Autoionization in liquid water

The dissociation of a water molecule in liquid water is the fundamental event in acid-base chemistry, determining the pH of water. Because of the short time scales and microscopic length scales involved, the dynamics of this autoionization have not been directly probed by experiment. Here, the autoionization mechanism is revealed by sampling and analyzing ab initio molecular dynamics trajectories. We identify the rare fluctuations in solvation energies that destabilize an oxygen-hydrogen bond. Through the transfer of protons along a hydrogen bond "wire," the nascent ions separate by three or more neighbors. If the hydrogen bond wire connecting the two ions is subsequently broken, a metastable charge-separated state is visited. The ions may then diffuse to large separations. If, however, the hydrogen bond wire remains unbroken, the ions recombine rapidly. Because of their concomitant large electric fields, the transient ionic species produced in this case may provide an experimentally detectable signal of the dynamics we report.     

Detection of first-order liquid/liquid phase transitions in yttrium oxide-aluminum oxide melts

We combine small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) with aerodynamic levitation techniques to study in situ phase transitions in the liquid state under contactless conditions. At very high temperatures, yttria-alumina melts show a first-order transition, previously inferred from phase separation in quenched glasses. We show how the transition coincides with a narrow and reversible maximum in SAXS indicative of liquid unmixing on the nanoscale, combined with an abrupt realignment in WAXS features related to reversible shifts in polyhedral packing on the atomic scale. We also observed a rotary action in the suspended supercooled drop driven by repetitive transitions (a polyamorphic rotor) from which the reversible changes in molar volume (1.2 +/- 0.2 cubic centimeters) and entropy (19 +/- 4 joules mole(-1) kelvin(-1)) can be estimated.     

Droplet impacts upon liquid surfaces

The absorption and rebounding of single droplets and streams of droplets (of diameter less than 1200 micrometers) impacting upon the surface of a deep liquid have been examined experimentally. Conservation of mechanical energy and momentum have been used to explain rebounding droplet interactions, and impaction criteria have been established regarding the absorption of droplet streams. Surface tension is the dominant mechanism governing the observed behavior. Single droplets were never observed to rebound.     

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Lambda transition in liquid sulfur

Density measurements on liquid sulfur near the transition at 160 degrees C show a logarithmic singularity and discontinuous density. The transition shows the kinetic behavior of a zero-order reaction. The transition is expected to have a latent heat characteristic of a first-order phase transition but is of the cooperative nature associated with second-order transitions such as the lambda point in liquid helium.     

High-performance liquid chromatography of biopolymers

The ability to separate biological macromolecules with good resolution on liquid chromatographic columns has depended on the development of suitable packing materials. In size exclusion chromatography, molecules are separated by size on the basis of differential permeation of the packing. Ion exchange, hydrophobic interaction (or reversed-phase), and affinity chromatography are all surface-mediated separation methods, although they depend on different retention mechanisms. High-performance liquid chromatographic columns designed for biopolymers offer major advantages over conventional columns in both speed and resolving power. The exponential growth of literature on the high-performance separation of peptides and proteins in particular indicates that the technique will become the dominant form of column liquid chromatography.     

Polarization-modulated smectic liquid crystal phases

Any polar-ordered material with a spatially uniform polarization field is internally frustrated: The symmetry-required local preference for polarization is to be nonuniform, i.e., to be locally bouquet-like or "splayed." However, it is impossible to achieve splay of a preferred sign everywhere in space unless appropriate defects are introduced into the field. Typically, in materials like ferroelectric crystals or liquid crystals, such defects are not thermally stable, so that the local preference is globally frustrated and the polarization field remains uniform. Here, we report a class of fluid polar smectic liquid crystals in which local splay prevails in the form of periodic supermolecular-scale polarization modulation stripes coupled to layer undulation waves. The polar domains are locally chiral, and organized into patterns of alternating handedness and polarity. The fluid-layer undulations enable an extraordinary menagerie of filament and planar structures that identify such phases.     

Photocontraction of liquid spiropyran-merocyanine films

Amorphous films of a photochromic spiropyran containing a mesogenic group melt, when exposed to heat together with irradiation, to yield a red fluid. This fluid contains aggregates of merocyanine molecules and exhibits marked contraction under light illumination. The mechanism of the photocontraction is dependent upon a specialized microstructure, which may be termed a "quasi-liquid."     

Electrically supported column of liquid

Applicctiont of an electric field normal to the interface of certain liquids causes a liquid column of uniform diameter to be formed parallel to the electric field. A column of amyl alcohol supported in aim by a high voltage was investigated experimentally; the diameter of the column varied aS the voltage raised to the 3.5 power.     

Giant supramolecular liquid crystal lattice

Self-organized supramolecular organic nanostructures have potential applications that include molecular electronics, photonics, and precursors for nanoporous catalysts. Accordingly, understanding how self-assembly is controlled by molecular architecture will enable the design of increasingly complex structures. We report a liquid crystal (LC) phase with a tetragonal three-dimensional unit cell containing 30 globular supramolecular dendrimers, each of which is self-assembled from 12 dendron (tree-like) molecules, for the compounds described here. The present structure is one of the most complex LC phases yet discovered. A model explaining how spatial arrangement of self-assembled dendritic aggregates depends on molecular architecture and temperature is proposed.     

Surface-directed liquid flow inside microchannels

Self-assembled monolayer chemistry was used in combination with either multistream laminar flow or photolithography to pattern surface free energies inside microchannel networks. Aqueous liquids introduced into these patterned channels are confined to the hydrophilic pathways, provided the pressure is maintained below a critical value. The maximum pressure is determined by the surface free energy of the liquid, the advancing contact angle of the liquid on the hydrophobic regions, and the channel depth. Surface-directed liquid flow was used to create pressure-sensitive switches inside channel networks. The ability to confine liquid flow inside microchannels with only two physical walls is expected to be useful in applications where a large gas-liquid interface is critical, as demonstrated here by a gas-liquid reaction.     

The spatial structure in liquid water

Liquid state structure has traditionally been characterized with the radial distribution functions between atoms. Although these functions are routinely available from x-ray diffraction and neutron scattering experiments or from computer simulations, they cannot be interpreted unambiguously to provide the spatial order in a molecular liquid. A direct approach to determining the spatial structure in the liquid state is demonstrated here. Three-dimensional maps representing the local atomic densities are presented for several water models. These spatial maps provide a picture of the short-range order in liquid water which reveals specific details of its local structure that are important in the understanding of its properties.     

Self-assembly of phase-segregated liquid crystal structures

Additional functionality can be incorporated into liquid crystalline materials by using phase segregation and self-assembly. Intermolecular interactions such as hydrogen bonding and ionic interactions play key roles in the formation of these complex structures. One-, two-, and three-dimensional phase-segregated structures on various scales of length are formed by self-assembly of a variety of partially incompatible molecules. Such structures can enhance anisotropic properties such as ionic conductivity.     

Rupture mechanism of a liquid film

The rupture mechanism of edge-supported liquid films appears to involve the viscous and drag energies as well as previously postulated kinetic and surface energies. Although details are obscure, the mechanism appears to involve a liquid-gathering process at the free edge, followed by fragmentation of this thickened edge into drops whose radii are approximately 50 times the film's original thickness.