Unassociated liquids

It is best applied to nonpolar liquids which form unassociated vapors. 

Deflocculation is a state of the dispersion of a solid in a liquid in which each solid particle remains geometrically independent and unassociated with adjacent particles. 

The solubility parameters have been determined for several tetra-n-alkyl germanes for which the values are as follows (in J1/2cm 3/2) Ge(CH3)4, 13.9 Ge(C2H5)4, 17.6 Ge(n-C3H7)4, 18.0 Ge(n-C4H9)4, 20.3 and Ge(n-C5HU)4, 21.5. Note that all of these values are lower than those for A1(CH3)3 or A1(C2H5)3. The conclusion is that the properties of the liquid tetraalkylgermanes indicate that the liquids are unassociated, a conclusion that is supported by other evidence. 

The methods of measurement of the surface energy of liquids may be divided into two classes the static and dynamic methods. In general for pure unassociated liquids in contact with their vapour alone the values of the surface energy determined by the two methods do not differ beyond the range which may be attributed to experimental error. In other cases, however, marked divergence between the values obtained by the two methods is to be noted. This divergence is, as we shall have occasion to note, due to the comparatively slow rate of attainment by diffusion of equilibrium in the surface phase of solutions. 

Bennett and Mitchell3 showed that practically all the liquids usually recognized as unassociated have a constant value of the total molecular surface energy / j ... 

Walden 1 has adapted Trouton s Rule to a quantitative study of the molecular complexity of substances at the melting-point. Examination of a considerable number of normal, unassociated liquids shows that the expression... 

Thus, the vapor has a lower entropy than it would have if the molecules were completely unassociated. Even though acetic acid has an entropy of vaporization that is much lower than that for other hydrogen bonded liquids such as CH3OH or water, the reason is again hydrogen bonding, but in the vapor phase as well as in the liquid phase. In effect, only one half a mole of independent species is present in the vapor when a mole of the liquid vaporizes. 

In addition to the solubility parameter, the entropy of vaporization is a valuable piece of evidence in studying the association that occurs in liquids and vapors. In the case of [A1(C2H5)3]2, the entropy of vaporization (176.6 J mol-1 K-1) is almost exactly twice the value of 88 J mol-1 K-1 predicted by Trouton s rule (which applies for random, unassociated liquids),... 

Fig. 2.10. Schematic diagram to show that in liquid water there are networks of associated water molecules and also a certain fraction of free, unassociated water molecules.

One has to know the free volume available to the unbonded molecule, and its temperature dependence, so that the translational entropy may be calculated. The term V g may be found from sound velocity measurements [Eq. (2.96)]. If one takes a number of unassociated liquids and plots their free volumes Vy- obtained from the velocity of soimd against their molar weights, an extrapolation through a molar weight of 18 will give for a freely rotating monomer of water. A value of 0.2 cm mol for is obtained. The temperature dependence of V g is obtained from the integration of the heat capacity... 

Were water a simple unassociated dipolar liquid, the effect of an applied field would be simply to orient it, to inhibit its random libration and bend the average... 

Fig. 4.98. The dielectric constants of liquids as a function of their dipole moments ( = unassociated liquids, and = H-bonded liquids).

It has just been argued that the conductivities of simple ionic liquids, on the one hand, and liquid sihca and water, on the other, are vastly different because a fused salt is an unassociated liquid (it consists of individual particles) whereas both molten silica and water are associated liquids with network structures. What is the situation with regard to the viscosities of fused salts, water, and fused silica Experiments indicate that whereas water and fused NaCl have similar viscosities not far above the melting points of ice and solid salt, respectively, fused silica is a highly viscous liquid (Table 5.46). Here then is an interesting problem. 

Here is an equation for calculating the thermal conductivity of many unassociated industrial liquids. It is better than many other methods because it is more accurate and, more importantly, the input data are easy to obtain parameters such as density, critical temperature, critical pressure, boiling point, molecular weight. It is suitable for either polar or nonpolar liquids, but cannot be used for associated liquids such as water, alcohols, or organic acids. 

For spherical unassociated liquids (either polar or nonpolar), the dimensionle.ss thermal conductivity, A, is a function of dimensionless temperature, T", density, p, and dipole moment, Here, the shape limitation is... 

Lewis has tested this relationship as far as is possible with the data available in the literature, and finds that it is approximately true for all normal unassociated liquids. For associated liquids, such as water, the alcohols and the organic acids, the observed latent heats are considerably greater than those calculated from the coefficient of expansion and the compressibility. This may be due to the additional work necessary to split up the associated molecules. A deviation from Lewis rule may therefore be taken as an indication of the association of the liquid, and is perhaps a better criterion than most of the other methods used for this purpose. The table on p. 153 (taken from Lewis paper) contains the temperature f for which the latent heat was calculated, the calculated and observed latent heats, and, finally, the temperature at which the latent heat was determined. 

An insoluble system is the first example—water placed on/in microcrystalline cellulose. Water present with insoluble materials is solute free. It behaves as associated liquid close to the solid surface. As more layers of water are added less and less surface association occurs until at the outer layers water behaves as unassociated free water. Water in capillaries can be considered bound with more heat needed than even associated water to remove water from capillaries. Water thus remains in location after drying in a very predictable manner based on drying temperature and drying duration. As moisture remains solute free, the mass transferring during drying is water only. 

The specific structure of hquid water is poorly defined, but can be thought of as a slush of ice-like clumps floating in a pool of relatively unassociated H2O molecules. This t5q>e of mixture helps explain many of the maxima and minima in such physical properties as density and viscosity that are often observed when liquid water is cooled or pressurized. The best known of these trends is the maximum in liquid water density near 4°C (Fig. 3.5). This phenomenon... 

In sorption studies of polycarbonate (3) it was learned that this polymer absorbs water In two stages. In the initial period of absorption at an elevated temperature, but below T , all of the water was found In an unassociated state when cooled to room temperature. In the second stage at later times, most of the water gained by the polymer was identified in a separate liquid phase (clustered water). In addition after the polymer was saturated with water at a temperature above Tg and cooled, its solubility was lowered and water condensed in the form of microscopic water filled cavities. Below T the clusters were formed only after the polycarbonate s strength (Mjy=26,600) was decreased by hydrolysis whereas above Tg clusters were formed without degradation. 

The dielectric loss behavior of both polyethylene s Y transi-tion and polycarbonate s 0-transltion was enhanced by the presence of unassociated water. The area under the associated loss peak was found to increase in direct proportion to the concentration of unassociated water. In addition a secondary dielectric loss peak associated with frozen clustered water occurred in polycarbonate about 40°C below Its g-transition. Liquid clustered water at... 

The results of experimental studies, presented in Figure 1-5, indicate that for most unassociated single-component liquids the surface tension is a linear function of temperature ... 

Dialkyl derivatives of elements of the Second sub-Group, namely, zinc, cadmium, and mercury, contain an almost completely covalent metal-carbon bond. These compounds are normal, unassociated liquids with low boiling points e.g., the dimethyl derivative of zinc boils at 46°, that of cadmium at 105.5°, and that of mercury at 92°. 

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