Benzene spreading coefficient

However, the value of yab needs to be considered as the equilibrium value, and therefore if one considers the system at nonequilibrium, then the spreading coefficients would be different. For example, the instantaneous spreading of benzene is observed to give a value of Sa/b as 8.9 dyn/cm, and therefore benzene spreads on water. On the other hand, as the water becomes saturated with time, the value of water decreases, and benzene drops tend to form lenses. The short-chain hydrocarbons such as hexane and hexene also have positive initial spreading coefficients, and spread to give thicker films. Longer-chain alkanes, on the other hand, do not spread on water (e.g., the Sa/b for C16(hexadecane)/water is -1.3 dyn/cm at 25°C. 

The initial spreading coefficient does not consider the mutual saturation of one liquid with another for example, when benzene is spread on water,... 

Note that as a liquid spreads on a surface the interfacial tensions change, with the result that the spreading coefficient changes. For example, benzene spreads on a pure water surface, 9 x 10 N/m initially. When the water is saturated with benzene and the benzene saturated with water (o- )sat — 2 x 10 N/m and any additional benzene... 

The positive spreading coefficient indicates that benzene should spread spontaneously on water. When the experiment is carried out, it is found that after an initial rapid spreading, the benzene layer will retract and form a lens on the water. How can this seemingly anom ous result be explained ... 

In an experiment, a drop of dry benzene is put on the surface of pure water. First, the benzene becomes saturated with water, then the water becomes saturated with benzene. Calculate the spreading coefficients in all three stages and from the results describe the course of the physical process. 

If fi > 0 and 5 < 0, then an oil drop will form a lens, which may be in equilibrium with the original air-foaming liquid surface (i.e., partial wetting) or that surface after incorporation of material from the oil drop (i.e., pseudo-partial wetting). However, formation of oil lenses on the equilibrium liquid surface does not preclude the possibility that the initial spreading coefficient S is positive. If 5 > 0 and S < 0, then pseudo-partial wetting will occur and the oil drop may, for example, spread to form a duplex film, which is, however, unstable. That film will disproportionate to form oil lenses in equilibrium with oil-contaminated air-water surfaces The spreading of a drop of benzene on distilled water to form lenses in equilibrium with a benzene monolayer exemplifies this type of behavior. 

Despite the relative simplicity of the kinetics of molecular chlorination, there has so far been only one measurement of the rate coefficient with a heterocyclic compound and the need for more work in this area is indicated. Marino265 found that chlorination of thiophene by chlorine in acetic acid at 25 °C gave the second-order rate coefficient of 10.0 1.5, so that thiophene is 1.7 x 109 times as reactive as benzene in this reaction and this large rate spread is clearly consistent with the neutral and hence relatively unreactive electrophile. 

Robertson et al.261 measured rates of bromination of some aromatic hydrocarbons in acetic acid containing sodium acetate (to eliminate protonation of the aromatic by liberated hydrogen bromide) and lithium bromide (to reduce the rate to a measurable velocity ) at 25 °C, the second-order rate coefficients for 3-nitro-N,N-dimethylaniline and anisole being 14.2 and 0.016 respectively the former compound was thus stated to be about 1012 times as reactive as benzene (though no measurement of the latter rate coefficient, inferred to be 1.33 xlO-11, could be found in the literature) and this large rate spread gives one further indication of the unreactive nature of the electrophile. Other rates relative to benzene were ... 

Fig. 11. Plot of K (ReiReay (in cm. sec. " ) against C, (dynes cm." ) for spread monolayers of bovine plasma albumin. K refers to the over-all mass-transfer coefficient for isopropanol transferring from water to benzene, and various stirring speeds are employed in the apparatus of Fig. 5(b). R refers to the runs using redistilled water, H to those using 0.01 N HCl, N to those using 0.01 NaOH, and T to those using tap water (60).

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