Adsorbed nonionic

The presence of a pre-adsorbed nonionic polymer has almost negligible effects on surfactant adsorption except at high surfactant concentrations where surfactant adsorption is reduced. 

Electrokinetic studies revealed that the mobilities of particles with pre-adsorbed anionic polymer in the presence of surfactant were controlled by the charge associated with the polymer, while the mobilities were unaffected by the presence of pre-adsorbed nonionic polymer. 

The deviations from the Szyszkowski-Langmuir adsorption theory have led to the proposal of a munber of models for the equihbrium adsorption of surfactants at the gas-Uquid interface. The aim of this paper is to critically analyze the theories and assess their applicabihty to the adsorption of both ionic and nonionic surfactants at the gas-hquid interface. The thermodynamic approach of Butler [14] and the Lucassen-Reynders dividing surface [15] will be used to describe the adsorption layer state and adsorption isotherm as a function of partial molecular area for adsorbed nonionic surfactants. The traditional approach with the Gibbs dividing surface and Gibbs adsorption isotherm, and the Gouy-Chapman electrical double layer electrostatics will be used to describe the adsorption of ionic surfactants and ionic-nonionic surfactant mixtures. The fimdamental modeling of the adsorption processes and the molecular interactions in the adsorption layers will be developed to predict the parameters of the proposed models and improve the adsorption models for ionic surfactants. Finally, experimental data for surface tension will be used to validate the proposed adsorption models. 

Bridging flocculation. Partial coverage of adsorbing nonionic polymer generally results in a strong attractive minimum in the pair potential, since individual macromolecules span the gap and attach to both particles. This implies optimum conditions for flocculation at surface coverages of about one half monolayer per surface. 

As shown by Ono et al, (1974, 1975) decrease of the HLB of a mixed emulsifier by use of an increasing proportion of a nonionic emulsifier increases the stability of the latex to coagulation by electrolyte addition despite an increase in its average particle size. This is because purely eledrostatic stabilization by adsorbed ionic emulsifier is supplemented by steric stabilization by the adsorbed nonionic emulsifier which effectively decreases the van der Waals attractive force between the latex particles (which causes them to coalesce), thereby increasing their stalrility. 

Stability of Disperse Systems Containing Adsorbed Nonionic Surfactants or Polymers Steric Stabilisation... 

The interaction between particles containing adsorbed nonionic surfactants or polymer and the theory of steric stabihsation. Particular attention wiU be given to the solvency of the medium for the stabilising chains that determines the magnitude of steric repulsion. 

Interaction between Particles Containing Adsorbed Nonionic and Polymeric Sur ctant Layers (Steric Stabilisation)... 

Adsorption by particulate matter, movement in soils, and biological activity of adsorbed nonionic pesticides depends greatly upon the chemical properties of the compounds and the types of particulate matter involved. Highly water soluble compounds which are only weakly ad-... 

Figure 3.35 Schematic diagram of latex particles with adsorbed nonionic surfactant showing the interpenetration or overlap region...

This behavior has been confirmed for weakly adsorbing nonionic surfactants on hydrophilic surfaces in fact, despite the simple nature of the course-grained lattice model, the simulation can predict certain features that are also found experimentally. Even without a quantitative comparison, cac was found to be smaller than cmc, and, above the cac, a relatively large increase was observed in... 

Figure 20.15. The interaction between two hydrophobized mica surfaces with adsorbed nonionic surfactant C12E5. As the temperature is increased from room temperature ( ), the profile changes from purely repulsive (steric plus a small residual double-layer interaction) to strongly attractive ( ) as the cloud point is surpassed and the head-group interaction becomes favourable (water becomes a poorer solvent for polyoxyethylene) (148), reproduced by permission of The Royal Society of Chemistry...

The stability/instability of any agrochemical dispersion is determined by the balance of three main forces (i) Van der Waals attraction that is universal for all disperse systems and which results mainly from the London dispersion forces between the peu--ticles or droplets, (ii) Double layer repulsion that arises when using ionic surfactants or polyelectrolytes, (iii) Steric repulsion that arises when using adsorbed nonionic surfactants or polymers. A description of these three interaction forces is first given and this is followed by a combination of these forces and discussion of the theories of colloid stability. The latter can account for the stability/instability of the various dispersions. 

Several types of surface forces determine the interactions across thin liquid films. In addition to the universal van der Waals forces, the adsorbed ionic surfactants enhance the electrostatic (double-layer) repulsion. On the other hand, the adsorbed nonionics give rise to a steric repulsion due to the overlap of hydrophilic polymer brushes. The presence of surfactant micelles in the continuous phase gives rise to oscillatory structural forces, which can stabilize or destabilize the liquid films (and dispersions), depending on whether the micelle volume fraction is higher or lower. These and other surface forces, related to the surfactant properties, were considered in Sec. VI. 

Bosdorf, V., T. Bluhm, H. Kriissman, TLC determination of adsorbed nonionic surfactants on fabrics (in German), Melliand Textilher., 1994, 75, 311-312. 

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