Reduced spreading coefficient

Eqs. 4 and 6 enable the extent of contact between a liquid adhesive and a solid substrate to be gauged. Some consequences are shown in Table 1 where the concept of the reduced spreading coefficient S/yw, employed by Padday [10], was used to clarify the situation. As is readily seen, if S is positive, the liquid at equilibrium will be spread completely over the solid, but if S/yi is less than —2, spontaneous dewetting will occur. 

The same author [69] has been able to show from calculations using data from nine drugs that there is a parabolic relationship between the reduced spreading coefficient and the fractional polarity of the substrate. The relationship, which is independent of the method used and specific for each binder (Fig. 5), gives an explanation for the apparently surprising rank ordering of polymers and is a tool for predicting the optimum binder for any particular substrate. 

Fig- 5. Results of the quadratic curve fitting for the reduced spreading coefficient vs fractional polarity for HPMC, MC and PVP [69]... 

Finally, we may divide these equations by 3/23 to present them and plot the reduced spreading coefficient 5ci23/k23 as a function adhesion, W Jy2z as seen in Fig. 2. in dimensionless form of the reduced work of... 

Fig. 2. Reduced spreading coefficient Sc/y2 3 as a function of the reduced work of adhesion...

Hoek [86] proposed a radial spreading coefficient to characterize the liquid distribution. This coefficient is a measure of how quickly a packing can spread a vertical liquid stream radially as the liquid progresses down the column [86]. Radial mixing tends to reduce the effects of... 

Polymer molecules tend to spread out to a larger hydrodynamic size in a good solvent than they do in a poor solvent, which results in a reduced diffusion coefficient D as the Stoke-Einstein equation shows ... 

Subscripts PA, SA, and AB refer to the particle-air, substrate-air, and air-bath interfaces, respectively.) If the spreading coefficient is positive, then spreading occurs spontaneously if not, mechanical work must be done to wet the surface completely. Adsorption of surfactant from the bath at the air-bath interface or onto soil or substrate (with the hydrophilic group oriented toward the bath) can reduce /ab, Jpb, or jSB, respectively, and thereby increase the tendency to wet the soil and/ or substrate. Since the soil particle or the substrate is often hydrophobic, with the... 

The mechanisms for foam sensitivity to oils can also be compared to the results from core-flood experiments in which foams were made to flow through porous rock in the presence of residual oil. Holt and Kristiansen (26, 27, 56) studied foams flowing in cores under North Sea reservoir conditions and found that the presence of residual oil could reduce the effectiveness of flowing foams. They compared their results with the spreading and entering coefficients and found foam sensitivity to be correlated with the (oil) spreading coefficient. 

The difference in pore shape was explained by the difference of interfacial tension between the polymer solutirm and the solvent or water droplet. Indeed, spreading water droplets over a unit area of a polymer solution can be determined by the spreading coefficient (5) as follows 5 = yp (yw + Xw/pl where yp is the surface tension of the polymer solution, y is the surface tension of the water droplet, and yw/p is the interfacial tension between the polymer solution and the water droplets in this case [90]. Water has the largest surface tension compared with the two alcohols, thus the water droplet spreading is reduced and water droplets maintain their spherical shape [89]. On the other hand, the value of yw/p is assumed to be very low for alcohol droplets because both methanol and ethanol are miscible with carbon disulfide. It should be noticed that under such alcoholic vapors, the polymer concentration should be higher than under aqueous atmosphere as no regular patterns were formed for polymer concentrations less than 10 g L. ... 

The in situ-formed copolymer reduces the interfacial tension. In ternary systems of a major component (3) and two minor components (1 and 2), as schematically shown in Fig. 8.36, component 2 spreads over the component 1 particles when the spreading coefficient S, determined by a balance between the interfacial tensions r,/y, is positive. The 5 in a ternary system of EPR (ethylene-propylene rubber) (1)/PA(2)/PPS (poly(phenylene sulfide)) (3) defined by... 

The Pasquill-Giflfoid dispersion parameters as represented by Fig. 3 have been used in some algorithms to represent puff dispersion coefficients. There is a set of coefficients due to Slade which result in significantly reduced spread of the plume and calculated centerline concentrations which are greater than those found from the Pasquill-Giflford parameters of Fig. 3. The Slade coefficients are presented in Table Vin. Much less is known about diffusion in the downwind direction than in the lateral and vertical directions. Thus, there is no good estimate of Ox, and it is customary to assume that it is equal to Oy. 

The rise of the spreading coefficient will reduce the requirements to the liquid distributor which are very strict in the < ae of operating at eidrranefy low liquid superficial velocities. 

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