Dispersed stability

Aqueous emulsion polymerization is carried out using a fluorinated emulsifier, a chain-transfer agent to control molecular weight, and dispersion stabilizers such as manganic acid salts and ammonium oxalate (13,14). 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Substituted amides (not of the alkanolamide variety) are sold to diverse low volume markets. They have some utility ki polymers such as polyethylene, ethylene-vinyl acetate copolymers, acryUc polymers, PVC, polyamides, and polyesters. They have been found effective as pharmaceutical processkig aids, defoamers (qv), antimicrobials, pesticides, kisect repellents, dispersion stabilizers, and corrosion inhibitors. 

Dispersion Stability of Disperse Dyes at High Temperature. A disperse dye dyebath is treated under the desired test conditions at 130°C in a special apparatus (Gaston County Lab Dye and Chemical Tester) and filtered through cotton and polyester filters. The filter with the heaviest residue is then compared with a series of standard photographs of standard performance and rated equal to the one it most resembles (1 poor, 5 excellent). 

Esumi K (2003) Dendrimers for Nanoparticle Synthesis and Dispersion Stabilization. 227 31-52 Famulok M, Jenne A (1999) Catalysis Based on Nucleid Acid Structures. 202 101-131 Fechter MH, see de Raadt A (2001) 215 327-345... 

Esumi K (2003) Dendrimers for Nanoparticle Synthesis and Dispersion Stabilization. 227 31-52... 

Colorant containing annatto and Ca caseinate as carrier mixed with water to be added directly to cheese milk yielding uniform colored cheese mass Water-dispersible beadlet of p-carotene is mixed with oil to attein composition that remains stable even in presence of polyphosphates and with antioxidant action even in absence of ascorbic acid Blending carotenoid pigment and soybean fiber (wifii tomato juice) as effective ingredient for dispersion stability... 

Because stabilization in the Verwey and Hamaker picture is electrical, the use of electrical methods for predicting the stability of a dispersion appears to be mandatory. Other than the work of Voet described above, little has been done in this direction. Beyond doubt, the important developments in the area of dispersion stability that will come forth will be based either on electrokinetics (for high dielectric media, especially hydrocolloids) or electrostatics. 

At room temperature and in the presence of oxygen the colloidal dispersion stabilized by glucose is less stable than the PVA stabilized ones owing to the slow glucose aerobic oxidation growth of particles from 2.7 to 3.5 nm has been observed in a few hours. 

Monitoring the pH value during the preparation of gold sol, which leads to the below reported results, it has been observed that pH moves from ca. 3.2, before NaBH4 addition, to ca. 6.9, after NaBH4 addition. In this section a discussion of the influence of the initial pH value on the properties of the colloidal dispersion stabilized by a large amount (PVA/Au = 0.67) or a low amount (PVA/ Au = 0.05) of stabilizer is presented. Proper amounts of HCl or NaOH were used to produce the reported pH values. 

Steric stabilization is particularly useful and widely applied during emulsification processes. One major advantage compared to electrostatic stabilization is the relative insensitivity towards added electrolytes. An auxiliary effect promoting dispersion stability is the significant viscosity increase of the dispersion medium. 

K Thode, RH Muller, M Kresse. Two-time window and multiangle photon correlation spectroscopy size and zeta potential analysis—highly sensitive rapid assay for dispersion stability. J Pharm Sci 89 1317-1324, 2000. 

Since high concentrations of electrolyte can adversely affect dispersion stability, low-salt formulations of dispersing agents have been developed [95]. These also help to minimise the lowering of viscosity by electrolytes with certain synthetic thickening agents in printing applications. 

In this paper some of the current thinking in three closely-related areas is highlighted polymer adsorption the effect of polymer on the pairwise interaction between particles and the effect of polymers on dispersion stability. 

It would be an impossible task to summarize in one short review the many facets of this subject. This has been more than adequately attempted in several other recent reviews of the fields of polymer adsorption (1-4) and dispersion stability in the presence of polymers (J, 5-7). My objective, therefore, is primarily to set the scene for the papers that follow to highlight current theoretical and experimental work, and to indicate where future research efforts might conceivably be directed. 

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