Liquid structure hydrocarbons

Sham, T.-K. X-Ray Absorption Studies of Liquids Structure and Reactivity of Metal Complexes in Solution and X-Ray Photoconductivity of Hydrocarbon Solutions of Organometallics, 145, 81-106(1987). 

Theories of electron mobility are intimately related to the state of the electron in the fluid. The latter not only depends on molecular and liquid structure, it is also circumstantially influenced by temperature, density, pressure, and so forth. Moreover, the electron can simultaneously exist in multiple states of quite different quantum character, between which equilibrium transitions are possible. Therefore, there is no unique theory that will explain electron mobilities in different substances under different conditions. Conversely, given a set of experimental parameters, it is usually possible to construct a theoretical model that will be consistent with known experiments. Rather different physical pictures have thus emerged for high-, intermediate- and low-mobility liquids. In this section, we will first describe some general theoretical concepts. Following that, a detailed discussion will be presented in the subsequent subsections of specific theoretical models that have been found to be useful in low- and intermediate-mobility hydrocarbon liquids. 

On the basis of observations made on limited structural series, certain authors (e.g., Adamson, 1980) suggested that water absorption would occur by occupancy of the available free volume by water molecules. Despite its seductive intuitive character, this theory fails to explain why free-volume rich substances such as silicone rubbers, crosslinked polyethylene, or simply liquid aliphatic hydrocarbons are hydrophobic. Furthermore, experimentally determined apparent heat of dissolution values (Hs) and plasticization effects generally agree well with theoretical predic-... 

The exact shapes of the micelles are unknown, and this subject is open for discussion. Possible micellar structures could be spherical or nearly spherical over a wide range of concentrations not too far from the c.m.c. In a highly concentrated solution, the micellar shape is elongated and forms larger, nonspherical (i.e., cylindrical or lamellar) liquid structures, as illustrated in Figure 4.21. The size of a spherical micelle is determined by the length of the hydrocarbon chain in the... 

Cholesterol does not form micelles because (1) it is not amphiphilic and (2) its flat, rigid, fused-ring structure gives a solid rather than a liquid, mobile hydrocarbon phase necessary for micellar formation. Cholesterol forms mixed micelles with amphiphilic lipids and will enter monolayers. 

Chemical structure of the solute and its interactions with the solvent The structure (hydrocarbon chain length, branching, nature and location of polar functional groups) of the solute and its interactions with the solvent (solubility, complexation, micellization) have a marked effect on its adsorption. For example, it is well known from Traube s rule that for aqueous surfactant solutions the surface activity and hence the adsorption at the liquid-air interface increases with an increase in the chain length of the solute molecule. The solutes of interest, surfactants, are also capable of forming association structures in solution (micelles or reverse micelles depending on the solvent), which is a measure of their solvophobicity. 

Figure 1.1 Summary of the processes of carbon formation in the gas phase and the resulting carbon macro structures. (Hydrocarbon polymerization or decomposition can lead to interconversion of gaseous, liquid, or solid carbon precursors see also Figures 1.2 and 1.3.)...

J.K. Maranas, M. Mondello, G.S. Grest, S.K. Kiunar, P.G. Debenedetti, W.W. Graessley, Liquid structure, thermodynamics, and mixing behavior of saturated hydrocarbon polymers. 

Two aspects of solubilization which remain to be investigated, are the variation of the apparent distribution coefficient with so-lubilizate concentration in the micellar ph.ase, and the mechanism of the incorporation of solubilizate into micelle. Since a micelle is assumed to consist of a hydrocarbon core (in liquid state), and surrounded by a palisade layer of hydrophilic group. Fig. 1, the following possible ways have been suggested for the incorporation of a solubilizate in a micelle [5,74] (a) adsorption on the surface of the micelle, (b) deep or short penetration into the palisade layer, and (c) dissolution into the (liquid like) hydrocarbon core. These mechanisms of incorporation are closely related to the structure of the micelle. However, the effect of solubilizate on the structure of the micelle has not been satisfactori 1y studied in the current literature [75,76,77]. 

Sham, T. -K., X-ray absorption studies of liquids Structure and reactivity of metal complexes in solution and X-ray photoconductivity of hydrocarbon solutions of organometallics, in Topics in Current Chemistry, 145, Dewar, M. J. S., Dunitz, J. D., Hafner, K., et. al., Springer-Verlag, Berlin, 1988. 

Early deductions from observations on the macroscopic properties of micelles suggested an essentially liquid-like hydrocarbon core. Thus, for example, there was observed to be a similarity between the heat capacities [4] and compressibilities [5] of the micelles and those of the bulk hydrocarbon of which the core was composed. Mukerjee [6], however, drew attention to the irregular variation of the CMC with chain length in a homologous series of sodium alkyl sulphates which suggested a partial structuring of the core. 

Accurate equations of state for hydrocarbons are of considerable interest to the petroleum and natural gas industry, and this has fueled active research in this area. Early equations of state have used lattice or cell model descriptions. Although some of these approaches are in good agreement with experimental data, they contain adjustable parameters that cannot be determined a priori and the physical insights are clouded by several qualitative concepts such as free volume. The development of molecularly based equations of state has focused on predicting the volumetric properties of hard chain fluids. The reason for this is that the repulsive part of the potential is expected to dominate liquid structure and the effect of attractions can normally be treated as a perturbation as has been done successfully for simple liquids. 

The latter principle is demonstrated in a recent study of mixtures of linear and branched chain hydrocarbons. Mixing of two hydrocarbons can lead to a combination of liquid structure and isomeric changes. It is not possible using conventional equilibrium methods to separate the relative contributions of these processes to the excess thermodynamic properties for the mixture. Studies of the rotational isomeric process can be carried out at frequencies below 500 MHz, leaving changes in the contribution due to liquid structure to influence measurements above 1 GHz. The frequency dependent data can thus be separated and excess contributions due to rotational isomeric and liquid structure effects. In fact, it is observed that the main contribution to the excess thermodynamic functions in these mixtures arises from liquid structural contributions as proposed by Patterson rather than from rotational isomeric effects as suggested by Flory. " ... 

Alkenes are hydrocarbons that contain a carbon-carbon double bond A carbon-carbon double bond is both an important structural unit and an important func tional group m organic chemistry The shape of an organic molecule is influenced by the presence of this bond and the double bond is the site of most of the chemical reactions that alkenes undergo Some representative alkenes include isobutylene (an industrial chemical) a pmene (a fragrant liquid obtained from pine trees) md fame sene (a naturally occurring alkene with three double bonds)... 

As discussed in Sec. 4, the icomplex function of temperature, pressure, and equilibrium vapor- and hquid-phase compositions. However, for mixtures of compounds of similar molecular structure and size, the K value depends mainly on temperature and pressure. For example, several major graphical ilight-hydrocarbon systems. The easiest to use are the DePriester charts [Chem. Eng. Prog. Symp. Ser 7, 49, 1 (1953)], which cover 12 hydrocarbons (methane, ethylene, ethane, propylene, propane, isobutane, isobutylene, /i-butane, isopentane, /1-pentane, /i-hexane, and /i-heptane). These charts are a simplification of the Kellogg charts [Liquid-Vapor Equilibiia in Mixtures of Light Hydrocarbons, MWK Equilibnum Con.stants, Polyco Data, (1950)] and include additional experimental data. The Kellogg charts, and hence the DePriester charts, are based primarily on the Benedict-Webb-Rubin equation of state [Chem. Eng. Prog., 47,419 (1951) 47, 449 (1951)], which can represent both the liquid and the vapor phases and can predict K values quite accurately when the equation constants are available for the components in question. 

Hydrated bilayers containing one or more lipid components are commonly employed as models for biological membranes. These model systems exhibit a multiplicity of structural phases that are not observed in biological membranes. In the state that is analogous to fluid biological membranes, the liquid crystal or La bilayer phase present above the main bilayer phase transition temperature, Ta, the lipid hydrocarbon chains are conforma-tionally disordered and fluid ( melted ), and the lipids diffuse in the plane of the bilayer. At temperatures well below Ta, hydrated bilayers exist in the gel, or Lp, state in which the mostly all-trans chains are collectively tilted and pack in a regular two-dimensional... 

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