Anomalous liquids

FIG. 5 The density of liquid and supercooled water as a function of temperature, illustrating the anomalous liquid phase density maximum of water (data from Lide, 2002-2003). 

In the presence of colloidal solutions in contact with a liquid junction, anomalous liquid-junction potentials are often measured. This suspension or Palmarm effect [14] has not yet been satisfactorily explained. It is probably a Donnan-type potential with the electrically-charged colloidal species acting as indiffusible ions (cf. section 5.1.3). 

When a constant ionic strength of the test solution is maintained and the reference electrode liquid bridge is filled with a solution of a salt whose cation and anion have similar mobilities (for example solutions of KCl, KNO3 and NH4NO3), the liquid-junction potential is reasonably constant (cf. p. 24-5). However, problems may be encountered in measurements on suspensions (for example in blood or in soil extracts). The potential difference measured in the suspension may be very different from that obtained in the supernatant or in the filtrate. This phenomenon is called the suspension (Pallmann) effect [110] The appearance of the Pallmann effect depends on the position of the reference electrode, but not on that of ISE [65] (i.e. there is a difference between the potentials obtained with the reference electrode in the suspension and in the supernatant). This effect has not been satisfactorily explained it may be caused by the formation of an anomalous liquid-junction or Donnan potential. It... 

With an anomalous liquid of the pseudoplastic type, ij decreases with increasing shear stress and deformation rate, while ft increases with a dilatant liquid. There is no dependence of fj on the stress and deformation rate with a Newtonian liquid. 

A satisfactory casting slip exhibits a low or almost zero yield point, a high fluidity at low stress and a low water content. Clay casting slips usually belong to the group of anomalous liquids showing little difference from a Newtonian liquid (Fig. 155). 

It is possible to calculate the behavior of an anomalous liquid in the three cases discussed—capillary flow, falling sphere and Couette flow— by substituting the Bingham expression for the Newtonian law and obtaining different equations for the amount of liquid passing through the capillary, the times of fall, etc. 

The last anomaly we discuss here is structural anomaly. Initially, this anomaly was introduced via order parameters characterizing the local order in liquid. However, later on the local order was also related to excess entropy of the liquid that is defined as the difference between the entropy and the ideal gas entropy at the same (p, T) point Se% = S — 5id. In normal liquid, excess entropy is monotoni-cally decaying function of density along an isotherm, while in anomalous liquids it demonstrates increasing in some region. This allows to define the boundaries of stractural anomaly at given temperature as minimum and maximum of excess entropy. 

Xu, L., Buldyrev, S., Angell, C. A. Stanley, H. E. (2006). Thermodynamics and dynamics of the two-scale spherically symmetric jagla ramp model of anomalous liquids, Phys. Rev. E 74 031108. 

Another factor which may influence the liquid junction potential is termed the "suspension effect" in which the presence of colloids or suspended particles, e.g., red blood cells, produce an anomalous liquid junction potential. It has been suggested that this phenomenon is caused by the effect of colloidal particles on the relative rates of diffusion, i.e., transference numbers, of the salt bridge electrolyte. Another possibility is that colloids with ion-exchange properties give rise to a Donnan potential across the suspension/supernatant liquid interface. Whatever the cause, the effect may be significant and must be avoided in accurate studies with electrodes. 

Fl 3.12 (a) For substances that have phase diagrams resembling the one shown here (which is common for most substances, with the important exception of water), the triple point and the critical point mark the range of temperatures over which the substance can exist as a hquid. The shaded areas show the regions of temperature in which a liquid cannot exist as a stable phase, (b) A liquid cannot exist as a stable phase if the pressure is below that of the triple point for normal or anomalous liquids. 

Ability of water molecules to form various kinds of local order in condensed state causes variety of its crystalline and amorphous phases at low temperatures. The transitions between liquid water phases with different local orders at low temperatures strongly affect the properties of water at ambient conditions. This effect is presumably responsible for various water properties, which makes water different from most other fluids and often called anomalous (liquid density maximum, heat capacity minimum, etc.). Naturally, the bulk polyamorphism appears also in water properties near surfaces. A transition of liquid water to strongly tetrahe-drally ordered water upon cooling is the most important manifestation of this phenomenon as it occurs at ambient pressures. This transition is extremely difficult to detect in bulk water due to unavoidable crystallization. However, it is observed in many systems containing a confined water owing to the drastic change in various properties. 

Many other liquids, however, do not show this behaviour and are known as non-Newtonian or anomalous liquids. For all these liquids the quantity r/7 varies with 7 and sometimes with time as... 

It was commented that surface viscosities seem to correspond to anomalously high bulk liquid viscosities. Discuss whether the same comment applies to surface diffusion coefficients. 

Other SFA studies complicate the picture. Chan and Horn [107] and Horn and Israelachvili [108] could explain anomalous viscosities in thin layers if the first layer or two of molecules were immobile and the remaining intervening liquid were of normal viscosity. Other inteipretations are possible and the hydrodynamics not clear, since as Granick points out [109] the measurements average over a wide range of surface separations, thus confusing the definition of a layer thickness. McKenna and co-workers [110] point out that compliance effects can introduce serious corrections in constrained geometry systems. 

The reports were that water condensed from the vapor phase into 10-100-/im quartz or pyrex capillaries had physical properties distinctly different from those of bulk liquid water. Confirmations came from a variety of laboratories around the world (see the August 1971 issue of Journal of Colloid Interface Science), and it was proposed that a new phase of water had been found many called this water polywater rather than the original Deijaguin term, anomalous water. There were confirming theoretical calculations (see Refs. 121, 122) Eventually, however, it was determined that the micro-amoimts of water that could be isolated from small capillaries was always contaminated by salts and other impurities leached from the walls. The nonexistence of anomalous or poly water as a new, pure phase of water was acknowledged in 1974 by Deijaguin and co-workers [123]. There is a mass of fascinating anecdotal history omitted here for lack of space but told very well by Frank [124]. 

Torbaeke and Rasmuson (2001) report the empirieal influenee of different seales of mixing in reaetion erystallization of benzole aeid in a loop reaetor. The authors infer that the proeess is mainly governed by mesomixing in terms of liquid eireulation rate but find anomalous behaviour in respeet of feed pipe diameter. 

Variations in the reaction temperature and in the proportions of the ketone and PCI5 were appreciably reflected in the ratio of the amounts of compound 9 obtained in the first stage to the total content of 7 and 8 and then proportionally in the composition of the final products. In the interaction of the ketones with PCI5, an excess of the latter and high temperature make the anomalous reactions more significant. 4-(l,2-Dichlorovinyl)-3,5-dimethyl-l//-pyrazole (9) was obtained individually by the action of more than a twofold excess of PCI5 on the acetylpyrazole 6 at 80°C in 50% yield. Under the influence of NaNHa in liquid NH3, dichloroethy-lene 9 was converted into chloroacetylene 10 by loss of a molecule of HCl (yield 77%) (Scheme 28). 

The melting points of most liquids increase with pressure. Water s hydrogen bonds make it anomalous its melting point decreases with pressure. 

In these terms, Shatenshtein s partial rate factors (37) for the H—D exchange of monosubstituted benzenes in liquid ammonia are not anomalous (2m). The analysis of this rate data is included in Table XXVIII. Even though the data are not precise enough to meet the desired standard of precision of fits, the sequences > X and P/> p p - P/ are clearly evident in the results. Consequently, this data set (which is of the or type) may be taken as providing supporting evidence with the pyridinium ionization (which is of the gr type) for unique X blends for the positions o- and p- to ionization from the ring position as compared with the X blends for side-chain ionization. 

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