Low-density liquids

In such two-phase systems, a higher pressure increases the solubility of the gas in the liquid phase. The changes in the solution itself are similar to those which occur when a low-density liquid is mixed with a high-density solvent the volume of the solution increases and its density and internal pressure decrease. Ill (see Figure la). These effects are opposite to those observed in condensed singlephase systems, in which a pressure increase causes a volume decrease and a density increase /2,3/ (see Figure 1 b). 

Careful cooling of pure water at atmospheric pressure can result in water that is able to remain liquid to at least 38 °C below its normal freezing point (0 °C) without crystallizing. This supercooled water is metastable and will crystallize rapidly upon being disturbed. The lower the temperature of the supercooled water, the more likely that ice will nucleate. Bulk water can be supercooled to about — 38 °C (Ball, 2001 Chaplin, 2004). By increasing the pressure to about 210 MPa, liquid water may be supercooled to — 92 °C (Chaplin, 2004). A second critical point (C ) has been hypothesized (Tc = 220 K and Pc = 100 MPa), below which the supercooled liquid phase separates into two distinct liquid phases a low-density liquid (LDL) phase and a high-density liquid (HDL) phase (Mishima and Stanley, 1998 Poole et al., 1992 Stanley et al., 2000). Water near the hypothesized second critical point is a fluctuating mixture of LDL and HDL phases. 

Langmuir, in 1917, constructed the film balance for the measurement of the surface or spreading pressure. Thus, it became possible to experimentally observe that adsorbed films pass through several states of molecular arrangement. The various states resemble that of a two-dimensional gas, a low-density liquid, and finally a higher density or condensed-liquid state. In the latter case the spreading pressure can be described by the linear relationship,... 

Supercritical solutions can be regarded as dense solvating gasses or low-viscous low-density liquids. The most well-known and probably most interesting candidate is based on carbon dioxide. Supercritical carbon dioxide can be regarded as an organic solvent. Various concepts have been developed using supercritical flu-... 

E. Wasserman (The DuPont Company, U.S.A.). When you talk about the possible phases of something like C60 (is it a gas, a liquid or a low density liquid of high compressibility), we really have to compare it with another phase which may be accessible under the same temperature and pressure conditions. In many such cases, some of the features of C60 are due to intermolecular interactions, in some of the more condensed phases, rather than to individual molecular properties that you were concentrating on. For example, the very strong tenacity of one C60 molecule to bond to another, as well as to incorporate solvent molecules in the interstitial spaces, depends critically on how well they seem to fit together, as well as to the intrinsic forces that may be found in smaller molecules. We find that if you have small degrees of substitution of C6, for example, alkyl groups, the volatility increases dramatically. 

Raman spectra for the sample were conducted in a compression-decompression cycle. In this experiment, the crystalline diffraction began to disappear above 7-8 GPa during compression, and pressure-induced amorphization was indicated by the Raman spectra above 13 GPa (Fig. 14). The resultant HDA Si exhibits the Raman spectrum that differs from the spectrum of normal -Si (LDA Si). Rather, the characteristics of the spectrum for HDA Si resemble those of the (3-tin crystal, which indicates that HDA Si has a (locally) analogous structure to the (3-tin structure. The synthesis of the HDA form of Si by Deb et al. [263] has a strong resemblance to that of water (ice) by Mishima et al. [149, 196]. Whereas compression induced amorphization that was almost completed at 13-15 GPa, decompression induced an HDA-LDA transition below 10 GPa, which is clearly shown in the Raman spectra (Fig. 14). This is the first direct observation of an amorphous-amorphous transition in Si. The spectrum at 0 GPa after the pressure release exhibits the characteristic bands of tetrahedrally coordinated -Si (LDA Si). Based on their experimental findings Deb et al. [263] discussed the possible existence of liquid-liquid transition in Si by invoking a bond-excitation model [258, 259]. They have predicted a first-order transition between high-density liquid (HDL) and low-density liquid... 

Some indirect experimental evidence exists for the liquid-liquid critical point hypothesis from the changing slope of the melting curves, which was observed for different ice polymorphs (30, 31). A more direct route to the deeply supercooled region, by confining water in nanopores to avoid crystallization, has been used more recently by experimentalists. These researchers applied neutron-scattering, dielectric, and NMR-relaxation measurements (32-35). These studies focus on the dynamic properties and will be discussed later. They indicate a continuous transition from the high to the low-density liquid at ambient pressure. The absence of a discontinuity in this case could be explained by a shift of the second critical point to positive pressures in the confinement. This finding correlated with simulations, which yield such a shift when water is confined in a hydrophilic nanopore (36). 

It has recently been pointed out by R0nne et al. [344] that the structure and dynamics of liquid water constitute a central theme in contemporary natural science [345-353]. Modem theoretical considerations are aimed at (a) a detailed description of an electronic structure model of hydrogen bonding, applied to water molecules (see, e.g., Ref. 354), (b) models that involve a certain critical temperature where the thermodynamic response functions of water diverge (see, e.g., Ref. 353), and (c) models that presuppose a coexistence between two liquid phases [344] a low-density liquid phase at the low-pressure side and a high-density liquid phase at the high-pressure side (see also Refs. 355-357). 

In addition to vapor (V), high-density liquid (L2), or low-density liquid (Li) phase behavior, reservoir fluids, oils, and other organic fluids exhibit a variety of multiphase behaviors and critical phenomena as noted in Fig. 1. These include liquid-vapor (LiV or L2V), liquid-liquid (L1L2), and liquid-liquid-vapor (L1L2V) phase behavior and associated critical phenomena. 

The designations L = V or Li = L2 mean that the two phases in question are critically identical. They possess the same values for density, composition, molar volume, viscosity, and all other physical properties, and the boundary between the phases disappears (Fig. 1). Two phases can also become critically identical in the presence of a third phase, giving rise to the so-called K and L points. A K point arises when a low-density liquid (Li) becomes critically identical to a vapor in the presence of a high-density liquid (L2). 

This is designated as Li = V + L2. An L point arises when a low-density liquid (Li) and a high-density liquid (L2) become critically identical in the presence of a vapor phase. An L point is designated as Li = L2 -f V. Tricritical points, where three phases in equilibrium are also critically identical, are designated as Li = L2 = V. Such critical points, while present in phase diagrams and phase projections, are rarely observed in practice. At low temperatures, solid phases such as asphaltenes and wax can, and frequently do, coexist with the fluid phases noted here and are discussed in later sections. 

Davenport WG, Richardson FD, Bradshaw AV (1974) Spherical cap bubbles in low density liquids. Chem Eng Sci 22 1221-1235... 

When we place a drop of appreciably non-volatile low density liquid (1) on the surface of a high density sub-phase liquid (2) which is practically immiscible with liquid (1), there are three possibilities ... 

In this subsection we follow the RAK work (see also references therein), where the dielectric (0.1-2 THz) response of liquid H20 and D20 and the low-density-liquid (LDL) and high-density-liquid (HDL) concepts were considered with respect to isotopic dependence (ID) of the water spectra. Large ID of certain properties of water is well known, while other properties (e.g., the static dielectric constant es) do not show ID. Such a behavior of water is still far from being understood at a molecular level. 

Ans. Low-density liquids (alkanes and other hydrocarbons) float on top of higher-density liquids such as water. Density, like BP, melting point (MP), and solubility, is dependent on intermolecular forces. Density increases with an increase in the number of molecules packed into a unit volume. Water molecules pack closer to each other because of their stronger intermolecular forces and this results in higher density for water. 

When there is a relative density difference p2—pi)IP2>0.05 between the jet liquid and the bulk liquid then there is a critical jet velocity, 1, below which layers of high- and low-density liquids form and no mixing occurs. Fossett and Prosser studied this phenomenon which they attributed to gravitational effects. They correlated their data by... 

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