Stretched water

The addition of a small quantity of electrolyte (such as minerals dissolved from adjacent soil particles) increases surface tension. A small quantity of soluble organic compound (alcohol, soap, or acid) decreases the surface tension. The addition of glycerine to water reduces surface tension and thus makes it possible to stretch water him into bubbles, as with a child s bubble-blowing game. 

FIGURE 12.31 Differential scanning calorimeter endotherms of oriented and collapsed fiber at different levels of orientation stretch. Water was added to the fiber to depress the melting point and prevent thermal degradation. (From Frushonr, B.G., Polym. Bull. 4, 305, 1981.)... 

As discussed in Section IV.A, a step further has been recently achieved by Davitt et al. [55], who used the acoustic method to stretch water, and measured simultaneously two physical quantities of the metastable liquid the density with the FOPH, and the sound velocity with a time-resolved Brillouin scattering experiment. They were thus able to obtain the EoS down to —26 MPa at 23.3°C. They found that the EoS is compatible with the standard extrapolation of the positive pressure data [25,26]. 

Figure 16-10. HRTEM images of single molecular chains in the order structure of the stretched water-swollen gel lihns at the drawing ratio of 2.0 of (a) a-chitin and (b) cellulose/a-chitin (25/75) blend. The double arrows indicate the stretching direction...

In some cases, water may not be free because of two different constraints It may exist in very small clusters centered on hydrophilic groups or ions, clusters too small to form a nucleus for ice formation. In some cases, stretched water may not freeze because of its extreme viscosity at low temperatures, which yields vitrified wafer insfead of ice crystals since diffusion rather than nucleation becomes the rate-limiting step [184-186]. In some biological microstructures, non-freezing water is in a metastable viscous state [187]. Stretched water has an increased local partial molar volume owing to interaction with surfaces. 

Interfacial water exists in biopolymers in two states stretched water, which has expanded and thus increased its local partial molar volume, and compacted water, whose local partial molar volume has decreased. Compacted water is in the closest proximity to the surface. These changes in density are accompanied by changes in water-water hydrogen bond strength and therefore by changes in all physical and chemical properties of the liquid. 

Water can be supercooled to -39.5 °C at a pressure of one atmosphere, if ice nucleation and impurities are prevented. Water can also remain liquid if its pressure is lowered below its freezing point, at fixed temperature this is called stretched water. Compared with other supercooled and stretched materials, water has two anomalous properties the heat capacity and the isothermal compressibility grow large as the temperature approaches -45 °C (see Figure 29.18). Such divergences often indicate a phase transition. The microscopic origins of this behavior are not yet understood 8J. 

Netz, P. A., Starr, R, Barbosa, M. C. Stanley, H E. (2004). Computer simulation of dynamical anomalies in stretched water, Brazilian Journal of Physics 34 24. 

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

As a point of interest, it is possible to form very thin films or membranes in water, that is, to have the water-film-water system. Thus a solution of lipid can be stretched on an underwater wire frame and, on thinning, the film goes through a succession of interference colors and may end up as a black film of 60-90 A thickness [109]. The situation is reminiscent of soap films in air (see Section XIV-9) it also represents a potentially important modeling of biological membranes. A theoretical model has been discussed by Good [110]. 

To date, the IR-CRLAS studies have concentrated on water clusters (both FI2O and D2O), and methanol clusters. Most importantly, these studies have shown that it is in fact possible to carry out CRLAS in the IR. In one study, water cluster concentrations in the molecular beam source under a variety of expansion conditions were characterized [34]- hr a second study OD stretching bands in (020) clusters were measured [35]. These bands occur between 2300... 

Figure Bl.5.15 SFG spectrum for the water/air interface at 40 °C using the ssp polarization combination (s-, s- and p-polarized sum-frequency signal, visible input and infrared input beams, respectively). The peaks correspond to OH stretching modes. (After [ ].)...

Figure Bl.22.8. Sum-frequency generation (SFG) spectra in the C N stretching region from the air/aqueous acetonitrile interfaces of two solutions with different concentrations. The solid curve is the IR transmission spectrum of neat bulk CH CN, provided here for reference. The polar acetonitrile molecules adopt a specific orientation in the air/water interface with a tilt angle that changes with changing concentration, from 40° from the surface nonnal in dilute solutions (molar fractions less than 0.07) to 70° at higher concentrations. This change is manifested here by the shift in the C N stretching frequency seen by SFG [ ]. SFG is one of the very few teclnhques capable of probing liquid/gas, liquid/liquid, and even liquid/solid interfaces.

Intensive use of cross-terms is important in force fields designed to predict vibrational spectra, whereas for the calculation of molecular structure only a limited set of cross-terms was found to be necessary. For the above-mentioned example, the coupling of bond-stretching (f and / and angle-bending (B) within a water molecule (see Figure 7-1.3, top left) can be calculated according to Eq. (30). 

One can start building up a list of MM3 parameters by use of the TINKER analyze command. Don t expect to build up the entire set, which occupies about 100 pages in the MM3 user s manual, but do obtain a few representative examples to get an idea of how a parameter set is constr ucted. From previous exercises and projects, you should have input and output geometries for an alkene, an alkane, and water. From these, the object is to determine the stretching and bending parameters for the C—C, C=C, C—H, and O—H bonds. The C—H bond parameters are not the same... 

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

The second ceUulosic fiber process to be commercialized was invented by L. H. Despeissis (4) in 1890 and involved the direct dissolution of cotton fiber in ammoniacal copper oxide Uquor. This solvent had been developed by M. E. Schweizer in 1857 (5). The cuprammonium solution of ceUulose was spun into water, with dilute sulfuric acid being used to neutralize the ammonia and precipitate the ceUulose fibers. H. Pauly and co-workers (6) improved on the Despeissis patent, and a German company, Vereinigte Glanstoff Eabriken, was formed to exploit the technology. In 1901, Dr. Thiele at J. P. Bemberg developed an improved stretch-spinning system, the descendants of which survive today. 

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