Measurements in liquid

Here, fisAB denotes the angle as measured in liquid A, and the phases in parentheses have saturated the immediately preceding phase. A strictly rigorous nomenclature would be yet more complicated we simply assume that A and B are saturated by the solid and further take it for granted that the two phases at a particular interface are mutually saturated. mutual saturation effects are neglected, then the combination of Eqs. X-23 and X-21 gives... 

Passino S A, Nagasawa Y, Joo T and Fleming G R 1996 Photon echo measurements in liquids using pulses longer than the electronic dephasing time Ultrafast Phenomena X ed P Barbara, W Knox, WZinth and J Fujimoto (Berlin Springer) pp 199-200... 

Fig. 5.20. Full width of nitrogen Q-branch CARS spectra measured at 295 K versus densities (squares) and calculated width using the MEG law (circles) [14]. Shown also are the error bar and the width measured in liquid nitrogen (triangle), (a) Density range up to 700 amagat. (b) Density range up to 100 amagat showing part of Fig. 5.20(a) in more detail...

Cho, M. and Fleming, G. R. Photon-echo measurements in liquids numerical calculations with model systems, J. Chem.Phys 98 (1993), 2848-2859... 

SOLUBILITY MEASUREMENTS. The solubilities of the extracts were measured in liquid benzene. Approximately 100 mg of the extract was placed in a narrow tube. Excess benzene was added and the tube was shaken. After 24 hours, the tube was centrifuged and the supernatant was removed. Excess benzene was again added and the process was repeated. After 1 week, the insoluble portion was dried and weighed. The percent solubility is based on the weight of the insoluble extract that remained. 

A third example can be taken from analytical chemistry. Absorption and resonance Raman spectra of phenol blue were measured in liquid and supercritical solvents to determine the solvent dependence of absorption bandwidth and spectral shifts. Good correlation between absorption peak shift and resonance Raman bands and between Raman bands and bandwidth of C-N stretching mode were observed while anomalous solvent effect on the absorption bandwidth occnrred in liquid solvents. Large band-widths of absorption and resonance Raman spectra were seen in supercritical solvents as compared to liquid solvents. This was dne to the small refractive indices of the supercritical solvents. The large refractive index of the liqnid solvents only make the absorption peak shifts withont broadening the absorption spectra (Yamaguchi et al., 1997). 

The time-resolved emission spectra (TRES) and fluorescence lifetimes, ti, of the fluorene derivatives were measured in liquid solutions at room temperature with a PTI QuantaMaster spectrofluorimeter with 0.1 ns temporal resolution [20]. At this resolution, all investigated fluorenes exhibited TRES which were coincident with the corresponding steady-state fluorescence spectra. As an example, TRES for compounds 3 and 11 in hexane, THE, and ACN are presented in Eig. 8 for different nanosecond delays 0 ns (curves 2,4,6) and 5 ns, which modeled the steady-state condition (curves 3,5,7). No differences in the fluorescence spectra for these two delays were observed, indicating that all relaxation processes in the first excited state Si are sufficiently fast for fluorene molecifles and did not exceed the time resolution of the PTI system ( 0.1 ns). 

Fig. 12. Tip assembly for accurate temperature control and measurement in liquid helium. P, press seal Wi, tungsten leads (30-40 mil) Ws, tungsten heating loop (5-10 mil) N, nichrome thermal barriers (40 mil) IF3, tungsten potential leads (2 mil) T, tip.

As yet there appear to be no reports of wall shear stress measurements in liquid films with cocurrent gas streams. 

The aluminum oxide sensor is also used for moisture measurements in liquids (hydrocarbons). Because ot us low power usage, it is suitable lor use in explosion prool installations. These sensors are frequently used in petrochemical applications where low dew points are to he monitored on line and where the reduced accuracies and other limitations are acceptable. The advantages of the sensor must be weighted against the fact that... 

From Ambient Conditions to Measurement in Liquid and Vacuum... 

Molecular fluorescence spectrometry has long been regarded as a useful technique for the determination of polycyclic aromatic hydrocarbons (PAHs) and related materials, due to the very high sensitivities which can be achieved. However, molecular fluorescence spectra measured in liquid solution usually are broad and relatively featureless hence, spectral interferences are common in the liquid-solution fluorometric analysis of multicomponent samples. Moreover, the fluorescence of a particular component of a complex sample may be partially quenched by other sample constituents if quenching occurs to a significant extent, the fluorescence signal observed for a particular compound present at a particular concentration will also depend upon the identities and concentrations of other substances present in the sample. Under these conditions, it is virtually impossible to obtain accurate quantitative results. Therefore, it is generally observed that molecular fluorescence spectrometry in liquid solution media is useful for quantitative determination of individual components in complex samples only if the fluorescence measurement is preceded by extensive separation steps (ideally to produce individual pure compounds or, at worst, simple two- or three-component mixtures). 

The major interaction between die nuclear spin magnetic moments in H2 and D2 is the dipolar interaction, equation (8.10). We should at least mention the existence of an electron-coupled scalar interaction this is very small compared with the dipolar interaction, and plays a very minor role in the gas phase measurements. In liquids, however, the dipolar interaction averages to zero, and the scalar coupling becomes the important observable interaction between nuclear spins. The power and range of applications of high-resolution n.m.r. in liquids depends ultimately upon the scalar shielding and spin-spin interactions. 

Table 11.3 gives the effective average dipole moments in polymers in comparison with those measured in liquids. 

What is the relationship between the chemical shift tensor and the shifts measured in liquids The average, or isotropic, chemical shift of the tensor, that is, the mean chemical shift of a large collection of crystals distributed in all orientations in space, is given simply by the average of the three principal values ... 

The absolute rate constant for loss of CO from the acyl radical in the cage occupied by the other radical, k co, must be known. Laser flash photolyses carried out in both liquid solutions ° and bulk polymers on dibenzyl ketone and derivatives of it, yielding triplet benzylic/arylacetyl radical pairs, indicate that the presence of a benzylic radical within a cage has no discernible effect on the rate of loss of CO from the arylacetyl partner. Thus, where values of k co are not known in a polymer, rate constants measured in liquid media of similar polarity may be used. 

KdBlinger, C., Drost, S., Aberl, F., Wolf, H., Koch, S., and Woias, P. (1992). A quartz crystal biosensor for measurement in liquids. Biosens. Bioelectr, 1, 397-404. 

Raman optical activity can not only be measured in liquids or in solution, but also in crystals. As an example, the Raman CID spectra of both enantiomorphic forms of sodium chlorate single crystals (Lindner, 1994) together with their sum spectra are shown in Fig. 6.3-18. Here a broken line represents the (-)-form. The transitions examined belong to the triply degenerate polar F phonons split into transverse and longitudinal modes. 

Variables influencing ultrasound measurements in liquid systems... 

The most influential variables on US measurements in liquids are temperature, dissolved air oonoentration and pressure. Also, moisture is a key variable with non-aqueous media. 

In 1908, one century after Davy s discovery, C Kraus showed, by conductivity measurements in liquid ammonia solutions containing... 

Four different experimental techniques were employed in attempts to elucidate the structure of bicyclobutane. Haller and Srinivasan obtained some structural information from the analysis of partially resolved infrared vibration-rotation bands. However, this method is not expected to give results of high accuracy, especially since some of the fundamental parameters has to be assumed. Meiboom and Snyder used NMR measurements in liquid crystals for structure determination. One limitation of this method is that only ratios of internuclear distances rather than absolute values can be determined. Also, the authors point out that their results should not be considered as final since corrections for vibration were not made. The other two methods successfully employed were electron diffraction and microwave spectroscopy The structural parameters obtained by these methods are collected in Table 1. 

Zawodzinski et al. [64] have reported self-diffusion coefficients of water in Nafion 117 (EW 1100), Membrane C (EW 900), and Dow membranes (EW 800) equilibrated with water vapor at 303 K, and obtained results summarized in Fig. 36. The self-diffusion coefficients were deterinined by pulsed field gradient NMR methods. These studies probe water motion over a distance scale on the order of microns. The general conclusion was the PFSA membranes with similar water contents. A, had similar water self-diffusion coefficients. The measured self-diffusion coefficients in Nafion 117 equilibrated with water vapor decreased by more than an order of magnitude, from roughly 8 x 10 cm /s down to 5 x 10 cm /s as water content in the membrane decreased from A = 14 to A = 2. For a Nafion membrane equilibrated with water vapor at unit activity, the water self-diffusion coefficient drops to a level roughly four times lower than that in bulk liquid water whereas a difference of only a factor of two in local mobility is deduced from NMR relaxation measurements. This is reasonably ascribed to the additional effect of tortuosity of the diffusion path on the value of the macrodiffusion coefficient. For immersed Nafion membranes, NMR diffusion imaging studies showed that water diffusion coefficients similar to those measured in liquid water (2.2 x 10 cm /s) could be attained in a highly hydrated membrane (1.7 x 10 cm /s) [69]. 

Supercritical Alkanes. Figure 5 compares diffusion coefficients for reverse micelles diffusion coefficients measured in liquids generally decrease by 10 to 15 percent as pressure is increased to 400 bar, and show the expected systematic increase as alkane length decreases (and viscosity increases). 

Triple harmonic generation (THG) has also been measured in liquid water (Kajzar and Messier (1985)64) where y(—3m m, m, m) was found to have a value of 1.29 x 10 14 esu at a frequency of 0.0428 au. This quantity should be of the same order as ye, defined above, and the fact that it is very much smaller than the overall y value from the EFISH experiment is an indication that the major contribution to the latter comes from the fl term. The most striking difference between the gas and liquid values is that fl and, consequently, the overall effective y have opposite signs in the two phases. 

The situation is more complex for liquid-solid equilibria. The surface tension of solids is not readily measured. In liquid-solid equilibria the adsorbate always has to compete, at least with the solvent which is in large excess, for access to the solid sirrface, a phenomenon that does not take place in gas-solid equilibria imder the conditions prevailing in gas chromatography [5]. As a consequence, most of our imderstanding of liquid-solid equilibria remains empirical. 

For measurements in liquid, an additional correction factor that corrects the effect of refraction must be considered. By multiplication with the factor naiiMiquid (n refractive index) one can conveniently rescale the values of lateral photodiode sensitivity obtained in air (6LAlr) employing, e.g., the improved wedge calibration method using a universal calibration specimen, to obtain the correct value for... 

---