Colloidal particles, detachment from

In conclusion, field-flow fractionation is a relatively simple technique for the study of adhesion and detachment of submicrometer or supramicrometer colloidal particles on and from solid surfaces. 

Cleaver, J.W. Yates, B. Mechanism of detachment of colloidal particles from a flat substrate... 

Cleaver, J.W. and Yates, B., 1973, Mechanism of detachment of colloidal particles from flat substrate in a turbulent flow. J. Colloid and Interface Science, 44, 3, 464 - 473. 

Despite the criticisms above, the vOCG approach has been frequently and successfully used over recent years to interpret polymer solubility in water [14] (this is not possible using the y approach ), protein adsorption on clays [57] and conducting polymers (see Section IV.A.2 below), cell adhesion to copolymer surfaces [65], yeast-yeast and yeast-bacteria adhesion [72], fiber-matrix adhesion [69], and the hydrodynamic detachment of colloidal particles from glass plates [70]. 

Partial adhesion on the SdFFF channel wall was achieved by using monodisperse spherical particles of polymethyl methacrylate (PMMA) with nominal diameter 0.358 p.m." " The extent of the PMMA particles adhesion and detachment on and from the channel wall depends on the concentration of the indifferent electrolyte Ba(N03)2 added to the suspending medium to influence the total potential energy of interaction between the PMMA particles and the channel wall. When the concentration of the electrolyte exceeds a given value, which is called critical electrolyte concentration (CEC), total adhesion of the colloidal particles occurs at the beginning of the SdFFF channel wall. 

After extraction using e.g. ethanol the protecting shell of the colloid may be detached from the metal core giving nanometal powders under full conservation of the particle size of the colloidal starting material. 

PS colloids at all acrylic acid concentrations tested. However, at low acrylic acid concentrations the particles detached easily from the surface. Only at concentrations above % wt/wt the silica particles were sufficiently strongly bonded to the surface that they remained attached even after several centrifugation steps. The size of the silica particles did not depend on the size of the PS colloids but is determined by the amount of tetraethoxysilane. 

From the examples presented in this chapter papermaking suspensions are dearly fasdnating complex systems that show a richness of interesting phenomena. Both colloidal and hydrodynamic phenomena play a crudal role. The colloidal interactions can be modified, and thus optimized and controlled, by polymers and poly electrolytes. The time scales of polymer adsorption, partide deposition on fibers, particle detachment polymer transfer, flocculation and break-up of colloidal aggregates determine how a papermaking suspension behaves on a paper machine. These time scales can be controlled by dosage and addition points. Some of the relevant time scales can be predicted by theory, as some of the examples given here show, whereas others require experimental determination, such as polymer transfer rates, particle detachment and floe break-up rates, which are difficult to predict from first principles. Therefore, expensive pilot and mill trials are usually required to optimize and fine-tune the use of additives on a paper machine. Nevertheless, laboratory experiments can provide useful trends and help to eluddate the mechanisms by which additives function. 

Surface prop>erties can be modified by thin layers of grafted polymers on a surface (not only flat substrates, but also colloidal particles, fibers, etc). These layers can be fabricated by grafring-from (as radical polymerization at the interface) and grafring-to (as tethering of the polymer chains from solution) methods. Grafted surfaces using smart temperature-responsive polymers can modulate cell adhesion and detachment properties in dependence on the temprerature. Cells adhere and proliferate on hydrophobic surfaces rather than hydrophilic ones. They tend to adhere to the surface with appropriate hydrophobidty. Polymer brush systems can be used to control adsorption mechanism, for example, protein adsorption or adsorption of nanopartides. 

Once the dirty spot is removed from the substrate being laundered, it is important that it not be redeposited. Solubilization of the detached material in micelles of surfactant has been proposed as one mechanism that contributes to preventing the redeposition of foreign matter. Any process that promotes the stability of the detached dirt particles in the dispersed form will also facilitate this. We see in Chapter 11 how electrostatic effects promote colloidal stability. The adsorption of ions —especially amphipathic surfactant ions —onto the detached matter assists in blocking redeposition by stabilizing the dispersed particles. Materials such as carbox-ymethylcellulose are often added to washing preparations since these molecules also adsorb on the detached dirt particles and interfere with their redeposition. 

A second principle applying to these model systems is derived from their colloidal nature. With the usual thermodynamic parameters fixed, the systems come to a steady state in which they are either agglomerated or dispersed. No dynamic equilibrium exists between dispersed and agglomerated states. In the solid-soil systems, the particles (provided they are monodisperse, i.e., all of the same size and shape) either adhere to the substrate or separate from it. In the liquid-soil systems, the soil assumes a definite contact angle with the substrate, which may be anywhere from 0° (complete coverage of the substrate) to 180° (complete detachment). The governing thermodynamic parameters include pressure, temperature, concentration of dissolved... 

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