Surface tension stability considerations

Yih (Y2), 1963 A general consideration (theoretical) of the stability of film flow down an inclined plane, including the cases of long and short waves and small Nrs,. Results for long waves are in agreement with theory of Benjamin (B5). The effects of surface tension and viscosity on stability are discussed. 

The kinetic regularities of heterogeneous defoaming, i.e. the acceleration of foam breakdown with the decrease in hydrocarbon molecular weight (respectively, the decrease in hydrocarbon surface tension and the increase in the contact angle between the meniscus and the substrate) and with the increase in both foam expansion ratio and reduced pressure, indicate that foam breakdown can occur due to the lowered stability of film borders at their contact with the substrate (worsened wetting). The fact that the foam situated between the cuvette wall and the capillary decayed at a considerably slower rate is in benefit to this statement. 

In conclusion, lowering surface tension, which translates Into some surface accumulation, while necessary for foaming. Is only part of the process. A companion effect Is the formation of viscous surface and subsurface layers which can stabilize the lamellae. The new polymer would seem Ideal for the latter effect. A depiction of the situation prevailing Is attempted In Figure 6 which shows Inter-and Intramolecular bonds between hydrophobic groups In the polymer chains. Polymers which exhibit these types of Interaction are referred to as associating polymers. It should be noted that considerable levels of surface vlsco-elastlclty were also detected In adsorbed films of the polymer. 

The feedstock design is driven by target product characteristics and stability considerations as well as formulation dictated properties such as solubility, surface tension, viscosity, etc. 

Nebulizer formulations are normally solutions, but suspensions (particle size of less than 2 (jim) are also used. Important preformulation considerations include stability, solubility, viscosity, and surface tension of the solution of suspension. 

Nebulizer formulations are normally solutions, however, suspensions are also used, e.g., the insoluble steroid budesonide has been successfully formulated for delivery by nebulization (Dahlback 1994). Some important preformulation considerations for nebulizers are stability, solubility, viscosity and surface tension (McCallion et al. 1996 Nikander 1997). In terms of solubility, the common ion effect may be important where, e.g., a hydrochloride salt is to be dissolved in saline. In addition, the temperature dependence of the solubility of the drug may... 

Debye, P. Daen, J. Stability considerations of nonviscous Jets exhibiting surface or body tension. Phys. Fluids 2,416-421 (1959). 

Generally, it is easier to obtain a fine domain size under conditions where the two melt viscosities are dose. Furthermore, the domain size reduction easily occurs when the interfacial tension (k) between each polymer particle is low, even if there exists a considerable melt viscosity difference. This means that both the addition of a compatibilizer and interfacial copolymerization reactions result in lower surface tension and, consequently, the domain size reduction is effectively accelerated. To develop and stabilize the optimum morphology of a polymer alloy, it is very important to utilize a particular interfacial reaction or a pre-designed compatibilizer to improve the surface tension or interaction between the domain and matrix polymeric components, as well as to select the optimum operational conditions for mixing. 

---