Particles surfactants

Templates made of surfactants are very effective in order to control the size, shape, and polydispersity of nanosized metal particles. Surfactant micelles may enclose metal ions to form amphiphilic microreactors (Figure 11a). Water-in-oil reverse micelles (Figure 11b) or larger vesicles may function in similar ways. On the addition of reducing agents such as hydrazine nanosized metal particles are formed. The size and the shape of the products are pre-imprinted by the constrained environment in which they are grown. 

Surfactant solutions critical micelle concentration distribution of reactants among particles surfactant aggregation numbers interface properties and polarity dynamics of surfactant solutions partition coefficients phase transitions influence of additives... 

AFM images were obtained for films constructed, on freshly cleaved mica, from compressed monolayers of DDAB on a subphase of HMP-stabilized CdS (81). Particles, with dimensions of 8 3 nm, were seen to be evenly distributed. The determined area of 58 nm2/particle coincided well with the area per molecule determined for DDAB from its spreading isotherm, implying 1 1 particle/surfactant stoichiometry. This result is puzzling given that freshly cleaved mica is hydrophilic and therefore any particles would be buried under a layer of the hydrophobic tails of the DDAB and unaccessable to the AFM tip. 

The position of the ASV peak on the voltage scan reflects the nature of the ion being reduced, and for complex ions the peak position moves to more negative potentials as stability increases. In some cases formation of intermediate valency states (e.g. in chloride solution, Cu2+ — Cu+ — Cu°) results in split peaks. Adsorption of species (e.g. colloidal particles, surfactants) on the mercury electrode also causes peak movement (generally in an anodic direction). 

The improved excluded area concept was applied to the experimental data collected for the real binary particle-surfactant system [4], Employment of Eq. (8) to the dependence AS= AS ([yo/y] ) obtained for the binary monolayer comprised of 7 pm Si02 particles and stearic acid at pH 4 (Fig. 1) gives well-expressed linear fit (ft = -0.978) with the slope yielding the reasonable fto = 70 3°. 

Figure 1. Area shifts upon compression obtained for the binary particle-surfactant monolayer (SA and SiOa microparticles, squares) and the corresponding linear fit calculated by Eq, (8).

A considerable progress is achieved in the further theoretical development of the excluded area method for determination of the contact angle of nano- and microparticles. Theoretical solutions are found for some serious obstacles allowing them to be surmounted successfully. The proposed improvements are successfully examined using the data obtained for the real binary particle-surfactant monolayer. 

Monomer molecular weight (kg/mol) Average number of radicals per particle Surfactant agglomeration number Number of moles of monomer Total number concentration of particles (1/L)... 

Spectroturbidimetry, conductimetry, ultrafiltration, ultracentrifugation, vapor sorption, polarizing microscopy, and nuclear magnetic resonance spectroscopy were used to study phase behavior of pure sodium 8-phenyl-n-hexadecyl-p-sulfonate in water as a function of temperature and sodium chloride concentration, and in decane. The first four techniques gave information on solubility and states of dispersion ranging from visible, settling suspensions to transparent, stably dispersed submicro-scopic particles. Surfactant solubility in water was only 0.06 wt% at 25°C, increased 11-fold at 90°C, but decreased 300-fold with 3 wt% salt at 25°C. The surfactant-rich phase in... 

Depending on the particle-surfactant system, one or more of the above contributions can be responsible for adsorption. The dominating one would depend on the nature and concentration of the surfactant, the surface chemistry of the particle, and solution properties such as pH and ionic strength. Electrostatic and lateral interaction forces are usually the major factors determining the adsorption of surfactants on oxides and other non-metallic minerals. Chemical interactions become more dominant for surfactant adsorption on salt-type minerals, such as carbonates and sulfides. 

FIGURE 11.4. In a manner similar to stabilization by cxrlloidal particles, surfactant Uquid crystals may adsorb at the emulsion interface and provide mechanical, steric, and/or electrostatic stabilization. 

Yoshinaga K. Surface modification of inorganic particles Surfactant Science Series 92. Sugimoto T, editor. Fine particles, synthesis, characterization and mechanism of growth. New York, NY Marcel Dekker 2000. pp. 626-46. 

Interactions between soluble polymer and either colloidal particles, surfactant micelles, or proteins control the behavior and viability of a large number of chemical and biochemical products and processes. Considerable scientific interest also centers on these interactions because of their profound and, sometimes, unexpected effects on the thermodynamics and dynamics of the dispersions or solutions, known collectively as complex fluids. Syntheses of novel block copolymers, improved scattering and optical techniques for characterization, and predictions emerging from sophisticated statistical mechanical approaches provide additional stimulus. Thus, the area is vigorous academically and industrially as evidenced by the broad and international participation in this volume. 

Another important advantage of MR fluids is their relative insensitivity to temperature changes and contamination. This arises from the fact that the magnetic polarization of the particles is not influenced by the presence or movement of ions or electric charges near or on the surface of the particles. Surfactants and additives that affect the electrochemistry of the fluid do not play a role in the magnetic polarizability of the particles. Further, bubbles or voids in the fluid can never cause a catastrophic dielectric breakdown in an MR fluid. 

The gap between two colliding particles (bubbles, droplets, solid particles, surfactant micelles) in a colloidal dispersion can be treated as a film of uneven thickness. Then, it is possible to utilize the theory of thin films to calculate the energy of interaction between two colloidal particles. Deijaguin [276] has derived an approximate formula which expresses the energy of interaction between two spherical particles of radii and i 2 through integral of the excess surface free energy per unit area, f h), of a plane-parallel film of thickness h [see Eq. (161)] ... 

FIGURE3.12 The action of detergent molecules on a dirt particle. Surfactants coat the oily dirt, helping to isolate and remove it from a surface. 

Cosgrove, T, Mears, S.J., Obey, T., Thompson, L., and Wesley, R.D. 1999. Polymer, particle, surfactant interactions. Colloids Surf. A Physicochem. Eng. Aspects 149 329-38. 

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