Solvent volume, effect, stability dispersions

In the case of low-molecular-weight polar resins such as VE resins, relatively thin and dense adsorption layers can be assiuned. This should result in low viscosities due to low effective phase volumes of the dispersed phase and weak interparticulate interactions forces according to steric stabilization. However, addition of a solvent like styrene will influence the Hamaker constant of the liquid medium and of the adlayer and the structure of the adlayer in terms of swelling and/or multilayer formation. In particular, any multilayer formation could result in surface layer entanglement depending on the solvency of the liquid medium expressed in terms of the Flory-Huggins parameter % [11]. These effects should dramatically influence the viscosity and rest structure of the dispersion, as seen in the experiments. 

The mixing of surfactant and polymer in the porous medium occurs due to both dispersion and the excluded volume effect for the flow of polymer molecules in porous media, which in turn could lead to the phase separation. Figure 16 illustrates the schematic explanation of the surfactant-polymer incompatibility and concomittant phase separation. We propose that around each micelle there is a region of solvent that is excluded to polymer molecules. However, when these micelles approach each other, there is overlapping of this excluded region. Therefore, if all micelles separate out then the excluded region diminishes due to the overlap of the shell and more solvent becomes available for the polymer molecules. This effect is very similar to the polymer depletion stabilization (55). Therefore, this is similar to osmotic effect where the polymer molecule tends to maximize the solvent for all possible configurations. ... 

The emulsifying effect of a copolymer can be characterized by determining the type of emulsion (DMF in hexane or hexane in DMF), its stability, its viscosity, and the particle size of the dispersed phase. These characteristics of oil-in-oil emulsions obtained with PS-PI block copolymers were studied as functions of solvent volume ratio, molecular weight, composition, and structure of the copolymer (5). Although Bancroft s rule was established for conventional oil-water emulsions, it appears to apply also to oil-in-oil emulsions—the continuous phase of the emulsion is preferentially formed by the solvent having the best solubility for the emulsifier (6, 7). Thus, block or graft copolymers can be prepared giving hexane/DMF, DMF/hexane, or both types of emulsions. 

Besides temperature and addition of non-solvent, pressure can also be expected to affect the solvency of the dispersion medium for the solvated steric stabilizer. A previous analysis (3) of the effect of an applied pressure indicated that the UCFT should increase as the applied pressure increases, while the LCFT should be relatively insensitive to applied pressure. The purpose of this communication is to examine the UCFT of a nonaqueous dispersion as a function of applied pressure. For dispersions of polymer particles stabilized by polyisobutylene (PIB) and dispersed in 2-methylbutane, it was observed that the UCFT moves to higher temperatures with increasing applied pressure. These results can qualitatively be rationalized by considering the effect of pressure on the free volume dissimilarity contribution to the free energy of close approach of the interacting particles. 

In dispersions of particles and nonadsorbing polymer, flocculation may be induced at certain concentrations (11). At low concentrations the presence of free polymer has no effect on the dispersion stability, but as the concentration is raised flocculation occurs. As two particles approach each other, at separations corresponding to twice the radius of gyration of the polymer, polymer becomes excluded from the volume of solution between the particles. The particle separation is such that polymer is prevented from entering the interparticle space. The gap can now be considered as an osmotic membrane, permeable only to solvent molecules. The bulk solution thus exerts a compressive osmotic pressure and solvent drains from the space between the particles causing the particles to flocculate. 

Polymers, Copolymer, and Dispersions in Fluidized Forms Polymer Structure, Molecular Weight, and Molecular Weight Distribution The Effect of Environment on Polymer Structure Solubilization and the Effect of Thermal Ifistory The Effect of Low Molecular Weight Monomers Conformational Changes and Solvent Effect scosity and Conformational Effects End-Group Analysis Polymers and Copolymers in Solid State Free Volume Copolymer Architecture Polymer Blends Effects of Additives Conformational Analysis Thermal Properties Mechanical Properties Stability of Polymers Environmental Thermal Chemical Nuclear... 

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