S Spreading coefficient

Fig. 2. Schematic diagram of the attractive interaction between dispersed organic particles and a positively charged mercury electrode in an aqueous electrolyte solution (where Ong is smdace charge density, S spreading coefficient, I electrical cimrent, dA/dt rate of spreading into a monolayer film reproduced from Zutic et al. [23])...

PSV Primary separation (flotation) vessel in a continuous hot water processing plant S Spreading coefficient... 

For hquid systems these surface energies expressed in mj/m are numerically equivalent to the surface tensions in mN/m(= dyn/cm). If the adhesive is phase 1 and the release coating is phase 2, then the spreading coefficient, S, of 1 on 2 is as given in equation 2. 

The Spreading process is governed by the spreading coefficient S defined as in equation 4 (30) where c is the surface tension of the foaming medium, C the surface tension of the defoamer, and C. the interfacial tension between them. 

Contact angle, 0, and spreading coefficient for a liquid on a solid surface comparison of spreading coefficient S for a smooth surface with S for a surface of roughness factor r... 

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. 

Studies by Owen [7] have shown that a negative spreading coefficient, S. defined as... 

It can be readily seen that the spreading coefficient S becomes increasingly positive as the surface tension of the defoamer becomes smaller. This indicates the thermodynamic tendency of defoaming. 

The effect of mutual saturation on the L-V and L-L interfacial tensions is effectively illustrated by considering the spreading coefficient of one liquid on another using both the initial (unsaturated) and equilibrium values of 7. Use the following data to calculate Se/, (equilibrium) and S B/A (nonequilibrium) ... 

Q q R i l, i 2 Rb Rd Rg RP Ro r rc S Electric charge (As), heat (J), quality factor of a resonator Heat per unit area (J m-2), integer coefficient Radius of a (usually) spherical object (m), gas constant Two principal radii of curvature (m) Radius of a spherical bubble (m) Radius of a spherical drop (m) Radius of gyration of a polymer (m) Radius of a spherical particle (m) Size of a polymer chain (m) Radius (m), radial coordinate in cylindrical or spherical coordinates Radius of a capillary (m) Entropy (J K-1), number of adsorption binding sites per unit area (mol m-2), spreading coefficient (Nm-1)... 

Figure 35 shows droplet of PS (91 K) melt which was formed on a PS (91 K) brush layer. For this system, small contact angles are expected as estimated from 0=2( S /y)1/2. From SFM, the contact angle as low as 3 0 appeared to be lower that the calculated value of 15°. In addition to the entropy considerations, the effect of grafting or cross-linking induced roughness on the spreading coefficient was taken into account for polymer networks [336,337]. 

In spreading wetting, a liquid already in contact with the solid spreads so as to increase the solid-liquid and liquid-gas interfacial areas and decrease the solid-gas interfacial area. The spreading coefficient, S (cf. equation 4.31), is defined by the expression... 

Surfactants assist wetting because they lower surface and interfacial tension. The energy balance that determines spreading is expressed by the spreading coefficient, S, and is illustrated in Figure 6.21. 

The assumption 7ieq 0 is allowed for normal polymeric surfaces. lvCos 8 is called the adhesion tension. Complete wetting occurs when cos 8 = 1 or 8 = 0°. In that case the so-called spreading coefficient S, defined as ... 

In accordance with Harkins definition the following spreading coefficients are distinguished initial s, semi-initial s and final (equilibrium) se spreading coefficients... 

The comparison of the stability conditions of wetting films with the coefficients and pressure of spreading indicates that even when two spreading coefficients are used (s and se) or (sand n°B/A) the information about stability proves to be incomplete [531], For instance, at s > 0, but 0 < se < 0 there is a range of thicknesses in which the films are unstable but the position of the range of thicknesses where this instability is expressed remain unclear. 

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