Stabilizers, self-assembled surfactant

N. E. Baryla, J. E. Melanson, M. T. McDermott, and C. A. Lucy, Characterization of Surfactant Coatings in Capillary Electrophoresis by Atomic Force Microscopy, Anal. Chem. 2001, 73, 4558 M. M. Yassine and C. A. Lucy, Enhanced Stability Self-Assembled Coatings for Protein Separations by Capillary Zone Electrophoresis Through the Use of Long-Chained Surfactants, Anal. Chem. 2005, 77, 62. 

Surfactant adsorption at the surface As discussed in an earlier section, the adsorption of ionic surfactants can lead to charge development on the surface, and hence lead to stabilization of particulate dispersions. It has been shown recently by Adler et al. (10), that self-assembled surfactant layers at the particle surface can impart stability to nanoparticulate suspensions in extreme environments. It was proposed that the resistance to elastic deformation of the surface surfactant structures was the primary stabilization mechanism. 

Adler, J. J., Singh, P. K., Patist, A., Rabinovich, Y. I., Shah, D. O. and Moudgil, B. M., Correlation of particulate dispersion stability with the strength of self-assembled surfactant films, Langmuir, 16, 7255-7262 (2000). 

While the microemulsion method has been widely applied to the production and stabilization of spherical metal particles with various sizes and compositions, shape control of noble metallic particles using this procedure has only been demonstrated in a handful of studies to date. Pileni and co-workers demonstrated that it is possible to control nanocrystal shape to some extent within microemulsions.Although the shape of the templates plays a role during the growth of the nanocrystals, these authors showed that the particle shape can be controlled even if the microscopic structure of the self-assembled surfactant system used as a template remains unchanged and that addition of salt to the templates can induce drastic changes in the particle shape. Recently, the same group also reported the synthesis of silver nanodisks in reverse micellar solution by reduction of Ag(AOT) with hydrazine, with various sizes that depended on the relative amount of hydrazine, but with constant aspect ratio. 

B. Stabilization of Silica CMP Slurries Utilizing Self-Assembled Surfactant Aggregates ... 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

Table 6.3 Effect of protein self-assembly, induced by interaction with lecithin, on the stability of foams stabilized by complexes of sodium caseinate (1 % w/v) with soy phospholipids Lipoid S-21 (1(T5 M) (Istarova et al., 2005 Semenova, 2007). Values of Mw and A 2 are presented for the protein with and without surfactant at three pH values. Also shown are photographs of foams recorded 9 minutes following foam preparation. In each of the images the volume of the glass vessel containing die foam is 10 ml. 

We have already seen from Example 10.1 that van der Waals forces play a major role in the heat of vaporization of liquids, and it is not surprising, in view of our discussion in Section 10.2 about colloid stability, that they also play a significant part in (or at least influence) a number of macroscopic phenomena such as adhesion, cohesion, self-assembly of surfactants, conformation of biological macromolecules, and formation of biological cells. We see below in this chapter (Section 10.7) some additional examples of the relation between van der Waals forces and macroscopic properties of materials and investigate how, as a consequence, measurements of macroscopic properties could be used to determine the Hamaker constant, a material property that represents the strength of van der Waals attraction (or repulsion see Section 10.8b) between macroscopic bodies. In this section, we present one illustration of the macroscopic implications of van der Waals forces in thermodynamics, namely, the relation between the interaction forces discussed in the previous section and the van der Waals equation of state. In particular, our objective is to relate the molecular van der Waals parameter (e.g., 0n in Equation (33)) to the parameter a that appears in the van der Waals equation of state ... 

An explanation for this gel formation is sought in the phase transition behavior of span 60. At the elevated temperature (60 °C) which exceeds the span 60 membrane phase transition temperature (50 °C) [154], it is assumed that span 60 surfactant molecules are self-assembled to form a liquid crystal phase. The liquid crystal phase stabilizes the water droplets within the oil. However, below the phase transition temperature the gel phase persists and it is likely that the monolayer stabilizing the water collapses and span 60 precipitates within the oil. The span 60 precipitate thus immobilizes the liquid oil to form a gel. Water channels are subsequently formed when the w/o droplets collapse. This explanation is plausible as the aqueous volume marker CF was identified within these elongated water channels and non-spherical aqueous droplets were formed within the gel [153]. These v/w/o systems have been further evaluated as immunological adjuvants. 

If stabilizers or polymers are added post sonication or during sonication, then metal colloids result. These stabilizers could be alkyl thiols, PVP, oleic acid, and SDS. If the sonication is done in the presence of oxygen then oxides are formed. The size of the self-assembled monolayer-coated nanoparticles is determined by the surfactant concentration in the coating solution. 

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