Polymer surface interfacial tension

Polymer/water interfacial tension and particle surface... 

The adsorption of FENE-model chains on a structureless siuTace was studied by Milchev and Binder (307). The energetics was such that the polymer segments preferred to interact with themselves rather than with the siuTace, resulting in pol5mier droplet formation. By careful analysis of the fluctuations in the position of the free surface of the droplets, the authors were able to evaluate the polymer-vacuum interfacial tension. It would be of considerable interest to extend this method to more accurate force field descriptions of a variety of polymers. 

The film formation process is extremely complex, and there are a number of theories — or more accurately, schools of theories — to describe it. A major point of difference among them is the driving force for particle deformation surface tension of the polymer particles. Van der Waals attraction, polymer-water interfacial tension, capillary pressure at the air-water interface, or combinations of the above. These models of the mechanism of latex film formation are necessary in order to improve existing waterborne paints and to design the next generation. To improve the rate of film fonnation, for example, it is important to know if the main driving force for coalescence is located at the interface between polymer and water, between water and air, or between polymer particles. This location determines which surface tension or surface energies should be optimized. 

Gauthier and colleagues have pointed out that polymer-water interfacial tension and capillary pressure at the air-water interface are expressions of the same physical phenomenon and can be described by the Young and Laplace laws for surface energy [5]. The fact that there are two minimum film formation temperatures, one wet and one "dry," may be an indication that the receding polymer-water interface and evaporating interstitial water are both driving the film formation (see Section 3.4). 

Let us denote surface (interfacial) tensions for the water-air (constant value), substrate-air, and substrate-water interfaces directly at the boundary of the spreading droplet by Y,Yj (f), andYs CO. respectively. Note that the values of Yjv(f) and Yw(0 near the droplet edge differ from the constant values of surface tensions at the polymer-air and polymer-water interfaces far from the edge of the spreading droplet and in the depth of the droplet, respectively. It is assumed that Young s equation is satisfied at any moment at the boundary of the spreading droplet... 

The extensive use of the Young equation (Eq. X-18) reflects its general acceptance. Curiously, however, the equation has never been verified experimentally since surface tensions of solids are rather difficult to measure. While Fowkes and Sawyer [140] claimed verification for liquids on a fluorocarbon polymer, it is not clear that their assumptions are valid. Nucleation studies indicate that the interfacial tension between a solid and its liquid is appreciable (see Section K-3) and may not be ignored. Indirect experimental tests involve comparing the variation of the contact angle with solute concentration with separate adsorption studies [173]. 

MethylceUulose reduces surface and interfacial tension. MethylceUulose forms high strength films and sheets that are clear, water-soluble, and oU-and grease-resistant, and have low oxygen and moisture vapor transmission rates (see Barrier polymers). 

FIG. 20 (a) Density profiles p(z) vs z for e = —2 and four average bulk densities (f> as indicated, (b) Surface excess vs density in the bulk for four choices of e. (c) Profiles for the diagonal components of the pressure tensor and of the total pressure for (p = l.O and e = —2. Insert in (c) shows the difference between P, and Px to show that isotropic behavior in the bulk of the film is nicely obtained, (d) Interfacial tension between the polymer film and the repulsive wall vs bulk density for all four choices of e. Curve is only a guide for the eye [18]. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Polymer that lowers the surface tension of the medium in which it is dissolved, or the interfacial tension with another phase, or both. 

Alkali compounds are used in the Surtek process to reduce the interfacial tension between the oil phase and the aqueous phase. In addition, an alkaline agent neutralizes rock and clay surfaces and reduces the amount of exchangeable calcium and magnesium ions from the soil surface. Both of these functions reduce surfactant and polymer adsorption into the soil matrix. 

The direct determination of matrix/filler interaction is difficult, indirect techniques are used in most cases. These employ the principles discussed in Sect. 3.2. The surface tension of the components and interfacial tension or ac-id/base interaction parameters must be known in order to determine the reversible work of adhesion. Adsorption-desorption techniques, which use small molecular weight materials having an analogous structure to the polymer, can be used for the estimation of interfacial interaction. 

POLYMERIZATION (Emulsion). Since an aqueous system provides a medium for dissipation of the heat from exothermic addition polymerization processes, many commercial elastomers and vinyl polymers are produced by the emulsion process. This two-phase (warer-hydrophobic monomer) system employs soap or other emulsifiers to reduce the interfacial tension and disperse the monomers in the water phase. Aliphatic alcohols may be used as surface tension regulators,... 

The end groups of a PDMS polymer have been shown to affect the interfacial tension of blends with poly(butadiene)126. Thus, substitution of an amine-terminated PDMS for a trimethylsilyl-terminated PDMS can reduce the interfacial tension by up to 30%. This effect is postulated to arise due to the amine end group having a surface energy closer to that of butadiene than does the trimethylsilyl group and thus being present at the interface. 

Analyzes the ability of a paste to spread over a biological surface and calculates the interfacial tension between the two [110], The tension is considered proportional to X1/2, where X is the Flory polymer-polymer interaction parameter. Low values of this parameter correspond to structural similarities between polymers and an increased miscibility... 

Fig. 37. Theoretical predictions for thin film morphology of a phase-separating polymer mixture. Case I yA where yA and yB are the surface tensions of components A and B, respectively, and yAB is the interfacial tension. Case II yA

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