyclohexadiene intermediate (7). Heterolytic fission of the C–N bond in 7 will form a benzyl cation-nitrite anion pair, which recombines at the benzylic carbon atom via a C–N bond or via a C–O bond, giving benzyl nitrite or phenylnitromethane, respectively. Benzyl nitrite will be further converted into benzyl nitrate and benzyl alcohol, while benzyl acetate will arise from the incorporation of solvent molecules into the ion-pair.

Loss of Solvent from a Molecular Crystal Solvate. Phenylazotribenzoylmethane Hemietherate

Abstract In a study(1) of the rearrangement in the solid state of phenylazotribenzoylmethane (I) it was discovered that this compound crystallizes from diethyl ether as an etherate (II) with the approximate composition (C6H5CO)3CN[dbnd]NC6H5 · ½[(C2H5)2O]; the ether was lost when the crystals stood for long periods at room temperature. Although many molecules of intermediate size crystallize with the incorporation of solvent molecules,(2) little is known about the loss of solvent from such solvates or the structure remaining after the solvent loss. Since the “de-etherated etherate” remaining after the loss of ether from II might show unusual chemical behavior an investigation of the structure of the etherate and the mechanism of loss of ether from single crystals has been undertaken.

Effect of Ion Pairing on the g Value of the Naphthalene Anion Radical

Measurements have been made of the g values of the naphthalene radical anion associated with several alkali-metal cations at a series of temperatures and in different solvents. It has been suggested previously that the temperature dependences of the g factors of spectra exhibiting alkali-metal splittings can be explained either in terms of equilibrium changes between two paired species (Hirota model) or in terms of changes in the populations of the vibrational energy levels of a paired species of fixed electronic structure (Atherton–Weissman model). Evidence is presented to show that the Hirota model adequately accounts for the g-factor variations of the sodium naphthalenide ion pair in tetrahydrofuran, but not for the cesium naphthalenide ion pair in 1,2-dimethoxyethane. It is argued that the latter ion pair is probably a tight ion pair which does not incorporate solvent molecules, and that the variations of the spectral parameters of such complexes are best described by the Atherton–Weissman model.

Tetraphenylborate derivatives of titanium(III)

Three new titanium(III) compounds which incorporate solvent molecules have been prepared by replacing the chlorido ligand of cp2TiCl by the non-coordinating group BPh4-. The new compounds are formulated as [cp2Ti(H2O)3]2[BPh4]2, [cp2Ti(N≡CCH3)2]BPh4, and [cp2Ti(py)2]BPh4. The methyl cyanide and pyridine complexes are monomeric and show the normal paramagnetic behaviour of isolated titanium(III) compounds, but the aquo derivative is dimeric with magnetic interaction between titanium atoms.

Friction and Adhesion of Clean and Contaminated Mica Surfaces

In order to determine the shear strength of boundary lubricants it is essential to use a substrate which is smooth on a molecular scale. An apparatus is described in which it is possible to apply normal and tangential loads to sheets of mica covered with monomolecular layers of boundary lubricant. The shear strength obtained from these experiments explains in part why frictional force and pickup are not reduced proportionately, in the presence of a boundary lubricant. The remaining difference is probably due to elastic hysteresis losses in the sliding solids. The surface energy of mica in air has also been measured by determining the force necessary to propagate a crack in the material. Cycles of opening and closing the crack have been performed and the difference in energy which is observed is attributed to the adsorption and migration of an interfacial film of air or water vapor. An electronmicrographic study of the structure of monolayers deposited by retraction from nonpolar solution is also described. This indicates that the area covered by the monolayer is only about ⅓ the total surface area. This poor coverage arises from incorporation of solvent molecules in the monolayer, which later evaporate.