Surfactant-free dispersions

Surfactant-free dispersions, or those in which the surfEictant present is tighdy bound to the latex, should have a contact angle close to 90° on a glass substrate. In this case fhe meniscus will be flat If the dispersion contains a distribution of particle sizes or otherwise does not cxda, drying also occurs frcsn the edges inward. 

A process is described for the production of finely divided gelatin-free dispersions of photographic additives in an aqueous medium in the presence of a high-boiling solvent and a phosphorus-containing surfactant. Thus, a yellow... 

R.M. Pashley Effect of Degassing on the Eormation and Stability of Surfactant-Free Emulsions and Eine Teflon Dispersions. J. Phys. Chem. B 107, 1714 (2003). 

Formation of free milk fat in DWM powder particles as a result of atomization and drying may also contribute significantly to poor solubility and dispersibility. Free milk fat, which is extractable from the powder by a 50 50 mixture (v/v) of ethyl and petroleum ether (Brunner, 1974), probably coats the powder particles and prevents their rehydration. The physical state of the milk fat, as controlled by the liquid-to-solid ratio and the presence of free milk fat on the particle surface, strongly influences DWM particle dispersibility. Spray coating of DWM particles with lecithin or other surfactants and dispersion in warm water improve their dispersibility. 

Schechter, R.S., Wade, W.H., Weerasooriya, U., Weerasooriya, V. and Yiv, S. (1985) Synthesis and performance of isomer-free secondary alkane sulfonate surfactants. J. Dispersion Sci. Techn., 6, 223. 

RAFT in miniemulsion has also been reported" and is more readily used to produce polymers with a narrow molecular weight distribution. Moad et used RAFT in miniemulsion to provide narrow dispersity PS in a batch process. Significant retardation w as observed with the dithiobenzoate RAFT agent used. However, this is markedly reduced when aliphatic dithioesters "" or trithiocarbonate RAFT agents are used. " One of the issues with traditional miniemulsion polymerization is the high level of surfactant and co-stabilizer that is typically employed. Pham et have recently described surfactant-free... 

The dispersion stability can be increased due to thickeners added, e.g. ethoxylated urethanes, which are able to form associates with the film forming latex [201]. At the same time, the dispersion contains a certain amount of surfactants these is free surfactant present in the latex, and added surfactant to disperse pigments and fillers. Stability is achieved by varying interaction with the two dispersed phases - latex particles associated with the thickener, and pigment particles. 

Zn", and Co [10]. The amphiphilic ligands which were embedded in micelles enhanced the reachon rate in comparison with a dispersion in surfactant-free water. 

R. M. Pashley, Effect of degassing on the formation and stability of surfactant-free emulsions and fine teflon dispersions, J. Phys. Chem. B, 2003, 107, 1714—1720. 

Fig. 16 Overall conversion versus (a) time and (b) number-average molar mass, M , and poly-dispersity index, A/w/Afn (the line represents the theoretical M ) for the nitroxide-mediated surfactant-free emulsion copolymerizations of methyl methacrylate and styrene in the presence of poly(PEGMA-ct>-MAA-co-styrene)-SGl macroalkoxyamines of different molar masses triangles 9400, and squares 44(X)gmol ) [145]...

Maeda, N., Rosenberg, K.J., Israelachvili, J.N., Pashley, R.M. Further studies on the effect of degassing on the dispersion and stability of surfactant-free emulsions. Langmuir 20, 3129-3137 (2004)... 

Interestingly, the nodulus approach is applicable in aqueous dispersed media via C/LRP, occasionally in the absence of a conventional surfactant (i.e., surfactant-free polymerization). Auto-stabilized core-shell particles may be formed at rather high solids contents by using, for instance, charged polymer precursors [13,14, 30]. 

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