Mobile polar liquids

The term cracking at simultaneous action of stress and environment was introduced for the description of polymers (mainly polyethylenes) brittle fracture, which are present in a stressed state in the presence of mobile polar liquids. It was shown [1], that, what all is said and done, for material strength at this fracture mode is responsible the weakest amorphous part of semi-ciystalline polymer. This allows to connect occurring at cracking phenomenon with polar liquid diffusion into amorphous regions. 

The existence of the so-called microwave effect has not been proved. It does, however, seem to have been demonstrated that overheating of polar liquids [17] occurs and that hot spots are present in heterogeneous systems, especially at the interface [38]. Similarly, microwave irradiation results in an increase in the molecular mobility in solids [5 b]. 

Reinitzer discovered liquid crystallinity in 1888 the so-called fourth state of matter.4 Liquid crystalline molecules combine the properties of mobility of liquids and orientational order of crystals. This phenomenon results from the anisotropy in the molecules from which the liquid crystals are built. Different factors may govern this anisotropy, for example, the presence of polar and apolar parts in the molecule, the fact that it contains flexible and rigid parts, or often a combination of both. Liquid crystals may be thermotropic, being a state of matter in between the solid and the liquid phase, or they may be lyotropic, that is, ordering induced by the solvent. In the latter case the solvent usually solvates a certain part of the molecule while the other part of the molecule helps induce aggregation, leading to mesoscopic assemblies. The first thermotropic mesophase discovered was a chiral nematic or cholesteric phase (N )4 named after the fact that it was observed in a cholesterol derivative. In hindsight, one can conclude that this was not the simplest mesophase possible. In fact, this mesophase is chiral, since the molecules are ordered in... 

Reverse phase HPLC describes methods that utilize a polar mobile phase in combination with a nonpolar stationary phase. As stated above, the nonpolar stationary phase structure is a bonded phase—a structure that is chemically bonded to the silica particles. Here, typical column names often have the carbon number designation indicating the length of a carbon chain to which the nonpolar nature is attributed. Typical designations are C8, C18 (or ODS, meaning octadecyl silane), etc. Common mobile phase liquids are water, methanol, acetonitrile (CH3CN), and acetic acid buffered solutions. 

Mobile Phases. There are few requirements the mobile liquid must meet it should (1) be a good solvent for the sample (2) have a low viscosity, like any LC solvent (3) wet the stationary phase and, if possible, help deactivate it and (4) be compatible with the detector being used. For soft gels, it must also cause the gel to swell. In general, polar liquids like water, THF, and chloroform are used. 

Liquid-Liquid Chromatography. Liquid-liquid chromatographic (LLC) separations result from partitioning of solute (analyte) molecules between two immiscible liquid phases (10). The liquid mobile and liquid stationary phases ideally have little or no mutual solubility. The stationary liquid phase is dispersed on a column of finely divided support. The use of a nonpolar mobile phase and a polar stationary phase is referred to as normal phase LLC. Under these conditions, less polar solutes are preferentially eluted from the column. Reverse phase chromatography employs a nonpolar stationary phase and a polar mobile phase. Generally, polar compounds elute more rapidly with this technique. Reverse phase chromatography, useful for the separation of less polar solutes, has found increased application in occupational health chemistry. It is optimally suited to the separation of low-to-medium molecular weight compounds of intermediate polarity. 

Most methods for determining the electron mobility use pulse radiolysis techniques in which the concentration of electrons is followed during or after the ionizing pulse, either by the time-of-flight method or by measurement of the change in conductivity. However, due to the inherent conductance of polar liquids, direct conductivity measurements of solvated electrons are generally difficult in these media. Therefore, the diffusion coefficient and the mobility of the solvated... 

Partition chromatography is categorized as either GLC or liquid-liquid chromatography (LLC). LEG is further categorized as either normal phase or reversed phase. For normal-phase LLC a polar liquid is used as the stationary phase, and a relatively nonpolar solvent or solvent mixture is used as the mobile phase. In reversed-phase partition chromatography, the stationary phase is nonpolar, and the mobile phase is relatively polar. ... 

Appropriate mobile-phase liquid conductivity is a necessary consideration in electrospray. Pure benzene, carbon tetrachloride, and hexane possess insufficient conductivity to form charged droplets and must be mixed with polar solvents before ion formation will occur. Typically this concern exists only when normal-phase or chiral separations are conducted. Trifluoroacetic acid is sometimes added to increase mobile-phase conductivity but its detrimental effects via ion pairing and surface tension increases can cause signal suppression [47]. An alternative approach to electrospray is to chose atmospheric pressure, which through a corona discharge, can produce a stable beam under normal-phase conditions. 

Siesler, H.W., Zebger, L, Kulinna, C Okretic, S., Shilov, S. and Hoffmann, U. (1999) Segmental mobility oF liquid crystals and liquid-crystalline polymers under external fields characterization by fourier-transform infrared polarization spectroscopy, in Modem Polymer Spectroscopy (ed. G. Zerbi), Wiley-VCH Verlag GmbH, Weinheim, p. 33. 

Figure 5.13 shows the dependence on pressure, for various temperatures, of the rotational and translational molecular mobility for trifluoromethane. Rotational mobility is characterized by the deuteron spin-lattice relaxation time, Tj, and translational mobility is characterized by the self-diffusion coefficient. In all nonpolar liquids, and also in most polar liquids, changes in temperature and pressure have a stronger influence upon the translational mobility than upon the rotational mobility. 

Deigen and Pekar (16) have shown that in the polarons the energy correction caused by the hyperfine interaction equals zero in the first approximation. Hence, the width of the polaron line determined by the hyperfine interaction also equals zero. At the same time for the local electron centers such an interaction is actually a predominant factor which determines the width of the line. This makes it possible to distinguish by way of experiments the polarons from the local electron centers. Evidently, the solvated electrons produced during irradiation of the polar liquids are the mobile polarons. At low temperatures the polarons are stabilized in the form of local electron centers (peculiar F-centers) (6, 19). Actually, in the metal-ammonia solutions the width of the EPR line of the solvated electron comprises some hundredths of oersted however, the freezing of the solution at 77 °K. results in widening of this line up to 3.4 (37) or 11 (58) oe. 

A wealth of information about photolumescent materials, their properties and conditions for their optimum preparation is found in [257]. In combination with glass substrates coated with transparent electrodes, the electro-optical properties of liquid crystal films, which themselves emit no light, offer some interesting possibilities [258, 259]. Liquid crystals have the mobility of liquids and the optical properties of solids. The molecular structure lies between the liquid and solid state. Liquid crystals are organic compounds of relatively long molecules compared with their diameter, and often contain polar groups and multiple bonds. 

The effects of the interaction of radiation with water are of great importance in cancer treatment, synthesis of material in aqueous solution, and dosimetry as well. For these applications, only the final products are important however, knowledge of the early stages of the interaction may lead to the improvement of approaches and techniques. In water, or even any polar liquid, the secondary electron cloud, discussed earlier, is trapped by the solvent molecules to form another class of electronic structures, the solvated electrons, sometimes called aqueous electrons (ej,). These trapped electrons have mobility inside the liquid medium determined by the physicochemical nature of the liquid. These diffusion-limited processes carry the effect of radiation from the nanometer-scale to the bulk scale through temporal stages that identify the radiolysis of the liquid. The processes of ionization and excitation compete with the solvation processes of elections and recombination between chemical radicals in the spurs. The principal relation between the concentration of the aqueous electrons (or any of their effective residual interactions products) and the time may be expressed as (cf. Balcom et al., 1995)... 

Retention factor A measure of the amount of time an analyte spends in the stationary phase relative to the mobile phase Retention time The time taken for an analyte to travel from the point of injection to the point of detection within an HPLC system Reverse phase chromatography Describes the chromatographic separation in which the stationary phase is nonpolar and the mobile phase is composed of an aqueous, moderately polar liquid Robustness A measure of a method s ability to withstand small but deliberate changes in the method parameters it provides an indication of its reliability during normal usage Selectivity factor See separation factor... 

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